Testing in QEMU

This document describes the testing infrastructure in QEMU.

Testing with “make check”

The “make check” testing family includes most of the C based tests in QEMU. For a quick help, run make check-help from the source tree.

The usual way to run these tests is:

make check

which includes QAPI schema tests, unit tests, QTests and some iotests. Different sub-types of “make check” tests will be explained below.

Before running tests, it is best to build QEMU programs first. Some tests expect the executables to exist and will fail with obscure messages if they cannot find them.

Unit tests

Unit tests, which can be invoked with make check-unit, are simple C tests that typically link to individual QEMU object files and exercise them by calling exported functions.

If you are writing new code in QEMU, consider adding a unit test, especially for utility modules that are relatively stateless or have few dependencies. To add a new unit test:

  1. Create a new source file. For example, tests/unit/foo-test.c.

  2. Write the test. Normally you would include the header file which exports the module API, then verify the interface behaves as expected from your test. The test code should be organized with the glib testing framework. Copying and modifying an existing test is usually a good idea.

  3. Add the test to tests/unit/meson.build. The unit tests are listed in a dictionary called tests. The values are any additional sources and dependencies to be linked with the test. For a simple test whose source is in tests/unit/foo-test.c, it is enough to add an entry like:

    {
  ...
  'foo-test': [],
  ...
}

Since unit tests don’t require environment variables, the simplest way to debug a unit test failure is often directly invoking it or even running it under gdb. However there can still be differences in behavior between make invocations and your manual run, due to $MALLOC_PERTURB_ environment variable (which affects memory reclamation and catches invalid pointers better) and gtester options. If necessary, you can run

make check-unit V=1

and copy the actual command line which executes the unit test, then run it from the command line.

QTest

QTest is a device emulation testing framework. It can be very useful to test device models; it could also control certain aspects of QEMU (such as virtual clock stepping), with a special purpose “qtest” protocol. Refer to QTest Device Emulation Testing Framework for more details.

QTest cases can be executed with

make check-qtest

QAPI schema tests

The QAPI schema tests validate the QAPI parser used by QMP, by feeding predefined input to the parser and comparing the result with the reference output.

The input/output data is managed under the tests/qapi-schema directory. Each test case includes four files that have a common base name:

  • ${casename}.json - the file contains the JSON input for feeding the parser

  • ${casename}.out - the file contains the expected stdout from the parser

  • ${casename}.err - the file contains the expected stderr from the parser

  • ${casename}.exit - the expected error code

Consider adding a new QAPI schema test when you are making a change on the QAPI parser (either fixing a bug or extending/modifying the syntax). To do this:

  1. Add four files for the new case as explained above. For example:

$EDITOR tests/qapi-schema/foo.{json,out,err,exit}.

  1. Add the new test in tests/Makefile.include. For example:

qapi-schema += foo.json

check-block

make check-block runs a subset of the block layer iotests (the tests that are in the “auto” group). See the “QEMU iotests” section below for more information.

QEMU iotests

QEMU iotests, under the directory tests/qemu-iotests, is the testing framework widely used to test block layer related features. It is higher level than “make check” tests and 99% of the code is written in bash or Python scripts. The testing success criteria is golden output comparison, and the test files are named with numbers.

To run iotests, make sure QEMU is built successfully, then switch to the tests/qemu-iotests directory under the build directory, and run ./check with desired arguments from there.

By default, “raw” format and “file” protocol is used; all tests will be executed, except the unsupported ones. You can override the format and protocol with arguments:

# test with qcow2 format
./check -qcow2
# or test a different protocol
./check -nbd

It’s also possible to list test numbers explicitly:

# run selected cases with qcow2 format
./check -qcow2 001 030 153

Cache mode can be selected with the “-c” option, which may help reveal bugs that are specific to certain cache mode.

More options are supported by the ./check script, run ./check -h for help.

Writing a new test case

Consider writing a tests case when you are making any changes to the block layer. An iotest case is usually the choice for that. There are already many test cases, so it is possible that extending one of them may achieve the goal and save the boilerplate to create one. (Unfortunately, there isn’t a 100% reliable way to find a related one out of hundreds of tests. One approach is using git grep.)

Usually an iotest case consists of two files. One is an executable that produces output to stdout and stderr, the other is the expected reference output. They are given the same number in file names. E.g. Test script 055 and reference output 055.out.

In rare cases, when outputs differ between cache mode none and others, a .out.nocache file is added. In other cases, when outputs differ between image formats, more than one .out files are created ending with the respective format names, e.g. 178.out.qcow2 and 178.out.raw.

There isn’t a hard rule about how to write a test script, but a new test is usually a (copy and) modification of an existing case. There are a few commonly used ways to create a test:

  • A Bash script. It will make use of several environmental variables related to the testing procedure, and could source a group of common.* libraries for some common helper routines.

