QEMU options

There are two ways to use QEMU in LAVA.

Virtualisation testing

If you want to test virtualisation 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 an x86 virtual machine and emulation of other architectures 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_args 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.

Specific support

The breadth of the possible options available with QEMU means that there is a lot of scope for customisation. 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 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_args 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

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_args in the test job definition.

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

    • -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

Note

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_args support in the test job definition.

    actions:
    - deploy:
        timeout:
          minutes: 5
        to: tmpfs
        images:
          rootfs:
            image_arg: -drive format=raw,file={rootfs}
            url: https://images.validation.linaro.org/kvm/standard/stretch-2.img.gz
            compression: gz
        os: debian
    
  • 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
    context:
      # 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.

    context:
      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:

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

    Note

    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.