Domain XML format
-
Element and attribute overview
- General metadata
- Operating system booting
- SMBIOS System Information
- CPU Allocation
- IOThreads Allocation
- CPU Tuning
- Memory Allocation
- Memory Backing
- Memory Tuning
- NUMA Node Tuning
- Block I/O Tuning
- Resource partitioning
- CPU model and topology
- Events configuration
- Power Management
- Hypervisor features
- Time keeping
- Performance monitoring events
-
Devices
- Hard drives, floppy disks, CDROMs
- Filesystems
- Device Addresses
- Virtio-related options
- Controllers
- Device leases
- Host device assignment
- Redirected devices
- Smartcard devices
-
Network interfaces
- Virtual network
- Bridge to LAN
- Userspace SLIRP stack
- Generic ethernet connection
- Direct attachment to physical interface
- PCI Passthrough
- Multicast tunnel
- TCP tunnel
- UDP unicast tunnel
- Setting the NIC model
- Setting NIC driver-specific options
- Setting network backend-specific options
- Overriding the target element
- Specifying boot order
- Interface ROM BIOS configuration
- Setting up a network backend in a driver domain
- Quality of service
- Setting VLAN tag (on supported network types only)
- Modifying virtual link state
- MTU configuration
- Coalesce settings
- IP configuration
- vhost-user interface
- Traffic filtering with NWFilter
- Input devices
- Hub devices
- Graphical framebuffers
- Video devices
- Consoles, serial, parallel & channel devices
- Sound devices
- Watchdog device
- Memory balloon device
- Random number generator device
- TPM device
- NVRAM device
- panic device
- Shared memory device
- Memory devices
- IOMMU devices
- Security label
- Key Wrap
- Example configs
This section describes the XML format used to represent domains, there are variations on the format based on the kind of domains run and the options used to launch them. For hypervisor specific details consult the driver docs
Element and attribute overview ¶
The root element required for all virtual machines is
named domain. It has two attributes, the
type specifies the hypervisor used for running
the domain. The allowed values are driver specific, but
include "xen", "kvm", "qemu", "lxc" and "kqemu". The
second attribute is id which is a unique
integer identifier for the running guest machine. Inactive
machines have no id value.
General metadata ¶
<domain type='xen' id='3'>
<name>fv0</name>
<uuid>4dea22b31d52d8f32516782e98ab3fa0</uuid>
<title>A short description - title - of the domain</title>
<description>Some human readable description</description>
<metadata>
<app1:foo xmlns:app1="http://app1.org/app1/">..</app1:foo>
<app2:bar xmlns:app2="http://app1.org/app2/">..</app2:bar>
</metadata>
...
-
name - The content of the
nameelement provides a short name for the virtual machine. This name should consist only of alpha-numeric characters and is required to be unique within the scope of a single host. It is often used to form the filename for storing the persistent configuration file. Since 0.0.1 -
uuid - The content of the
uuidelement provides a globally unique identifier for the virtual machine. The format must be RFC 4122 compliant, eg3e3fce45-4f53-4fa7-bb32-11f34168b82b. If omitted when defining/creating a new machine, a random UUID is generated. It is also possible to provide the UUID via asysinfospecification. Since 0.0.1, sysinfo since 0.8.7 -
title - The optional element
titleprovides space for a short description of the domain. The title should not contain any newlines. Since 0.9.10. -
description - The content of the
descriptionelement provides a human readable description of the virtual machine. This data is not used by libvirt in any way, it can contain any information the user wants. Since 0.7.2 -
metadata - The
metadatanode can be used by applications to store custom metadata in the form of XML nodes/trees. Applications must use custom namespaces on their XML nodes/trees, with only one top-level element per namespace (if the application needs structure, they should have sub-elements to their namespace element). Since 0.9.10
Operating system booting ¶
There are a number of different ways to boot virtual machines each with their own pros and cons.
BIOS bootloader ¶
Booting via the BIOS is available for hypervisors supporting full virtualization. In this case the BIOS has a boot order priority (floppy, harddisk, cdrom, network) determining where to obtain/find the boot image.
... <os> <type>hvm</type> <loader readonly='yes' secure='no' type='rom'>/usr/lib/xen/boot/hvmloader</loader> <nvram template='/usr/share/OVMF/OVMF_VARS.fd'>/var/lib/libvirt/nvram/guest_VARS.fd</nvram> <boot dev='hd'/> <boot dev='cdrom'/> <bootmenu enable='yes' timeout='3000'/> <smbios mode='sysinfo'/> <bios useserial='yes' rebootTimeout='0'/> </os> ...
-
type - The content of the
typeelement specifies the type of operating system to be booted in the virtual machine.hvmindicates that the OS is one designed to run on bare metal, so requires full virtualization.linux(badly named!) refers to an OS that supports the Xen 3 hypervisor guest ABI. There are also two optional attributes,archspecifying the CPU architecture to virtualization, andmachinereferring to the machine type. The Capabilities XML provides details on allowed values for these. Since 0.0.1 -
loader - The optional
loadertag refers to a firmware blob, which is specified by absolute path, used to assist the domain creation process. It is used by Xen fully virtualized domains as well as setting the QEMU BIOS file path for QEMU/KVM domains. Xen since 0.1.0, QEMU/KVM since 0.9.12 Then, since 1.2.8 it's possible for the element to have two optional attributes:readonly(accepted values areyesandno) to reflect the fact that the image should be writable or read-only. The second attributetypeaccepts valuesromandpflash. It tells the hypervisor where in the guest memory the file should be mapped. For instance, if the loader path points to an UEFI image,typeshould bepflash. Moreover, some firmwares may implement the Secure boot feature. Attributesecurecan be used then to control it. Since 2.1.0 -
nvram - Some UEFI firmwares may want to use a non-volatile memory to store
some variables. In the host, this is represented as a file and the
absolute path to the file is stored in this element. Moreover, when the
domain is started up libvirt copies so called master NVRAM store file
defined in
qemu.conf. If needed, thetemplateattribute can be used to per domain override map of master NVRAM stores from the config file. Note, that for transient domains if the NVRAM file has been created by libvirt it is left behind and it is management application's responsibility to save and remove file (if needed to be persistent). Since 1.2.8 -
boot - The
devattribute takes one of the values "fd", "hd", "cdrom" or "network" and is used to specify the next boot device to consider. Thebootelement can be repeated multiple times to setup a priority list of boot devices to try in turn. Multiple devices of the same type are sorted according to their targets while preserving the order of buses. After defining the domain, its XML configuration returned by libvirt (through virDomainGetXMLDesc) lists devices in the sorted order. Once sorted, the first device is marked as bootable. Thus, e.g., a domain configured to boot from "hd" with vdb, hda, vda, and hdc disks assigned to it will boot from vda (the sorted list is vda, vdb, hda, hdc). Similar domain with hdc, vda, vdb, and hda disks will boot from hda (sorted disks are: hda, hdc, vda, vdb). It can be tricky to configure in the desired way, which is why per-device boot elements (see disks, network interfaces, and USB and PCI devices sections below) were introduced and they are the preferred way providing full control over booting order. Thebootelement and per-device boot elements are mutually exclusive. Since 0.1.3, per-device boot since 0.8.8 -
smbios - How to populate SMBIOS information visible in the guest.
The
modeattribute must be specified, and is either "emulate" (let the hypervisor generate all values), "host" (copy all of Block 0 and Block 1, except for the UUID, from the host's SMBIOS values; thevirConnectGetSysinfocall can be used to see what values are copied), or "sysinfo" (use the values in the sysinfo element). If not specified, the hypervisor default is used. Since 0.8.7
Up till here the BIOS/UEFI configuration knobs are generic enough to
be implemented by majority (if not all) firmwares out there. However,
from now on not every single setting makes sense to all firmwares. For
instance, rebootTimeout doesn't make sense for UEFI,
useserial might not be usable with a BIOS firmware that
doesn't produce any output onto serial line, etc. Moreover, firmwares
don't usually export their capabilities for libvirt (or users) to check.
And the set of their capabilities can change with every new release.
Hence users are advised to try the settings they use before relying on
them in production.
-
bootmenu - Whether or not to enable an interactive boot menu prompt on guest
startup. The
enableattribute can be either "yes" or "no". If not specified, the hypervisor default is used. Since 0.8.3 Additional attributetimeouttakes the number of milliseconds the boot menu should wait until it times out. Allowed values are numbers in range [0, 65535] inclusive and it is ignored unlessenableis set to "yes". Since 1.2.8 -
bios - This element has attribute
useserialwith possible valuesyesorno. It enables or disables Serial Graphics Adapter which allows users to see BIOS messages on a serial port. Therefore, one needs to have serial port defined. Since 0.9.4. Since 0.10.2 (QEMU only) there is another attribute,rebootTimeoutthat controls whether and after how long the guest should start booting again in case the boot fails (according to BIOS). The value is in milliseconds with maximum of65535and special value-1disables the reboot.
Host bootloader ¶
Hypervisors employing paravirtualization do not usually emulate
a BIOS, and instead the host is responsible to kicking off the
operating system boot. This may use a pseudo-bootloader in the
host to provide an interface to choose a kernel for the guest.
An example is pygrub with Xen. The Bhyve hypervisor
also uses a host bootloader, either bhyveload or
grub-bhyve.
... <bootloader>/usr/bin/pygrub</bootloader> <bootloader_args>--append single</bootloader_args> ...
-
bootloader - The content of the
bootloaderelement provides a fully qualified path to the bootloader executable in the host OS. This bootloader will be run to choose which kernel to boot. The required output of the bootloader is dependent on the hypervisor in use. Since 0.1.0 -
bootloader_args - The optional
bootloader_argselement allows command line arguments to be passed to the bootloader. Since 0.2.3
Direct kernel boot ¶
When installing a new guest OS it is often useful to boot directly from a kernel and initrd stored in the host OS, allowing command line arguments to be passed directly to the installer. This capability is usually available for both para and full virtualized guests.
...
<os>
<type>hvm</type>
<loader>/usr/lib/xen/boot/hvmloader</loader>
<kernel>/root/f8-i386-vmlinuz</kernel>
<initrd>/root/f8-i386-initrd</initrd>
<cmdline>console=ttyS0 ks=http://example.com/f8-i386/os/</cmdline>
<dtb>/root/ppc.dtb</dtb>
<acpi>
<table type='slic'>/path/to/slic.dat</table>
</acpi>
</os>
...
-
type - This element has the same semantics as described earlier in the BIOS boot section
-
loader - This element has the same semantics as described earlier in the BIOS boot section
-
kernel - The contents of this element specify the fully-qualified path to the kernel image in the host OS.
-
initrd - The contents of this element specify the fully-qualified path to the (optional) ramdisk image in the host OS.
-
cmdline - The contents of this element specify arguments to be passed to the kernel (or installer) at boot time. This is often used to specify an alternate primary console (eg serial port), or the installation media source / kickstart file
-
dtb - The contents of this element specify the fully-qualified path to the (optional) device tree binary (dtb) image in the host OS. Since 1.0.4
-
acpi - The
tableelement contains a fully-qualified path to the ACPI table. Thetypeattribute contains the ACPI table type (currently onlyslicis supported) Since 1.3.5 (QEMU only)
Container boot ¶
When booting a domain using container based virtualization, instead
of a kernel / boot image, a path to the init binary is required, using
the init element. By default this will be launched with
no arguments. To specify the initial argv, use the initarg
element, repeated as many time as is required. The cmdline
element, if set will be used to provide an equivalent to /proc/cmdline
but will not affect init argv.
To set environment variables, use the initenv element, one
for each variable.
To set a custom work directory for the init, use the initdir
element.
To run the init command as a given user or group, use the inituser
or initgroup elements respectively. Both elements can be provided
either a user (resp. group) id or a name. Prefixing the user or group id with
a + will force it to be considered like a numeric value. Without
this, it will be first tried as a user or group name.
<os>
<type arch='x86_64'>exe</type>
<init>/bin/systemd</init>
<initarg>--unit</initarg>
<initarg>emergency.service</initarg>
<initenv name='MYENV'>some value</initenv>
<initdir>/my/custom/cwd</initdir>
<inituser>tester</inituser>
<initgroup>1000</initgroup>
</os>
If you want to enable user namespace, set the idmap element.
The uid and gid elements have three attributes:
-
start - First user ID in container. It must be '0'.
-
target - The first user ID in container will be mapped to this target user ID in host.
-
count - How many users in container are allowed to map to host's user.
<idmap>
<uid start='0' target='1000' count='10'/>
<gid start='0' target='1000' count='10'/>
</idmap>
SMBIOS System Information ¶
Some hypervisors allow control over what system information is
presented to the guest (for example, SMBIOS fields can be
populated by a hypervisor and inspected via
the dmidecode command in the guest). The
optional sysinfo element covers all such categories
of information. Since 0.8.7
...
<os>
<smbios mode='sysinfo'/>
...
</os>
<sysinfo type='smbios'>
<bios>
<entry name='vendor'>LENOVO</entry>
</bios>
<system>
<entry name='manufacturer'>Fedora</entry>
<entry name='product'>Virt-Manager</entry>
<entry name='version'>0.9.4</entry>
</system>
<baseBoard>
<entry name='manufacturer'>LENOVO</entry>
<entry name='product'>20BE0061MC</entry>
<entry name='version'>0B98401 Pro</entry>
<entry name='serial'>W1KS427111E</entry>
</baseBoard>
</sysinfo>
...
The sysinfo element has a mandatory
attribute type that determine the layout of
sub-elements, with supported values of:
-
smbios - Sub-elements call out specific SMBIOS values, which will
affect the guest if used in conjunction with
the
smbiossub-element of theoselement. Each sub-element ofsysinfonames a SMBIOS block, and within those elements can be a list ofentryelements that describe a field within the block. The following blocks and entries are recognized:bios-
This is block 0 of SMBIOS, with entry names drawn from:
vendor- BIOS Vendor's Name
version- BIOS Version
date- BIOS release date. If supplied, is in either mm/dd/yy or mm/dd/yyyy format. If the year portion of the string is two digits, the year is assumed to be 19yy.
release- System BIOS Major and Minor release number values concatenated together as one string separated by a period, for example, 10.22.
system-
This is block 1 of SMBIOS, with entry names drawn from:
manufacturer- Manufacturer of BIOS
product- Product Name
version- Version of the product
serial- Serial number
uuid- Universal Unique ID number. If this entry is provided
alongside a top-level
uuidelement, then the two values must match. sku- SKU number to identify a particular configuration.
family- Identify the family a particular computer belongs to.
baseBoard-
This is block 2 of SMBIOS. This element can be repeated multiple
times to describe all the base boards; however, not all
hypervisors necessarily support the repetition. The element can
have the following children:
manufacturer- Manufacturer of BIOS
product- Product Name
version- Version of the product
serial- Serial number
asset- Asset tag
location- Location in chassis
bios,systemorbaseBoardblocks will be ignored without error. Other thanuuidvalidation anddateformat checking, all values are passed as strings to the hypervisor driver.
CPU Allocation ¶
<domain>
...
<vcpu placement='static' cpuset="1-4,^3,6" current="1">2</vcpu>
<vcpus>
<vcpu id='0' enabled='yes' hotpluggable='no' order='1'/>
<vcpu id='1' enabled='no' hotpluggable='yes'/>
</vcpus>
...
</domain>
-
vcpu - The content of this element defines the maximum number of virtual
CPUs allocated for the guest OS, which must be between 1 and
the maximum supported by the hypervisor.
cpuset-
The optional attribute
cpusetis a comma-separated list of physical CPU numbers that domain process and virtual CPUs can be pinned to by default. (NB: The pinning policy of domain process and virtual CPUs can be specified separately bycputune. If the attributeemulatorpinofcputuneis specified, thecpusetspecified byvcpuhere will be ignored. Similarly, for virtual CPUs which have thevcpupinspecified, thecpusetspecified bycpusethere will be ignored. For virtual CPUs which don't havevcpupinspecified, each will be pinned to the physical CPUs specified bycpusethere). Each element in that list is either a single CPU number, a range of CPU numbers, or a caret followed by a CPU number to be excluded from a previous range. Since 0.4.4 current-
The optional attribute
currentcan be used to specify whether fewer than the maximum number of virtual CPUs should be enabled. Since 0.8.5 placement-
The optional attribute
placementcan be used to indicate the CPU placement mode for domain process. The value can be either "static" or "auto", but defaults toplacementofnumatuneor "static" ifcpusetis specified. Using "auto" indicates the domain process will be pinned to the advisory nodeset from querying numad and the value of attributecpusetwill be ignored if it's specified. If bothcpusetandplacementare not specified or ifplacementis "static", but nocpusetis specified, the domain process will be pinned to all the available physical CPUs. Since 0.9.11 (QEMU and KVM only)
-
vcpus -
The vcpus element allows to control state of individual vcpus.
The
idattribute specifies the vCPU id as used by libvirt in other places such as vcpu pinning, scheduler information and NUMA assignment. Note that the vcpu ID as seen in the guest may differ from libvirt ID in certain cases. Valid IDs are from 0 to the maximum vcpu count as set by thevcpuelement minus 1. Theenabledattribute allows to control the state of the vcpu. Valid values areyesandno.hotpluggablecontrols whether given vcpu can be hotplugged and hotunplugged in cases when the cpu is enabled at boot. Note that all disabled vcpus must be hotpluggable. Valid values areyesandno.orderallows to specify the order to add the online vcpus. For hypervisors/platforms that require to insert multiple vcpus at once the order may be duplicated accross all vcpus that need to be enabled at once. Specifying order is not necessary, vcpus are then added in an arbitrary order. If order info is used, it must be used for all online vcpus. Hypervisors may clear or update ordering information during certain operations to assure valid configuration. Note that hypervisors may create hotpluggable vcpus differently from boot vcpus thus special initialization may be necessary. Hypervisors may require that vcpus enabled on boot which are not hotpluggable are clustered at the beginning starting with ID 0. It may be also required that vcpu 0 is always present and non-hotpluggable. Note that providing state for individual cpus may be necessary to enable support of addressable vCPU hotplug and this feature may not be supported by all hypervisors. For QEMU the following conditions are required. Vcpu 0 needs to be enabled and non-hotpluggable. On PPC64 along with it vcpus that are in the same core need to be enabled as well. All non-hotpluggable cpus present at boot need to be grouped after vcpu 0. Since 2.2.0 (QEMU only)
IOThreads Allocation ¶
IOThreads are dedicated event loop threads for supported disk devices to perform block I/O requests in order to improve scalability especially on an SMP host/guest with many LUNs. Since 1.2.8 (QEMU only)
<domain> ... <iothreads>4</iothreads> ... </domain>
<domain>
...
<iothreadids>
<iothread id="2"/>
<iothread id="4"/>
<iothread id="6"/>
<iothread id="8"/>
</iothreadids>
...
</domain>
-
iothreads - The content of this optional element defines the number of IOThreads to be assigned to the domain for use by supported target storage devices. There should be only 1 or 2 IOThreads per host CPU. There may be more than one supported device assigned to each IOThread. Since 1.2.8
-
iothreadids -
The optional
iothreadidselement provides the capability to specifically define the IOThread ID's for the domain. By default, IOThread ID's are sequentially numbered starting from 1 through the number ofiothreadsdefined for the domain. Theidattribute is used to define the IOThread ID. Theidattribute must be a positive integer greater than 0. If there are lessiothreadidsdefined thaniothreadsdefined for the domain, then libvirt will sequentially filliothreadidsstarting at 1 avoiding any predefinedid. If there are moreiothreadidsdefined thaniothreadsdefined for the domain, then theiothreadsvalue will be adjusted accordingly. Since 1.2.15
CPU Tuning ¶
<domain>
...
<cputune>
<vcpupin vcpu="0" cpuset="1-4,^2"/>
<vcpupin vcpu="1" cpuset="0,1"/>
<vcpupin vcpu="2" cpuset="2,3"/>
<vcpupin vcpu="3" cpuset="0,4"/>
<emulatorpin cpuset="1-3"/>
<iothreadpin iothread="1" cpuset="5,6"/>
<iothreadpin iothread="2" cpuset="7,8"/>
<shares>2048</shares>
<period>1000000</period>
<quota>-1</quota>
<emulator_period>1000000</emulator_period>
<emulator_quota>-1</emulator_quota>
<iothread_period>1000000</iothread_period>
<iothread_quota>-1</iothread_quota>
<vcpusched vcpus='0-4,^3' scheduler='fifo' priority='1'/>
<iothreadsched iothreads='2' scheduler='batch'/>
</cputune>
...
</domain>
-
cputune -
The optional
cputuneelement provides details regarding the cpu tunable parameters for the domain. Since 0.9.0 -
vcpupin -
The optional
vcpupinelement specifies which of host's physical CPUs the domain VCPU will be pinned to. If this is omitted, and attributecpusetof elementvcpuis not specified, the vCPU is pinned to all the physical CPUs by default. It contains two required attributes, the attributevcpuspecifies vcpu id, and the attributecpusetis same as attributecpusetof elementvcpu. (NB: Only qemu driver support) Since 0.9.0 -
emulatorpin -
The optional
emulatorpinelement specifies which of host physical CPUs the "emulator", a subset of a domain not including vcpu or iothreads will be pinned to. If this is omitted, and attributecpusetof elementvcpuis not specified, "emulator" is pinned to all the physical CPUs by default. It contains one required attributecpusetspecifying which physical CPUs to pin to. -
iothreadpin -
The optional
iothreadpinelement specifies which of host physical CPUs the IOThreads will be pinned to. If this is omitted and attributecpusetof elementvcpuis not specified, the IOThreads are pinned to all the physical CPUs by default. There are two required attributes, the attributeiothreadspecifies the IOThread ID and the attributecpusetspecifying which physical CPUs to pin to. See theiothreadidsdescriptionfor validiothreadvalues. Since 1.2.9 -
shares -
The optional
shareselement specifies the proportional weighted share for the domain. If this is omitted, it defaults to the OS provided defaults. NB, There is no unit for the value, it's a relative measure based on the setting of other VM, e.g. A VM configured with value 2048 will get twice as much CPU time as a VM configured with value 1024. Since 0.9.0 -
period -
The optional
periodelement specifies the enforcement interval(unit: microseconds). Withinperiod, each vcpu of the domain will not be allowed to consume more thanquotaworth of runtime. The value should be in range [1000, 1000000]. A period with value 0 means no value. Only QEMU driver support since 0.9.4, LXC since 0.9.10 -
quota -
The optional
quotaelement specifies the maximum allowed bandwidth(unit: microseconds). A domain withquotaas any negative value indicates that the domain has infinite bandwidth, which means that it is not bandwidth controlled. The value should be in range [1000, 18446744073709551] or less than 0. A quota with value 0 means no value. You can use this feature to ensure that all vcpus run at the same speed. Only QEMU driver support since 0.9.4, LXC since 0.9.10 -
emulator_period -
The optional
emulator_periodelement specifies the enforcement interval(unit: microseconds). Withinemulator_period, emulator threads(those excluding vcpus) of the domain will not be allowed to consume more thanemulator_quotaworth of runtime. The value should be in range [1000, 1000000]. A period with value 0 means no value. Only QEMU driver support since 0.10.0 -
emulator_quota -
The optional
emulator_quotaelement specifies the maximum allowed bandwidth(unit: microseconds) for domain's emulator threads(those excluding vcpus). A domain withemulator_quotaas any negative value indicates that the domain has infinite bandwidth for emulator threads (those excluding vcpus), which means that it is not bandwidth controlled. The value should be in range [1000, 18446744073709551] or less than 0. A quota with value 0 means no value. Only QEMU driver support since 0.10.0 -
iothread_period -
The optional
iothread_periodelement specifies the enforcement interval(unit: microseconds) for IOThreads. Withiniothread_period, each IOThread of the domain will not be allowed to consume more thaniothread_quotaworth of runtime. The value should be in range [1000, 1000000]. An iothread_period with value 0 means no value. Only QEMU driver support since 2.1.0 -
iothread_quota -
The optional
iothread_quotaelement specifies the maximum allowed bandwidth(unit: microseconds) for IOThreads. A domain withiothread_quotaas any negative value indicates that the domain IOThreads have infinite bandwidth, which means that it is not bandwidth controlled. The value should be in range [1000, 18446744073709551] or less than 0. Aniothread_quotawith value 0 means no value. You can use this feature to ensure that all IOThreads run at the same speed. Only QEMU driver support since 2.1.0 vcpuschedandiothreadsched-
The optional
vcpuschedelements specifies the scheduler type (valuesbatch,idle,fifo,rr) for particular vCPU/IOThread threads (based onvcpusandiothreads, leaving outvcpus/iothreadssets the default). Validvcpusvalues start at 0 through one less than the number of vCPU's defined for the domain. Validiothreadsvalues are described in theiothreadidsdescription. If noiothreadidsare defined, then libvirt numbers IOThreads from 1 to the number ofiothreadsavailable for the domain. For real-time schedulers (fifo,rr), priority must be specified as well (and is ignored for non-real-time ones). The value range for the priority depends on the host kernel (usually 1-99). Since 1.2.13
Memory Allocation ¶
<domain> ... <maxMemory slots='16' unit='KiB'>1524288</maxMemory> <memory unit='KiB'>524288</memory> <currentMemory unit='KiB'>524288</currentMemory> ... </domain>
-
memory - The maximum allocation of memory for the guest at boot time. The
memory allocation includes possible additional memory devices specified
at start or hotplugged later.