  • A Python unittest script. Import iotests and create a subclass of iotests.QMPTestCase, then call iotests.main method. The downside of this approach is that the output is too scarce, and the script is considered harder to debug.

  • A simple Python script without using unittest module. This could also import iotests for launching QEMU and utilities etc, but it doesn’t inherit from iotests.QMPTestCase therefore doesn’t use the Python unittest execution. This is a combination of 1 and 2.

Pick the language per your preference since both Bash and Python have comparable library support for invoking and interacting with QEMU programs. If you opt for Python, it is strongly recommended to write Python 3 compatible code.

Both Python and Bash frameworks in iotests provide helpers to manage test images. They can be used to create and clean up images under the test directory. If no I/O or any protocol specific feature is needed, it is often more convenient to use the pseudo block driver, null-co://, as the test image, which doesn’t require image creation or cleaning up. Avoid system-wide devices or files whenever possible, such as /dev/null or /dev/zero. Otherwise, image locking implications have to be considered. For example, another application on the host may have locked the file, possibly leading to a test failure. If using such devices are explicitly desired, consider adding locking=off option to disable image locking.

Debugging a test case

The following options to the check script can be useful when debugging a failing test:

  • -gdb wraps every QEMU invocation in a gdbserver, which waits for a connection from a gdb client. The options given to gdbserver (e.g. the address on which to listen for connections) are taken from the $GDB_OPTIONS environment variable. By default (if $GDB_OPTIONS is empty), it listens on localhost:12345. It is possible to connect to it for example with gdb -iex "target remote $addr", where $addr is the address gdbserver listens on. If the -gdb option is not used, $GDB_OPTIONS is ignored, regardless of whether it is set or not.

  • -valgrind attaches a valgrind instance to QEMU. If it detects warnings, it will print and save the log in $TEST_DIR/<valgrind_pid>.valgrind. The final command line will be valgrind --log-file=$TEST_DIR/ <valgrind_pid>.valgrind --error-exitcode=99 $QEMU ...

  • -d (debug) just increases the logging verbosity, showing for example the QMP commands and answers.

  • -p (print) redirects QEMU’s stdout and stderr to the test output, instead of saving it into a log file in $TEST_DIR/qemu-machine-<random_string>.

Test case groups

“Tests may belong to one or more test groups, which are defined in the form of a comment in the test source file. By convention, test groups are listed in the second line of the test file, after the “#!/…” line, like this:

#!/usr/bin/env python3
# group: auto quick
#
...

Another way of defining groups is creating the tests/qemu-iotests/group.local file. This should be used only for downstream (this file should never appear in upstream). This file may be used for defining some downstream test groups or for temporarily disabling tests, like this:

# groups for some company downstream process
#
# ci - tests to run on build
# down - our downstream tests, not for upstream
#
# Format of each line is:
# TEST_NAME TEST_GROUP [TEST_GROUP ]...

013 ci
210 disabled
215 disabled
our-ugly-workaround-test down ci

Note that the following group names have a special meaning:

  • quick: Tests in this group should finish within a few seconds.

  • auto: Tests in this group are used during “make check” and should be runnable in any case. That means they should run with every QEMU binary (also non-x86), with every QEMU configuration (i.e. must not fail if an optional feature is not compiled in - but reporting a “skip” is ok), work at least with the qcow2 file format, work with all kind of host filesystems and users (e.g. “nobody” or “root”) and must not take too much memory and disk space (since CI pipelines tend to fail otherwise).

  • disabled: Tests in this group are disabled and ignored by check.

Container based tests

Introduction

The container testing framework in QEMU utilizes public images to build and test QEMU in predefined and widely accessible Linux environments. This makes it possible to expand the test coverage across distros, toolchain flavors and library versions. The support was originally written for Docker although we also support Podman as an alternative container runtime. Although the many of the target names and scripts are prefixed with “docker” the system will automatically run on whichever is configured.

The container images are also used to augment the generation of tests for testing TCG. See Testing with “make check-tcg” for more details.

Docker Prerequisites

Install “docker” with the system package manager and start the Docker service on your development machine, then make sure you have the privilege to run Docker commands. Typically it means setting up passwordless sudo docker command or login as root. For example:

$ sudo yum install docker
$ # or `apt-get install docker` for Ubuntu, etc.
$ sudo systemctl start docker
$ sudo docker ps

The last command should print an empty table, to verify the system is ready.

An alternative method to set up permissions is by adding the current user to “docker” group and making the docker daemon socket file (by default /var/run/docker.sock) accessible to the group:

$ sudo groupadd docker
$ sudo usermod $USER -a -G docker
$ sudo chown :docker /var/run/docker.sock

Note that any one of above configurations makes it possible for the user to exploit the whole host with Docker bind mounting or other privileged operations. So only do it on development machines.

