CI

Most of QEMU’s CI is run on GitLab’s infrastructure although a number of other CI services are used for specialised purposes. The most up to date information about them and their status can be found on the project wiki testing page.

Definition of terms

This section defines the terms used in this document and correlates them with what is currently used on QEMU.

Automated tests

An automated test is written on a test framework using its generic test functions/classes. The test framework can run the tests and report their success or failure [1].

An automated test has essentially three parts:

1. The test initialization of the parameters, where the expected parameters, like inputs and expected results, are set up;

2. The call to the code that should be tested;

3. An assertion, comparing the result from the previous call with the expected result set during the initialization of the parameters. If the result matches the expected result, the test has been successful; otherwise, it has failed.

Unit testing

A unit test is responsible for exercising individual software components as a unit, like interfaces, data structures, and functionality, uncovering errors within the boundaries of a component. The verification effort is in the smallest software unit and focuses on the internal processing logic and data structures. A test case of unit tests should be designed to uncover errors due to erroneous computations, incorrect comparisons, or improper control flow [2].

On QEMU, unit testing is represented by the ‘check-unit’ target from ‘make’.

Functional testing

A functional test focuses on the functional requirement of the software. Deriving sets of input conditions, the functional tests should fully exercise all the functional requirements for a program. Functional testing is complementary to other testing techniques, attempting to find errors like incorrect or missing functions, interface errors, behavior errors, and initialization and termination errors [3].

On QEMU, functional testing is represented by the ‘check-qtest’ target from ‘make’.

System testing

System tests ensure all application elements mesh properly while the overall functionality and performance are achieved [4]. Some or all system components are integrated to create a complete system to be tested as a whole. System testing ensures that components are compatible, interact correctly, and transfer the right data at the right time across their interfaces. As system testing focuses on interactions, use case-based testing is a practical approach to system testing [5]. Note that, in some cases, system testing may require interaction with third-party software, like operating system images, databases, networks, and so on.

On QEMU, system testing is represented by the ‘check-avocado’ target from ‘make’.

Flaky tests

A flaky test is defined as a test that exhibits both a passing and a failing result with the same code on different runs. Some usual reasons for an intermittent/flaky test are async wait, concurrency, and test order dependency [6].

Gating

A gate restricts the move of code from one stage to another on a test/deployment pipeline. The step move is granted with approval. The approval can be a manual intervention or a set of tests succeeding [7].

On QEMU, the gating process happens during the pull request. The approval is done by the project leader running its own set of tests. The pull request gets merged when the tests succeed.

Continuous Integration (CI)

Continuous integration (CI) requires the builds of the entire application and the execution of a comprehensive set of automated tests every time there is a need to commit any set of changes [8]. The automated tests can be composed of the unit, functional, system, and other tests.

Keynotes about continuous integration (CI) [9]:

1. System tests may depend on external software (operating system images, firmware, database, network).

2. It may take a long time to build and test. It may be impractical to build the system being developed several times per day.

3. If the development platform is different from the target platform, it may not be possible to run system tests in the developer’s private workspace. There may be differences in hardware, operating system, or installed software. Therefore, more time is required for testing the system.

References

[1]

Sommerville, Ian (2016). Software Engineering. p. 233.

[2]

Pressman, Roger S. & Maxim, Bruce R. (2020). Software Engineering, A Practitioner’s Approach. p. 48, 376, 378, 381.

[3]

Pressman, Roger S. & Maxim, Bruce R. (2020). Software Engineering, A Practitioner’s Approach. p. 388.

[4]

Pressman, Roger S. & Maxim, Bruce R. (2020). Software Engineering, A Practitioner’s Approach. Software Engineering, p. 377.

[5]

Sommerville, Ian (2016). Software Engineering. p. 59, 232, 240.

[6]

Luo, Qingzhou, et al. An empirical analysis of flaky tests. Proceedings of the 22nd ACM SIGSOFT International Symposium on Foundations of Software Engineering. 2014.

[7]

Humble, Jez & Farley, David (2010). Continuous Delivery: Reliable Software Releases Through Build, Test, and Deployment, p. 122.

[8]

Humble, Jez & Farley, David (2010). Continuous Delivery: Reliable Software Releases Through Build, Test, and Deployment, p. 55.

[9]

Sommerville, Ian (2016). Software Engineering. p. 743.