The units for this value are determined by the optional
attribute
unit, which defaults to "KiB" (kibibytes, 210 or blocks of 1024 bytes). Valid units are "b" or "bytes" for bytes, "KB" for kilobytes (103 or 1,000 bytes), "k" or "KiB" for kibibytes (1024 bytes), "MB" for megabytes (106 or 1,000,000 bytes), "M" or "MiB" for mebibytes (220 or 1,048,576 bytes), "GB" for gigabytes (109 or 1,000,000,000 bytes), "G" or "GiB" for gibibytes (230 or 1,073,741,824 bytes), "TB" for terabytes (1012 or 1,000,000,000,000 bytes), or "T" or "TiB" for tebibytes (240 or 1,099,511,627,776 bytes). However, the value will be rounded up to the nearest kibibyte by libvirt, and may be further rounded to the granularity supported by the hypervisor. Some hypervisors also enforce a minimum, such as 4000KiB. In case NUMA is configured for the guest thememoryelement can be omitted. In the case of crash, optional attributedumpCorecan be used to control whether the guest memory should be included in the generated coredump or not (values "on", "off").unitsince 0.9.11,dumpCoresince 0.10.2 (QEMU only) -
maxMemory - The run time maximum memory allocation of the guest. The initial
memory specified by either the
<memory>element or the NUMA cell size configuration can be increased by hot-plugging of memory to the limit specified by this element. Theunitattribute behaves the same as for<memory>. Theslotsattribute specifies the number of slots available for adding memory to the guest. The bounds are hypervisor specific. Note that due to alignment of the memory chunks added via memory hotplug the full size allocation specified by this element may be impossible to achieve. Since 1.2.14 supported by the QEMU driver. -
currentMemory - The actual allocation of memory for the guest. This value can
be less than the maximum allocation, to allow for ballooning
up the guests memory on the fly. If this is omitted, it defaults
to the same value as the
memoryelement. Theunitattribute behaves the same as formemory.
Memory Backing ¶
<domain>
...
<memoryBacking>
<hugepages>
<page size="1" unit="G" nodeset="0-3,5"/>
<page size="2" unit="M" nodeset="4"/>
</hugepages>
<nosharepages/>
<locked/>
<source type="file|anonymous"/>
<access mode="shared|private"/>
<allocation mode="immediate|ondemand"/>
</memoryBacking>
...
</domain>
The optional memoryBacking element may contain several
elements that influence how virtual memory pages are backed by host
pages.
-
hugepages - This tells the hypervisor that the guest should have its memory
allocated using hugepages instead of the normal native page size.
Since 1.2.5 it's possible to set hugepages
more specifically per numa node. The
pageelement is introduced. It has one compulsory attributesizewhich specifies which hugepages should be used (especially useful on systems supporting hugepages of different sizes). The default unit for thesizeattribute is kilobytes (multiplier of 1024). If you want to use different unit, use optionalunitattribute. For systems with NUMA, the optionalnodesetattribute may come handy as it ties given guest's NUMA nodes to certain hugepage sizes. From the example snippet, one gigabyte hugepages are used for every NUMA node except node number four. For the correct syntax see this. -
nosharepages - Instructs hypervisor to disable shared pages (memory merge, KSM) for this domain. Since 1.0.6
-
locked - When set and supported by the hypervisor, memory pages belonging
to the domain will be locked in host's memory and the host will not
be allowed to swap them out, which might be required for some
workloads such as real-time. For QEMU/KVM guests, the memory used by
the QEMU process itself will be locked too: unlike guest memory, this
is an amount libvirt has no way of figuring out in advance, so it has
to remove the limit on locked memory altogether. Thus, enabling this
option opens up to a potential security risk: the host will be unable
to reclaim the locked memory back from the guest when it's running out
of memory, which means a malicious guest allocating large amounts of
locked memory could cause a denial-of-service attack on the host.
Because of this, using this option is discouraged unless your workload
demands it; even then, it's highly recommended to set an
hard_limit(see memory tuning) on memory allocation suitable for the specific environment at the same time to mitigate the risks described above. Since 1.0.6 -
source - In this attribute you can switch to file memorybacking or keep default anonymous.
-
access - Specify if memory is shared or private. This can be overridden per numa node by
memAccess -
allocation - Specify when allocate the memory
Memory Tuning ¶
<domain>
...
<memtune>
<hard_limit unit='G'>1</hard_limit>
<soft_limit unit='M'>128</soft_limit>
<swap_hard_limit unit='G'>2</swap_hard_limit>
<min_guarantee unit='bytes'>67108864</min_guarantee>
</memtune>
...
</domain>
-
memtune - The optional
memtuneelement provides details regarding the memory tunable parameters for the domain. If this is omitted, it defaults to the OS provided defaults. For QEMU/KVM, the parameters are applied to the QEMU process as a whole. Thus, when counting them, one needs to add up guest RAM, guest video RAM, and some memory overhead of QEMU itself. The last piece is hard to determine so one needs guess and try. For each tunable, it is possible to designate which unit the number is in on input, using the same values as for<memory>. For backwards compatibility, output is always in KiB.unitsince 0.9.11 Possible values for all *_limit parameters are in range from 0 to VIR_DOMAIN_MEMORY_PARAM_UNLIMITED. -
hard_limit - The optional
hard_limitelement is the maximum memory the guest can use. The units for this value are kibibytes (i.e. blocks of 1024 bytes). Users of QEMU and KVM are strongly advised not to set this limit as domain may get killed by the kernel if the guess is too low, and determining the memory needed for a process to run is an undecidable problem; that said, if you already setlockedin memory backing because your workload demands it, you'll have to take into account the specifics of your deployment and figure out a value forhard_limitthat balances the risk of your guest being killed because the limit was set too low and the risk of your host crashing because it cannot reclaim the memory used by the guest due tolocked. Good luck! -
soft_limit - The optional
soft_limitelement is the memory limit to enforce during memory contention. The units for this value are kibibytes (i.e. blocks of 1024 bytes) -
swap_hard_limit - The optional
swap_hard_limitelement is the maximum memory plus swap the guest can use. The units for this value are kibibytes (i.e. blocks of 1024 bytes). This has to be more than hard_limit value provided -
min_guarantee - The optional
min_guaranteeelement is the guaranteed minimum memory allocation for the guest. The units for this value are kibibytes (i.e. blocks of 1024 bytes). This element is only supported by VMware ESX and OpenVZ drivers.
NUMA Node Tuning ¶
<domain>
...
<numatune>
<memory mode="strict" nodeset="1-4,^3"/>
<memnode cellid="0" mode="strict" nodeset="1"/>
<memnode cellid="2" mode="preferred" nodeset="2"/>
</numatune>
...
</domain>
-
numatune -
The optional
numatuneelement provides details of how to tune the performance of a NUMA host via controlling NUMA policy for domain process. NB, only supported by QEMU driver. Since 0.9.3 -
memory -
The optional
memoryelement specifies how to allocate memory for the domain process on a NUMA host. It contains several optional attributes. Attributemodeis either 'interleave', 'strict', or 'preferred', defaults to 'strict'. Attributenodesetspecifies the NUMA nodes, using the same syntax as attributecpusetof elementvcpu. Attributeplacement(since 0.9.12) can be used to indicate the memory placement mode for domain process, its value can be either "static" or "auto", defaults toplacementofvcpu, or "static" ifnodesetis specified. "auto" indicates the domain process will only allocate memory from the advisory nodeset returned from querying numad, and the value of attributenodesetwill be ignored if it's specified. Ifplacementofvcpuis 'auto', andnumatuneis not specified, a defaultnumatunewithplacement'auto' andmode'strict' will be added implicitly. Since 0.9.3 -
memnode -
Optional
memnodeelements can specify memory allocation policies per each guest NUMA node. For those nodes having no correspondingmemnodeelement, the default from elementmemorywill be used. Attributecellidaddresses guest NUMA node for which the settings are applied. Attributesmodeandnodesethave the same meaning and syntax as inmemoryelement. This setting is not compatible with automatic placement. QEMU Since 1.2.7
Block I/O Tuning ¶
<domain>
...
<blkiotune>
<weight>800</weight>
<device>
<path>/dev/sda</path>
<weight>1000</weight>
</device>
<device>
<path>/dev/sdb</path>
<weight>500</weight>
<read_bytes_sec>10000</read_bytes_sec>
<write_bytes_sec>10000</write_bytes_sec>
<read_iops_sec>20000</read_iops_sec>
<write_iops_sec>20000</write_iops_sec>
</device>
</blkiotune>
...
</domain>
-
blkiotune - The optional
blkiotuneelement provides the ability to tune Blkio cgroup tunable parameters for the domain. If this is omitted, it defaults to the OS provided defaults. Since 0.8.8 -
weight - The optional
weightelement is the overall I/O weight of the guest. The value should be in the range [100, 1000]. After kernel 2.6.39, the value could be in the range [10, 1000]. -
device - The domain may have multiple
deviceelements that further tune the weights for each host block device in use by the domain. Note that multiple guest disks can share a single host block device, if they are backed by files within the same host file system, which is why this tuning parameter is at the global domain level rather than associated with each guest disk device (contrast this to the<iotune>element which can apply to an individual<disk>). Eachdeviceelement has two mandatory sub-elements,pathdescribing the absolute path of the device, andweightgiving the relative weight of that device, in the range [100, 1000]. After kernel 2.6.39, the value could be in the range [10, 1000]. Since 0.9.8
Additionally, the following optional sub-elements can be used:read_bytes_sec- Read throughput limit in bytes per second. Since 1.2.2
write_bytes_sec- Write throughput limit in bytes per second. Since 1.2.2
read_iops_sec- Read I/O operations per second limit. Since 1.2.2
write_iops_sec- Write I/O operations per second limit. Since 1.2.2
Resource partitioning ¶
Hypervisors may allow for virtual machines to be placed into
resource partitions, potentially with nesting of said partitions.
The resource element groups together configuration
related to resource partitioning. It currently supports a child
element partition whose content defines the absolute path
of the resource partition in which to place the domain. If no
partition is listed, then the domain will be placed in a default
partition. It is the responsibility of the app/admin to ensure
that the partition exists prior to starting the guest. Only the
(hypervisor specific) default partition can be assumed to exist
by default.
... <resource> <partition>/virtualmachines/production</partition> </resource> ...
Resource partitions are currently supported by the QEMU and LXC drivers, which map partition paths to cgroups directories, in all mounted controllers. Since 1.0.5
CPU model and topology ¶
Requirements for CPU model, its features and topology can be specified using the following collection of elements. Since 0.7.5
... <cpu match='exact'> <model fallback='allow'>core2duo</model> <vendor>Intel</vendor> <topology sockets='1' cores='2' threads='1'/> <cache level='3' mode='emulate'/> <feature policy='disable' name='lahf_lm'/> </cpu> ...
<cpu mode='host-model'> <model fallback='forbid'/> <topology sockets='1' cores='2' threads='1'/> </cpu> ...
<cpu mode='host-passthrough'> <cache mode='passthrough'/> <feature policy='disable' name='lahf_lm'/> ...
In case no restrictions need to be put on CPU model and its features, a
simpler cpu element can be used.
Since 0.7.6
... <cpu> <topology sockets='1' cores='2' threads='1'/> </cpu> ...
-
cpu - The
cpuelement is the main container for describing guest CPU requirements. Itsmatchattribute specifies how strictly the virtual CPU provided to the guest matches these requirements. Since 0.7.6 thematchattribute can be omitted iftopologyis the only element withincpu. Possible values for thematchattribute are:minimum- The specified CPU model and features describes the minimum
requested CPU. A better CPU will be provided to the guest if it
is possible with the requested hypervisor on the current host.
This is a constrained
host-modelmode; the domain will not be created if the provided virtual CPU does not meet the requirements. exact- The virtual CPU provided to the guest should exactly match the specification. If such CPU is not supported, libvirt will refuse to start the domain.
strict- The domain will not be created unless the host CPU exactly matches the specification. This is not very useful in practice and should only be used if there is a real reason.
matchattribute can be omitted and will default toexact. Sometimes the hypervisor is not able to create a virtual CPU exactly matching the specification passed by libvirt. Since 3.2.0, an optionalcheckattribute can be used to request a specific way of checking whether the virtual CPU matches the specification. It is usually safe to omit this attribute when starting a domain and stick with the default value. Once the domain starts, libvirt will automatically change thecheckattribute to the best supported value to ensure the virtual CPU does not change when the domain is migrated to another host. The following values can be used:none- Libvirt does no checking and it is up to the hypervisor to refuse to start the domain if it cannot provide the requested CPU. With QEMU this means no checking is done at all since the default behavior of QEMU is to emit warnings, but start the domain anyway.
partial- Libvirt will check the guest CPU specification before starting a domain, but the rest is left on the hypervisor. It can still provide a different virtual CPU.
full- The virtual CPU created by the hypervisor will be checked against the CPU specification and the domain will not be started unless the two CPUs match.
modeattribute may be used to make it easier to configure a guest CPU to be as close to host CPU as possible. Possible values for themodeattribute are:custom- In this mode, the
cpuelement describes the CPU that should be presented to the guest. This is the default when nomodeattribute is specified. This mode makes it so that a persistent guest will see the same hardware no matter what host the guest is booted on. host-model- The
host-modelmode is essentially a shortcut to copying host CPU definition from capabilities XML into domain XML. Since the CPU definition is copied just before starting a domain, exactly the same XML can be used on different hosts while still providing the best guest CPU each host supports. Thematchattribute can't be used in this mode. Specifying CPU model is not supported either, butmodel'sfallbackattribute may still be used. Using thefeatureelement, specific flags may be enabled or disabled specifically in addition to the host model. This may be used to fine tune features that can be emulated. (Since 1.1.1). Libvirt does not model every aspect of each CPU so the guest CPU will not match the host CPU exactly. On the other hand, the ABI provided to the guest is reproducible. During migration, complete CPU model definition is transferred to the destination host so the migrated guest will see exactly the same CPU model even if the destination host contains more capable CPUs for the running instance of the guest; but shutting down and restarting the guest may present different hardware to the guest according to the capabilities of the new host. Prior to libvirt 3.2.0 and QEMU 2.9.0 detection of the host CPU model via QEMU is not supported. Thus the CPU configuration created usinghost-modelmay not work as expected. Since 3.2.0 and QEMU 2.9.0 this mode works the way it was designed and it is indicated by thefallbackattribute set toforbidin the host-model CPU definition advertised in domain capabilities XML. Whenfallbackattribute is set toallowin the domain capabilities XML, it is recommended to usecustommode with just the CPU model from the host capabilities XML. Since 1.2.11 PowerISA allows processors to run VMs in binary compatibility mode supporting an older version of ISA. Libvirt on PowerPC architecture uses thehost-modelto signify a guest mode CPU running in binary compatibility mode. Example: When a user needs a power7 VM to run in compatibility mode on a Power8 host, this can be described in XML as follows :<cpu mode='host-model'> <model>power7</model> </cpu> ...
host-passthrough- With this mode, the CPU visible to the guest should be exactly
the same as the host CPU even in the aspects that libvirt does not
understand. Though the downside of this mode is that the guest
environment cannot be reproduced on different hardware. Thus, if you
hit any bugs, you are on your own. Further details of that CPU can
be changed using
featureelements. Migration of a guest using host-passthrough is dangerous if the source and destination hosts are not identical in both hardware and configuration. If such a migration is attempted then the guest may hang or crash upon resuming execution on the destination host.
host-modelandhost-passthroughmodes make sense when a domain can run directly on the host CPUs (for example, domains with typekvm). The actual host CPU is irrelevant for domains with emulated virtual CPUs (such as domains with typeqemu). However, for backward compatibilityhost-modelmay be implemented even for domains running on emulated CPUs in which case the best CPU the hypervisor is able to emulate may be used rather then trying to mimic the host CPU model. -
model - The content of the
modelelement specifies CPU model requested by the guest. The list of available CPU models and their definition can be found incpu_map.xmlfile installed in libvirt's data directory. If a hypervisor is not able to use the exact CPU model, libvirt automatically falls back to a closest model supported by the hypervisor while maintaining the list of CPU features. Since 0.9.10, an optionalfallbackattribute can be used to forbid this behavior, in which case an attempt to start a domain requesting an unsupported CPU model will fail. Supported values forfallbackattribute are:allow(this is the default), andforbid. The optionalvendor_idattribute (Since 0.10.0) can be used to set the vendor id seen by the guest. It must be exactly 12 characters long. If not set the vendor id of the host is used. Typical possible values are "AuthenticAMD" and "GenuineIntel". -
vendor - Since 0.8.3 the content of the
vendorelement specifies CPU vendor requested by the guest. If this element is missing, the guest can be run on a CPU matching given features regardless on its vendor. The list of supported vendors can be found incpu_map.xml. -
topology - The
topologyelement specifies requested topology of virtual CPU provided to the guest. Three non-zero values have to be given forsockets,cores, andthreads: total number of CPU sockets, number of cores per socket, and number of threads per core, respectively. Hypervisors may require that the maximum number of vCPUs specified by thecpuselement equals to the number of vcpus resulting from the topology. -
feature - The
cpuelement can contain zero or moreelementsused to fine-tune features provided by the selected CPU model. The list of known feature names can be found in the same file as CPU models. The meaning of eachfeatureelement depends on itspolicyattribute, which has to be set to one of the following values:force- The virtual CPU will claim the feature is supported regardless of it being supported by host CPU.
require- Guest creation will fail unless the feature is supported by host CPU.
optional- The feature will be supported by virtual CPU if and only if it is supported by host CPU.
disable- The feature will not be supported by virtual CPU.
forbid- Guest creation will fail if the feature is supported by host CPU.
policyattribute can be omitted and will default torequire. -
cache - Since 3.3.0 the
cacheelement describes the virtual CPU cache. If the element is missing, the hypervisor will use a sensible default.level- This optional attribute specifies which cache level is described
by the element. Missing attribute means the element describes all
CPU cache levels at once. Mixing
cacheelements with thelevelattribute set and those without the attribute is forbidden. mode-
The following values are supported:
emulate- The hypervisor will provide a fake CPU cache data.
passthrough- The real CPU cache data reported by the host CPU will be passed through to the virtual CPU.
disable- The virtual CPU will report no CPU cache of the specified
level (or no cache at all if the
levelattribute is missing).
Guest NUMA topology can be specified using the numa element.
Since 0.9.8
...
<cpu>
...
<numa>
<cell id='0' cpus='0-3' memory='512000' unit='KiB'/>
<cell id='1' cpus='4-7' memory='512000' unit='KiB' memAccess='shared'/>
</numa>
...
</cpu>
...
Each cell element specifies a NUMA cell or a NUMA node.
cpus specifies the CPU or range of CPUs that are
part of the node. memory specifies the node memory
in kibibytes (i.e. blocks of 1024 bytes).
Since 1.2.11 one can use an additional unit attribute to
define units in which memory is specified.
Since 1.2.7 all cells should
have id attribute in case referring to some cell is
necessary in the code, otherwise the cells are
assigned ids in the increasing order starting from
0. Mixing cells with and without the id attribute
is not recommended as it may result in unwanted behaviour.
Since 1.2.9 the optional attribute
memAccess can control whether the memory is to be
mapped as "shared" or "private". This is valid only for
hugepages-backed memory and nvdimm modules.
This guest NUMA specification is currently available only for QEMU/KVM and Xen.
A NUMA hardware architecture supports the notion of distances
between NUMA cells. Since 3.10.0 it
is possible to define the distance between NUMA cells using the
distances element within a NUMA cell
description. The sibling sub-element is used to
specify the distance value between sibling NUMA cells. For more
details, see the chapter explaining the system's SLIT (System
Locality Information Table) within the ACPI (Advanced
Configuration and Power Interface) specification.
...
<cpu>
...
<numa>
<cell id='0' cpus='0,4-7' memory='512000' unit='KiB'>
<distances>
<sibling id='0' value='10'/>
<sibling id='1' value='21'/>
<sibling id='2' value='31'/>
<sibling id='3' value='41'/>
</distances>
</cell>
<cell id='1' cpus='1,8-10,12-15' memory='512000' unit='KiB' memAccess='shared'>
<distances>
<sibling id='0' value='21'/>
<sibling id='1' value='10'/>
<sibling id='2' value='21'/>
<sibling id='3' value='31'/>
</distances>
</cell>
<cell id='2' cpus='2,11' memory='512000' unit='KiB' memAccess='shared'>
<distances>
<sibling id='0' value='31'/>
<sibling id='1' value='21'/>
<sibling id='2' value='10'/>
<sibling id='3' value='21'/>
</distances>
</cell>
<cell id='3' cpus='3' memory='512000' unit='KiB'>
<distances>
<sibling id='0' value='41'/>
<sibling id='1' value='31'/>
<sibling id='2' value='21'/>
<sibling id='3' value='10'/>
</distances>
</cell>
</numa>
...
</cpu>
...
Describing distances between NUMA cells is currently only supported
by Xen and QEMU. If no distances are given to describe
the SLIT data between different cells, it will default to a scheme
using 10 for local and 20 for remote distances.
Events configuration ¶
It is sometimes necessary to override the default actions taken
on various events. Not all hypervisors support all events and actions.
The actions may be taken as a result of calls to libvirt APIs
virDomainReboot,
virDomainShutdown,
or
virDomainShutdownFlags.
Using virsh reboot or virsh shutdown would
also trigger the event.
... <on_poweroff>destroy</on_poweroff> <on_reboot>restart</on_reboot> <on_crash>restart</on_crash> <on_lockfailure>poweroff</on_lockfailure> ...
The following collections of elements allow the actions to be specified when a guest OS triggers a lifecycle operation. A common use case is to force a reboot to be treated as a poweroff when doing the initial OS installation. This allows the VM to be re-configured for the first post-install bootup.
-
on_poweroff - The content of this element specifies the action to take when the guest requests a poweroff.
-
on_reboot - The content of this element specifies the action to take when the guest requests a reboot.
-
on_crash - The content of this element specifies the action to take when the guest crashes.
Each of these states allow for the same four possible actions.
-
destroy - The domain will be terminated completely and all resources released.
-
restart - The domain will be terminated and then restarted with the same configuration.
-
preserve - The domain will be terminated and its resource preserved to allow analysis.
-
rename-restart - The domain will be terminated and then restarted with a new name.
QEMU/KVM supports the on_poweroff and on_reboot
events handling the destroy and restart actions.
The preserve action for an on_reboot event
is treated as a destroy and the rename-restart
action for an on_poweroff event is treated as a
restart event.
The on_crash event supports these additional
actions since 0.8.4.
-
coredump-destroy - The crashed domain's core will be dumped, and then the domain will be terminated completely and all resources released
-
coredump-restart - The crashed domain's core will be dumped, and then the domain will be restarted with the same configuration
Since 3.9.0, the lifecycle events can
be configured via the
virDomainSetLifecycleAction API.
The on_lockfailure element (since
1.0.0) may be used to configure what action should be
taken when a lock manager loses resource locks. The following
actions are recognized by libvirt, although not all of them need
to be supported by individual lock managers. When no action is
specified, each lock manager will take its default action.
-
poweroff - The domain will be forcefully powered off.
-
restart - The domain will be powered off and started up again to reacquire its locks.
-
pause - The domain will be paused so that it can be manually resumed when lock issues are solved.
-
ignore - Keep the domain running as if nothing happened.
Power Management ¶
Since 0.10.2 it is possible to forcibly enable or disable BIOS advertisements to the guest OS. (NB: Only qemu driver support)
... <pm> <suspend-to-disk enabled='no'/> <suspend-to-mem enabled='yes'/> </pm> ...
-
pm - These elements enable ('yes') or disable ('no') BIOS support
for S3 (suspend-to-mem) and S4 (suspend-to-disk) ACPI sleep
states. If nothing is specified, then the hypervisor will be
left with its default value.
Note: This setting cannot prevent the guest OS from performing a suspend as the guest OS itself can choose to circumvent the unavailability of the sleep states (e.g. S4 by turning off completely).
Hypervisor features ¶
Hypervisors may allow certain CPU / machine features to be toggled on/off.
...
<features>
<pae/>
<acpi/>
<apic/>
<hap/>
<privnet/>
<hyperv>
<relaxed state='on'/>
<vapic state='on'/>
<spinlocks state='on' retries='4096'/>
<vpindex state='on'/>
<runtime state='on'/>
<synic state='on'/>
<reset state='on'/>
<vendor_id state='on' value='KVM Hv'/>
</hyperv>
<kvm>
<hidden state='on'/>
</kvm>
<pvspinlock state='on'/>
<gic version='2'/>
<ioapic driver='qemu'/>
<hpt resizing='required'/>
</features>
...
All features are listed within the features
element, omitting a togglable feature tag turns it off.
The available features can be found by asking
for the capabilities XML and
domain capabilities XML,
but a common set for fully virtualized domains are:
-
pae - Physical address extension mode allows 32-bit guests to address more than 4 GB of memory.
-
acpi - ACPI is useful for power management, for example, with KVM guests it is required for graceful shutdown to work.