Podman Prerequisites

Install “podman” with the system package manager.

$ sudo dnf install podman
$ podman ps

The last command should print an empty table, to verify the system is ready.

Quickstart

From source tree, type make docker-help to see the help. Testing can be started without configuring or building QEMU (configure and make are done in the container, with parameters defined by the make target):

make docker-test-build@centos8

This will create a container instance using the centos8 image (the image is downloaded and initialized automatically), in which the test-build job is executed.

Registry

The QEMU project has a container registry hosted by GitLab at registry.gitlab.com/qemu-project/qemu which will automatically be used to pull in pre-built layers. This avoids unnecessary strain on the distro archives created by multiple developers running the same container build steps over and over again. This can be overridden locally by using the NOCACHE build option:

make docker-image-debian10 NOCACHE=1

Images

Along with many other images, the centos8 image is defined in a Dockerfile in tests/docker/dockerfiles/, called centos8.docker. make docker-help command will list all the available images.

A .pre script can be added beside the .docker file, which will be executed before building the image under the build context directory. This is mainly used to do necessary host side setup. One such setup is binfmt_misc, for example, to make qemu-user powered cross build containers work.

Most of the existing Dockerfiles were written by hand, simply by creating a a new .docker file under the tests/docker/dockerfiles/ directory. This has led to an inconsistent set of packages being present across the different containers.

Thus going forward, QEMU is aiming to automatically generate the Dockerfiles using the lcitool program provided by the libvirt-ci project:

In that project, there is a mappings.yml file defining the distro native package names for a wide variety of third party projects. This is processed in combination with a project defined list of build pre-requisites to determine the list of native packages to install on each distribution. This can be used to generate dockerfiles, VM package lists and Cirrus CI variables needed to setup build environments across OS distributions with a consistent set of packages present.

When preparing a patch series that adds a new build pre-requisite to QEMU, updates to various lcitool data files may be required.

Adding new build pre-requisites

In the simple case where the pre-requisite is already known to libvirt-ci the following steps are needed

  • Edit tests/lcitool/projects/qemu.yml and add the pre-requisite

  • Run make lcitool-refresh to re-generate all relevant build environment manifests

In some cases libvirt-ci will not know about the build pre-requisite and thus some extra preparation steps will be required first

  • Fork the libvirt-ci project on gitlab

  • Edit the mappings.yml change to add an entry for the new build prerequisite, listing its native package name on as many OS distros as practical.

  • Commit the mappings.yml change and submit a merge request to the libvirt-ci project, noting in the description that this is a new build pre-requisite desired for use with QEMU

  • CI pipeline will run to validate that the changes to mappings.yml are correct, by attempting to install the newly listed package on all OS distributions supported by libvirt-ci.

  • Once the merge request is accepted, go back to QEMU and update the libvirt-ci submodule to point to a commit that contains the mappings.yml update.

Adding new OS distros

In some cases libvirt-ci will not know about the OS distro that is desired to be tested. Before adding a new OS distro, discuss the proposed addition:

  • Send a mail to qemu-devel, copying people listed in the MAINTAINERS file for Build and test automation.

    There are limited CI compute resources available to QEMU, so the cost/benefit tradeoff of adding new OS distros needs to be considered.

  • File an issue at https://gitlab.com/libvirt/libvirt-ci/-/issues pointing to the qemu-devel mail thread in the archives.

    This alerts other people who might be interested in the work to avoid duplication, as well as to get feedback from libvirt-ci maintainers on any tips to ease the addition

Assuming there is agreement to add a new OS distro then

  • Fork the libvirt-ci project on gitlab

  • Add metadata under guests/lcitool/lcitool/ansible/group_vars/ for the new OS distro. There might be code changes required if the OS distro uses a package format not currently known. The libvirt-ci maintainers can advise on this when the issue is file.

  • Edit the mappings.yml change to update all the existing package entries, providing details of the new OS distro

  • Commit the mappings.yml change and submit a merge request to the libvirt-ci project, noting in the description that this is a new build pre-requisite desired for use with QEMU

  • CI pipeline will run to validate that the changes to mappings.yml are correct, by attempting to install the newly listed package on all OS distributions supported by libvirt-ci.

  • Once the merge request is accepted, go back to QEMU and update the libvirt-ci submodule to point to a commit that contains the mappings.yml update.

Tests

Different tests are added to cover various configurations to build and test QEMU. Docker tests are the executables under tests/docker named test-*. They are typically shell scripts and are built on top of a shell library, tests/docker/common.rc, which provides helpers to find the QEMU source and build it.

The full list of tests is printed in the make docker-help help.

