QEMU options

There are two ways to use QEMU in LAVA.

Virtualization testing

If you want to test virtualization on a DUT, then you have complete freedom to launch QEMU in any way you desire, including from a locally compiled source tree with custom patches. It is often useful to separate the output of the virtual machine from the host device or to run a test shell inside the virtual machine as well as on the host device, so a Secondary Connection can be used. This is a relatively complex test job with particular issues about how to identify the IP address of the virtual machine so that the secondary connection can login over SSH.

The rest of this page deals with how to specify the options to QEMU when using QEMU on the dispatcher for testing emulation within QEMU.

Emulation testing

LAVA also supports running QEMU on the dispatcher, allowing testing of QEMU running on the host architecture of the worker. In many, but not all, cases this will create an x86 virtual machine. Emulation of other architectures is possible using the same device. The QEMU command line is built up by combining settings from the jinja2 template, the device dictionary and the job context.

The Jinja2 template for QEMU tries to cover a range of use cases but QEMU has a very long and complex set of possible options and commands.

The LAVA support for QEMU has three elements:

  1. substituted - options into which values must be inserted by LAVA.

  2. mandatory - options which LAVA needs to use to ensure the automation operates.

  3. specific - options which are specific to particular test jobs.

Substitution support

To execute QEMU in LAVA, various files need to be downloaded by LAVA, some may need to be modified or decompressed by LAVA, but all of the final paths to the files will be determined by LAVA. These paths need to be substituted into the commands so that QEMU is able to locate the files.

This is handled in the test job definition using image_arg with placeholders like {{KERNEL}}. The Job Definition uses this method.

Mandatory support

Mandatory commands and options include -nographic so that LAVA is able to interact with the virtual machine on the serial console instead of letting QEMU launch a new window which would be problematic on dispatchers when X11 is not available.

Mandatory commands also include admin constraints like limiting the amount of memory available to each QEMU test job. This is achieved by allowing the -m option to take a variable in the device type template but setting a value for that variable in the device dictionary. This value cannot then be overridden by the test writer.

Other options of this kind include networking support, for example the MAC address used by QEMU devices needs to be strictly controlled by admins so that no two QEMU devices on one subnet have the same MAC address.

The arch option in the job context is used in the jinja2 template to determine which QEMU binary to execute.

Specific support

The breadth of the possible options available with QEMU means that there is a lot of scope for customization. Some of these elements have defaults in the device type template which can be overridden by the test writer. Other options can be specific to individual test jobs.

When writing a new test job, it is best to start with an example command line based on how you would use QEMU to run the same test on your local machines.

Example command lines

An example QEMU command line might look like this:

/usr/bin/qemu-system-x86_64 -cpu host -enable-kvm -nographic \
 -net nic,model=virtio,macaddr=DE:AD:BE:EF:28:05 \
 -net tap -m 1024 -monitor none \
 -drive format=raw,file=/tmp/tmpUHeIM6/large-stable-6.img \
 -drive format=qcow2,file=/tmp/tmp2sbOlI/lava-guest.qcow2,media=disk

This example, on an x86_64 worker, would break into:

  • Mandatory from the device type template (using values from the device dictionary or the job context).

    • /usr/bin/qemu-system-x86_64

    • -cpu host

    • -enable-kvm

    • -nographic

  • Substituted using image_arg in the test job definition.

    • -drive format=raw,file=/tmp/tmpUHeIM6/large-stable-6.img

    • -drive format=qcow2,file=/tmp/tmp2sbOlI/lava-guest.qcow2,media=disk

A more complex QEMU command line would need to use extra_options in the test job context. e.g.

/usr/bin/qemu-system-aarch64 -nographic -machine virt -cpu cortex-a57 -smp 1 \
 -m 2048 -global virtio-blk-device.scsi=off -device virtio-scsi-device,id=scsi \
 -kernel /tmp/tmpQi2ZR3/Image --append "console=ttyAMA0 root=/dev/vda rw" \
 -drive format=raw,file=/tmp/tmpQi2ZR3/ubuntu-core-14.04.1-core-arm64-ext4.img \
 -drive format=qcow2,file=/tmp/tmpMgsuvB/lava-guest.qcow2,media=disk


The use of the cpu option in the job context disables the use of -enable-kvm. If the worker can support KVM acceleration, this can be enabled using more QEMU options.

This example would break into:

  • Mandatory from the device type template (using values from the device dictionary or the job context).