-
apic - APIC allows the use of programmable IRQ
management. Since 0.10.2 (QEMU only) there is
an optional attribute
eoiwith valuesonandoffwhich toggles the availability of EOI (End of Interrupt) for the guest. -
hap - Depending on the
stateattribute (valueson,off) enable or disable use of Hardware Assisted Paging. The default isonif the hypervisor detects availability of Hardware Assisted Paging. -
viridian - Enable Viridian hypervisor extensions for paravirtualizing guest operating systems
-
privnet - Always create a private network namespace. This is automatically set if any interface devices are defined. This feature is only relevant for container based virtualization drivers, such as LXC.
-
hyperv - Enable various features improving behavior of guests
running Microsoft Windows.
Feature Description Value Since relaxed Relax constraints on timers on, off 1.0.0 (QEMU 2.0) vapic Enable virtual APIC on, off 1.1.0 (QEMU 2.0) spinlocks Enable spinlock support on, off; retries - at least 4095 1.1.0 (QEMU 2.0) vpindex Virtual processor index on, off 1.3.3 (QEMU 2.5) runtime Processor time spent on running guest code and on behalf of guest code on, off 1.3.3 (QEMU 2.5) synic Enable Synthetic Interrupt Controller (SyNIC) on, off 1.3.3 (QEMU 2.6) stimer Enable SyNIC timers on, off 1.3.3 (QEMU 2.6) reset Enable hypervisor reset on, off 1.3.3 (QEMU 2.5) vendor_id Set hypervisor vendor id on, off; value - string, up to 12 characters 1.3.3 (QEMU 2.5) -
pvspinlock - Notify the guest that the host supports paravirtual spinlocks
for example by exposing the pvticketlocks mechanism. This feature
can be explicitly disabled by using
state='off'attribute. -
kvm - Various features to change the behavior of the KVM hypervisor.
Feature Description Value Since hidden Hide the KVM hypervisor from standard MSR based discovery on, off 1.2.8 (QEMU 2.1.0) -
pmu - Depending on the
stateattribute (valueson,off, defaulton) enable or disable the performance monitoring unit for the guest. Since 1.2.12 -
vmport - Depending on the
stateattribute (valueson,off, defaulton) enable or disable the emulation of VMware IO port, for vmmouse etc. Since 1.2.16 -
gic - Enable for architectures using a General Interrupt
Controller instead of APIC in order to handle interrupts.
For example, the 'aarch64' architecture uses
gicinstead ofapic. The optional attributeversionspecifies the GIC version; however, it may not be supported by all hypervisors. Accepted values are2,3andhost. Since 1.2.16 -
smm - Enable System Management Mode. Possible values are
onandoff. The default is left for hypervisor to decide. Since 2.1.0 -
ioapic - Tune the I/O APIC. Possible values for the
driverattribute are:kvm(default for KVM domains) andqemuwhich puts I/O APIC in userspace which is also known as a split I/O APIC mode. Since 3.4.0 (QEMU/KVM only) -
hpt - Configure the HPT (Hash Page Table) of a pSeries guest. Possible
values for the
resizingattribute areenabled, which causes HPT resizing to be enabled if both the guest and the host support it;disabled, which causes HPT resizing to be disabled regardless of guest and host support; andrequired, which prevents the guest from starting unless both the guest and the host support HPT resizing. If the attribute is not defined, the hypervisor default will be used. Since 3.10.0 (QEMU/KVM only) -
vmcoreinfo - Enable QEMU vmcoreinfo device to let the guest kernel save debug details. Since 3.10.0 (QEMU only)
Time keeping ¶
The guest clock is typically initialized from the host clock. Most operating systems expect the hardware clock to be kept in UTC, and this is the default. Windows, however, expects it to be in so called 'localtime'.
...
<clock offset='localtime'>
<timer name='rtc' tickpolicy='catchup' track='guest'>
<catchup threshold='123' slew='120' limit='10000'/>
</timer>
<timer name='pit' tickpolicy='delay'/>
</clock>
...
-
clock -
The
offsetattribute takes four possible values, allowing fine grained control over how the guest clock is synchronized to the host. NB, not all hypervisors support all modes.-
utc -
The guest clock will always be synchronized to UTC when
booted.
Since 0.9.11 'utc' mode can be converted
to 'variable' mode, which can be controlled by using the
adjustmentattribute. If the value is 'reset', the conversion is never done (not all hypervisors can synchronize to UTC on each boot; use of 'reset' will cause an error on those hypervisors). A numeric value forces the conversion to 'variable' mode using the value as the initial adjustment. The defaultadjustmentis hypervisor specific. -
localtime -
The guest clock will be synchronized to the host's configured
timezone when booted, if any.
Since 0.9.11, the
adjustmentattribute behaves the same as in 'utc' mode. -
timezone -
The guest clock will be synchronized to the requested timezone
using the
timezoneattribute. Since 0.7.7 -
variable -
The guest clock will have an arbitrary offset applied
relative to UTC or localtime, depending on the
basisattribute. The delta relative to UTC (or localtime) is specified in seconds, using theadjustmentattribute. The guest is free to adjust the RTC over time and expect that it will be honored at next reboot. This is in contrast to 'utc' and 'localtime' mode (with the optional attribute adjustment='reset'), where the RTC adjustments are lost at each reboot. Since 0.7.7 Since 0.9.11 thebasisattribute can be either 'utc' (default) or 'localtime'.
A
clockmay have zero or moretimersub-elements. Since 0.8.0 -
-
timer -
Each timer element requires a
nameattribute, and has other optional attributes that depend on thenamespecified. Various hypervisors support different combinations of attributes.-
name -
The
nameattribute selects which timer is being modified, and can be one of "platform" (currently unsupported), "hpet" (libxl, xen, qemu), "kvmclock" (qemu), "pit" (qemu), "rtc" (qemu), "tsc" (libxl) or "hypervclock" (qemu - since 1.2.2). Thehypervclocktimer adds support for the reference time counter and the reference page for iTSC feature for guests running the Microsoft Windows operating system. -
track -
The
trackattribute specifies what the timer tracks, and can be "boot", "guest", or "wall". Only valid forname="rtc"orname="platform". -
tickpolicy -
The
tickpolicyattribute determines what happens when QEMU misses a deadline for injecting a tick to the guest:-
delay - Continue to deliver ticks at the normal rate. The guest time will be delayed due to the late tick
-
catchup - Deliver ticks at a higher rate to catch up with the missed tick. The guest time should not be delayed once catchup is complete.
-
merge - Merge the missed tick(s) into one tick and inject. The guest time may be delayed, depending on how the OS reacts to the merging of ticks
-
discard - Throw away the missed tick(s) and continue with future injection normally. The guest time may be delayed, unless the OS has explicit handling of lost ticks
If the policy is "catchup", there can be further details in the
catchupsub-element.-
catchup -
The
catchupelement has three optional attributes, each a positive integer. The attributes arethreshold,slew, andlimit.
Note that hypervisors are not required to support all policies across all time sources
-
-
frequency -
The
frequencyattribute is an unsigned integer specifying the frequency at whichname="tsc"runs. -
mode -
The
modeattribute controls how thename="tsc"timer is managed, and can be "auto", "native", "emulate", "paravirt", or "smpsafe". Other timers are always emulated. -
present -
The
presentattribute can be "yes" or "no" to specify whether a particular timer is available to the guest.
-
Performance monitoring events ¶
Some platforms allow monitoring of performance of the virtual machine and
the code executed inside. To enable the performance monitoring events
you can either specify them in the perf element or enable
them via virDomainSetPerfEvents API. The performance values
are then retrieved using the virConnectGetAllDomainStats API.
Since 2.0.0
... <perf> <event name='cmt' enabled='yes'/> <event name='mbmt' enabled='no'/> <event name='mbml' enabled='yes'/> <event name='cpu_cycles' enabled='no'/> <event name='instructions' enabled='yes'/> <event name='cache_references' enabled='no'/> <event name='cache_misses' enabled='no'/> <event name='branch_instructions' enabled='no'/> <event name='branch_misses' enabled='no'/> <event name='bus_cycles' enabled='no'/> <event name='stalled_cycles_frontend' enabled='no'/> <event name='stalled_cycles_backend' enabled='no'/> <event name='ref_cpu_cycles' enabled='no'/> <event name='cpu_clock' enabled='no'/> <event name='task_clock' enabled='no'/> <event name='page_faults' enabled='no'/> <event name='context_switches' enabled='no'/> <event name='cpu_migrations' enabled='no'/> <event name='page_faults_min' enabled='no'/> <event name='page_faults_maj' enabled='no'/> <event name='alignment_faults' enabled='no'/> <event name='emulation_faults' enabled='no'/> </perf> ...
| event name | Description | stats parameter name |
|---|---|---|
cmt
|
usage of l3 cache in bytes by applications running on the platform |
perf.cmt
|
mbmt
|
total system bandwidth from one level of cache |
perf.mbmt
|
mbml
|
bandwidth of memory traffic for a memory controller |
perf.mbml
|
cpu_cycles
|
the count of cpu cycles (total/elapsed) |
perf.cpu_cycles
|
instructions
|
the count of instructions by applications running on the platform |
perf.instructions
|
cache_references
|
the count of cache hits by applications running on the platform |
perf.cache_references
|
cache_misses
|
the count of cache misses by applications running on the platform |
perf.cache_misses
|
branch_instructions
|
the count of branch instructions by applications running on the platform |
perf.branch_instructions
|
branch_misses
|
the count of branch misses by applications running on the platform |
perf.branch_misses
|
bus_cycles
|
the count of bus cycles by applications running on the platform |
perf.bus_cycles
|
stalled_cycles_frontend
|
the count of stalled cpu cycles in the frontend of the instruction processor pipeline by applications running on the platform |
perf.stalled_cycles_frontend
|
stalled_cycles_backend
|
the count of stalled cpu cycles in the backend of the instruction processor pipeline by applications running on the platform |
perf.stalled_cycles_backend
|
ref_cpu_cycles
|
the count of total cpu cycles not affected by CPU frequency scaling by applications running on the platform |
perf.ref_cpu_cycles
|
cpu_clock
|
the count of cpu clock time, as measured by a monotonic high-resolution per-CPU timer, by applications running on the platform |
perf.cpu_clock
|
task_clock
|
the count of task clock time, as measured by a monotonic high-resolution CPU timer, specific to the task that is run by applications running on the platform |
perf.task_clock
|
page_faults
|
the count of page faults by applications running on the platform. This includes minor, major, invalid and other types of page faults |
perf.page_faults
|
context_switches
|
the count of context switches by applications running on the platform |
perf.context_switches
|
cpu_migrations
|
the count of cpu migrations, that is, where the process moved from one logical processor to another, by applications running on the platform |
perf.cpu_migrations
|
page_faults_min
|
the count of minor page faults, that is, where the page was present in the page cache, and therefore the fault avoided loading it from storage, by applications running on the platform |
perf.page_faults_min
|
page_faults_maj
|
the count of major page faults, that is, where the page was not present in the page cache, and therefore had to be fetched from storage, by applications running on the platform |
perf.page_faults_maj
|
alignment_faults
|
the count of alignment faults, that is when the load or store is not aligned properly, by applications running on the platform |
perf.alignment_faults
|
emulation_faults
|
the count of emulation faults, that is when the kernel traps on unimplemented instrucions and emulates them for user space, by applications running on the platform |
perf.emulation_faults
|
Devices ¶
The final set of XML elements are all used to describe devices
provided to the guest domain. All devices occur as children
of the main devices element.
Since 0.1.3
... <devices> <emulator>/usr/lib/xen/bin/qemu-dm</emulator> </devices> ...
-
emulator -
The contents of the
emulatorelement specify the fully qualified path to the device model emulator binary. The capabilities XML specifies the recommended default emulator to use for each particular domain type / architecture combination.
To help users identifying devices they care about, every
device can have direct child alias element
which then has name attribute where users can
store identifier for the device. The identifier has to have
"ua-" prefix and must be unique within the domain. Additionally, the
identifier must consist only of the following characters:
[a-zA-Z0-9_-].
Since 3.9.0
<devices>
<disk type='file'>
<alias name='ua-myDisk'/>
</disk>
<interface type='network' trustGuestRxFilters='yes'>
<alias name='ua-myNIC'/>
</interface>
...
</devices>
Hard drives, floppy disks, CDROMs ¶
Any device that looks like a disk, be it a floppy, harddisk,
cdrom, or paravirtualized driver is specified via the disk
element.
...
<devices>
<disk type='file' snapshot='external'>
<driver name="tap" type="aio" cache="default"/>
<source file='/var/lib/xen/images/fv0' startupPolicy='optional'>
<seclabel relabel='no'/>
</source>
<target dev='hda' bus='ide'/>
<iotune>
<total_bytes_sec>10000000</total_bytes_sec>
<read_iops_sec>400000</read_iops_sec>
<write_iops_sec>100000</write_iops_sec>
</iotune>
<boot order='2'/>
<encryption type='...'>
...
</encryption>
<shareable/>
<serial>
...
</serial>
</disk>
...
<disk type='network'>
<driver name="qemu" type="raw" io="threads" ioeventfd="on" event_idx="off"/>
<source protocol="sheepdog" name="image_name">
<host name="hostname" port="7000"/>
</source>
<target dev="hdb" bus="ide"/>
<boot order='1'/>
<transient/>
<address type='drive' controller='0' bus='1' unit='0'/>
</disk>
<disk type='network'>
<driver name="qemu" type="raw"/>
<source protocol="rbd" name="image_name2">
<host name="hostname" port="7000"/>
<snapshot name="snapname"/>
<config file="/path/to/file"/>
<auth username='myuser'>
<secret type='ceph' usage='mypassid'/>
</auth>
</source>
<target dev="hdc" bus="ide"/>
</disk>
<disk type='block' device='cdrom'>
<driver name='qemu' type='raw'/>
<target dev='hdd' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='network' device='cdrom'>
<driver name='qemu' type='raw'/>
<source protocol="http" name="url_path">
<host name="hostname" port="80"/>
</source>
<target dev='hde' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='network' device='cdrom'>
<driver name='qemu' type='raw'/>
<source protocol="https" name="url_path">
<host name="hostname" port="443"/>
</source>
<target dev='hdf' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='network' device='cdrom'>
<driver name='qemu' type='raw'/>
<source protocol="ftp" name="url_path">
<host name="hostname" port="21"/>
</source>
<target dev='hdg' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='network' device='cdrom'>
<driver name='qemu' type='raw'/>
<source protocol="ftps" name="url_path">
<host name="hostname" port="990"/>
</source>
<target dev='hdh' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='network' device='cdrom'>
<driver name='qemu' type='raw'/>
<source protocol="tftp" name="url_path">
<host name="hostname" port="69"/>
</source>
<target dev='hdi' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='block' device='lun'>
<driver name='qemu' type='raw'/>
<source dev='/dev/sda'/>
<target dev='sda' bus='scsi'/>
<address type='drive' controller='0' bus='0' target='3' unit='0'/>
</disk>
<disk type='block' device='disk'>
<driver name='qemu' type='raw'/>
<source dev='/dev/sda'/>
<geometry cyls='16383' heads='16' secs='63' trans='lba'/>
<blockio logical_block_size='512' physical_block_size='4096'/>
<target dev='hdj' bus='ide'/>
</disk>
<disk type='volume' device='disk'>
<driver name='qemu' type='raw'/>
<source pool='blk-pool0' volume='blk-pool0-vol0'/>
<target dev='hdk' bus='ide'/>
</disk>
<disk type='network' device='disk'>
<driver name='qemu' type='raw'/>
<source protocol='iscsi' name='iqn.2013-07.com.example:iscsi-nopool/2'>
<host name='example.com' port='3260'/>
<auth username='myuser'>
<secret type='iscsi' usage='libvirtiscsi'/>
</auth>
</source>
<target dev='vda' bus='virtio'/>
</disk>
<disk type='network' device='lun'>
<driver name='qemu' type='raw'/>
<source protocol='iscsi' name='iqn.2013-07.com.example:iscsi-nopool/1'>
<host name='example.com' port='3260'/>
<auth username='myuser'>
<secret type='iscsi' usage='libvirtiscsi'/>
</auth>
</source>
<target dev='sdb' bus='scsi'/>
</disk>
<disk type='volume' device='disk'>
<driver name='qemu' type='raw'/>
<source pool='iscsi-pool' volume='unit:0:0:1' mode='host'/>
<target dev='vdb' bus='virtio'/>
</disk>
<disk type='volume' device='disk'>
<driver name='qemu' type='raw'/>
<source pool='iscsi-pool' volume='unit:0:0:2' mode='direct'/>
<target dev='vdc' bus='virtio'/>
</disk>
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2' queues='4'/>
<source file='/var/lib/libvirt/images/domain.qcow'/>
<backingStore type='file'>
<format type='qcow2'/>
<source file='/var/lib/libvirt/images/snapshot.qcow'/>
<backingStore type='block'>
<format type='raw'/>
<source dev='/dev/mapper/base'/>
<backingStore/>
</backingStore>
</backingStore>
<target dev='vdd' bus='virtio'/>
</disk>
</devices>
...
-
disk - The
diskelement is the main container for describing disks and supports the following attributes:type- Valid values are "file", "block", "dir" (since 0.7.5), "network" (since 0.8.7), or "volume" (since 1.0.5) and refer to the underlying source for the disk. Since 0.0.3
device-
Indicates how the disk is to be exposed to the guest OS. Possible
values for this attribute are "floppy", "disk", "cdrom", and "lun",
defaulting to "disk".
Using "lun" (since 0.9.10) is only valid when the
typeis "block" or "network" forprotocol='iscsi'or when thetypeis "volume" when using an iSCSI sourcepoolformode"host" or as an NPIV virtual Host Bus Adapter (vHBA) using a Fibre Channel storage pool. Configured in this manner, the LUN behaves identically to "disk", except that generic SCSI commands from the guest are accepted and passed through to the physical device. Also note that device='lun' will only be recognized for actual raw devices, but never for individual partitions or LVM partitions (in those cases, the kernel will reject the generic SCSI commands, making it identical to device='disk'). Since 0.1.4 rawio-
Indicates whether the disk needs rawio capability. Valid
settings are "yes" or "no" (default is "no"). If any one disk
in a domain has rawio='yes', rawio capability will be enabled
for all disks in the domain (because, in the case of QEMU, this
capability can only be set on a per-process basis). This attribute
is only valid when device is "lun". NB,
rawiointends to confine the capability per-device, however, current QEMU implementation gives the domain process broader capability than that (per-process basis, affects all the domain disks). To confine the capability as much as possible for QEMU driver as this stage,sgiois recommended, it's more secure thanrawio. Since 0.9.10 sgio-
If supported by the hypervisor and OS, indicates whether
unprivileged SG_IO commands are filtered for the disk. Valid
settings are "filtered" or "unfiltered" where the default is
"filtered". Only available when the
deviceis 'lun'. Since 1.0.2 snapshot-
Indicates the default behavior of the disk during disk snapshots:
"
internal" requires a file format such as qcow2 that can store both the snapshot and the data changes since the snapshot; "external" will separate the snapshot from the live data; and "no" means the disk will not participate in snapshots. Read-only disks default to "no", while the default for other disks depends on the hypervisor's capabilities. Some hypervisors allow a per-snapshot choice as well, during domain snapshot creation. Not all snapshot modes are supported; for example, enabling snapshots with a transient disk generally does not make sense. Since 0.9.5
-
source - Representation of the disk
sourcedepends on the disktypeattribute value as follows:file-
The
fileattribute specifies the fully-qualified path to the file holding the disk. Since 0.0.3 block-
The
devattribute specifies the fully-qualified path to the host device to serve as the disk. Since 0.0.3 dir-
The
dirattribute specifies the fully-qualified path to the directory to use as the disk. Since 0.7.5 network-
The
protocolattribute specifies the protocol to access to the requested image. Possible values are "nbd", "iscsi", "rbd", "sheepdog", "gluster" or "vxhs".If the
protocolattribute is "rbd", "sheepdog", "gluster", or "vxhs", an additional attributenameis mandatory to specify which volume/image will be used.For "nbd", the
nameattribute is optional.For "iscsi" (since 1.0.4), the
nameattribute may include a logical unit number, separated from the target's name by a slash (e.g.,iqn.2013-07.com.example:iscsi-pool/1). If not specified, the default LUN is zero.For "vxhs" (since 3.8.0), the
Since 0.8.7nameis the UUID of the volume, assigned by the HyperScale server. Additionally, an optional attributetls(QEMU only) can be used to control whether a VxHS block device would utilize a hypervisor configured TLS X.509 certificate environment in order to encrypt the data channel. For the QEMU hypervisor, usage of a TLS environment can also be globally controlled on the host by thevxhs_tlsandvxhs_tls_x509_cert_dirordefault_tls_x509_cert_dirsettings in the file /etc/libvirt/qemu.conf. Ifvxhs_tlsis enabled, then unless the domaintlsattribute is set to "no", libvirt will use the host configured TLS environment. If thetlsattribute is set to "yes", then regardless of the qemu.conf setting, TLS authentication will be attempted. volume-
The underlying disk source is represented by attributes
poolandvolume. Attributepoolspecifies the name of the storage pool (managed by libvirt) where the disk source resides. Attributevolumespecifies the name of storage volume (managed by libvirt) used as the disk source. The value for thevolumeattribute will be the output from the "Name" column of avirsh vol-list [pool-name]command.Use the attribute
mode(since 1.1.1) to indicate how to represent the LUN as the disk source. Valid values are "direct" and "host". Ifmodeis not specified, the default is to use "host". Using "direct" as themodevalue indicates to use the storage pool'ssourceelementhostattribute as the disk source to generate the libiscsi URI (e.g. 'file=iscsi://example.com:3260/iqn.2013-07.com.example:iscsi-pool/1'). Using "host" as themodevalue indicates to use the LUN's path as it shows up on host (e.g. 'file=/dev/disk/by-path/ip-example.com:3260-iscsi-iqn.2013-07.com.example:iscsi-pool-lun-1'). Using a LUN from an iSCSI source pool provides the same features as adiskconfigured usingtype'block' or 'network' anddeviceof 'lun' with respect to how the LUN is presented to and may be used by the guest. Since 1.0.5
seclabel, described below (and since 0.9.9), can be used to override the domain security labeling policy for just that source file. (NB, for "volume" type disk,seclabelis only valid when the specified storage volume is of 'file' or 'block' type).The
sourceelement may contain the following sub elements:hostWhen the disk
typeis "network", thesourcemay have zero or morehostsub-elements used to specify the hosts to connect. Thehostelement supports 4 attributes, viz. "name", "port", "transport" and "socket", which specify the hostname, the port number, transport type and path to socket, respectively. The meaning of this element and the number of the elements depend on the protocol attribute.Protocol Meaning Number of hosts Default port nbd a server running nbd-server only one 10809 iscsi an iSCSI server only one 3260 rbd monitor servers of RBD one or more librados default sheepdog one of the sheepdog servers (default is localhost:7000) zero or one 7000 gluster a server running glusterd daemon one or more (Since 2.1.0), just one prior to that 24007 vxhs a server running Veritas HyperScale daemon only one 9999 gluster supports "tcp", "rdma", "unix" as valid values for the transport attribute. nbd supports "tcp" and "unix". Others only support "tcp". If nothing is specified, "tcp" is assumed. If the transport is "unix", the socket attribute specifies the path to an AF_UNIX socket.
snapshot-
The
nameattribute ofsnapshotelement can optionally specify an internal snapshot name to be used as the source for storage protocols. Supported for 'rbd' since 1.2.11 (QEMU only). config-
The
fileattribute for theconfigelement provides a fully qualified path to a configuration file to be provided as a parameter to the client of a networked storage protocol. Supported for 'rbd' since 1.2.11 (QEMU only). auth- Since libvirt 3.9.0, the
authelement is supported for a disktype"network" that is using asourceelement with theprotocolattributes "rbd" or "iscsi". If present, theauthelement provides the authentication credentials needed to access the source. It includes a mandatory attributeusername, which identifies the username to use during authentication, as well as a sub-elementsecretwith mandatory attributetype, to tie back to a libvirt secret object that holds the actual password or other credentials (the domain XML intentionally does not expose the password, only the reference to the object that does manage the password). Known secret types are "ceph" for Ceph RBD network sources and "iscsi" for CHAP authentication of iSCSI targets. Both will require either auuidattribute with the UUID of the secret object or ausageattribute matching the key that was specified in the secret object. - Since libvirt 3.9.0, the
encryptioncan be a sub-element of thesourceelement for encrypted storage sources. If present, specifies how the storage source is encrypted See the Storage Encryption page for more information.