Debugging a Docker test failure

When CI tasks, maintainers or yourself report a Docker test failure, follow the below steps to debug it:

  1. Locally reproduce the failure with the reported command line. E.g. run make docker-test-mingw@fedora J=8.

  2. Add “V=1” to the command line, try again, to see the verbose output.

  3. Further add “DEBUG=1” to the command line. This will pause in a shell prompt in the container right before testing starts. You could either manually build QEMU and run tests from there, or press Ctrl-D to let the Docker testing continue.

  4. If you press Ctrl-D, the same building and testing procedure will begin, and will hopefully run into the error again. After that, you will be dropped to the prompt for debug.

Options

Various options can be used to affect how Docker tests are done. The full list is in the make docker help text. The frequently used ones are:

  • V=1: the same as in top level make. It will be propagated to the container and enable verbose output.

  • J=$N: the number of parallel tasks in make commands in the container, similar to the -j $N option in top level make. (The -j option in top level make will not be propagated into the container.)

  • DEBUG=1: enables debug. See the previous “Debugging a Docker test failure” section.

Thread Sanitizer

Thread Sanitizer (TSan) is a tool which can detect data races. QEMU supports building and testing with this tool.

For more information on TSan:

https://github.com/google/sanitizers/wiki/ThreadSanitizerCppManual

Thread Sanitizer in Docker

TSan is currently supported in the ubuntu2004 docker.

The test-tsan test will build using TSan and then run make check.

make docker-test-tsan@ubuntu2004

TSan warnings under docker are placed in files located at build/tsan/.

We recommend using DEBUG=1 to allow launching the test from inside the docker, and to allow review of the warnings generated by TSan.

Building and Testing with TSan

It is possible to build and test with TSan, with a few additional steps. These steps are normally done automatically in the docker.

There is a one time patch needed in clang-9 or clang-10 at this time:

sed -i 's/^const/static const/g' \
    /usr/lib/llvm-10/lib/clang/10.0.0/include/sanitizer/tsan_interface.h

To configure the build for TSan:

../configure --enable-tsan --cc=clang-10 --cxx=clang++-10 \
             --disable-werror --extra-cflags="-O0"

The runtime behavior of TSAN is controlled by the TSAN_OPTIONS environment variable.

More information on the TSAN_OPTIONS can be found here:

https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags

For example:

export TSAN_OPTIONS=suppressions=<path to qemu>/tests/tsan/suppressions.tsan \
                    detect_deadlocks=false history_size=7 exitcode=0 \
                    log_path=<build path>/tsan/tsan_warning

The above exitcode=0 has TSan continue without error if any warnings are found. This allows for running the test and then checking the warnings afterwards. If you want TSan to stop and exit with error on warnings, use exitcode=66.

TSan Suppressions

Keep in mind that for any data race warning, although there might be a data race detected by TSan, there might be no actual bug here. TSan provides several different mechanisms for suppressing warnings. In general it is recommended to fix the code if possible to eliminate the data race rather than suppress the warning.

A few important files for suppressing warnings are:

tests/tsan/suppressions.tsan - Has TSan warnings we wish to suppress at runtime. The comment on each suppression will typically indicate why we are suppressing it. More information on the file format can be found here:

https://github.com/google/sanitizers/wiki/ThreadSanitizerSuppressions

tests/tsan/blacklist.tsan - Has TSan warnings we wish to disable at compile time for test or debug. Add flags to configure to enable:

“–extra-cflags=-fsanitize-blacklist=<src path>/tests/tsan/blacklist.tsan”

More information on the file format can be found here under “Blacklist Format”:

https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags

TSan Annotations

include/qemu/tsan.h defines annotations. See this file for more descriptions of the annotations themselves. Annotations can be used to suppress TSan warnings or give TSan more information so that it can detect proper relationships between accesses of data.

Annotation examples can be found here:

https://github.com/llvm/llvm-project/tree/master/compiler-rt/test/tsan/

Good files to start with are: annotate_happens_before.cpp and ignore_race.cpp

The full set of annotations can be found here:

https://github.com/llvm/llvm-project/blob/master/compiler-rt/lib/tsan/rtl/tsan_interface_ann.cpp

VM testing

This test suite contains scripts that bootstrap various guest images that have necessary packages to build QEMU. The basic usage is documented in Makefile help which is displayed with make vm-help.

Quickstart

Run make vm-help to list available make targets. Invoke a specific make command to run build test in an image. For example, make vm-build-freebsd will build the source tree in the FreeBSD image. The command can be executed from either the source tree or the build dir; if the former, ./configure is not needed. The command will then generate the test image in ./tests/vm/ under the working directory.

Note: images created by the scripts accept a well-known RSA key pair for SSH access, so they SHOULD NOT be exposed to external interfaces if you are concerned about attackers taking control of the guest and potentially exploiting a QEMU security bug to compromise the host.