Custom CI/CD variables

QEMU CI pipelines can be tuned by setting some CI environment variables.

Set variable globally in the user’s CI namespace

Variables can be set globally in the user’s CI namespace setting.

For further information about how to set these variables, please refer to:

https://docs.gitlab.com/ee/ci/variables/#add-a-cicd-variable-to-a-project

Set variable manually when pushing a branch or tag to the user’s repository

Variables can be set manually when pushing a branch or tag, using git-push command line arguments.

Example setting the QEMU_CI_EXAMPLE_VAR variable:

git push -o ci.variable="QEMU_CI_EXAMPLE_VAR=value" myrepo mybranch

For further information about how to set these variables, please refer to:

https://docs.gitlab.com/ee/user/project/push_options.html#push-options-for-gitlab-cicd

Setting aliases in your git config

You can use aliases to make it easier to push branches with different CI configurations. For example define an alias for triggering CI:

git config --local alias.push-ci "push -o ci.variable=QEMU_CI=1"
git config --local alias.push-ci-now "push -o ci.variable=QEMU_CI=2"

Which lets you run:

git push-ci

to create the pipeline, or:

git push-ci-now

to create and run the pipeline

Variable naming and grouping

The variables used by QEMU’s CI configuration are grouped together in a handful of namespaces

• QEMU_JOB_nnnn - variables to be defined in individual jobs or templates, to influence the shared rules defined in the .base_job_template.

• QEMU_CI_nnn - variables to be set by contributors in their repository CI settings, or as git push variables, to influence which jobs get run in a pipeline

• QEMU_CI_CONTAINER_TAG - the tag used to publish containers in stage 1, for use by build jobs in stage 2. Defaults to ‘latest’, but if running pipelines for different branches concurrently, it should be overridden per pipeline.

• QEMU_CI_UPSTREAM - gitlab namespace that is considered to be the ‘upstream’. This defaults to ‘qemu-project’. Contributors may choose to override this if they are modifying rules in base.yml and need to validate how they will operate when in an upstream context, as opposed to their fork context.

• nnn - other misc variables not falling into the above categories, or using different names for historical reasons and not yet converted.

Maintainer controlled job variables

The following variables may be set when defining a job in the CI configuration file.

QEMU_JOB_CIRRUS

The job makes use of Cirrus CI infrastructure, requiring the configuration setup for cirrus-run to be present in the repository

QEMU_JOB_OPTIONAL

The job is expected to be successful in general, but is not run by default due to need to conserve limited CI resources. It is available to be started manually by the contributor in the CI pipelines UI.

QEMU_JOB_ONLY_FORKS

The job results are only of interest to contributors prior to submitting code. They are not required as part of the gating CI pipeline.

QEMU_JOB_SKIPPED

The job is not reliably successsful in general, so is not currently suitable to be run by default. Ideally this should be a temporary marker until the problems can be addressed, or the job permanently removed.

QEMU_JOB_PUBLISH

The job is for publishing content after a branch has been merged into the upstream default branch.

QEMU_JOB_AVOCADO

The job runs the Avocado integration test suite

Contributor controlled runtime variables

The following variables may be set by contributors to control job execution

QEMU_CI

By default, no pipelines will be created on contributor forks in order to preserve CI credits

Set this variable to 1 to create the pipelines, but leave all the jobs to be manually started from the UI

Set this variable to 2 to create the pipelines and run all the jobs immediately, as was historicaly behaviour

QEMU_CI_AVOCADO_TESTING

By default, tests using the Avocado framework are not run automatically in the pipelines (because multiple artifacts have to be downloaded, and if these artifacts are not already cached, downloading them make the jobs reach the timeout limit). Set this variable to have the tests using the Avocado framework run automatically.

Other misc variables

These variables are primarily to control execution of jobs on private runners

AARCH64_RUNNER_AVAILABLE

If you’ve got access to an aarch64 host that can be used as a gitlab-CI runner, you can set this variable to enable the tests that require this kind of host. The runner should be tagged with “aarch64”.

AARCH32_RUNNER_AVAILABLE

If you’ve got access to an armhf host or an arch64 host that can run aarch32 EL0 code to be used as a gitlab-CI runner, you can set this variable to enable the tests that require this kind of host. The runner should be tagged with “aarch32”.