For a "file" or "volume" disk type which represents a cdrom or floppy (the
deviceattribute), it is possible to define policy what to do with the disk if the source file is not accessible. (NB,startupPolicyis not valid for "volume" disk unless the specified storage volume is of "file" type). This is done by thestartupPolicyattribute (since 0.9.7), accepting these values:mandatory fail if missing for any reason (the default) requisite fail if missing on boot up, drop if missing on migrate/restore/revert optional drop if missing at any start attempt Since 1.1.2 the
startupPolicyis extended to support hard disks besides cdrom and floppy. On guest cold bootup, if a certain disk is not accessible or its disk chain is broken, with startupPolicy 'optional' the guest will drop this disk. This feature doesn't support migration currently. -
backingStore -
This element describes the backing store used by the disk
specified by sibling
sourceelement. It is currently ignored on input and only used for output to describe the detected backing chains of running domains since 1.2.4 (although a future version of libvirt may start accepting chains on input, or output information for offline domains). An emptybackingStoreelement means the sibling source is self-contained and is not based on any backing store. For backing chain information to be accurate, the backing format must be correctly specified in the metadata of each file of the chain (files created by libvirt satisfy this property, but using existing external files for snapshot or block copy operations requires the end user to pre-create the file correctly). The following attributes are supported inbackingStore:type-
The
typeattribute represents the type of disk used by the backing store, see disk type attribute above for more details and possible values. index-
This attribute is only valid in output (and ignored on input) and
it can be used to refer to a specific part of the disk chain when
doing block operations (such as via the
virDomainBlockRebaseAPI). For example,vda[2]refers to the backing store withindex='2'of the disk withvdatarget.
backingStoresupports the following sub-elements:format-
The
formatelement containstypeattribute which specifies the internal format of the backing store, such asraworqcow2. source-
This element has the same structure as the
sourceelement indisk. It specifies which file, device, or network location contains the data of the described backing store. backingStore-
If the backing store is not self-contained, the next element
in the chain is described by nested
backingStoreelement.
-
mirror -
This element is present if the hypervisor has started a
long-running block job operation, where the mirror location in
the
sourcesub-element will eventually have the same contents as the source, and with the file format in the sub-elementformat(which might differ from the format of the source). The details of thesourcesub-element are determined by thetypeattribute of the mirror, similar to what is done for the overalldiskdevice element. Thejobattribute mentions which API started the operation ("copy" for thevirDomainBlockRebaseAPI, or "active-commit" for thevirDomainBlockCommitAPI), since 1.2.7. The attributeready, if present, tracks progress of the job:yesif the disk is known to be ready to pivot, or, since 1.2.7,abortorpivotif the job is in the process of completing. Ifreadyis not present, the disk is probably still copying. For now, this element only valid in output; it is ignored on input. Thesourcesub-element exists for all two-phase jobs since 1.2.6. Older libvirt supported only block copy to a file, since 0.9.12; for compatibility with older clients, such jobs include redundant information in the attributesfileandformatin themirrorelement. -
target - The
targetelement controls the bus / device under which the disk is exposed to the guest OS. Thedevattribute indicates the "logical" device name. The actual device name specified is not guaranteed to map to the device name in the guest OS. Treat it as a device ordering hint. The optionalbusattribute specifies the type of disk device to emulate; possible values are driver specific, with typical values being "ide", "scsi", "virtio", "xen", "usb", "sata", or "sd" "sd" since 1.1.2. If omitted, the bus type is inferred from the style of the device name (e.g. a device named 'sda' will typically be exported using a SCSI bus). The optional attributetrayindicates the tray status of the removable disks (i.e. CDROM or Floppy disk), the value can be either "open" or "closed", defaults to "closed". NB, the value oftraycould be updated while the domain is running. The optional attributeremovablesets the removable flag for USB disks, and its value can be either "on" or "off", defaulting to "off". Since 0.0.3;busattribute since 0.4.3;trayattribute since 0.9.11; "usb" attribute value since after 0.4.4; "sata" attribute value since 0.9.7; "removable" attribute value since 1.1.3 -
iotune - The optional
iotuneelement provides the ability to provide additional per-device I/O tuning, with values that can vary for each device (contrast this to the<blkiotune>element, which applies globally to the domain). Currently, the only tuning available is Block I/O throttling for qemu. This element has optional sub-elements; any sub-element not specified or given with a value of 0 implies no limit. Since 0.9.8total_bytes_sec- The optional
total_bytes_secelement is the total throughput limit in bytes per second. This cannot appear withread_bytes_secorwrite_bytes_sec. read_bytes_sec- The optional
read_bytes_secelement is the read throughput limit in bytes per second. write_bytes_sec- The optional
write_bytes_secelement is the write throughput limit in bytes per second. total_iops_sec- The optional
total_iops_secelement is the total I/O operations per second. This cannot appear withread_iops_secorwrite_iops_sec. read_iops_sec- The optional
read_iops_secelement is the read I/O operations per second. write_iops_sec- The optional
write_iops_secelement is the write I/O operations per second. total_bytes_sec_max- The optional
total_bytes_sec_maxelement is the maximum total throughput limit in bytes per second. This cannot appear withread_bytes_sec_maxorwrite_bytes_sec_max. read_bytes_sec_max- The optional
read_bytes_sec_maxelement is the maximum read throughput limit in bytes per second. write_bytes_sec_max- The optional
write_bytes_sec_maxelement is the maximum write throughput limit in bytes per second. total_iops_sec_max- The optional
total_iops_sec_maxelement is the maximum total I/O operations per second. This cannot appear withread_iops_sec_maxorwrite_iops_sec_max. read_iops_sec_max- The optional
read_iops_sec_maxelement is the maximum read I/O operations per second. write_iops_sec_max- The optional
write_iops_sec_maxelement is the maximum write I/O operations per second. size_iops_sec- The optional
size_iops_secelement is the size of I/O operations per second.Throughput limits since 1.2.11 and QEMU 1.7
group_name- The optional
group_nameprovides the cability to share I/O throttling quota between multiple drives. This prevents end-users from circumventing a hosting provider's throttling policy by splitting 1 large drive in N small drives and getting N times the normal throttling quota. Any name may be used.group_name since 3.0.0 and QEMU 2.4
total_bytes_sec_max_length- The optional
total_bytes_sec_max_lengthelement is the maximum duration in seconds for thetotal_bytes_sec_maxburst period. Only valid when thetotal_bytes_sec_maxis set. read_bytes_sec_max_length- The optional
read_bytes_sec_max_lengthelement is the maximum duration in seconds for theread_bytes_sec_maxburst period. Only valid when theread_bytes_sec_maxis set. write_bytes_sec_max- The optional
write_bytes_sec_max_lengthelement is the maximum duration in seconds for thewrite_bytes_sec_maxburst period. Only valid when thewrite_bytes_sec_maxis set. total_iops_sec_max_length- The optional
total_iops_sec_max_lengthelement is the maximum duration in seconds for thetotal_iops_sec_maxburst period. Only valid when thetotal_iops_sec_maxis set. read_iops_sec_max_length- The optional
read_iops_sec_max_lengthelement is the maximum duration in seconds for theread_iops_sec_maxburst period. Only valid when theread_iops_sec_maxis set. write_iops_sec_max- The optional
write_iops_sec_max_lengthelement is the maximum duration in seconds for thewrite_iops_sec_maxburst period. Only valid when thewrite_iops_sec_maxis set.Throughput length since 2.4.0 and QEMU 2.6
-
driver -
The optional driver element allows specifying further details
related to the hypervisor driver used to provide the disk.
Since 0.1.8
-
If the hypervisor supports multiple backend drivers, then
the
nameattribute selects the primary backend driver name, while the optionaltypeattribute provides the sub-type. For example, xen supports a name of "tap", "tap2", "phy", or "file", with a type of "aio", while qemu only supports a name of "qemu", but multiple types including "raw", "bochs", "qcow2", and "qed". -
The optional
cacheattribute controls the cache mechanism, possible values are "default", "none", "writethrough", "writeback", "directsync" (like "writethrough", but it bypasses the host page cache) and "unsafe" (host may cache all disk io, and sync requests from guest are ignored). Since 0.6.0, "directsync" since 0.9.5, "unsafe" since 0.9.7 -
The optional
error_policyattribute controls how the hypervisor will behave on a disk read or write error, possible values are "stop", "report", "ignore", and "enospace".Since 0.8.0, "report" since 0.9.7 The default is left to the discretion of the hypervisor. There is also an optionalrerror_policythat controls behavior for read errors only. Since 0.9.7. If no rerror_policy is given, error_policy is used for both read and write errors. If rerror_policy is given, it overrides theerror_policyfor read errors. Also note that "enospace" is not a valid policy for read errors, so iferror_policyis set to "enospace" and norerror_policyis given, the read error policy will be left at its default. -
The optional
ioattribute controls specific policies on I/O; qemu guests support "threads" and "native". Since 0.8.8 -
The optional
ioeventfdattribute allows users to set domain I/O asynchronous handling for disk device. The default is left to the discretion of the hypervisor. Accepted values are "on" and "off". Enabling this allows qemu to execute VM while a separate thread handles I/O. Typically guests experiencing high system CPU utilization during I/O will benefit from this. On the other hand, on overloaded host it could increase guest I/O latency. Since 0.9.3 (QEMU and KVM only) In general you should leave this option alone, unless you are very certain you know what you are doing. -
The optional
event_idxattribute controls some aspects of device event processing. The value can be either 'on' or 'off' - if it is on, it will reduce the number of interrupts and exits for the guest. The default is determined by QEMU; usually if the feature is supported, default is on. In case there is a situation where this behavior is suboptimal, this attribute provides a way to force the feature off. Since 0.9.5 (QEMU and KVM only) In general you should leave this option alone, unless you are very certain you know what you are doing. -
The optional
copy_on_readattribute controls whether to copy read backing file into the image file. The value can be either "on" or "off". Copy-on-read avoids accessing the same backing file sectors repeatedly and is useful when the backing file is over a slow network. By default copy-on-read is off. Since 0.9.10 (QEMU and KVM only) -
The optional
discardattribute controls whether discard requests (also known as "trim" or "unmap") are ignored or passed to the filesystem. The value can be either "unmap" (allow the discard request to be passed) or "ignore" (ignore the discard request). Since 1.0.6 (QEMU and KVM only) -
The optional
detect_zeroesattribute controls whether to detect zero write requests. The value can be "off", "on" or "unmap". First two values turn the detection off and on, respectively. The third value ("unmap") turns the detection on and additionally tries to discard such areas from the image based on the value ofdiscardabove (it will act as "on" ifdiscardis set to "ignore"). NB enabling the detection is a compute intensive operation, but can save file space and/or time on slow media. Since 2.0.0 -
The optional
iothreadattribute assigns the disk to an IOThread as defined by the range for the domainiothreadsvalue. Multiple disks may be assigned to the same IOThread and are numbered from 1 to the domain iothreads value. Available for a disk devicetargetconfigured to use "virtio"busand "pci" or "ccw"addresstypes. Since 1.2.8 (QEMU 2.1) -
The optional
queuesattribute specifies the number of virt queues for virtio-blk. (Since 3.9.0) - For virtio disks, Virtio-specific options can also be set. (Since 3.5.0)
-
If the hypervisor supports multiple backend drivers, then
the
-
backenddomain - The optional
backenddomainelement allows specifying a backend domain (aka driver domain) hosting the disk. Use thenameattribute to specify the backend domain name. Since 1.2.13 (Xen only) -
boot - Specifies that the disk is bootable. The
orderattribute determines the order in which devices will be tried during boot sequence. On the S390 architecture only the first boot device is used. The optionalloadparmattribute is an 8 character string which can be queried by guests on S390 via sclp or diag 308. Linux guests on S390 can useloadparmto select a boot entry. Since 3.5.0 The per-devicebootelements cannot be used together with general boot elements in BIOS bootloader section. Since 0.8.8 -
encryption - Starting with libvirt 3.9.0 the
encryptionelement is preferred to be a sub-element of thesourceelement. If present, specifies how the volume is encrypted using "qcow". See the Storage Encryption page for more information. -
readonly - If present, this indicates the device cannot be modified by
the guest. For now, this is the default for disks with
attribute
device='cdrom'. -
shareable - If present, this indicates the device is expected to be shared between domains (assuming the hypervisor and OS support this), which means that caching should be deactivated for that device.
-
transient - If present, this indicates that changes to the device contents should be reverted automatically when the guest exits. With some hypervisors, marking a disk transient prevents the domain from participating in migration or snapshots. Since 0.9.5
-
serial - If present, this specify serial number of virtual hard drive.
For example, it may look
like
<serial>WD-WMAP9A966149</serial>. Not supported for scsi-block devices, that is those using disktype'block' usingdevice'lun' onbus'scsi'. Since 0.7.1 -
wwn - If present, this element specifies the WWN (World Wide Name) of a virtual hard disk or CD-ROM drive. It must be composed of 16 hexadecimal digits. Since 0.10.1
-
vendor - If present, this element specifies the vendor of a virtual hard disk or CD-ROM device. It must not be longer than 8 printable characters. Since 1.0.1
-
product - If present, this element specifies the product of a virtual hard disk or CD-ROM device. It must not be longer than 16 printable characters. Since 1.0.1
-
address - If present, the
addresselement ties the disk to a given slot of a controller (the actual<controller>device can often be inferred by libvirt, although it can be explicitly specified). Thetypeattribute is mandatory, and is typically "pci" or "drive". For a "pci" controller, additional attributes forbus,slot, andfunctionmust be present, as well as optionaldomainandmultifunction. Multifunction defaults to 'off'; any other value requires QEMU 0.1.3 and libvirt 0.9.7. For a "drive" controller, additional attributescontroller,bus,target(libvirt 0.9.11), andunitare available, each defaulting to 0. -
auth - Starting with libvirt 3.9.0 the
authelement is preferred to be a sub-element of thesourceelement. The element is still read and managed as adisksub-element. It is invalid to useauthas both a sub-element ofdiskandsource. Theauthelement was introduced as adisksub-element in libvirt 0.9.7. -
geometry - The optional
geometryelement provides the ability to override geometry settings. This mostly useful for S390 DASD-disks or older DOS-disks. 0.10.0cyls- The
cylsattribute is the number of cylinders. heads- The
headsattribute is the number of heads. secs- The
secsattribute is the number of sectors per track. trans- The optional
transattribute is the BIOS-Translation-Modus (none, lba or auto)
-
blockio - If present, the
blockioelement allows to override any of the block device properties listed below. Since 0.10.2 (QEMU and KVM)logical_block_size- The logical block size the disk will report to the guest OS. For Linux this would be the value returned by the BLKSSZGET ioctl and describes the smallest units for disk I/O.
physical_block_size- The physical block size the disk will report to the guest OS. For Linux this would be the value returned by the BLKPBSZGET ioctl and describes the disk's hardware sector size which can be relevant for the alignment of disk data.
Filesystems ¶
A directory on the host that can be accessed directly from the guest. since 0.3.3, since 0.8.5 for QEMU/KVM
...
<devices>
<filesystem type='template'>
<source name='my-vm-template'/>
<target dir='/'/>
</filesystem>
<filesystem type='mount' accessmode='passthrough'>
<driver type='path' wrpolicy='immediate'/>
<source dir='/export/to/guest'/>
<target dir='/import/from/host'/>
<readonly/>
</filesystem>
<filesystem type='file' accessmode='passthrough'>
<driver name='loop' type='raw'/>
<driver type='path' wrpolicy='immediate'/>
<source file='/export/to/guest.img'/>
<target dir='/import/from/host'/>
<readonly/>
</filesystem>
...
</devices>
...
-
filesystem -
The filesystem attribute
typespecifies the type of thesource. The possible values are:mount-
A host directory to mount in the guest. Used by LXC,
OpenVZ (since 0.6.2)
and QEMU/KVM (since 0.8.5).
This is the default
typeif one is not specified. This mode also has an optional sub-elementdriver, with an attributetype='path'ortype='handle'(since 0.9.7). The driver block has an optional attributewrpolicythat further controls interaction with the host page cache; omitting the attribute gives default behavior, while the valueimmediatemeans that a host writeback is immediately triggered for all pages touched during a guest file write operation (since 0.9.10). template- OpenVZ filesystem template. Only used by OpenVZ driver.
file- A host file will be treated as an image and mounted in the guest. The filesystem format will be autodetected. Only used by LXC driver.
block- A host block device to mount in the guest. The filesystem format will be autodetected. Only used by LXC driver (since 0.9.5).
ram-
An in-memory filesystem, using memory from the host OS.
The source element has a single attribute
usagewhich gives the memory usage limit in KiB, unless units are specified by theunitsattribute. Only used by LXC driver. (since 0.9.13) bind- A directory inside the guest will be bound to another directory inside the guest. Only used by LXC driver (since 0.9.13)
accessmodewhich specifies the security mode for accessing the source (since 0.8.5). Currently this only works withtype='mount'for the QEMU/KVM driver. The possible values are:passthrough-
The
sourceis accessed with the permissions of the user inside the guest. This is the defaultaccessmodeif one is not specified. More info mapped-
The
sourceis accessed with the permissions of the hypervisor (QEMU process). More info squash- Similar to 'passthrough', the exception is that failure of privileged operations like 'chown' are ignored. This makes a passthrough-like mode usable for people who run the hypervisor as non-root. More info
-
driver -
The optional driver element allows specifying further details
related to the hypervisor driver used to provide the filesystem.
Since 1.0.6
-
If the hypervisor supports multiple backend drivers, then
the
typeattribute selects the primary backend driver name, while theformatattribute provides the format type. For example, LXC supports a type of "loop", with a format of "raw" or "nbd" with any format. QEMU supports a type of "path" or "handle", but no formats. Virtuozzo driver supports a type of "ploop" with a format of "ploop". - For virtio-backed devices, Virtio-specific options can also be set. (Since 3.5.0)
-
If the hypervisor supports multiple backend drivers, then
the
-
source -
The resource on the host that is being accessed in the guest. The
nameattribute must be used withtype='template', and thedirattribute must be used withtype='mount'. Theusageattribute is used withtype='ram'to set the memory limit in KiB, unless units are specified by theunitsattribute. -
target -
Where the
sourcecan be accessed in the guest. For most drivers this is an automatic mount point, but for QEMU/KVM this is merely an arbitrary string tag that is exported to the guest as a hint for where to mount. -
readonly - Enables exporting filesystem as a readonly mount for guest, by default read-write access is given (currently only works for QEMU/KVM driver).
-
space_hard_limit - Maximum space available to this guest's filesystem. Since 0.9.13
-
space_soft_limit - Maximum space available to this guest's filesystem. The container is permitted to exceed its soft limits for a grace period of time. Afterwards the hard limit is enforced. Since 0.9.13
Device Addresses ¶
Many devices have an optional <address>
sub-element to describe where the device is placed on the
virtual bus presented to the guest. If an address (or any
optional attribute within an address) is omitted on
input, libvirt will generate an appropriate address; but an
explicit address is required if more control over layout is
required. See below for device examples including an address
element.
Every address has a mandatory attribute type that
describes which bus the device is on. The choice of which
address to use for a given device is constrained in part by the
device and the architecture of the guest. For example,
a <disk> device
uses type='drive', while
a <console> device would
use type='pci' on i686 or x86_64 guests,
or type='spapr-vio' on PowerPC64 pseries guests.
Each address type has further optional attributes that control
where on the bus the device will be placed:
-
pci - PCI addresses have the following additional
attributes:
domain(a 2-byte hex integer, not currently used by qemu),bus(a hex value between 0 and 0xff, inclusive),slot(a hex value between 0x0 and 0x1f, inclusive), andfunction(a value between 0 and 7, inclusive). Also available is themultifunctionattribute, which controls turning on the multifunction bit for a particular slot/function in the PCI control register (since 0.9.7, requires QEMU 0.13).multifunctiondefaults to 'off', but should be set to 'on' for function 0 of a slot that will have multiple functions used.
Since 1.3.5, some hypervisor drivers may accept an<address type='pci'/>element with no other attributes as an explicit request to assign a PCI address for the device rather than some other type of address that may also be appropriate for that same device (e.g. virtio-mmio). -
drive - Drive addresses have the following additional
attributes:
controller(a 2-digit controller number),bus(a 2-digit bus number),target(a 2-digit target number), andunit(a 2-digit unit number on the bus). -
virtio-serial - Each virtio-serial address has the following additional
attributes:
controller(a 2-digit controller number),bus(a 2-digit bus number), andslot(a 2-digit slot within the bus). -
ccid - A CCID address, for smart-cards, has the following
additional attributes:
bus(a 2-digit bus number), andslotattribute (a 2-digit slot within the bus). Since 0.8.8. -
usb - USB addresses have the following additional
attributes:
bus(a hex value between 0 and 0xfff, inclusive), andport(a dotted notation of up to four octets, such as 1.2 or 2.1.3.1). -
spapr-vio - On PowerPC pseries guests, devices can be assigned to the
SPAPR-VIO bus. It has a flat 64-bit address space; by
convention, devices are generally assigned at a non-zero
multiple of 0x1000, but other addresses are valid and
permitted by libvirt. Each address has the following
additional attribute:
reg(the hex value address of the starting register). Since 0.9.9. -
ccw - S390 guests with a
machinevalue of s390-ccw-virtio use the native CCW bus for I/O devices. CCW bus addresses have the following additional attributes:cssid(a hex value between 0 and 0xfe, inclusive),ssid(a value between 0 and 3, inclusive) anddevno(a hex value between 0 and 0xffff, inclusive). Partially specified bus addresses are not allowed. If omitted, libvirt will assign a free bus address with cssid=0xfe and ssid=0. Virtio-ccw devices must have their cssid set to 0xfe. Since 1.0.4 -
virtio-mmio - This places the device on the virtio-mmio transport, which is
currently only available for some
armv7landaarch64virtual machines. virtio-mmio addresses do not have any additional attributes. Since 1.1.3
If the guest architecture isaarch64and the machine type isvirt, libvirt will automatically assign PCI addresses to devices; however, the presence of a single device with virtio-mmio address in the guest configuration will cause libvirt to assign virtio-mmio addresses to all further devices. Since 3.0.0 -
isa - ISA addresses have the following additional
attributes:
iobaseandirq. Since 1.2.1
Virtio-related options ¶
QEMU's virtio devices have some attributes related to the virtio transport under
the driver element:
The iommu attribute enables the use of emulated IOMMU
by the device. The attribute ats controls the Address
Translation Service support for PCIe devices. This is needed to make use
of IOTLB support (see IOMMU device).
Possible values are on or off.
Since 3.5.0
Controllers ¶
Depending on the guest architecture, some device buses can appear more than once, with a group of virtual devices tied to a virtual controller. Normally, libvirt can automatically infer such controllers without requiring explicit XML markup, but sometimes it is necessary to provide an explicit controller element, notably when planning the PCI topology for guests where device hotplug is expected.
...
<devices>
<controller type='ide' index='0'/>
<controller type='virtio-serial' index='0' ports='16' vectors='4'/>
<controller type='virtio-serial' index='1'>
<address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/>
</controller>
<controller type='scsi' index='0' model='virtio-scsi'>
<driver iothread='4'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/>
</controller>
...
</devices>
...
Each controller has a mandatory attribute type,
which must be one of 'ide', 'fdc', 'scsi', 'sata', 'usb',
'ccid', 'virtio-serial' or 'pci', and a mandatory
attribute index which is the decimal integer
describing in which order the bus controller is encountered (for
use in controller attributes of
<address> elements).
Since 1.3.5 the index is optional; if
not specified, it will be auto-assigned to be the lowest unused
index for the given controller type. Some controller types have
additional attributes that control specific features, such as:
-
virtio-serial - The
virtio-serialcontroller has two additional optional attributesportsandvectors, which control how many devices can be connected through the controller. -
scsi - A
scsicontroller has an optional attributemodel, which is one of 'auto', 'buslogic', 'ibmvscsi', 'lsilogic', 'lsisas1068', 'lsisas1078', 'virtio-scsi' or 'vmpvscsi'. -
usb - A
usbcontroller has an optional attributemodel, which is one of "piix3-uhci", "piix4-uhci", "ehci", "ich9-ehci1", "ich9-uhci1", "ich9-uhci2", "ich9-uhci3", "vt82c686b-uhci", "pci-ohci", "nec-xhci", "qusb1" (xen pvusb with qemu backend, version 1.1), "qusb2" (xen pvusb with qemu backend, version 2.0) or "qemu-xhci". Additionally, since 0.10.0, if the USB bus needs to be explicitly disabled for the guest,model='none'may be used. Since 1.0.5, no default USB controller will be built on s390. Since 1.3.5, USB controllers accept aportsattribute to configure how many devices can be connected to the controller. -
ide - Since 3.10.0 for the vbox driver, the
idecontroller has an optional attributemodel, which is one of "piix3", "piix4" or "ich6".
Note: The PowerPC64 "spapr-vio" addresses do not have an associated controller.
For controllers that are themselves devices on a PCI or USB bus,
an optional sub-element <address> can specify
the exact relationship of the controller to its master bus, with
semantics given above.