    • /usr/bin/qemu-system-aarch64

    • -nographic

    • -m 2048

  • Substituted using image_arg in the test job definition.

    Use substituted for the complete argument. Include any other options which relate to the filepath into the image_arg.

    • -kernel /tmp/tmpQi2ZR3/Image --append "console=ttyAMA0 root=/dev/vda rw"

    • -drive format=raw,file=/tmp/tmpQi2ZR3/ubuntu-core-14.04.1-core-arm64-ext4.img

    • -drive format=qcow2,file=/tmp/tmpMgsuvB/lava-guest.qcow2,media=disk

  • Specific - using the job context to override defaults:

    • -machine virt

    • -cpu cortex-a57

    To use /usr/bin/qemu-system-aarch64, the job context also needs to include arch: arm64 or arch: aarch64:

  • Specific - using extra_options in the job context:

    • -smp 1

    • -global virtio-blk-device.scsi=off

    • -device virtio-scsi-device,id=scsi

How to override variables


The specifics of which variables, the names of the variables themselves and the possible values are determined by the device type template and this can be modified by the local admin. This guide can only cover the general principles and give examples using the default templates.

  • Substitution support is handled by the test job pipeline once the relevant files have been downloaded. The test writer has the ability to add relevant options and flags to these commands using the image_arg support in the test job definition.

    - deploy:
          minutes: 5
        to: tmpfs
            image_arg: -drive format=raw,file={rootfs}
            url: https://images.validation.linaro.org/kvm/standard/stretch-2.img.gz
            compression: gz
  • Mandatory options and commands cannot be overridden. These will either be hard-coded values in the device type template or variables set by the admin using the device dictionary.

  • Specific options can be overridden in the job context. One of the most common specific options for QEMU in LAVA is arch. This allows admins to configure QEMU devices in LAVA to support multiple architectures instead of needing at least one device for each supported architecture. The test writer specifies the architecture of the files provided in the test job definition and this then determines which QEMU binary is used to execute the files.

    # context allows specific values to be overridden or included
      # tell the qemu template which architecture is being tested
      # the template uses that to ensure that qemu-system-x86_64 is executed.
      arch: amd64

    When using the multiple architecture support, it is common to change the machine and cpu arguments passed to QEMU.

      arch: aarch64
      netdevice: tap
      machine: virt
      cpu: cortex-a57

    (This example simply restates the defaults but any value which QEMU would accept as an argument to -machine and -cpu respectively could be used.)

    If using QEMU to emulate a microcontroller, you might need to use the vga and serial options which each take a complete argument, passed unchanged to QEMU.

    Specific options can also extend beyond the range that the device type template needs to cover and in order to build a working QEMU command line, it is sometimes necessary to pass a list of further commands and options which LAVA needs to include into the final command line. This support is available using the extra_options job context variable:

      arch: arm64
      - -global
      - virtio-blk-device.scsi=off
      - -smp
      - 1
      - -device
      - virtio-scsi-device,id=scsi


    When specifying a QEMU command, ensure that the preceding hyphen is included as well as the hyphen indicating that the extra_options list is continuing. (- -device). When specifying an option to that command, ensure that there is only the hyphen for the list. (- virtio...). Errors in this syntax will cause the test job to fail as Incomplete when the QEMU command line is constructed.

How to specify QEMU environment options

  • QEMU also evaluates environment options that are used at runtime to determine e.g. what subsystem should be used for the sound output on the host. For obvious security reasons there is no way to influence environment variables from within a job. But LAVA provides the capability to specify (globally at the server level) what environment variables are to be used for jobs in the file env.yaml. See Simple Administration.

  • One example is the use of -soundhw hda which emulates a soundcard on the target. To avoid having any sound output on the host (or worker), you can specify QEMU_AUDIO_DRV like so in /etc/lava-server/env.yaml:

    # A dictionary of (key, value) that will be added to the inherited environment.
    # If a key does not already exist in the inherited environment, it's added.
    # default: an empty dictionary
      LC_ALL: C.UTF-8
      LANG: C
    #  http_proxy: http://lava-lab-proxy
    #  https_proxy: http://lava-lab-proxy
    #  ftp_proxy: http://lava-lab-proxy
      PATH: /usr/local/bin:/usr/local/sbin:/bin:/usr/bin:/usr/sbin:/sbin
    # For qemu-system-* (device_type qemu) if -soundhw is passed,
    # enable this to not forward sound to the host.
    # Check qemu-system-x86_64 --audio-help for other options.
      QEMU_AUDIO_DRV: none