QEMU binaries

By default, qemu-system-x86_64 is searched in $PATH to run the guest. If there isn’t one, or if it is older than 2.10, the test won’t work. In this case, provide the QEMU binary in env var: QEMU=/path/to/qemu-2.10+.

Likewise the path to qemu-img can be set in QEMU_IMG environment variable.

Make jobs

The -j$X option in the make command line is not propagated into the VM, specify J=$X to control the make jobs in the guest.

Debugging

Add DEBUG=1 and/or V=1 to the make command to allow interactive debugging and verbose output. If this is not enough, see the next section. V=1 will be propagated down into the make jobs in the guest.

Manual invocation

Each guest script is an executable script with the same command line options. For example to work with the netbsd guest, use $QEMU_SRC/tests/vm/netbsd:

$ cd $QEMU_SRC/tests/vm

# To bootstrap the image
$ ./netbsd --build-image --image /var/tmp/netbsd.img
<...>

# To run an arbitrary command in guest (the output will not be echoed unless
# --debug is added)
$ ./netbsd --debug --image /var/tmp/netbsd.img uname -a

# To build QEMU in guest
$ ./netbsd --debug --image /var/tmp/netbsd.img --build-qemu $QEMU_SRC

# To get to an interactive shell
$ ./netbsd --interactive --image /var/tmp/netbsd.img sh

Adding new guests

Please look at existing guest scripts for how to add new guests.

Most importantly, create a subclass of BaseVM and implement build_image() method and define BUILD_SCRIPT, then finally call basevm.main() from the script’s main().

  • Usually in build_image(), a template image is downloaded from a predefined URL. BaseVM._download_with_cache() takes care of the cache and the checksum, so consider using it.

  • Once the image is downloaded, users, SSH server and QEMU build deps should be set up:

    • Root password set to BaseVM.ROOT_PASS

    • User BaseVM.GUEST_USER is created, and password set to BaseVM.GUEST_PASS

    • SSH service is enabled and started on boot, $QEMU_SRC/tests/keys/id_rsa.pub is added to ssh’s authorized_keys file of both root and the normal user

    • DHCP client service is enabled and started on boot, so that it can automatically configure the virtio-net-pci NIC and communicate with QEMU user net (10.0.2.2)

    • Necessary packages are installed to untar the source tarball and build QEMU

  • Write a proper BUILD_SCRIPT template, which should be a shell script that untars a raw virtio-blk block device, which is the tarball data blob of the QEMU source tree, then configure/build it. Running “make check” is also recommended.

Image fuzzer testing

An image fuzzer was added to exercise format drivers. Currently only qcow2 is supported. To start the fuzzer, run

tests/image-fuzzer/runner.py -c '[["qemu-img", "info", "$test_img"]]' /tmp/test qcow2

Alternatively, some command different from qemu-img info can be tested, by changing the -c option.

Integration tests using the Avocado Framework

The tests/avocado directory hosts integration tests. They’re usually higher level tests, and may interact with external resources and with various guest operating systems.

These tests are written using the Avocado Testing Framework (which must be installed separately) in conjunction with a the avocado_qemu.Test class, implemented at tests/avocado/avocado_qemu.

Tests based on avocado_qemu.Test can easily:

  • Customize the command line arguments given to the convenience self.vm attribute (a QEMUMachine instance)

  • Interact with the QEMU monitor, send QMP commands and check their results

  • Interact with the guest OS, using the convenience console device (which may be useful to assert the effectiveness and correctness of command line arguments or QMP commands)

  • Interact with external data files that accompany the test itself (see self.get_data())

  • Download (and cache) remote data files, such as firmware and kernel images

  • Have access to a library of guest OS images (by means of the avocado.utils.vmimage library)

  • Make use of various other test related utilities available at the test class itself and at the utility library:

Running tests

You can run the avocado tests simply by executing:

make check-avocado

This involves the automatic creation of Python virtual environment within the build tree (at tests/venv) which will have all the right dependencies, and will save tests results also within the build tree (at tests/results).

Note: the build environment must be using a Python 3 stack, and have the venv and pip packages installed. If necessary, make sure configure is called with --python= and that those modules are available. On Debian and Ubuntu based systems, depending on the specific version, they may be on packages named python3-venv and python3-pip.