An optional sub-element driver can specify the driver
specific options:
-
queues -
The optional
queuesattribute specifies the number of queues for the controller. For best performance, it's recommended to specify a value matching the number of vCPUs. Since 1.0.5 (QEMU and KVM only) -
cmd_per_lun -
The optional
cmd_per_lunattribute specifies the maximum number of commands that can be queued on devices controlled by the host. Since 1.2.7 (QEMU and KVM only) -
max_sectors -
The optional
max_sectorsattribute specifies the maximum amount of data in bytes that will be transferred to or from the device in a single command. The transfer length is measured in sectors, where a sector is 512 bytes. Since 1.2.7 (QEMU and KVM only) -
ioeventfd -
The optional
ioeventfdattribute specifies whether the controller should use I/O asynchronous handling or not. Accepted values are "on" and "off". Since 1.2.18 -
iothread -
Supported for controller type
scsiusing modelvirtio-scsiforaddresstypespciandccwsince 1.3.5 (QEMU 2.4). The optionaliothreadattribute assigns the controller to an IOThread as defined by the range for the domainiothreadsvalue. Each SCSIdiskassigned to use the specifiedcontrollerwill utilize the same IOThread. If a specific IOThread is desired for a specific SCSIdisk, then multiple controllers must be defined each having a specificiothreadvalue. Theiothreadvalue must be within the range 1 to the domain iothreads value. - virtio options
- For virtio controllers, Virtio-specific options can also be set. (Since 3.5.0)
USB companion controllers have an optional
sub-element <master> to specify the exact
relationship of the companion to its master controller.
A companion controller is on the same bus as its master, so
the companion index value should be equal.
Not all controller models can be used as companion controllers
and libvirt might provide some sensible defaults (settings
of master startport and function of an
address) for some particular models.
Preferred companion controllers are ich-uhci[123].
...
<devices>
<controller type='usb' index='0' model='ich9-ehci1'>
<address type='pci' domain='0' bus='0' slot='4' function='7'/>
</controller>
<controller type='usb' index='0' model='ich9-uhci1'>
<master startport='0'/>
<address type='pci' domain='0' bus='0' slot='4' function='0' multifunction='on'/>
</controller>
...
</devices>
...
PCI controllers have an optional model attribute with
possible values pci-root, pcie-root,
pcie-root-port, pci-bridge,
dmi-to-pci-bridge, pcie-switch-upstream-port,
pcie-switch-downstream-port, pci-expander-bus,
or pcie-expander-bus. (pci-root and
pci-bridge since 1.0.5, pcie-root and
dmi-to-pci-bridge since 1.1.2,
pcie-root-port, pcie-switch-upstream-port,
pcie-switch-downstream-port since
1.2.19, and pci-expander-bus and
pcie-expander-bus since 1.3.4) The
root controllers (pci-root
and pcie-root) have an
optional pcihole64 element specifying how big (in
kilobytes, or in the unit specified by pcihole64's
unit attribute) the 64-bit PCI hole should be. Some guests (like
Windows XP or Windows Server 2003) might crash when QEMU and Seabios
are recent enough to support 64-bit PCI holes, unless this is disabled
(set to 0). Since 1.1.2 (QEMU only)
PCI controllers also have an optional
subelement <model> with an attribute
name. The name attribute holds the name of the
specific device that qemu is emulating (e.g. "i82801b11-bridge")
rather than simply the class of device ("dmi-to-pci-bridge",
"pci-bridge"), which is set in the controller element's
model attribute. In almost all cases, you should not
manually add a <model> subelement to a
controller, nor should you modify one that is automatically
generated by libvirt. Since 1.2.19 (QEMU
only).
PCI controllers also have an optional
subelement <target> with the attributes and
subelements listed below. These are configurable items that 1)
are visible to the guest OS so must be preserved for guest ABI
compatibility, and 2) are usually left to default values or
derived automatically by libvirt. In almost all cases, you
should not manually add a <target> subelement
to a controller, nor should you modify the values in the those
that are automatically generated by
libvirt. Since 1.2.19 (QEMU only).
-
chassisNr -
PCI controllers that have attribute model="pci-bridge", can
also have a
chassisNrattribute in the<target>subelement, which is used to control QEMU's "chassis_nr" option for the pci-bridge device (normally libvirt automatically sets this to the same value as the index attribute of the pci controller). If set, chassisNr must be between 1 and 255. -
chassis -
pcie-root-port and pcie-switch-downstream-port controllers can
also have a
chassisattribute in the<target>subelement, which is used to set the controller's "chassis" configuration value, which is visible to the virtual machine. If set, chassis must be between 0 and 255. -
port -
pcie-root-port and pcie-switch-downstream-port controllers can
also have a
portattribute in the<target>subelement, which is used to set the controller's "port" configuration value, which is visible to the virtual machine. If set, port must be between 0 and 255. -
busNr -
pci-expander-bus and pcie-expander-bus controllers can have an
optional
busNrattribute (1-254). This will be the bus number of the new bus; All bus numbers between that specified and 255 will be available only for assignment to PCI/PCIe controllers plugged into the hierarchy starting with this expander bus, and bus numbers less than the specified value will be available to the next lower expander-bus (or the root-bus if there are no lower expander buses). If you do not specify a busNumber, libvirt will find the lowest existing busNumber in all other expander buses (or use 256 if there are no others) and auto-assign the busNr of that found bus - 2, which provides one bus number for the pci-expander-bus and one for the pci-bridge that is automatically attached to it (if you plan on adding more pci-bridges to the hierarchy of the bus, you should manually set busNr to a lower value).A similar algorithm is used for automatically determining the busNr attribute for pcie-expander-bus, but since the pcie-expander-bus doesn't have any built-in pci-bridge, the 2nd bus-number is just being reserved for the pcie-root-port that must necessarily be connected to the bus in order to actually plug in an endpoint device. If you intend to plug multiple devices into a pcie-expander-bus, you must connect a pcie-switch-upstream-port to the pcie-root-port that is plugged into the pcie-expander-bus, and multiple pcie-switch-downstream-ports to the pcie-switch-upstream-port, and of course for this to work properly, you will need to decrease the pcie-expander-bus' busNr accordingly so that there are enough unused bus numbers above it to accomodate giving out one bus number for the upstream-port and one for each downstream-port (in addition to the pcie-root-port and the pcie-expander-bus itself).
-
node -
Some PCI controllers (
pci-expander-busfor the pc machine type,pcie-expander-busfor the q35 machine type and, since 3.6.0,pci-rootfor the pseries machine type) can have an optional<node>subelement within the<target>subelement, which is used to set the NUMA node reported to the guest OS for that bus - the guest OS will then know that all devices on that bus are a part of the specified NUMA node (it is up to the user of the libvirt API to attach host devices to the correct pci-expander-bus when assigning them to the domain). -
index - pci-root controllers for pSeries guests use this attribute to record the order they will show up in the guest. Since 3.6.0
For machine types which provide an implicit PCI bus, the pci-root controller with index=0 is auto-added and required to use PCI devices. pci-root has no address. PCI bridges are auto-added if there are too many devices to fit on the one bus provided by pci-root, or a PCI bus number greater than zero was specified. PCI bridges can also be specified manually, but their addresses should only refer to PCI buses provided by already specified PCI controllers. Leaving gaps in the PCI controller indexes might lead to an invalid configuration.
...
<devices>
<controller type='pci' index='0' model='pci-root'/>
<controller type='pci' index='1' model='pci-bridge'>
<address type='pci' domain='0' bus='0' slot='5' function='0' multifunction='off'/>
</controller>
</devices>
...
For machine types which provide an implicit PCI Express (PCIe)
bus (for example, the machine types based on the Q35 chipset),
the pcie-root controller with index=0 is auto-added to the
domain's configuration. pcie-root has also no address, provides
31 slots (numbered 1-31) that can be used to attach PCIe or PCI
devices (although libvirt will never auto-assign a PCI device to
a PCIe slot, it will allow manual specification of such an
assignment). Devices connected to pcie-root cannot be
hotplugged. In order to make standard PCI slots available on a
system which has a pcie-root controller, a pci controller
with model='dmi-to-pci-bridge' is automatically
added, usually at the defacto standard location of slot=0x1e. A
dmi-to-pci-bridge controller plugs into a PCIe slot (as provided
by pcie-root), and itself provides 31 standard PCI slots (which
also do not support device hotplug). In order to have
hot-pluggable PCI slots in the guest system, a pci-bridge
controller will also be automatically created and connected to
one of the slots of the auto-created dmi-to-pci-bridge
controller; all guest PCI devices with addresses that are
auto-determined by libvirt will be placed on this pci-bridge
device. (since 1.1.2).
Domains with an implicit pcie-root can also add controllers
with model='pcie-root-port',
model='pcie-switch-upstream-port',
and model='pcie-switch-downstream-port'. pcie-root-port
is a simple type of bridge device that can connect only to one
of the 31 slots on the pcie-root bus on its upstream side, and
makes a single (PCIe, hotpluggable) port available on the
downstream side (at slot='0'). pcie-root-port can be used to
provide a single slot to later hotplug a PCIe device (but is not
itself hotpluggable - it must be in the configuration when the
domain is started).
(since 1.2.19)
pcie-switch-upstream-port is a more flexible (but also more complex) device that can only plug into a pcie-root-port or pcie-switch-downstream-port on the upstream side (and only before the domain is started - it is not hot-pluggable), and provides 32 ports on the downstream side (slot='0' - slot='31') that accept only pcie-switch-downstream-port devices; each pcie-switch-downstream-port device can only plug into a pcie-switch-upstream-port on its upstream side (again, not hot-pluggable), and on its downstream side provides a single hotpluggable pcie port that can accept any standard pci or pcie device (or another pcie-switch-upstream-port), i.e. identical in function to a pcie-root-port. (since 1.2.19)
...
<devices>
<controller type='pci' index='0' model='pcie-root'/>
<controller type='pci' index='1' model='dmi-to-pci-bridge'>
<address type='pci' domain='0' bus='0' slot='0xe' function='0'/>
</controller>
<controller type='pci' index='2' model='pci-bridge'>
<address type='pci' domain='0' bus='1' slot='1' function='0'/>
</controller>
</devices>
...
Device leases ¶
When using a lock manager, it may be desirable to record device leases against a VM. The lock manager will ensure the VM won't start unless the leases can be acquired.
...
<devices>
...
<lease>
<lockspace>somearea</lockspace>
<key>somekey</key>
<target path='/some/lease/path' offset='1024'/>
</lease>
...
</devices>
...
-
lockspace - This is an arbitrary string, identifying the lockspace within which the key is held. Lock managers may impose extra restrictions on the format, or length of the lockspace name.
-
key - This is an arbitrary string, uniquely identifying the lease to be acquired. Lock managers may impose extra restrictions on the format, or length of the key.
-
target - This is the fully qualified path of the file associated with the lockspace. The offset specifies where the lease is stored within the file. If the lock manager does not require a offset, just pass 0.
Host device assignment ¶
USB / PCI / SCSI devices ¶
USB, PCI and SCSI devices attached to the host can be passed through
to the guest using the hostdev element.
since after 0.4.4 for USB, 0.6.0 for PCI(KVM only)
and 1.0.6 for SCSI(KVM only):
...
<devices>
<hostdev mode='subsystem' type='usb'>
<source startupPolicy='optional'>
<vendor id='0x1234'/>
<product id='0xbeef'/>
</source>
<boot order='2'/>
</hostdev>
</devices>
...
or:
...
<devices>
<hostdev mode='subsystem' type='pci' managed='yes'>
<source>
<address domain='0x0000' bus='0x06' slot='0x02' function='0x0'/>
</source>
<boot order='1'/>
<rom bar='on' file='/etc/fake/boot.bin'/>
</hostdev>
</devices>
...
or:
...
<devices>
<hostdev mode='subsystem' type='scsi' sgio='filtered' rawio='yes'>
<source>
<adapter name='scsi_host0'/>
<address bus='0' target='0' unit='0'/>
</source>
<readonly/>
<address type='drive' controller='0' bus='0' target='0' unit='0'/>
</hostdev>
</devices>
...
or:
...
<devices>
<hostdev mode='subsystem' type='scsi'>
<source protocol='iscsi' name='iqn.2014-08.com.example:iscsi-nopool/1'>
<host name='example.com' port='3260'/>
<auth username='myuser'>
<secret type='iscsi' usage='libvirtiscsi'/>
</auth>
</source>
<address type='drive' controller='0' bus='0' target='0' unit='0'/>
</hostdev>
</devices>
...
or:
...
<devices>
<hostdev mode='subsystem' type='scsi_host'>
<source protocol='vhost' wwpn='naa.50014057667280d8'/>
</hostdev>
</devices>
...
or:
...
<devices>
<hostdev mode='subsystem' type='mdev' model='vfio-pci'>
<source>
<address uuid='c2177883-f1bb-47f0-914d-32a22e3a8804'/>
</source>
</hostdev>
</devices>
...
-
hostdev - The
hostdevelement is the main container for describing host devices. For each device, themodeis always "subsystem" and thetypeis one of the following values with additional attributes noted.usb- USB devices are detached from the host on guest startup and reattached after the guest exits or the device is hot-unplugged.
pci- For PCI devices, when
managedis "yes" it is detached from the host before being passed on to the guest and reattached to the host after the guest exits. Ifmanagedis omitted or "no", the user is responsible to callvirNodeDeviceDetachFlags(orvirsh nodedev-detachbefore starting the guest or hot-plugging the device andvirNodeDeviceReAttach(orvirsh nodedev-reattach) after hot-unplug or stopping the guest. scsi- For SCSI devices, user is responsible to make sure the device
is not used by host. If supported by the hypervisor and OS, the
optional
sgio(since 1.0.6) attribute indicates whether unprivileged SG_IO commands are filtered for the disk. Valid settings are "filtered" or "unfiltered", where the default is "filtered". The optionalrawio(since 1.2.9) attribute indicates whether the lun needs the rawio capability. Valid settings are "yes" or "no". See the rawio description within the disk section. If a disk lun in the domain already has the rawio capability, then this setting not required. scsi_host- since 2.5.0For SCSI devices, user
is responsible to make sure the device is not used by host. This
typepasses all LUNs presented by a single HBA to the guest. mdev- For mediated devices (Since 3.2.0)
the
modelattribute specifies the device API which determines how the host's vfio driver will expose the device to the guest. Currently, onlymodel='vfio-pci'is supported. There are also some implications on the usage of guest's address type depending on themodelattribute, see theaddresselement below.
Note: The
managedattribute is only used withtype='pci'and is ignored by all the other device types, thus settingmanagedexplicitly with other than a PCI device has the same effect as omitting it. Similarly,modelattribute is only supported by mediated devices and ignored by all other device types. -
source - The source element describes the device as seen from the host using
the following mechanism to describe:
usb- The USB device can either be addressed by vendor / product id
using the
vendorandproductelements or by the device's address on the host using theaddresselement.Since 1.0.0, the
sourceelement of USB devices may containstartupPolicyattribute which can be used to define policy what to do if the specified host USB device is not found. The attribute accepts the following values:mandatory fail if missing for any reason (the default) requisite fail if missing on boot up, drop if missing on migrate/restore/revert optional drop if missing at any start attempt pci- PCI devices can only be described by their
address. scsi- SCSI devices are described by both the
adapterandaddresselements. Theaddresselement includes abusattribute (a 2-digit bus number), atargetattribute (a 10-digit target number), and aunitattribute (a 20-digit unit number on the bus). Not all hypervisors support largertargetandunitvalues. It is up to each hypervisor to determine the maximum value supported for the adapter.Since 1.2.8, the
sourceelement of a SCSI device may contain theprotocolattribute. When the attribute is set to "iscsi", the host device XML follows the network disk device using the samenameattribute and optionally using theauthelement to provide the authentication credentials to the iSCSI server. scsi_host- Since 2.5.0, multiple LUNs behind a
single SCSI HBA are described by a
protocolattribute set to "vhost" and awwpnattribute that is the vhost_scsi wwpn (16 hexadecimal digits with a prefix of "naa.") established in the host configfs. mdev- Mediated devices (Since 3.2.0) are
described by the
addresselement. Theaddresselement contains a single mandatory attributeuuid.
vendor,product- The
vendorandproductelements each have anidattribute that specifies the USB vendor and product id. The ids can be given in decimal, hexadecimal (starting with 0x) or octal (starting with 0) form. -
boot - Specifies that the device is bootable. The
orderattribute determines the order in which devices will be tried during boot sequence. The per-devicebootelements cannot be used together with general boot elements in BIOS bootloader section. Since 0.8.8 for PCI devices, Since 1.0.1 for USB devices. -
rom - The
romelement is used to change how a PCI device's ROM is presented to the guest. The optionalbarattribute can be set to "on" or "off", and determines whether or not the device's ROM will be visible in the guest's memory map. (In PCI documentation, the "rombar" setting controls the presence of the Base Address Register for the ROM). If no rom bar is specified, the qemu default will be used (older versions of qemu used a default of "off", while newer qemus have a default of "on"). Since 0.9.7 (QEMU and KVM only). The optionalfileattribute contains an absolute path to a binary file to be presented to the guest as the device's ROM BIOS. This can be useful, for example, to provide a PXE boot ROM for a virtual function of an sr-iov capable ethernet device (which has no boot ROMs for the VFs). Since 0.9.10 (QEMU and KVM only). -
address - The
addresselement for USB devices has abusanddeviceattribute to specify the USB bus and device number the device appears at on the host. The values of these attributes can be given in decimal, hexadecimal (starting with 0x) or octal (starting with 0) form. For PCI devices the element carries 4 attributes allowing to designate the device as can be found with thelspcior withvirsh nodedev-list. For SCSI devices a 'drive' address type must be used. For mediated devices, which are software-only devices defining an allocation of resources on the physical parent device, the address type used must conform to themodelattribute of elementhostdev, e.g. any address type other than PCI forvfio-pcidevice API will result in an error. See above for more details on the address element. -
driver -
PCI devices can have an optional
driversubelement that specifies which backend driver to use for PCI device assignment. Use thenameattribute to select either "vfio" (for the new VFIO device assignment backend, which is compatible with UEFI SecureBoot) or "kvm" (the legacy device assignment handled directly by the KVM kernel module)Since 1.0.5 (QEMU and KVM only, requires kernel 3.6 or newer). When specified, device assignment will fail if the requested method of device assignment isn't available on the host. When not specified, the default is "vfio" on systems where the VFIO driver is available and loaded, and "kvm" on older systems, or those where the VFIO driver hasn't been loaded Since 1.1.3 (prior to that the default was always "kvm"). -
readonly - Indicates that the device is readonly, only supported by SCSI host device now. Since 1.0.6 (QEMU and KVM only)
-
shareable - If present, this indicates the device is expected to be shared
between domains (assuming the hypervisor and OS support this).
Only supported by SCSI host device.
Since 1.0.6
Note: Although
shareablewas introduced in 1.0.6, it did not work as as expected until 1.2.2.
Block / character devices ¶
Block / character devices from the host can be passed through
to the guest using the hostdev element. This is
only possible with container based virtualization. Devices are specified
by a fully qualified path.
since after 1.0.1 for LXC:
...
<hostdev mode='capabilities' type='storage'>
<source>
<block>/dev/sdf1</block>
</source>
</hostdev>
...
...
<hostdev mode='capabilities' type='misc'>
<source>
<char>/dev/input/event3</char>
</source>
</hostdev>
...
...
<hostdev mode='capabilities' type='net'>
<source>
<interface>eth0</interface>
</source>
</hostdev>
...
-
hostdev - The
hostdevelement is the main container for describing host devices. For block/character device passthroughmodeis always "capabilities" andtypeis "storage" for a block device, "misc" for a character device and "net" for a host network interface. -
source - The source element describes the device as seen from the host. For block devices, the path to the block device in the host OS is provided in the nested "block" element, while for character devices the "char" element is used. For network interfaces, the name of the interface is provided in the "interface" element.
Redirected devices ¶
USB device redirection through a character device is supported since after 0.9.5 (KVM only):
...
<devices>
<redirdev bus='usb' type='tcp'>
<source mode='connect' host='localhost' service='4000'/>
<boot order='1'/>
</redirdev>
<redirfilter>
<usbdev class='0x08' vendor='0x1234' product='0xbeef' version='2.56' allow='yes'/>
<usbdev allow='no'/>
</redirfilter>
</devices>
...
-
redirdev - The
redirdevelement is the main container for describing redirected devices.busmust be "usb" for a USB device. An additional attributetypeis required, matching one of the supported serial device types, to describe the host side of the tunnel;type='tcp'ortype='spicevmc'(which uses the usbredir channel of a SPICE graphics device) are typical. The redirdev element has an optional sub-element<address>which can tie the device to a particular controller. Further sub-elements, such as<source>, may be required according to the given type, although a<target>sub-element is not required (since the consumer of the character device is the hypervisor itself, rather than a device visible in the guest). -
boot - Specifies that the device is bootable.
The
orderattribute determines the order in which devices will be tried during boot sequence. The per-devicebootelements cannot be used together with general boot elements in BIOS bootloader section. (Since 1.0.1) -
redirfilter - The
redirfilterelement is used for creating the filter rule to filter out certain devices from redirection. It uses sub-element<usbdev>to define each filter rule.classattribute is the USB Class code, for example, 0x08 represents mass storage devices. The USB device can be addressed by vendor / product id using thevendorandproductattributes.versionis the device revision from the bcdDevice field (not the version of the USB protocol). These four attributes are optional and-1can be used to allow any value for them.allowattribute is mandatory, 'yes' means allow, 'no' for deny.
Smartcard devices ¶
A virtual smartcard device can be supplied to the guest via the
smartcard element. A USB smartcard reader device on
the host cannot be used on a guest with simple device
passthrough, since it will then not be available on the host,
possibly locking the host computer when it is "removed".
Therefore, some hypervisors provide a specialized virtual device
that can present a smartcard interface to the guest, with
several modes for describing how credentials are obtained from
the host or even a from a channel created to a third-party
smartcard provider. Since 0.8.8
...
<devices>
<smartcard mode='host'/>
<smartcard mode='host-certificates'>
<certificate>cert1</certificate>
<certificate>cert2</certificate>
<certificate>cert3</certificate>
<database>/etc/pki/nssdb/</database>
</smartcard>
<smartcard mode='passthrough' type='tcp'>
<source mode='bind' host='127.0.0.1' service='2001'/>
<protocol type='raw'/>
<address type='ccid' controller='0' slot='0'/>
</smartcard>
<smartcard mode='passthrough' type='spicevmc'/>
</devices>
...
The <smartcard> element has a mandatory
attribute mode. The following modes are supported;
in each mode, the guest sees a device on its USB bus that
behaves like a physical USB CCID (Chip/Smart Card Interface
Device) card.
-
host - The simplest operation, where the hypervisor relays all
requests from the guest into direct access to the host's
smartcard via NSS. No other attributes or sub-elements are
required. See below about the use of an
optional
<address>sub-element. -
host-certificates - Rather than requiring a smartcard to be plugged into the
host, it is possible to provide three NSS certificate names
residing in a database on the host. These certificates can be
generated via the command
certutil -d /etc/pki/nssdb -x -t CT,CT,CT -S -s CN=cert1 -n cert1, and the resulting three certificate names must be supplied as the content of each of three<certificate>sub-elements. An additional sub-element<database>can specify the absolute path to an alternate directory (matching the-doption of thecertutilcommand when creating the certificates); if not present, it defaults to /etc/pki/nssdb. -
passthrough - Rather than having the hypervisor directly communicate with
the host, it is possible to tunnel all requests through a
secondary character device to a third-party provider (which may
in turn be talking to a smartcard or using three certificate
files). In this mode of operation, an additional
attribute
typeis required, matching one of the supported serial device types, to describe the host side of the tunnel;type='tcp'ortype='spicevmc'(which uses the smartcard channel of a SPICE graphics device) are typical. Further sub-elements, such as<source>, may be required according to the given type, although a<target>sub-element is not required (since the consumer of the character device is the hypervisor itself, rather than a device visible in the guest).
Each mode supports an optional
sub-element <address>, which fine-tunes the
correlation between the smartcard and a ccid bus
controller, documented above.
For now, qemu only supports at most one
smartcard, with an address of bus=0 slot=0.
Network interfaces ¶
...
<devices>
<interface type='direct' trustGuestRxFilters='yes'>
<source dev='eth0'/>
<mac address='52:54:00:5d:c7:9e'/>
<boot order='1'/>
<rom bar='off'/>
</interface>
</devices>
...
There are several possibilities for specifying a network interface visible to the guest. Each subsection below provides more details about common setup options.
Since 1.2.10),
the interface element
property trustGuestRxFilters provides the
capability for the host to detect and trust reports from the
guest regarding changes to the interface mac address and receive
filters by setting the attribute to yes. The default
setting for the attribute is no for security
reasons and support depends on the guest network device model as
well as the type of connection on the host - currently it is
only supported for the virtio device model and for macvtap
connections on the host.
Each <interface> element has an
optional <address> sub-element that can tie
the interface to a particular pci slot, with
attribute type='pci'
as documented above.
Virtual network ¶
This is the recommended config for general guest connectivity on
hosts with dynamic / wireless networking configs (or multi-host
environments where the host hardware details are described
separately in a <network>
definition Since 0.9.4).
Provides a connection whose details are described by the named
network definition. Depending on the virtual network's "forward
mode" configuration, the network may be totally isolated
(no <forward> element given), NAT'ing to an
explicit network device or to the default route
(<forward mode='nat'>), routed with no NAT
(<forward mode='route'/>), or connected
directly to one of the host's network interfaces (via macvtap)
or bridge devices ((<forward
mode='bridge|private|vepa|passthrough'/> Since
0.9.4)
For networks with a forward mode of bridge, private, vepa, and
passthrough, it is assumed that the host has any necessary DNS
and DHCP services already setup outside the scope of libvirt. In
the case of isolated, nat, and routed networks, DHCP and DNS are
provided on the virtual network by libvirt, and the IP range can
be determined by examining the virtual network config with
'virsh net-dumpxml [networkname]'. There is one
virtual network called 'default' setup out of the box which does
NAT'ing to the default route and has an IP range
of 192.168.122.0/255.255.255.0. Each guest will
have an associated tun device created with a name of vnetN,
which can also be overridden with the <target> element
(see
overriding the target element).