S390X_RUNNER_AVAILABLE

If you’ve got access to an IBM Z host that can be used as a gitlab-CI runner, you can set this variable to enable the tests that require this kind of host. The runner should be tagged with “s390x”.

CENTOS_STREAM_8_x86_64_RUNNER_AVAILABLE

If you’ve got access to a CentOS Stream 8 x86_64 host that can be used as a gitlab-CI runner, you can set this variable to enable the tests that require this kind of host. The runner should be tagged with both “centos_stream_8” and “x86_64”.

CCACHE_DISABLE

The jobs are configured to use “ccache” by default since this typically reduces compilation time, at the cost of increased storage. If the use of “ccache” is suspected to be hurting the overall job execution time, setting the “CCACHE_DISABLE=1” env variable to disable it.

Jobs on Custom Runners

Besides the jobs run under the various CI systems listed before, there are a number additional jobs that will run before an actual merge. These use the same GitLab CI’s service/framework already used for all other GitLab based CI jobs, but rely on additional systems, not the ones provided by GitLab as “shared runners”.

The architecture of GitLab’s CI service allows different machines to be set up with GitLab’s “agent”, called gitlab-runner, which will take care of running jobs created by events such as a push to a branch. Here, the combination of a machine, properly configured with GitLab’s gitlab-runner, is called a “custom runner”.

The GitLab CI jobs definition for the custom runners are located under:

.gitlab-ci.d/custom-runners.yml

Custom runners entail custom machines. To see a list of the machines currently deployed in the QEMU GitLab CI and their maintainers, please refer to the QEMU wiki.

Machine Setup Howto

For all Linux based systems, the setup can be mostly automated by the execution of two Ansible playbooks. Create an inventory file under scripts/ci/setup, such as this:

fully.qualified.domain
other.machine.hostname

You may need to set some variables in the inventory file itself. One very common need is to tell Ansible to use a Python 3 interpreter on those hosts. This would look like:

fully.qualified.domain ansible_python_interpreter=/usr/bin/python3
other.machine.hostname ansible_python_interpreter=/usr/bin/python3

Build environment

The scripts/ci/setup/build-environment.yml Ansible playbook will set up machines with the environment needed to perform builds and run QEMU tests. This playbook consists on the installation of various required packages (and a general package update while at it). It currently covers a number of different Linux distributions, but it can be expanded to cover other systems.

The minimum required version of Ansible successfully tested in this playbook is 2.8.0 (a version check is embedded within the playbook itself). To run the playbook, execute:

cd scripts/ci/setup
ansible-playbook -i inventory build-environment.yml

Please note that most of the tasks in the playbook require superuser privileges, such as those from the root account or those obtained by sudo. If necessary, please refer to ansible-playbook options such as --become, --become-method, --become-user and --ask-become-pass.

gitlab-runner setup and registration

The gitlab-runner agent needs to be installed on each machine that will run jobs. The association between a machine and a GitLab project happens with a registration token. To find the registration token for your repository/project, navigate on GitLab’s web UI to:

• Settings (the gears-like icon at the bottom of the left hand side vertical toolbar), then

• CI/CD, then

• Runners, and click on the “Expand” button, then

• Under “Set up a specific Runner manually”, look for the value under “And this registration token:”

Copy the scripts/ci/setup/vars.yml.template file to scripts/ci/setup/vars.yml. Then, set the gitlab_runner_registration_token variable to the value obtained earlier.

To run the playbook, execute:

cd scripts/ci/setup
ansible-playbook -i inventory gitlab-runner.yml

Following the registration, it’s necessary to configure the runner tags, and optionally other configurations on the GitLab UI. Navigate to:

• Settings (the gears like icon), then

• CI/CD, then

• Runners, and click on the “Expand” button, then

• “Runners activated for this project”, then

• Click on the “Edit” icon (next to the “Lock” Icon)

Tags are very important as they are used to route specific jobs to specific types of runners, so it’s a good idea to double check that the automatically created tags are consistent with the OS and architecture. For instance, an Ubuntu 20.04 aarch64 system should have tags set as:

ubuntu_20.04,aarch64

Because the job definition at .gitlab-ci.d/custom-runners.yml would contain:

ubuntu-20.04-aarch64-all:
 tags:
 - ubuntu_20.04
 - aarch64

It’s also recommended to:

• increase the “Maximum job timeout” to something like 2h

• give it a better Description