It is also possible to run tests based on tags using the make check-avocado command and the AVOCADO_TAGS environment variable:

make check-avocado AVOCADO_TAGS=quick

Note that tags separated with commas have an AND behavior, while tags separated by spaces have an OR behavior. For more information on Avocado tags, see:

To run a single test file, a couple of them, or a test within a file using the make check-avocado command, set the AVOCADO_TESTS environment variable with the test files or test names. To run all tests from a single file, use:

make check-avocado AVOCADO_TESTS=$FILEPATH

The same is valid to run tests from multiple test files:

make check-avocado AVOCADO_TESTS='$FILEPATH1 $FILEPATH2'

To run a single test within a file, use:

make check-avocado AVOCADO_TESTS=$FILEPATH:$TESTCLASS.$TESTNAME

The same is valid to run single tests from multiple test files:

make check-avocado AVOCADO_TESTS='$FILEPATH1:$TESTCLASS1.$TESTNAME1 $FILEPATH2:$TESTCLASS2.$TESTNAME2'

The scripts installed inside the virtual environment may be used without an “activation”. For instance, the Avocado test runner may be invoked by running:

tests/venv/bin/avocado run $OPTION1 $OPTION2 tests/avocado/

Note that if make check-avocado was not executed before, it is possible to create the Python virtual environment with the dependencies needed running:

make check-venv

It is also possible to run tests from a single file or a single test within a test file. To run tests from a single file within the build tree, use:

tests/venv/bin/avocado run tests/avocado/$TESTFILE

To run a single test within a test file, use:

tests/venv/bin/avocado run tests/avocado/$TESTFILE:$TESTCLASS.$TESTNAME

Valid test names are visible in the output from any previous execution of Avocado or make check-avocado, and can also be queried using:

tests/venv/bin/avocado list tests/avocado

Manual Installation

To manually install Avocado and its dependencies, run:

pip install --user avocado-framework

Alternatively, follow the instructions on this link:

Overview

The tests/avocado/avocado_qemu directory provides the avocado_qemu Python module, containing the avocado_qemu.Test class. Here’s a simple usage example:

from avocado_qemu import QemuSystemTest


class Version(QemuSystemTest):
    """
    :avocado: tags=quick
    """
    def test_qmp_human_info_version(self):
        self.vm.launch()
        res = self.vm.command('human-monitor-command',
                              command_line='info version')
        self.assertRegexpMatches(res, r'^(\d+\.\d+\.\d)')

To execute your test, run:

avocado run version.py

Tests may be classified according to a convention by using docstring directives such as :avocado: tags=TAG1,TAG2. To run all tests in the current directory, tagged as “quick”, run:

avocado run -t quick .

The avocado_qemu.Test base test class

The avocado_qemu.Test class has a number of characteristics that are worth being mentioned right away.

First of all, it attempts to give each test a ready to use QEMUMachine instance, available at self.vm. Because many tests will tweak the QEMU command line, launching the QEMUMachine (by using self.vm.launch()) is left to the test writer.

The base test class has also support for tests with more than one QEMUMachine. The way to get machines is through the self.get_vm() method which will return a QEMUMachine instance. The self.get_vm() method accepts arguments that will be passed to the QEMUMachine creation and also an optional name attribute so you can identify a specific machine and get it more than once through the tests methods. A simple and hypothetical example follows:

from avocado_qemu import QemuSystemTest


class MultipleMachines(QemuSystemTest):
    def test_multiple_machines(self):
        first_machine = self.get_vm()
        second_machine = self.get_vm()
        self.get_vm(name='third_machine').launch()

        first_machine.launch()
        second_machine.launch()

        first_res = first_machine.command(
            'human-monitor-command',
            command_line='info version')

        second_res = second_machine.command(
            'human-monitor-command',
            command_line='info version')

        third_res = self.get_vm(name='third_machine').command(
            'human-monitor-command',
            command_line='info version')

        self.assertEquals(first_res, second_res, third_res)

At test “tear down”, avocado_qemu.Test handles all the QEMUMachines shutdown.

The avocado_qemu.LinuxTest base test class

The avocado_qemu.LinuxTest is further specialization of the avocado_qemu.Test class, so it contains all the characteristics of the later plus some extra features.

First of all, this base class is intended for tests that need to interact with a fully booted and operational Linux guest. At this time, it uses a Fedora 31 guest image. The most basic example looks like this:

from avocado_qemu import LinuxTest


class SomeTest(LinuxTest):

    def test(self):
        self.launch_and_wait()
        self.ssh_command('some_command_to_be_run_in_the_guest')

Please refer to tests that use avocado_qemu.LinuxTest under tests/avocado for more examples.

QEMUMachine

The QEMUMachine API is already widely used in the Python iotests, device-crash-test and other Python scripts. It’s a wrapper around the execution of a QEMU binary, giving its users:

  • the ability to set command line arguments to be given to the QEMU binary

  • a ready to use QMP connection and interface, which can be used to send commands and inspect its results, as well as asynchronous events

  • convenience methods to set commonly used command line arguments in a more succinct and intuitive way

QEMU binary selection

The QEMU binary used for the self.vm QEMUMachine instance will primarily depend on the value of the qemu_bin parameter. If it’s not explicitly set, its default value will be the result of a dynamic probe in the same source tree. A suitable binary will be one that targets the architecture matching host machine.