When the source of an interface is a network,
a portgroup can be specified along with the name of
the network; one network may have multiple portgroups defined,
with each portgroup containing slightly different configuration
information for different classes of network
connections. Since 0.9.4.
Also, similar to direct network connections
(described below), a connection of type network may
specify a virtualport element, with configuration
data to be forwarded to a vepa (802.1Qbg) or 802.1Qbh compliant
switch (Since 0.8.2), or to an
Open vSwitch virtual switch (Since
0.9.11).
Since the actual type of switch may vary depending on the
configuration in the <network> on the host,
it is acceptable to omit the virtualport type
attribute, and specify attributes from multiple different
virtualport types (and also to leave out certain attributes); at
domain startup time, a complete <virtualport>
element will be constructed by merging together the type and
attributes defined in the network and the portgroup referenced
by the interface. The newly-constructed virtualport is a combination
of them. The attributes from lower virtualport can't make change
on the ones defined in higher virtualport.
Interface takes the highest priority, portgroup is lowest priority.
(Since 0.10.0). For example, in order
to work properly with both an 802.1Qbh switch and an Open vSwitch
switch, you may choose to specify no type, but both
an profileid (in case the switch is 802.1Qbh) and
an interfaceid (in case the switch is Open vSwitch)
(you may also omit the other attributes, such as managerid,
typeid, or profileid, to be filled in from the
network's <virtualport>). If you want to
limit a guest to connecting only to certain types of switches,
you can specify the virtualport type, but still omit some/all of
the parameters - in this case if the host's network has a
different type of virtualport, connection of the interface will
fail.
...
<devices>
<interface type='network'>
<source network='default'/>
</interface>
...
<interface type='network'>
<source network='default' portgroup='engineering'/>
<target dev='vnet7'/>
<mac address="00:11:22:33:44:55"/>
<virtualport>
<parameters instanceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/>
</virtualport>
</interface>
</devices>
...
Bridge to LAN ¶
This is the recommended config for general guest connectivity on hosts with static wired networking configs.
Provides a bridge from the VM directly to the LAN. This assumes there is a bridge device on the host which has one or more of the hosts physical NICs enslaved. The guest VM will have an associated tun device created with a name of vnetN, which can also be overridden with the <target> element (see overriding the target element). The tun device will be enslaved to the bridge. The IP range / network configuration is whatever is used on the LAN. This provides the guest VM full incoming & outgoing net access just like a physical machine.
On Linux systems, the bridge device is normally a standard Linux
host bridge. On hosts that support Open vSwitch, it is also
possible to connect to an Open vSwitch bridge device by adding
a <virtualport type='openvswitch'/> to the
interface definition. (Since
0.9.11). The Open vSwitch type virtualport accepts two
parameters in its <parameters> element -
an interfaceid which is a standard uuid used to
uniquely identify this particular interface to Open vSwitch (if
you do not specify one, a random interfaceid will be generated
for you when you first define the interface), and an
optional profileid which is sent to Open vSwitch as
the interfaces "port-profile".
...
<devices>
...
<interface type='bridge'>
<source bridge='br0'/>
</interface>
<interface type='bridge'>
<source bridge='br1'/>
<target dev='vnet7'/>
<mac address="00:11:22:33:44:55"/>
</interface>
<interface type='bridge'>
<source bridge='ovsbr'/>
<virtualport type='openvswitch'>
<parameters profileid='menial' interfaceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/>
</virtualport>
</interface>
...
</devices>
...
On hosts that support Open vSwitch on the kernel side and have the
Midonet Host Agent configured, it is also possible to connect to the
'midonet' bridge device by adding a
<virtualport type='midonet'/> to the
interface definition. (Since
1.2.13). The Midonet virtualport type requires an
interfaceid attribute in its
<parameters> element. This interface id is the UUID
that specifies which port in the virtual network topology will be bound
to the interface.
...
<devices>
...
<interface type='bridge'>
<source bridge='br0'/>
</interface>
<interface type='bridge'>
<source bridge='br1'/>
<target dev='vnet7'/>
<mac address="00:11:22:33:44:55"/>
</interface>
<interface type='bridge'>
<source bridge='midonet'/>
<virtualport type='midonet'>
<parameters interfaceid='0b2d64da-3d0e-431e-afdd-804415d6ebbb'/>
</virtualport>
</interface>
...
</devices>
...
Userspace SLIRP stack ¶
Provides a virtual LAN with NAT to the outside world. The virtual
network has DHCP & DNS services and will give the guest VM addresses
starting from 10.0.2.15. The default router will be
10.0.2.2 and the DNS server will be 10.0.2.3.
This networking is the only option for unprivileged users who need their
VMs to have outgoing access. Since 3.8.0
it is possible to override the default network address by
including an ip element specifying an IPv4
address in its one mandatory attribute, address.
Optionally, a second ip element with a
family attribute set to "ipv6" can be
specified to add an IPv6 address to the interface.
address. Optionally, address
prefix can be specified.
...
<devices>
<interface type='user'/>
...
<interface type='user'>
<mac address="00:11:22:33:44:55"/>
<ip family='ipv4' address='172.17.2.0' prefix='24'/>
<ip family='ipv6' address='2001:db8:ac10:fd01::' prefix='64'/>
</interface>
</devices>
...
Generic ethernet connection ¶
Provides a means for the administrator to execute an arbitrary script to connect the guest's network to the LAN. The guest will have a tun device created with a name of vnetN, which can also be overridden with the <target> element. After creating the tun device a shell script will be run which is expected to do whatever host network integration is required. By default this script is called /etc/qemu-ifup but can be overridden.
...
<devices>
<interface type='ethernet'/>
...
<interface type='ethernet'>
<target dev='vnet7'/>
<script path='/etc/qemu-ifup-mynet'/>
</interface>
</devices>
...
Direct attachment to physical interface ¶
Provides direct attachment of the virtual machine's NIC to the given
physical interface of the host.
Since 0.7.7 (QEMU and KVM only)
This setup requires the Linux macvtap
driver to be available. (Since Linux 2.6.34.)
One of the modes 'vepa'
(
'Virtual Ethernet Port Aggregator'), 'bridge' or 'private'
can be chosen for the operation mode of the macvtap device, 'vepa'
being the default mode. The individual modes cause the delivery of
packets to behave as follows:
If the model type is set to virtio and
interface's trustGuestRxFilters attribute is set
to yes, changes made to the interface mac address,
unicast/multicast receive filters, and vlan settings in the
guest will be monitored and propagated to the associated macvtap
device on the host (Since
1.2.10). If trustGuestRxFilters is not set,
or is not supported for the device model in use, an attempted
change to the mac address originating from the guest side will
result in a non-working network connection.
-
vepa - All VMs' packets are sent to the external bridge. Packets whose destination is a VM on the same host as where the packet originates from are sent back to the host by the VEPA capable bridge (today's bridges are typically not VEPA capable).
-
bridge - Packets whose destination is on the same host as where they
originate from are directly delivered to the target macvtap device.
Both origin and destination devices need to be in bridge mode
for direct delivery. If either one of them is in
vepamode, a VEPA capable bridge is required. -
private - All packets are sent to the external bridge and will only be
delivered to a target VM on the same host if they are sent through an
external router or gateway and that device sends them back to the
host. This procedure is followed if either the source or destination
device is in
privatemode. -
passthrough - This feature attaches a virtual function of a SRIOV capable NIC directly to a VM without losing the migration capability. All packets are sent to the VF/IF of the configured network device. Depending on the capabilities of the device additional prerequisites or limitations may apply; for example, on Linux this requires kernel 2.6.38 or newer. Since 0.9.2
...
<devices>
...
<interface type='direct' trustGuestRxFilters='no'>
<source dev='eth0' mode='vepa'/>
</interface>
</devices>
...
The network access of direct attached virtual machines can be managed by the hardware switch to which the physical interface of the host machine is connected to.
The interface can have additional parameters as shown below, if the switch is conforming to the IEEE 802.1Qbg standard. The parameters of the virtualport element are documented in more detail in the IEEE 802.1Qbg standard. The values are network specific and should be provided by the network administrator. In 802.1Qbg terms, the Virtual Station Interface (VSI) represents the virtual interface of a virtual machine. Since 0.8.2
Please note that IEEE 802.1Qbg requires a non-zero value for the VLAN ID.
-
managerid - The VSI Manager ID identifies the database containing the VSI type and instance definitions. This is an integer value and the value 0 is reserved.
-
typeid - The VSI Type ID identifies a VSI type characterizing the network access. VSI types are typically managed by network administrator. This is an integer value.
-
typeidversion - The VSI Type Version allows multiple versions of a VSI Type. This is an integer value.
-
instanceid - The VSI Instance ID Identifier is generated when a VSI instance (i.e. a virtual interface of a virtual machine) is created. This is a globally unique identifier.
...
<devices>
...
<interface type='direct'>
<source dev='eth0.2' mode='vepa'/>
<virtualport type="802.1Qbg">
<parameters managerid="11" typeid="1193047" typeidversion="2" instanceid="09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f"/>
</virtualport>
</interface>
</devices>
...
The interface can have additional parameters as shown below if the switch is conforming to the IEEE 802.1Qbh standard. The values are network specific and should be provided by the network administrator. Since 0.8.2
-
profileid - The profile ID contains the name of the port profile that is to be applied to this interface. This name is resolved by the port profile database into the network parameters from the port profile, and those network parameters will be applied to this interface.
...
<devices>
...
<interface type='direct'>
<source dev='eth0' mode='private'/>
<virtualport type='802.1Qbh'>
<parameters profileid='finance'/>
</virtualport>
</interface>
</devices>
...
PCI Passthrough ¶
A PCI network device (specified by the <source> element) is directly assigned to the guest using generic device passthrough, after first optionally setting the device's MAC address to the configured value, and associating the device with an 802.1Qbh capable switch using an optionally specified <virtualport> element (see the examples of virtualport given above for type='direct' network devices). Note that - due to limitations in standard single-port PCI ethernet card driver design - only SR-IOV (Single Root I/O Virtualization) virtual function (VF) devices can be assigned in this manner; to assign a standard single-port PCI or PCIe ethernet card to a guest, use the traditional <hostdev> device definition and Since 0.9.11
To use VFIO device assignment rather than traditional/legacy KVM
device assignment (VFIO is a new method of device assignment
that is compatible with UEFI Secure Boot), a type='hostdev'
interface can have an optional driver sub-element
with a name attribute set to "vfio". To use legacy
KVM device assignment you can set name to "kvm" (or
simply omit the <driver> element, since "kvm"
is currently the default).
Since 1.0.5 (QEMU and KVM only, requires kernel 3.6 or newer)
Note that this "intelligent passthrough" of network devices is very similar to the functionality of a standard <hostdev> device, the difference being that this method allows specifying a MAC address and <virtualport> for the passed-through device. If these capabilities are not required, if you have a standard single-port PCI, PCIe, or USB network card that doesn't support SR-IOV (and hence would anyway lose the configured MAC address during reset after being assigned to the guest domain), or if you are using a version of libvirt older than 0.9.11, you should use standard <hostdev> to assign the device to the guest instead of <interface type='hostdev'/>.
Similar to the functionality of a standard <hostdev> device,
when managed is "yes", it is detached from the host
before being passed on to the guest, and reattached to the host
after the guest exits. If managed is omitted or "no",
the user is responsible to call virNodeDeviceDettach
(or virsh nodedev-detach) before starting the guest
or hot-plugging the device, and virNodeDeviceReAttach
(or virsh nodedev-reattach) after hot-unplug or
stopping the guest.
...
<devices>
<interface type='hostdev' managed='yes'>
<driver name='vfio'/>
<source>
<address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
</source>
<mac address='52:54:00:6d:90:02'/>
<virtualport type='802.1Qbh'>
<parameters profileid='finance'/>
</virtualport>
</interface>
</devices>
...
Multicast tunnel ¶
A multicast group is setup to represent a virtual network. Any VMs whose network devices are in the same multicast group can talk to each other even across hosts. This mode is also available to unprivileged users. There is no default DNS or DHCP support and no outgoing network access. To provide outgoing network access, one of the VMs should have a 2nd NIC which is connected to one of the first 4 network types and do the appropriate routing. The multicast protocol is compatible with that used by user mode linux guests too. The source address used must be from the multicast address block.
...
<devices>
<interface type='mcast'>
<mac address='52:54:00:6d:90:01'/>
<source address='230.0.0.1' port='5558'/>
</interface>
</devices>
...
TCP tunnel ¶
A TCP client/server architecture provides a virtual network. One VM provides the server end of the network, all other VMS are configured as clients. All network traffic is routed between the VMs via the server. This mode is also available to unprivileged users. There is no default DNS or DHCP support and no outgoing network access. To provide outgoing network access, one of the VMs should have a 2nd NIC which is connected to one of the first 4 network types and do the appropriate routing.
...
<devices>
<interface type='server'>
<mac address='52:54:00:22:c9:42'/>
<source address='192.168.0.1' port='5558'/>
</interface>
...
<interface type='client'>
<mac address='52:54:00:8b:c9:51'/>
<source address='192.168.0.1' port='5558'/>
</interface>
</devices>
...
UDP unicast tunnel ¶
A UDP unicast architecture provides a virtual network which enables connections between QEMU instances using QEMU's UDP infrastructure. The xml "source" address is the endpoint address to which the UDP socket packets will be sent from the host running QEMU. The xml "local" address is the address of the interface from which the UDP socket packets will originate from the QEMU host. Since 1.2.20
...
<devices>
<interface type='udp'>
<mac address='52:54:00:22:c9:42'/>
<source address='127.0.0.1' port='11115'>
<local address='127.0.0.1' port='11116'/>
</source>
</interface>
</devices>
...
Setting the NIC model ¶
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<model type='ne2k_pci'/>
</interface>
</devices>
...
For hypervisors which support this, you can set the model of emulated network interface card.
The values for type aren't defined specifically by
libvirt, but by what the underlying hypervisor supports (if
any). For QEMU and KVM you can get a list of supported models
with these commands:
qemu -net nic,model=? /dev/null qemu-kvm -net nic,model=? /dev/null
Typical values for QEMU and KVM include: ne2k_isa i82551 i82557b i82559er ne2k_pci pcnet rtl8139 e1000 virtio
Setting NIC driver-specific options ¶
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<model type='virtio'/>
<driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off' queues='5' rx_queue_size='256' tx_queue_size='256'>
<host csum='off' gso='off' tso4='off' tso6='off' ecn='off' ufo='off' mrg_rxbuf='off'/>
<guest csum='off' tso4='off' tso6='off' ecn='off' ufo='off'/>
</driver>
</interface>
</devices>
...
Some NICs may have tunable driver-specific options. These are
set as attributes of the driver sub-element of the
interface definition. Currently the following attributes are
available for the "virtio" NIC driver:
-
name -
The optional
nameattribute forces which type of backend driver to use. The value can be either 'qemu' (a user-space backend) or 'vhost' (a kernel backend, which requires the vhost module to be provided by the kernel); an attempt to require the vhost driver without kernel support will be rejected. If this attribute is not present, then the domain defaults to 'vhost' if present, but silently falls back to 'qemu' without error. Since 0.8.8 (QEMU and KVM only) -
For interfaces of type='hostdev' (PCI passthrough devices)
the
nameattribute can optionally be set to "vfio" or "kvm". "vfio" tells libvirt to use VFIO device assignment rather than traditional KVM device assignment (VFIO is a new method of device assignment that is compatible with UEFI Secure Boot), and "kvm" tells libvirt to use the legacy device assignment performed directly by the kvm kernel module (the default is currently "kvm", but is subject to change). Since 1.0.5 (QEMU and KVM only, requires kernel 3.6 or newer) -
For interfaces of type='vhostuser', the
nameattribute is ignored. The backend driver used is always vhost-user. -
txmode -
The
txmodeattribute specifies how to handle transmission of packets when the transmit buffer is full. The value can be either 'iothread' or 'timer'. Since 0.8.8 (QEMU and KVM only)
If set to 'iothread', packet tx is all done in an iothread in the bottom half of the driver (this option translates into adding "tx=bh" to the qemu commandline -device virtio-net-pci option).
If set to 'timer', tx work is done in qemu, and if there is more tx data than can be sent at the present time, a timer is set before qemu moves on to do other things; when the timer fires, another attempt is made to send more data.
The resulting difference, according to the qemu developer who added the option is: "bh makes tx more asynchronous and reduces latency, but potentially causes more processor bandwidth contention since the cpu doing the tx isn't necessarily the cpu where the guest generated the packets."
In general you should leave this option alone, unless you are very certain you know what you are doing. -
ioeventfd -
This optional attribute allows users to set
domain I/O asynchronous handling for interface device.
The default is left to the discretion of the hypervisor.
Accepted values are "on" and "off". Enabling this allows
qemu to execute VM while a separate thread handles I/O.
Typically guests experiencing high system CPU utilization
during I/O will benefit from this. On the other hand,
on overloaded host it could increase guest I/O latency.
Since 0.9.3 (QEMU and KVM only)
In general you should leave this option alone, unless you are very certain you know what you are doing. -
event_idx -
The
event_idxattribute controls some aspects of device event processing. The value can be either 'on' or 'off' - if it is on, it will reduce the number of interrupts and exits for the guest. The default is determined by QEMU; usually if the feature is supported, default is on. In case there is a situation where this behavior is suboptimal, this attribute provides a way to force the feature off. Since 0.9.5 (QEMU and KVM only)
In general you should leave this option alone, unless you are very certain you know what you are doing. -
queues -
The optional
queuesattribute controls the number of queues to be used for either Multiqueue virtio-net or vhost-user network interfaces. Use of multiple packet processing queues requires the interface having the<model type='virtio'/>element. Each queue will potentially be handled by a different processor, resulting in much higher throughput. virtio-net since 1.0.6 (QEMU and KVM only) vhost-user since 1.2.17 (QEMU and KVM only) -
rx_queue_size -
The optional
rx_queue_sizeattribute controls the size of virtio ring for each queue as described above. The default value is hypervisor dependent and may change across its releases. Moreover, some hypervisors may pose some restrictions on actual value. For instance, latest QEMU (as of 2016-09-01) requires value to be a power of two from [256, 1024] range. Since 2.3.0 (QEMU and KVM only)
In general you should leave this option alone, unless you are very certain you know what you are doing. -
tx_queue_size -
The optional
tx_queue_sizeattribute controls the size of virtio ring for each queue as described above. The default value is hypervisor dependent and may change across its releases. Moreover, some hypervisors may pose some restrictions on actual value. For instance, QEMU v2.9 requires value to be a power of two from [256, 1024] range. In addition to that, this may work only for a subset of interface types, e.g. aforementioned QEMU enables this option only forvhostusertype. Since 3.7.0 (QEMU and KVM only)
In general you should leave this option alone, unless you are very certain you know what you are doing. - virtio options
- For virtio interfaces, Virtio-specific options can also be set. (Since 3.5.0)
Offloading options for the host and guest can be configured using the following sub-elements:
-
host -
The
csum,gso,tso4,tso6,ecnandufoattributes with possible valuesonandoffcan be used to turn off host offloading options. By default, the supported offloads are enabled by QEMU. Since 1.2.9 (QEMU only) Themrg_rxbufattribute can be used to control mergeable rx buffers on the host side. Possible values areon(default) andoff. Since 1.2.13 (QEMU only) -
guest -
The
csum,tso4,tso6,ecnandufoattributes with possible valuesonandoffcan be used to turn off guest offloading options. By default, the supported offloads are enabled by QEMU. Since 1.2.9 (QEMU only)
Setting network backend-specific options ¶
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<model type='virtio'/>
<backend tap='/dev/net/tun' vhost='/dev/vhost-net'/>
<driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off' queues='5'/>
<tune>
<sndbuf>1600</sndbuf>
</tune>
</interface>
</devices>
...
For tuning the backend of the network, the backend element
can be used. The vhost attribute can override the default vhost
device path (/dev/vhost-net) for devices with virtio model.
The tap attribute overrides the tun/tap device path (default:
/dev/net/tun) for network and bridge interfaces. This does not work
in session mode. Since 1.2.9
For tap devices there is also sndbuf element which can
adjust the size of send buffer in the host. Since
0.8.8
Overriding the target element ¶
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
</interface>
</devices>
...
If no target is specified, certain hypervisors will automatically generate a name for the created tun device. This name can be manually specified, however the name should not start with either 'vnet', 'vif', 'macvtap', or 'macvlan', which are prefixes reserved by libvirt and certain hypervisors. Manually specified targets using these prefixes may be ignored.
Note that for LXC containers, this defines the name of the interface
on the host side. Since 1.2.7, to define
the name of the device on the guest side, the guest
element should be used, as in the following snippet:
...
<devices>
<interface type='network'>
<source network='default'/>
<guest dev='myeth'/>
</interface>
</devices>
...
Specifying boot order ¶
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<boot order='1'/>
</interface>
</devices>
...
For hypervisors which support this, you can set a specific NIC to
be used for network boot. The order attribute determines
the order in which devices will be tried during boot sequence. The
per-device boot elements cannot be used together with
general boot elements in
BIOS bootloader section.
Since 0.8.8
Interface ROM BIOS configuration ¶
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<rom bar='on' file='/etc/fake/boot.bin'/>
</interface>
</devices>
...
For hypervisors which support this, you can change how a PCI Network
device's ROM is presented to the guest. The bar
attribute can be set to "on" or "off", and determines whether
or not the device's ROM will be visible in the guest's memory
map. (In PCI documentation, the "rombar" setting controls the
presence of the Base Address Register for the ROM). If no rom
bar is specified, the qemu default will be used (older
versions of qemu used a default of "off", while newer qemus
have a default of "on").
The optional file attribute is used to point to a
binary file to be presented to the guest as the device's ROM
BIOS. This can be useful to provide an alternative boot ROM for a
network device.
Since 0.9.10 (QEMU and KVM only).
Setting up a network backend in a driver domain ¶
...
<devices>
...
<interface type='bridge'>
<source bridge='br0'/>
<backenddomain name='netvm'/>
</interface>
...
</devices>
...
The optional backenddomain element allows specifying a
backend domain (aka driver domain) for the interface. Use the
name attribute to specify the backend domain name. You
can use it to create a direct network link between domains (so data
will not go through host system). Use with type 'ethernet' to create
plain network link, or with type 'bridge' to connect to a bridge inside
the backend domain.
Since 1.2.13 (Xen only)
Quality of service ¶
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<bandwidth>
<inbound average='1000' peak='5000' floor='200' burst='1024'/>
<outbound average='128' peak='256' burst='256'/>
</bandwidth>
</interface>
</devices>
...
This part of interface XML provides setting quality of service. Incoming
and outgoing traffic can be shaped independently.
The bandwidth element and its child elements are described
in the QoS section of
the Network XML.
Setting VLAN tag (on supported network types only) ¶
...
<devices>
<interface type='bridge'>
<vlan>
<tag id='42'/>
</vlan>
<source bridge='ovsbr0'/>
<virtualport type='openvswitch'>
<parameters interfaceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/>
</virtualport>
</interface>
<interface type='bridge'>
<vlan trunk='yes'>
<tag id='42'/>
<tag id='123' nativeMode='untagged'/>
</vlan>
...
</interface>
</devices>
...
If (and only if) the network connection used by the guest
supports VLAN tagging transparent to the guest, an
optional <vlan> element can specify one or
more VLAN tags to apply to the guest's network
traffic Since 0.10.0. Network
connections that support guest-transparent VLAN tagging include
1) type='bridge' interfaces connected to an Open vSwitch bridge
Since 0.10.0, 2) SRIOV Virtual
Functions (VF) used via type='hostdev' (direct device
assignment) Since 0.10.0, and 3)
SRIOV VFs used via type='direct' with mode='passthrough'
(macvtap "passthru" mode) Since
1.3.5. All other connection types, including standard
linux bridges and libvirt's own virtual networks, do not
support it. 802.1Qbh (vn-link) and 802.1Qbg (VEPA) switches
provide their own way (outside of libvirt) to tag guest traffic
onto a specific VLAN. Each tag is given in a
separate <tag> subelement
of <vlan> (for example: <tag
id='42'/>). For VLAN trunking of multiple tags (which
is supported only on Open vSwitch connections),
multiple <tag> subelements can be specified,
which implies that the user wants to do VLAN trunking on the
interface for all the specified tags. In the case that VLAN
trunking of a single tag is desired, the optional
attribute trunk='yes' can be added to the toplevel
<vlan> element to differentiate trunking of a
single tag from normal tagging.
For network connections using Open vSwitch it is also possible
to configure 'native-tagged' and 'native-untagged' VLAN modes
Since 1.1.0. This is done with the
optional nativeMode attribute on
the <tag> subelement: nativeMode
may be set to 'tagged' or 'untagged'. The id
attribute of the <tag> subelement
containing nativeMode sets which VLAN is considered
to be the "native" VLAN for this interface, and
the nativeMode attribute determines whether or not
traffic for that VLAN will be tagged.