Host architecture support

QEMU will run test jobs of any supported combination of architecture, machine and CPU option. However, the underlying hardware of the worker can dramatically improve performance of QEMU test jobs if the appropriate acceleration can be used. This comes with a penalty that test jobs using hardware acceleration for virtual machines of one architecture will not transfer easily to another QEMU device (on this or some other LAVA instance) where hardware acceleration is only available for a different architecture. There will need to be changes to the test job submission. Running without hardware acceleration allows for portable test job submissions, however test jobs will not only run more slowly but also with wider variation in speed. This may make it hard to get sensible timeouts or usable results within a reasonable timeframe.

The -enable-kvm support is used as a default, based on x86_64 workers. Specifying the -cpu option disables the -enable-kvm option in the LAVA Jinja2 templates but test writers are able to add KVM acceleration using more QEMU options.

There are administrative issues here. It is entirely possible for a worker to not be x86_64 architecture. It is also possible to have QEMU devices on more than one worker and for those workers to be of differing architectures. To handle this, admins will need to:

  • Create a copy of the qemu.jinja2 template and name it according to their own convention, for example qemu-arm.jinja2.

  • Set the extends of the QEMU devices on each worker to the corresponding QEMU jinja2 template.

  • Create a new health check for the new Jinja2 template. For example, qemu-arm.jinja2 needs a health check called qemu-arm.yaml in the health-checks directory of the master.

  • Add device tags so that test writers can specify KVM acceleration where required. For example, kvm_arm on the devices extending qemu-arm.jinja2 and kvm_x86_64 on the devices extending the existing qemu.jinja2.

The device_type of all the QEMU devices can remain the same.

The changes to the test job may not be intuitive - the QEMU support can require some experimentation and reading, depending on the hardware.

For example, using the SynQuacer the options required to be able to run 32bit ARM code using the KVM accelerator require running the 64bit QEMU binary:

  arch: arm64
  netdevice: user
  machine: virt-2.10,accel=kvm
  cpu: host,aarch64=off
  guestfs_interface: virtio
  - kvm-arm


Even if there are no x86_64 workers running QEMU, there will still need to be a suitable health check and it is recommended to have a copy of the Jinja2 template in case an x86_64 worker is added later.

LAVA test storage

If one or more test actions are included in a QEMU job, LAVA will create a disk image and will attach it to QEMU using a command like:

-drive format=qcow2,file=<temporary_path>/lava-guest.qcow2,media=disk,if=<interface>,id=lavatest

The interface can be set in the device_type template or in the test job context using the guestfs_interface key in the context. Supported values include ide scsi virtio none with a default of ide. The size of the image is controlled via the guestfs_size parameter (default 512M).

Some emulated devices have no bus available for attaching this image (Ex: cubieboard). Some emulated devices have an available bus but qemu is unable to attach to it due to the selected architecture (like vexpress). For these boards, you need to set guestfs_interface to None and add a device with drive=lavatest. The “lavatest” id can be set via the guestfs_driveid job option. If no storage bus is available, you will also need to attach a device which permit to attach a storage bus.

Example for qemu cubieboard: (Cubieboard have an AHCI bus, but the support is incomplete)

2  arch: arm
3  cpu: cortex-a7
4  extra_options:
5  - -append "console=ttyS0 root=/dev/ram0"
6  - -device ide-hd,drive=lavatest
7  guestfs_interface: none
8  machine: cubieboard
9  model: model=allwinner-emac

Example for qemu vexpress-a9: (vexpress have a virtio bus, but by default, qemu try to add the drive as PCI virtio)

2  arch: arm
3  cpu: cortex-a9
4  extra_options:
5  - -append "console=ttyAMA0 root=/dev/ram0"
6  - -device virtio-bk-device,drive=lavatest
7  guestfs_interface: none
8  machine: vexpress-a9
9  model: model=lan9118

Example for Qemu PPC bamboo:

2  arch: ppc
3  extra_options:
4  - -append "console=ttyS0 root=/dev/ram0"
5  - -device virtio-scsi-pci,id=scsi
6  - -device scsi-hd,drive=test
7  guestfs_driveid: test
8  guestfs_interface: none
9  machine: bamboo