Based on this description, test writers will usually rely on one of the following approaches:

  1. Set qemu_bin, and use the given binary

  2. Do not set qemu_bin, and use a QEMU binary named like “qemu-system-${arch}”, either in the current working directory, or in the current source tree.

The resulting qemu_bin value will be preserved in the avocado_qemu.Test as an attribute with the same name.

Attribute reference

Test

Besides the attributes and methods that are part of the base avocado.Test class, the following attributes are available on any avocado_qemu.Test instance.

vm

A QEMUMachine instance, initially configured according to the given qemu_bin parameter.

arch

The architecture can be used on different levels of the stack, e.g. by the framework or by the test itself. At the framework level, it will currently influence the selection of a QEMU binary (when one is not explicitly given).

Tests are also free to use this attribute value, for their own needs. A test may, for instance, use the same value when selecting the architecture of a kernel or disk image to boot a VM with.

The arch attribute will be set to the test parameter of the same name. If one is not given explicitly, it will either be set to None, or, if the test is tagged with one (and only one) :avocado: tags=arch:VALUE tag, it will be set to VALUE.

cpu

The cpu model that will be set to all QEMUMachine instances created by the test.

The cpu attribute will be set to the test parameter of the same name. If one is not given explicitly, it will either be set to None ``, or, if the test is tagged with one (and only one) ``:avocado: tags=cpu:VALUE tag, it will be set to VALUE.

machine

The machine type that will be set to all QEMUMachine instances created by the test.

The machine attribute will be set to the test parameter of the same name. If one is not given explicitly, it will either be set to None, or, if the test is tagged with one (and only one) :avocado: tags=machine:VALUE tag, it will be set to VALUE.

qemu_bin

The preserved value of the qemu_bin parameter or the result of the dynamic probe for a QEMU binary in the current working directory or source tree.

LinuxTest

Besides the attributes present on the avocado_qemu.Test base class, the avocado_qemu.LinuxTest adds the following attributes:

distro

The name of the Linux distribution used as the guest image for the test. The name should match the Provider column on the list of images supported by the avocado.utils.vmimage library:

https://avocado-framework.readthedocs.io/en/latest/guides/writer/libs/vmimage.html#supported-images

distro_version

The version of the Linux distribution as the guest image for the test. The name should match the Version column on the list of images supported by the avocado.utils.vmimage library:

https://avocado-framework.readthedocs.io/en/latest/guides/writer/libs/vmimage.html#supported-images

distro_checksum

The sha256 hash of the guest image file used for the test.

If this value is not set in the code or by a test parameter (with the same name), no validation on the integrity of the image will be performed.

Parameter reference

To understand how Avocado parameters are accessed by tests, and how they can be passed to tests, please refer to:

https://avocado-framework.readthedocs.io/en/latest/guides/writer/chapters/writing.html#accessing-test-parameters

Parameter values can be easily seen in the log files, and will look like the following:

PARAMS (key=qemu_bin, path=*, default=./qemu-system-x86_64) => './qemu-system-x86_64

Test

arch

The architecture that will influence the selection of a QEMU binary (when one is not explicitly given).

Tests are also free to use this parameter value, for their own needs. A test may, for instance, use the same value when selecting the architecture of a kernel or disk image to boot a VM with.

This parameter has a direct relation with the arch attribute. If not given, it will default to None.

cpu

The cpu model that will be set to all QEMUMachine instances created by the test.

machine

The machine type that will be set to all QEMUMachine instances created by the test.

qemu_bin

The exact QEMU binary to be used on QEMUMachine.

LinuxTest

Besides the parameters present on the avocado_qemu.Test base class, the avocado_qemu.LinuxTest adds the following parameters:

distro

The name of the Linux distribution used as the guest image for the test. The name should match the Provider column on the list of images supported by the avocado.utils.vmimage library:

https://avocado-framework.readthedocs.io/en/latest/guides/writer/libs/vmimage.html#supported-images

distro_version

The version of the Linux distribution as the guest image for the test. The name should match the Version column on the list of images supported by the avocado.utils.vmimage library:

https://avocado-framework.readthedocs.io/en/latest/guides/writer/libs/vmimage.html#supported-images

distro_checksum

The sha256 hash of the guest image file used for the test.

If this value is not set in the code or by this parameter no validation on the integrity of the image will be performed.

Skipping tests

The Avocado framework provides Python decorators which allow for easily skip tests running under certain conditions. For example, on the lack of a binary on the test system or when the running environment is a CI system. For further information about those decorators, please refer to:

https://avocado-framework.readthedocs.io/en/latest/guides/writer/chapters/writing.html#skipping-tests

While the conditions for skipping tests are often specifics of each one, there are recurring scenarios identified by the QEMU developers and the use of environment variables became a kind of standard way to enable/disable tests.