Modifying virtual link state ¶
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<link state='down'/>
</interface>
</devices>
...
This element provides means of setting state of the virtual network link.
Possible values for attribute state are up and
down. If down is specified as the value, the interface
behaves as if it had the network cable disconnected. Default behavior if this
element is unspecified is to have the link state up.
Since 0.9.5
MTU configuration ¶
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<mtu size='1500'/>
</interface>
</devices>
...
This element provides means of setting MTU of the virtual network link.
Currently there is just one attribute size which accepts a
non-negative integer which specifies the MTU size for the interface.
Since 3.1.0
Coalesce settings ¶
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<coalesce>
<rx>
<frames max='7'/>
</rx>
</coalesce>
</interface>
</devices>
...
This element provides means of setting coalesce settings for
some interface devices (currently only type network
and bridge. Currently there is just one attribute,
max, to tweak, in element frames for
the rx group, which accepts a non-negative integer
that specifies the maximum number of packets that will be
received before an interrupt.
Since 3.3.0
IP configuration ¶
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<ip address='192.168.122.5' prefix='24'/>
<ip address='192.168.122.5' prefix='24' peer='10.0.0.10'/>
<route family='ipv4' address='192.168.122.0' prefix='24' gateway='192.168.122.1'/>
<route family='ipv4' address='192.168.122.8' gateway='192.168.122.1'/>
</interface>
...
<hostdev mode='capabilities' type='net'>
<source>
<interface>eth0</interface>
</source>
<ip address='192.168.122.6' prefix='24'/>
<route family='ipv4' address='192.168.122.0' prefix='24' gateway='192.168.122.1'/>
<route family='ipv4' address='192.168.122.8' gateway='192.168.122.1'/>
</hostdev>
</devices>
...
Since 1.2.12 network devices and
hostdev devices with network capabilities can optionally be provided
one or more IP addresses to set on the network device in the
guest. Note that some hypervisors or network device types will
simply ignore them or only use the first one.
The family attribute can be set to
either ipv4 or ipv6, and the
address attribute contains the IP address. The
optional prefix is the number of 1 bits in the
netmask, and will be automatically set if not specified - for
IPv4 the default prefix is determined according to the network
"class" (A, B, or C - see RFC870), and for IPv6 the default
prefix is 64. The optional peer attribute holds the
IP address of the other end of a point-to-point network
device (since 2.1.0).
Since 1.2.12 route elements can also be
added to define IP routes to add in the guest. The attributes of
this element are described in the documentation for
the route element
in network
definitions. This is used by the LXC driver.
...
<devices>
<interface type='ethernet'>
<source/>
<ip address='192.168.123.1' prefix='24'/>
<ip address='10.0.0.10' prefix='24' peer='192.168.122.5'/>
<route family='ipv4' address='192.168.42.0' prefix='24' gateway='192.168.123.4'/>
<source/>
...
</interface>
...
</devices>
...
Since 2.1.0 network devices of type
"ethernet" can optionally be provided one or more IP addresses
and one or more routes to set on the host side of the
network device. These are configured as subelements of
the <source> element of the interface, and
have the same attributes as the similarly named elements used to
configure the guest side of the interface (described above).
vhost-user interface ¶
Since 1.2.7 the vhost-user enables the communication between a QEMU virtual machine and other userspace process using the Virtio transport protocol. A char dev (e.g. Unix socket) is used for the control plane, while the data plane is based on shared memory.
...
<devices>
<interface type='vhostuser'>
<mac address='52:54:00:3b:83:1a'/>
<source type='unix' path='/tmp/vhost1.sock' mode='server'/>
<model type='virtio'/>
</interface>
<interface type='vhostuser'>
<mac address='52:54:00:3b:83:1b'/>
<source type='unix' path='/tmp/vhost2.sock' mode='client'/>
<model type='virtio'/>
<driver queues='5'/>
</interface>
</devices>
...
The <source> element has to be specified
along with the type of char device.
Currently, only type='unix' is supported, where the path (the
directory path of the socket) and mode attributes are required.
Both mode='server' and mode='client'
are supported.
vhost-user requires the virtio model type, thus the
<model> element is mandatory.
Traffic filtering with NWFilter ¶
Since 0.8.0 an nwfilter profile
can be assigned to a domain interface, which allows configuring
traffic filter rules for the virtual machine.
See the nwfilter documentation for more
complete details.
...
<devices>
<interface ...>
...
<filterref filter='clean-traffic'/>
</interface>
<interface ...>
...
<filterref filter='myfilter'>
<parameter name='IP' value='104.207.129.11'/>
<parameter name='IP6_ADDR' value='2001:19f0:300:2102::'/>
<parameter name='IP6_MASK' value='64'/>
...
</filterref>
</interface>
</devices>
...
The filter attribute specifies the name of the nwfilter
to use. Optional <parameter> elements may be
specified for passing additional info to the nwfilter via the
name and value attributes. See
the nwfilter
docs for info on parameters.
Input devices ¶
Input devices allow interaction with the graphical framebuffer in the guest virtual machine. When enabling the framebuffer, an input device is automatically provided. It may be possible to add additional devices explicitly, for example, to provide a graphics tablet for absolute cursor movement.
...
<devices>
<input type='mouse' bus='usb'/>
<input type='keyboard' bus='usb'/>
<input type='mouse' bus='virtio'/>
<input type='keyboard' bus='virtio'/>
<input type='tablet' bus='virtio'/>
<input type='passthrough' bus='virtio'>
<source evdev='/dev/input/event1/>
</input>
</devices>
...
-
input - The
inputelement has one mandatory attribute, thetypewhose value can be 'mouse', 'tablet', (since 1.2.2) 'keyboard' or (since 1.3.0) 'passthrough'. The tablet provides absolute cursor movement, while the mouse uses relative movement. The optionalbusattribute can be used to refine the exact device type. It takes values "xen" (paravirtualized), "ps2" and "usb" or (since 1.3.0) "virtio".
The input element has an optional
sub-element <address> which can tie the
device to a particular PCI
slot, documented above.
For type passthrough, the mandatory sub-element source
must have an evdev attribute containing the absolute path to the
event device passed through to guests. (KVM only)
The subelement driver can be used to tune the virtio
options of the device:
Virtio-specific options can also be
set. (Since 3.5.0)
Hub devices ¶
A hub is a device that expands a single port into several so that there are more ports available to connect devices to a host system.
... <devices> <hub type='usb'/> </devices> ...
-
hub - The
hubelement has one mandatory attribute, thetypewhose value can only be 'usb'.
The hub element has an optional
sub-element <address>
with type='usb'which can tie the device to a
particular controller, documented
above.
Graphical framebuffers ¶
A graphics device allows for graphical interaction with the guest OS. A guest will typically have either a framebuffer or a text console configured to allow interaction with the admin.
...
<devices>
<graphics type='sdl' display=':0.0'/>
<graphics type='vnc' port='5904' sharePolicy='allow-exclusive'>
<listen type='address' address='1.2.3.4'/>
</graphics>
<graphics type='rdp' autoport='yes' multiUser='yes' />
<graphics type='desktop' fullscreen='yes'/>
<graphics type='spice'>
<listen type='network' network='rednet'/>
</graphics>
</devices>
...
-
graphics -
The
graphicselement has a mandatorytypeattribute which takes the valuesdl,vnc,spice,rdpordesktop:-
sdl -
This displays a window on the host desktop, it can take 3 optional arguments: a
displayattribute for the display to use, anxauthattribute for the authentication identifier, and an optionalfullscreenattribute accepting valuesyesorno. -
vnc -
Starts a VNC server. The
portattribute specifies the TCP port number (with -1 as legacy syntax indicating that it should be auto-allocated). Theautoportattribute is the new preferred syntax for indicating auto-allocation of the TCP port to use. Thepasswdattribute provides a VNC password in clear text. If thepasswdattribute is set to an empty string, then VNC access is disabled. Thekeymapattribute specifies the keymap to use. It is possible to set a limit on the validity of the password by giving an timestamppasswdValidTo='2010-04-09T15:51:00'assumed to be in UTC. Theconnectedattribute allows control of connected client during password changes. VNC acceptskeepvalue only since 0.9.3. NB, this may not be supported by all hypervisors.The optional
sharePolicyattribute specifies vnc server display sharing policy.allow-exclusiveallows clients to ask for exclusive access by dropping other connections. Connecting multiple clients in parallel requires all clients asking for a shared session (vncviewer: -Shared switch). This is the default value.force-shareddisables exclusive client access, every connection has to specify -Shared switch for vncviewer.ignorewelcomes every connection unconditionally since 1.0.6.Rather than using listen/port, QEMU supports a
socketattribute for listening on a unix domain socket path Since 0.8.8.For VNC WebSocket functionality,
websocketattribute may be used to specify port to listen on (with -1 meaning auto-allocation andautoporthaving no effect due to security reasons) Since 1.0.6. -
spiceSince 0.8.6 -
Starts a SPICE server. The
portattribute specifies the TCP port number (with -1 as legacy syntax indicating that it should be auto-allocated), whiletlsPortgives an alternative secure port number. Theautoportattribute is the new preferred syntax for indicating auto-allocation of needed port numbers. Thepasswdattribute provides a SPICE password in clear text. If thepasswdattribute is set to an empty string, then SPICE access is disabled. Thekeymapattribute specifies the keymap to use. It is possible to set a limit on the validity of the password by giving an timestamppasswdValidTo='2010-04-09T15:51:00'assumed to be in UTC.The
connectedattribute allows control of connected client during password changes. SPICE acceptskeepto keep client connected,disconnectto disconnect client andfailto fail changing password . NB, this may not be supported by all hypervisors. Since 0.9.3The
defaultModeattribute sets the default channel security policy, valid values aresecure,insecureand the defaultany(which is secure if possible, but falls back to insecure rather than erroring out if no secure path is available). Since 0.9.12When SPICE has both a normal and TLS secured TCP port configured, it can be desirable to restrict what channels can be run on each port. This is achieved by adding one or more
<channel>elements inside the main<graphics>element and setting themodeattribute to eithersecureorinsecure. Setting the mode attribute overrides the default value as set by thedefaultModeattribute. (Note that specifyinganyas mode discards the entry as the channel would inherit the default mode anyways.) Valid channel names includemain,display,inputs,cursor,playback,record(all since 0.8.6);smartcard(since 0.8.8); andusbredir(since 0.9.12).<graphics type='spice' port='-1' tlsPort='-1' autoport='yes'> <channel name='main' mode='secure'/> <channel name='record' mode='insecure'/> <image compression='auto_glz'/> <streaming mode='filter'/> <clipboard copypaste='no'/> <mouse mode='client'/> <filetransfer enable='no'/> <gl enable='yes' rendernode='/dev/dri/by-path/pci-0000:00:02.0-render'/> </graphics>
Spice supports variable compression settings for audio, images and streaming. These settings are accessible via the
compressionattribute in all following elements:imageto set image compression (acceptsauto_glz,auto_lz,quic,glz,lz,off),jpegfor JPEG compression for images over wan (acceptsauto,never,always),zlibfor configuring wan image compression (acceptsauto,never,always) andplaybackfor enabling audio stream compression (acceptsonoroff). Since 0.9.1Streaming mode is set by the
streamingelement, settings itsmodeattribute to one offilter,alloroff. Since 0.9.2Copy & Paste functionality (via Spice agent) is set by the
clipboardelement. It is enabled by default, and can be disabled by setting thecopypasteproperty tono. Since 0.9.3Mouse mode is set by the
mouseelement, setting itsmodeattribute to one ofserverorclient. If no mode is specified, the qemu default will be used (client mode). Since 0.9.11File transfer functionality (via Spice agent) is set using the
filetransferelement. It is enabled by default, and can be disabled by setting theenableproperty tono. Since 1.2.2Spice may provide accelerated server-side rendering with OpenGL. You can enable or disable OpenGL support explicitly with the
glelement, by setting theenableproperty. (QEMU only, since 1.3.3).By default, QEMU will pick the first available GPU DRM render node. You may specify a DRM render node path to use instead. (QEMU only, since 3.1.0).
-
rdp -
Starts a RDP server. The
portattribute specifies the TCP port number (with -1 as legacy syntax indicating that it should be auto-allocated). Theautoportattribute is the new preferred syntax for indicating auto-allocation of the TCP port to use. In the VirtualBox driver, theautoportwill make the hypervisor pick available port from 3389-3689 range when the VM is started. The chosen port will be reflected in theportattribute. ThemultiUserattribute is a boolean deciding whether multiple simultaneous connections to the VM are permitted. ThereplaceUserattribute is a boolean deciding whether the existing connection must be dropped and a new connection must be established by the VRDP server, when a new client connects in single connection mode. -
desktop -
This value is reserved for VirtualBox domains for the moment. It displays a window on the host desktop, similarly to "sdl", but using the VirtualBox viewer. Just like "sdl", it accepts the optional attributes
displayandfullscreen.
-
Graphics device uses a <listen> to set up where
the device should listen for clients. It has a mandatory attribute
type which specifies the listen type. Only vnc,
spice and rdp supports <listen>
element. Since 0.9.4.
Available types are:
-
address -
Tells a graphics device to use an address specified in the
addressattribute, which will contain either an IP address or hostname (which will be resolved to an IP address via a DNS query) to listen on.It is possible to omit the
addressattribute in order to use an address from config files Since 1.3.5.The
addressattribute is duplicated aslistenattribute ingraphicselement for backward compatibility. If both are provided they must be equal. -
network -
This is used to specify an existing network in the
networkattribute from libvirt's list of configured networks. The named network configuration will be examined to determine an appropriate listen address and the address will be stored in live XML inaddressattribute. For example, if the network has an IPv4 address in its configuration (e.g. if it has a forward type ofroute,nat, or no forward type (isolated)), the first IPv4 address listed in the network's configuration will be used. If the network is describing a host bridge, the first IPv4 address associated with that bridge device will be used, and if the network is describing one of the 'direct' (macvtap) modes, the first IPv4 address of the first forward dev will be used. -
socketsince 2.0.0 (QEMU only) -
This listen type tells a graphics server to listen on unix socket. Attribute
socketcontains a path to unix socket. If this attribute is omitted libvirt will generate this path for you. Supported by graphics typevncandspice.For
vncgraphics be backward compatible thesocketattribute of firstlistenelement is duplicated assocketattribute ingraphicselement. Ifgraphicselement contains asocketattribute alllistenelements are ignored. -
nonesince 2.0.0 (QEMU only) -
This listen type doesn't have any other attribute. Libvirt supports passing a file descriptor through our APIs virDomainOpenGraphics() and virDomainOpenGraphicsFD(). No other listen types are allowed if this one is used and the graphics device doesn't listen anywhere. You need to use one of the two APIs to pass a FD to QEMU in order to connect to this graphics device. Supported by graphics type
vncandspice.
Video devices ¶
A video device.
...
<devices>
<video>
<model type='vga' vram='16384' heads='1'>
<acceleration accel3d='yes' accel2d='yes'/>
</model>
</video>
</devices>
...
-
video -
The
videoelement is the container for describing video devices. For backwards compatibility, if novideois set but there is agraphicsin domain xml, then libvirt will add a defaultvideoaccording to the guest type.For a guest of type "kvm", the default
videois:typewith value "cirrus",vramwith value "16384" andheadswith value "1". By default, the first video device in domain xml is the primary one, but the optional attributeprimary(since 1.0.2) with value 'yes' can be used to mark the primary in cases of multiple video device. The non-primary must be type of "qxl" or (since 2.4.0) "virtio". -
model -
The
modelelement has a mandatorytypeattribute which takes the value "vga", "cirrus", "vmvga", "xen", "vbox", "qxl" (since 0.8.6), "virtio" (since 1.3.0) or "gop" (since 3.2.0) depending on the hypervisor features available.You can provide the amount of video memory in kibibytes (blocks of 1024 bytes) using
vram. This is supported only for guest type of "libxl", "vz", "qemu", "vbox", "vmx" and "xen". If no value is provided the default is used. If the size is not a power of two it will be rounded to closest one.The number of screen can be set using
heads. This is supported only for guests type of "vz", "kvm", "vbox" and "vmx".For guest type of "kvm" or "qemu" and model type "qxl" there are optional attributes. Attribute
ram( since 1.0.2) specifies the size of the primary bar, while the attributevramspecifies the secondary bar size. Iframorvramare not supplied a default value is used. Theramshould also be rounded to power of two asvram. There is also optional attributevgamem(since 1.2.11) to set the size of VGA framebuffer for fallback mode of QXL device. Attributevram64(since 1.3.3) extends secondary bar and makes it addressable as 64bit memory. -
acceleration -
Configure if video acceleration should be enabled.
accel2d- Enable 2D acceleration (for vbox driver only, since 0.7.1)
accel3d- Enable 3D acceleration (for vbox driver since 0.7.1, qemu driver since 1.3.0)
-
address -
The optional
addresssub-element can be used to tie the video device to a particular PCI slot. -
driver -
The subelement
drivercan be used to tune the device:- virtio options
- Virtio-specific options can also be set (Since 3.5.0)
- VGA configuration
-
Control how the video devices exposed to the guest using the
vgaconfattribute which takes the value "io", "on" or "off". At present, it's only applicable to the bhyve's "gop" video model type (Since 3.5.0)
Consoles, serial, parallel & channel devices ¶
A character device provides a way to interact with the virtual machine. Paravirtualized consoles, serial ports, parallel ports and channels are all classed as character devices and so represented using the same syntax.
...
<devices>
<parallel type='pty'>
<source path='/dev/pts/2'/>
<target port='0'/>
</parallel>
<serial type='pty'>
<source path='/dev/pts/3'/>
<target port='0'/>
</serial>
<serial type='file'>
<source path='/tmp/file' append='on'>
<seclabel model='dac' relabel='no'/>
</source>
<target port='0'/>
</serial>
<console type='pty'>
<source path='/dev/pts/4'/>
<target port='0'/>
</console>
<channel type='unix'>
<source mode='bind' path='/tmp/guestfwd'/>
<target type='guestfwd' address='10.0.2.1' port='4600'/>
</channel>
</devices>
...
In each of these directives, the top-level element name (parallel, serial,
console, channel) describes how the device is presented to the guest. The
guest interface is configured by the target element.
The interface presented to the host is given in the type
attribute of the top-level element. The host interface is
configured by the source element.
The source element may contain an optional
seclabel to override the way that labelling
is done on the socket path. If this element is not present,
the security label is inherited from
the per-domain setting.
If the interface type presented to the host is "file",
then the source element may contain an optional attribute
append that specifies whether or not the information in
the file should be preserved on domain restart. Allowed values are
"on" and "off" (default). Since 1.3.1.
Regardless of the type, character devices can
have an optional log file associated with them. This is
expressed via a log sub-element, with a
file attribute. There can also be an append
attribute which takes the same values described above.
Since 1.3.3.
... <log file="/var/log/libvirt/qemu/guestname-serial0.log" append="off"/> ...
Each character device element has an optional
sub-element <address> which can tie the
device to a
particular controller or PCI
slot.
For character device with type unix or tcp
the source has an optional element reconnect
which configures reconnect timeout if the connection is lost.
There are two attributes, enabled where possible
values are "yes" and "no" and timeout which is in
seconds. The reconnect attribute is valid only
for connect mode.
Since 3.7.0 (QEMU driver only).
Guest interface ¶
A character device presents itself to the guest as one of the following types.
Parallel port ¶
...
<devices>
<parallel type='pty'>
<source path='/dev/pts/2'/>
<target port='0'/>
</parallel>
</devices>
...
target can have a port attribute, which
specifies the port number. Ports are numbered starting from 0. There are
usually 0, 1 or 2 parallel ports.
Serial port ¶
...
<devices>
<!-- Serial port -->
<serial type='pty'>
<source path='/dev/pts/3'/>
<target port='0'/>
</serial>
</devices>
...
...
<devices>
<!-- USB serial port -->
<serial type='pty'>
<target type='usb-serial' port='0'>
<model name='usb-serial'/>
</target>
<address type='usb' bus='0' port='1'/>
</serial>
</devices>
...
The target element can have an optional port
attribute, which specifies the port number (starting from 0), and an
optional type attribute: valid values are,
since 1.0.2, isa-serial (usable
with x86 guests), usb-serial (usable whenever USB support
is available) and pci-serial (usable whenever PCI support
is available); since 3.10.0,
spapr-vio-serial (usable with ppc64/pseries guests),
system-serial (usable with aarch64/virt guests) and
sclp-serial (usable with s390 and s390x guests) are
available as well.
Since 3.10.0, the target
element can have an optional model subelement;
valid values for its name attribute are:
isa-serial (usable with the isa-serial target
type); usb-serial (usable with the usb-serial
target type); pci-serial
(usable with the pci-serial target type);
spapr-vty (usable with the spapr-vio-serial
target type); pl011 (usable with the
system-serial target type); sclpconsole and
sclplmconsole (usable with the sclp-serial
target type).
If any of the attributes is not specified by the user, libvirt will choose a value suitable for most users.
Most target types support configuring the guest-visible device
address as documented above; more
specifically, acceptable address types are isa (for
isa-serial), usb (for usb-serial),
pci (for pci-serial) and spapr-vio
(for spapr-vio-serial). The system-serial
and sclp-serial target types don't support specifying an
address.
For the relationship between serial ports and consoles, see below.
Console ¶
...
<devices>
<!-- Serial console -->
<console type='pty'>
<source path='/dev/pts/2'/>
<target type='serial' port='0'/>
</console>
</devices>
...
...
<devices>
<!-- KVM virtio console -->
<console type='pty'>
<source path='/dev/pts/5'/>
<target type='virtio' port='0'/>
</console>
</devices>
...
The console element is used to represent interactive
serial consoles. Depending on the type of guest in use and the specifics
of the configuration, the console element might represent
the same device as an existing serial element or a separate
device.
A target subelement is supported and works the same
way as with the serial element
(see above for details).
Valid values for the type attribute are:
serial (described below);
virtio (usable whenever VirtIO support is available);
xen, lxc, uml and
openvz (available when the corresponding hypervisor is in
use). sclp and sclplm (usable for s390 and
s390x QEMU guests) are supported for compatibility reasons but should
not be used for new guests: use the sclpconsole and
sclplmconsole target models, respectively, with the
serial element instead.
Of the target types listed above, serial is special in
that it doesn't represents a separate device, but rather the same
device as the first serial element. Due to this, there can
only be a single console element with target type
serial per guest.
Virtio consoles are usually accessible as /dev/hvc[0-7]
from inside the guest; for more information, see
http://fedoraproject.org/wiki/Features/VirtioSerial.
Since 0.8.3
For the relationship between serial ports and consoles, see below.
Relationship between serial ports and consoles ¶
Due to hystorical reasons, the serial and
console elements have partially overlapping scopes.
In general, both elements are used to configure one or more serial
consoles to be used for interacting with the guest. The main difference
between the two is that serial is used for emulated,
usually native, serial consoles, whereas console is used
for paravirtualized ones.
Both emulated and paravirtualized serial consoles have advantages and disadvantages:
- emulated serial consoles are usually initialized much earlier than paravirtualized ones, so they can be used to control the bootloader and display both firmware and early boot messages;
- on several platforms, there can only be a single emulated serial console per guest but paravirtualized consoles don't suffer from the same limitation.
A configuration such as:
...
<devices>
<console type='pty'>
<target type='serial'/>
</console>
<console type='pty'>
<target type='virtio'/>
</console>
</devices>
...
will work on any platform and will result in one emulated serial console
for early boot logging / interactive / recovery use, and one
paravirtualized serial console to be used eg. as a side channel. Most
people will be fine with having just the first console
element in their configuration.
Note that, due to the compatibility concerns mentioned earlier, all the following configurations:
... <devices> <serial type='pty'/> </devices> ...
... <devices> <console type='pty'/> </devices> ...
... <devices> <serial type='pty'/> <console type='pty'/> </devices> ...
will be treated the same and will result in a single emulated serial console being available to the guest.
Channel ¶
This represents a private communication channel between the host and the guest.
...
<devices>
<channel type='unix'>
<source mode='bind' path='/tmp/guestfwd'/>
<target type='guestfwd' address='10.0.2.1' port='4600'/>
</channel>
<!-- KVM virtio channel -->
<channel type='pty'>
<target type='virtio' name='arbitrary.virtio.serial.port.name'/>
</channel>
<channel type='unix'>
<source mode='bind' path='/var/lib/libvirt/qemu/f16x86_64.agent'/>
<target type='virtio' name='org.qemu.guest_agent.0' state='connected'/>
</channel>
<channel type='spicevmc'>
<target type='virtio' name='com.redhat.spice.0'/>
</channel>
</devices>
...
This can be implemented in a variety of ways. The specific type of
channel is given in the type attribute of the
target element. Different channel types have different
target attributes.
-
guestfwd - TCP traffic sent by the guest to a given IP address and port is
forwarded to the channel device on the host. The
targetelement must haveaddressandportattributes. Since 0.7.3 -
virtio - Paravirtualized virtio channel. Channel is exposed in the guest under
/dev/vport*, and if the optional element
nameis specified, /dev/virtio-ports/$name (for more info, please see http://fedoraproject.org/wiki/Features/VirtioSerial). The optional elementaddresscan tie the channel to a particulartype='virtio-serial'controller, documented above. With qemu, ifnameis "org.qemu.guest_agent.0", then libvirt can interact with a guest agent installed in the guest, for actions such as guest shutdown or file system quiescing. Since 0.7.7, guest agent interaction since 0.9.10 Moreover, since 1.0.6 it is possible to have source path auto generated for virtio unix channels. This is very useful in case of a qemu guest agent, where users don't usually care about the source path since it's libvirt who talks to the guest agent. In case users want to utilize this feature, they should leave<source>element out. Since 1.2.11 the active XML for a virtio channel may contain an optionalstateattribute that reflects whether a process in the guest is active on the channel. This is an output-only attribute. Possible values for thestateattribute areconnectedanddisconnected. -
xen - Paravirtualized Xen channel. Channel is exposed in the guest as a
Xen console but identified with a name. Setup and consumption of a Xen
channel depends on software and configuration in the guest
(for more info, please see http://xenbits.xen.org/docs/unstable/misc/channel.txt).
Channel source path semantics are the same as the virtio target type.
The
stateattribute is not supported since Xen channels lack the necessary probing mechanism. Since 2.3.0 -
spicevmc - Paravirtualized SPICE channel. The domain must also have a
SPICE server as a graphics
device, at which point the host piggy-backs messages
across the
mainchannel. Thetargetelement must be present, with attributetype='virtio'; an optional attributenamecontrols how the guest will have access to the channel, and defaults toname='com.redhat.spice.0'. The optionaladdresselement can tie the channel to a particulartype='virtio-serial'controller. Since 0.8.8
Host interface ¶
A character device presents itself to the host as one of the following types.
Domain logfile ¶
This disables all input on the character device, and sends output into the virtual machine's logfile
...
<devices>
<console type='stdio'>
<target port='1'/>
</console>
</devices>
...
Device logfile ¶
A file is opened and all data sent to the character device is written to the file.
...
<devices>
<serial type="file">
<source path="/var/log/vm/vm-serial.log"/>
<target port="1"/>
</serial>
</devices>
...
Virtual console ¶
Connects the character device to the graphical framebuffer in a virtual console. This is typically accessed via a special hotkey sequence such as "ctrl+alt+3"
...
<devices>
<serial type='vc'>
<target port="1"/>
</serial>
</devices>
...
Null device ¶
Connects the character device to the void. No data is ever provided to the input. All data written is discarded.
...
<devices>
<serial type='null'>
<target port="1"/>
</serial>
</devices>
...
Pseudo TTY ¶
A Pseudo TTY is allocated using /dev/ptmx. A suitable client such as 'virsh console' can connect to interact with the serial port locally.
...
<devices>
<serial type="pty">
<source path="/dev/pts/3"/>
<target port="1"/>
</serial>
</devices>
...
NB special case if <console type='pty'>, then the TTY path is also duplicated as an attribute tty='/dev/pts/3' on the top level <console> tag. This provides compat with existing syntax for <console> tags.
Host device proxy ¶
The character device is passed through to the underlying physical character device. The device types must match, eg the emulated serial port should only be connected to a host serial port - don't connect a serial port to a parallel port.
...
<devices>
<serial type="dev">
<source path="/dev/ttyS0"/>
<target port="1"/>
</serial>
</devices>
...
Named pipe ¶
The character device writes output to a named pipe. See pipe(7) for more info.
...
<devices>
<serial type="pipe">
<source path="/tmp/mypipe"/>
<target port="1"/>
</serial>
</devices>
...
TCP client/server ¶
The character device acts as a TCP client connecting to a remote server.
...
<devices>
<serial type="tcp">
<source mode="connect" host="0.0.0.0" service="2445"/>
<protocol type="raw"/>
<target port="1"/>
</serial>
</devices>
...
Or as a TCP server waiting for a client connection.
...
<devices>
<serial type="tcp">
<source mode="bind" host="127.0.0.1" service="2445"/>
<protocol type="raw"/>
<target port="1"/>
</serial>
</devices>
...
Alternatively you can use telnet instead
of raw TCP in order to utilize the telnet protocol
for the connection.
Since 0.8.5, some hypervisors support
use of either telnets (secure telnet) or tls
(via secure sockets layer) as the transport protocol for connections.
...
<devices>
<serial type="tcp">
<source mode="connect" host="0.0.0.0" service="2445"/>
<protocol type="telnet"/>
<target port="1"/>
</serial>
...
<serial type="tcp">
<source mode="bind" host="127.0.0.1" service="2445"/>
<protocol type="telnet"/>
<target port="1"/>
</serial>
</devices>
...
Since 2.4.0, the optional attribute
tls can be used to control whether a chardev
TCP communication channel would utilize a hypervisor configured
TLS X.509 certificate environment in order to encrypt the data
channel. For the QEMU hypervisor, usage of a TLS environment can
be controlled on the host by the chardev_tls and
chardev_tls_x509_cert_dir or
default_tls_x509_cert_dir settings in the file
/etc/libvirt/qemu.conf. If chardev_tls is enabled,
then unless the tls attribute is set to "no", libvirt
will use the host configured TLS environment.
If chardev_tls is disabled, but the tls
attribute is set to "yes", then libvirt will attempt to use the
host TLS environment if either the chardev_tls_x509_cert_dir
or default_tls_x509_cert_dir TLS directory structure exists.
...
<devices>
<serial type="tcp">
<source mode='connect' host="127.0.0.1" service="5555" tls="yes"/>
<protocol type="raw"/>
<target port="0"/>
</serial>
</devices>
...
UDP network console ¶
The character device acts as a UDP netconsole service, sending and receiving packets. This is a lossy service.
...
<devices>
<serial type="udp">
<source mode="bind" host="0.0.0.0" service="2445"/>
<source mode="connect" host="0.0.0.0" service="2445"/>
<target port="1"/>
</serial>
</devices>
...
UNIX domain socket client/server ¶
The character device acts as a UNIX domain socket server, accepting connections from local clients.
...
<devices>
<serial type="unix">
<source mode="bind" path="/tmp/foo"/>
<target port="1"/>
</serial>
</devices>
...
Spice channel ¶
The character device is accessible through spice connection
under a channel name specified in the channel
attribute. Since 1.2.2
Note: depending on the hypervisor, spiceports might (or might not) be enabled on domains with or without spice graphics.
...
<devices>
<serial type="spiceport">
<source channel="org.qemu.console.serial.0"/>
<target port="1"/>
</serial>
</devices>
...
Nmdm device ¶
The nmdm device driver, available on FreeBSD, provides two tty devices connected together by a virtual null modem cable. Since 1.2.4
...
<devices>
<serial type="nmdm">
<source master="/dev/nmdm0A" slave="/dev/nmdm0B"/>
</serial>
</devices>
...
The source element has these attributes:
-
master - Master device of the pair, that is passed to the hypervisor. Device is specified by a fully qualified path.
-
slave - Slave device of the pair, that is passed to the clients for connection to the guest console. Device is specified by a fully qualified path.
Sound devices ¶
A virtual sound card can be attached to the host via the
sound element. Since 0.4.3
... <devices> <sound model='es1370'/> </devices> ...
-
sound -
The
soundelement has one mandatory attribute,model, which specifies what real sound device is emulated. Valid values are specific to the underlying hypervisor, though typical choices are 'es1370', 'sb16', 'ac97', 'ich6' and 'usb'. ( 'ac97' only since 0.6.0, 'ich6' only since 0.8.8, 'usb' only since 1.2.7)
Since 0.9.13, a sound element
with ich6 model can have optional
sub-elements <codec> to attach various audio
codecs to the audio device. If not specified, a default codec
will be attached to allow playback and recording. Valid values
are 'duplex' (advertise a line-in and a line-out) and 'micro'
(advertise a speaker and a microphone).
...
<devices>
<sound model='ich6'>
<codec type='micro'/>
</sound>
</devices>
...
Each sound element has an optional
sub-element <address> which can tie the
device to a particular PCI
slot, documented above.
Watchdog device ¶
A virtual hardware watchdog device can be added to the guest via
the watchdog element.
Since 0.7.3, QEMU and KVM only
The watchdog device requires an additional driver and management daemon in the guest. Just enabling the watchdog in the libvirt configuration does not do anything useful on its own.
Currently libvirt does not support notification when the watchdog fires. This feature is planned for a future version of libvirt.
... <devices> <watchdog model='i6300esb'/> </devices> ...
...
<devices>
<watchdog model='i6300esb' action='poweroff'/>
</devices>
</domain>
-
model -
The required
modelattribute specifies what real watchdog device is emulated. Valid values are specific to the underlying hypervisor.QEMU and KVM support:
- 'i6300esb' - the recommended device, emulating a PCI Intel 6300ESB
- 'ib700' - emulating an ISA iBase IB700
- 'diag288' - emulating an S390 DIAG288 device Since 1.2.17
-
action -
The optional
actionattribute describes what action to take when the watchdog expires. Valid values are specific to the underlying hypervisor.QEMU and KVM support:
- 'reset' - default, forcefully reset the guest
- 'shutdown' - gracefully shutdown the guest (not recommended)
- 'poweroff' - forcefully power off the guest
- 'pause' - pause the guest
- 'none' - do nothing
- 'dump' - automatically dump the guest Since 0.8.7
- 'inject-nmi' - inject a non-maskable interrupt into the guest Since 1.2.17
Note 1: the 'shutdown' action requires that the guest is responsive to ACPI signals. In the sort of situations where the watchdog has expired, guests are usually unable to respond to ACPI signals. Therefore using 'shutdown' is not recommended.
Note 2: the directory to save dump files can be configured by
auto_dump_pathin file /etc/libvirt/qemu.conf.
Memory balloon device ¶
A virtual memory balloon device is added to all Xen and KVM/QEMU
guests. It will be seen as memballoon element.
It will be automatically added when appropriate, so there is no
need to explicitly add this element in the guest XML unless a
specific PCI slot needs to be assigned.
Since 0.8.3, Xen, QEMU and KVM only
Additionally, since 0.8.4, if the
memballoon device needs to be explicitly disabled,
model='none' may be used.
Example: automatically added device with KVM
... <devices> <memballoon model='virtio'/> </devices> ...
Example: manually added device with static PCI slot 2 requested
...
<devices>
<memballoon model='virtio'>
<address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
<stats period='10'/>
<driver iommu='on' ats='on'/>
</memballoon>
</devices>
</domain>
-
model -
The required
modelattribute specifies what type of balloon device is provided. Valid values are specific to the virtualization platform- 'virtio' - default with QEMU/KVM
- 'xen' - default with Xen
-
autodeflate -
The optional
autodeflateattribute allows to enable/disable (values "on"/"off", respectively) the ability of the QEMU virtio memory balloon to release some memory at the last moment before a guest's process get killed by Out of Memory killer. Since 1.3.1, QEMU and KVM only -
period -
The optional
periodallows the QEMU virtio memory balloon driver to provide statistics through thevirsh dommemstat [domain]command. By default, collection is not enabled. In order to enable, use thevirsh dommemstat [domain] --period [number]command orvirsh editcommand to add the option to the XML definition. Thevirsh dommemstatwill accept the options--live,--current, or--config. If an option is not provided, the change for a running domain will only be made to the active guest. If the QEMU driver is not at the right revision, the attempt to set the period will fail. Large values (e.g. many years) might be ignored. Since 1.1.1, requires QEMU 1.5 -
driver -
For model
virtiomemballoon, Virtio-specific options can also be set. (Since 3.5.0)
Random number generator device ¶
The virtual random number generator device allows the host to pass through entropy to guest operating systems. Since 1.0.3
Example: usage of the RNG device:
...
<devices>
<rng model='virtio'>
<rate period="2000" bytes="1234"/>
<backend model='random'>/dev/random</backend>
<!-- OR -->
<backend model='egd' type='udp'>
<source mode='bind' service='1234'/>
<source mode='connect' host='1.2.3.4' service='1234'/>
</backend>
</rng>
</devices>
...
-
model -
The required
modelattribute specifies what type of RNG device is provided. Valid values are specific to the virtualization platform:- 'virtio' - supported by qemu and virtio-rng kernel module
-
rate -
The optional
rateelement allows limiting the rate at which entropy can be consumed from the source. The mandatory attributebytesspecifies how many bytes are permitted to be consumed per period. An optionalperiodattribute specifies the duration of a period in milliseconds; if omitted, the period is taken as 1000 milliseconds (1 second). Since 1.0.4 -
backend -
The
backendelement specifies the source of entropy to be used for the domain. The source model is configured using themodelattribute. Supported source models are:-
random -
This backend type expects a non-blocking character device as input. The file name is specified as contents of the
backendelement. Since 1.3.4 any path is accepted. Before that /dev/random and /dev/hwrng were the only accepted paths. When no file name is specified the hypervisor default is used. For qemu, the default is /dev/random -
egd -
This backend connects to a source using the EGD protocol. The source is specified as a character device. Refer to character device host interface for more information.
-
-
driver -
The subelement
drivercan be used to tune the device:- virtio options
- Virtio-specific options can also be set. (Since 3.5.0)
TPM device ¶
The TPM device enables a QEMU guest to have access to TPM functionality.
The TPM passthrough device type provides access to the host's TPM for one QEMU guest. No other software may be using the TPM device, typically /dev/tpm0, at the time the QEMU guest is started. 'passthrough' since 1.0.5
Example: usage of the TPM passthrough device
...
<devices>
<tpm model='tpm-tis'>
<backend type='passthrough'>
<device path='/dev/tpm0'/>
</backend>
</tpm>
</devices>
...
-
model -
The
modelattribute specifies what device model QEMU provides to the guest. If no model name is provided,tpm-tiswill automatically be chosen. -
backend -
The
backendelement specifies the type of TPM device. The following types are supported:-
passthrough -
Use the host's TPM device.
This backend type requires exclusive access to a TPM device on the host. An example for such a device is /dev/tpm0. The fully qualified file name is specified by path attribute of the
sourceelement. If no file name is specified then /dev/tpm0 is automatically used.
-
NVRAM device ¶
nvram device is always added to pSeries guest on PPC64, and its address
is allowed to be changed. Element nvram (only valid for
pSeries guest, since 1.0.5) is provided to
enable the address setting.
Example: usage of NVRAM configuration
...
<devices>
<nvram>
<address type='spapr-vio' reg='0x3000'/>
</nvram>
</devices>
...
-
spapr-vio -
VIO device address type, only valid for PPC64.
-
reg -
Device address
panic device ¶
panic device enables libvirt to receive panic notification from a QEMU guest. Since 1.2.1, QEMU and KVM only
This feature is always enabled for:
- pSeries guests, since it's implemented by the guest firmware
- S390 guests, since it's an integral part of the S390 architecture
For the guest types listed above, libvirt automatically adds a
panic element to the domain XML.
Example: usage of panic configuration
...
<devices>
<panic model='hyperv'/>
<panic model='isa'>
<address type='isa' iobase='0x505'/>
</panic>
</devices>
...
-
model -
The optional
modelattribute specifies what type of panic device is provided. The panic model used when this attribute is missing depends on the hypervisor and guest arch.- 'isa' - for ISA pvpanic device
- 'pseries' - default and valid only for pSeries guests.
- 'hyperv' - for Hyper-V crash CPU feature. Since 1.3.0, QEMU and KVM only
- 's390' - default for S390 guests. Since 1.3.5
-
address -
address of panic. The default ioport is 0x505. Most users don't need to specify an address, and doing so is forbidden altogether for s390, pseries and hyperv models.
Shared memory device ¶
A shared memory device allows to share a memory region between different virtual machines and the host. Since 1.2.10, QEMU and KVM only
...
<devices>
<shmem name='my_shmem0'>
<model type='ivshmem-plain'/>
<size unit='M'>4</size>
</shmem>
<shmem name='shmem_server'>
<model type='ivshmem-doorbell'/>
<size unit='M'>2</size>
<server path='/tmp/socket-shmem'/>
<msi vectors='32' ioeventfd='on'/>
</shmem>
</devices>
...
-
shmem -
The
shmemelement has one mandatory attribute,nameto identify the shared memory. -
model -
Attribute
typeof the optional elementmodelspecifies the model of the underlying device providing theshmemdevice. The models currently supported areivshmem(supports both server and server-less shmem, but is deprecated by newer QEMU in favour of the -plain and -doorbell variants),ivshmem-plain(only for server-less shmem) andivshmem-doorbell(only for shmem with the server). -
size -
The optional
sizeelement specifies the size of the shared memory. This must be power of 2 and greater than or equal to 1 MiB. -
server -
The optional
serverelement can be used to configure a server socket the device is supposed to connect to. The optionalpathattribute specifies the absolute path to the unix socket and defaults to/var/lib/libvirt/shmem/$shmem-$name-sock. -
msi -
The optional
msielement enables/disables (values "on"/"off", respectively) MSI interrupts. This option can currently be used only together with theserverelement. Thevectorsattribute can be used to specify the number of interrupt vectors. Theioeventdattribute enables/disables (values "on"/"off", respectively) ioeventfd.
Memory devices ¶
In addition to the initial memory assigned to the guest, memory devices allow additional memory to be assigned to the guest in the form of memory modules. A memory device can be hot-plugged or hot-unplugged depending on the guests' memory resource needs. Some hypervisors may require NUMA configured for the guest.
Example: usage of the memory devices
...
<devices>
<memory model='dimm' access='private'>
<target>
<size unit='KiB'>524287</size>
<node>0</node>
</target>
</memory>
<memory model='dimm'>
<source>
<pagesize unit='KiB'>4096</pagesize>
<nodemask>1-3</nodemask>
</source>
<target>
<size unit='KiB'>524287</size>
<node>1</node>
</target>
</memory>
<memory model='nvdimm'>
<source>
<path>/tmp/nvdimm</path>
</source>
<target>
<size unit='KiB'>524288</size>
<node>1</node>
<label>
<size unit='KiB'>128</size>
</label>
</target>
</memory>
</devices>
...
-
model -
Provide
dimmto add a virtual DIMM module to the guest. Since 1.2.14 Providenvdimmmodel adds a Non-Volatile DIMM module. Since 3.2.0 -
access -
An optional attribute
access(since 3.2.0) that provides capability to fine tune mapping of the memory on per module basis. Values are the same as Memory Backing:sharedandprivate. -
source -
For model
dimmthis element is optional and allows to fine tune the source of the memory used for the given memory device. If the element is not provided defaults configured vianumatuneare used. Ifdimmis provided, then the following optional elements can be provided as well:-
pagesize -
This element can be used to override the default host page size used for backing the memory device. The configured value must correspond to a page size supported by the host.
-
nodemask -
This element can be used to override the default set of NUMA nodes where the memory would be allocated.
For model
nvdimmthis element is mandatory and has a single child elementpaththat represents a path in the host that backs the nvdimm module in the guest. -
-
target -
The mandatory
targetelement configures the placement and sizing of the added memory from the perspective of the guest.The mandatory
sizesubelement configures the size of the added memory as a scaled integer.The
nodesubelement configures the guest NUMA node to attach the memory to. The element shall be used only if the guest has NUMA nodes configured.For NVDIMM type devices one can optionally use
labeland its subelementsizeto configure the size of namespaces label storage within the NVDIMM module. Thesizeelement has usual meaning described here. For QEMU domains the following restrictions apply:- the minimum label size is 128KiB,
- the remaining size (total-size - label-size) has to be aligned to 4KiB
IOMMU devices ¶
The iommu element can be used to add an IOMMU device.
Since 2.1.0
Example:
...
<devices>
<iommu model='intel'>
<driver intremap='on'/>
</iommu>
</devices>
...
-
model -
Currently only the
intelmodel is supported. -
driver -
The
driversubelement can be used to configure additional options:-
intremap -
The
intremapattribute with possible valuesonandoffcan be used to turn on interrupt remapping, a part of the VT-d functionality. Currently this requires split I/O APIC (<ioapic driver='qemu'/>). Since 3.4.0 (QEMU/KVM only) -
caching_mode -
The
caching_modeattribute with possible valuesonandoffcan be used to turn on the VT-d caching mode (useful for assigned devices). Since 3.4.0 (QEMU/KVM only) -
eim -
The
eimattribute (with possible valuesonandoff) can be used to configure Extended Interrupt Mode. A q35 domain with split I/O APIC (as described in hypervisor features), and both interrupt remapping and EIM turned on for the IOMMU, will be able to use more than 255 vCPUs. Since 3.4.0 (QEMU/KVM only) -
iotlb -
The
iotlbattribute with possible valuesonandoffcan be used to turn on the IOTLB used to cache address translation requests from devices. Since 3.5.0 (QEMU/KVM only)
-
Security label ¶
The seclabel element allows control over the
operation of the security drivers. There are three basic
modes of operation, 'dynamic' where libvirt automatically
generates a unique security label, 'static' where the
application/administrator chooses the labels, or 'none'
where confinement is disabled. With dynamic
label generation, libvirt will always automatically
relabel any resources associated with the virtual machine.
With static label assignment, by default, the administrator
or application must ensure labels are set correctly on any
resources, however, automatic relabeling can be enabled
if desired. 'dynamic' since 0.6.1, 'static'
since 0.6.2, and 'none' since 0.9.10.
If more than one security driver is used by libvirt, multiple
seclabel tags can be used, one for each driver and
the security driver referenced by each tag can be defined using
the attribute model
Valid input XML configurations for the top-level security label are:
<seclabel type='dynamic' model='selinux'/>
<seclabel type='dynamic' model='selinux'>
<baselabel>system_u:system_r:my_svirt_t:s0</baselabel>
</seclabel>
<seclabel type='static' model='selinux' relabel='no'>
<label>system_u:system_r:svirt_t:s0:c392,c662</label>
</seclabel>
<seclabel type='static' model='selinux' relabel='yes'>
<label>system_u:system_r:svirt_t:s0:c392,c662</label>
</seclabel>
<seclabel type='none'/>
If no 'type' attribute is provided in the input XML, then the security driver default setting will be used, which may be either 'none' or 'dynamic'. If a 'baselabel' is set but no 'type' is set, then the type is presumed to be 'dynamic'
When viewing the XML for a running guest with automatic
resource relabeling active, an additional XML element,
imagelabel, will be included. This is an
output-only element, so will be ignored in user supplied
XML documents
-
type - Either
static,dynamicornoneto determine whether libvirt automatically generates a unique security label or not. -
model - A valid security model name, matching the currently activated security model
-
relabel - Either
yesorno. This must always beyesif dynamic label assignment is used. With static label assignment it will default tono. -
label - If static labelling is used, this must specify the full
security label to assign to the virtual domain. The format
of the content depends on the security driver in use:
- SELinux: a SELinux context.
- AppArmor: an AppArmor profile.
- DAC: owner and group separated by colon. They can be defined both as user/group names or uid/gid. The driver will first try to parse these values as names, but a leading plus sign can used to force the driver to parse them as uid or gid.
-
baselabel - If dynamic labelling is used, this can optionally be
used to specify the base security label that will be used to generate
the actual label. The format of the content depends on the security
driver in use.
The SELinux driver uses only the
typefield of the baselabel in the generated label. Other fields are inherited from the parent process when using SELinux baselabels. (The example above demonstrates the use ofmy_svirt_tas the value for thetypefield.) -
imagelabel - This is an output only element, which shows the security label used on resources associated with the virtual domain. The format of the content depends on the security driver in use
When relabeling is in effect, it is also possible to fine-tune
the labeling done for specific source file names, by either
disabling the labeling (useful if the file lives on NFS or other
file system that lacks security labeling) or requesting an
alternate label (useful when a management application creates a
special label to allow sharing of some, but not all, resources
between domains), since 0.9.9. When
a seclabel element is attached to a specific path
rather than the top-level domain assignment, only the
attribute relabel or the
sub-element label are supported. Additionally,
since 1.1.2, an output-only
element labelskip will be present for active
domains on disks where labeling was skipped due to the image
being on a file system that lacks security labeling.
Key Wrap ¶
The content of the optional keywrap element specifies
whether the guest will be allowed to perform the S390 cryptographic key
management operations. A clear key can be protected by encrypting it
under a unique wrapping key that is generated for each guest VM running
on the host. Two variations of wrapping keys are generated: one version
for encrypting protected keys using the DEA/TDEA algorithm, and another
version for keys encrypted using the AES algorithm. If a
keywrap element is not included, the guest will be granted
access to both AES and DEA/TDEA key wrapping by default.
<domain>
...
<keywrap>
<cipher name='aes' state='off'/>
</keywrap>
...
</domain>
At least one cipher element must be nested within the
keywrap element.
-
cipher - The
nameattribute identifies the algorithm for encrypting a protected key. The values supported for this attribute areaesfor encryption under the AES wrapping key, ordeafor encryption under the DEA/TDEA wrapping key. Thestateattribute indicates whether the cryptographic key management operations should be turned on for the specified encryption algorithm. The value can be set toonoroff.
Note: DEA/TDEA is synonymous with DES/TDES.
Example configs ¶
Example configurations for each driver are provide on the driver specific pages listed below