Here is a list of the most used variables:

AVOCADO_ALLOW_LARGE_STORAGE

Tests which are going to fetch or produce assets considered large are not going to run unless that AVOCADO_ALLOW_LARGE_STORAGE=1 is exported on the environment.

The definition of large is a bit arbitrary here, but it usually means an asset which occupies at least 1GB of size on disk when uncompressed.

AVOCADO_ALLOW_UNTRUSTED_CODE

There are tests which will boot a kernel image or firmware that can be considered not safe to run on the developer’s workstation, thus they are skipped by default. The definition of not safe is also arbitrary but usually it means a blob which either its source or build process aren’t public available.

You should export AVOCADO_ALLOW_UNTRUSTED_CODE=1 on the environment in order to allow tests which make use of those kind of assets.

AVOCADO_TIMEOUT_EXPECTED

The Avocado framework has a timeout mechanism which interrupts tests to avoid the test suite of getting stuck. The timeout value can be set via test parameter or property defined in the test class, for further details:

https://avocado-framework.readthedocs.io/en/latest/guides/writer/chapters/writing.html#setting-a-test-timeout

Even though the timeout can be set by the test developer, there are some tests that may not have a well-defined limit of time to finish under certain conditions. For example, tests that take longer to execute when QEMU is compiled with debug flags. Therefore, the AVOCADO_TIMEOUT_EXPECTED variable has been used to determine whether those tests should run or not.

GITLAB_CI

A number of tests are flagged to not run on the GitLab CI. Usually because they proved to the flaky or there are constraints on the CI environment which would make them fail. If you encounter a similar situation then use that variable as shown on the code snippet below to skip the test:

@skipIf(os.getenv('GITLAB_CI'), 'Running on GitLab')
def test(self):
    do_something()

Uninstalling Avocado

If you’ve followed the manual installation instructions above, you can easily uninstall Avocado. Start by listing the packages you have installed:

pip list --user

And remove any package you want with:

pip uninstall <package_name>

If you’ve used make check-avocado, the Python virtual environment where Avocado is installed will be cleaned up as part of make check-clean.

Testing with “make check-tcg”

The check-tcg tests are intended for simple smoke tests of both linux-user and softmmu TCG functionality. However to build test programs for guest targets you need to have cross compilers available. If your distribution supports cross compilers you can do something as simple as:

apt install gcc-aarch64-linux-gnu

The configure script will automatically pick up their presence. Sometimes compilers have slightly odd names so the availability of them can be prompted by passing in the appropriate configure option for the architecture in question, for example:

$(configure) --cross-cc-aarch64=aarch64-cc

There is also a --cross-cc-cflags-ARCH flag in case additional compiler flags are needed to build for a given target.

If you have the ability to run containers as the user the build system will automatically use them where no system compiler is available. For architectures where we also support building QEMU we will generally use the same container to build tests. However there are a number of additional containers defined that have a minimal cross-build environment that is only suitable for building test cases. Sometimes we may use a bleeding edge distribution for compiler features needed for test cases that aren’t yet in the LTS distros we support for QEMU itself.

See Container based tests for more details.

Running subset of tests

You can build the tests for one architecture:

make build-tcg-tests-$TARGET

And run with:

make run-tcg-tests-$TARGET

Adding V=1 to the invocation will show the details of how to invoke QEMU for the test which is useful for debugging tests.

TCG test dependencies

The TCG tests are deliberately very light on dependencies and are either totally bare with minimal gcc lib support (for softmmu tests) or just glibc (for linux-user tests). This is because getting a cross compiler to work with additional libraries can be challenging.

Other TCG Tests

There are a number of out-of-tree test suites that are used for more extensive testing of processor features.

KVM Unit Tests

The KVM unit tests are designed to run as a Guest OS under KVM but there is no reason why they can’t exercise the TCG as well. It provides a minimal OS kernel with hooks for enabling the MMU as well as reporting test results via a special device:

https://git.kernel.org/pub/scm/virt/kvm/kvm-unit-tests.git

Linux Test Project

The LTP is focused on exercising the syscall interface of a Linux kernel. It checks that syscalls behave as documented and strives to exercise as many corner cases as possible. It is a useful test suite to run to exercise QEMU’s linux-user code:

https://linux-test-project.github.io/

GCC gcov support

gcov is a GCC tool to analyze the testing coverage by instrumenting the tested code. To use it, configure QEMU with --enable-gcov option and build. Then run the tests as usual.

If you want to gather coverage information on a single test the make clean-gcda target can be used to delete any existing coverage information before running a single test.

You can generate a HTML coverage report by executing make coverage-html which will create meson-logs/coveragereport/index.html.

Further analysis can be conducted by running the gcov command directly on the various .gcda output files. Please read the gcov documentation for more information.