Add a dev-tools/container.rst documentation page for the scripts/container tool. This covers the basic usage with additional information about environment variables and user IDs. It also includes a number of practical examples with a reference to the experimental kernel.org toolchain images.
Cc: Nathan Chancellor <[email protected]> Cc: Miguel Ojeda <[email protected]> Signed-off-by: Guillaume Tucker <[email protected]> --- Documentation/dev-tools/container.rst | 175 ++++++++++++++++++++++++++ Documentation/dev-tools/index.rst | 1 + 2 files changed, 176 insertions(+) create mode 100644 Documentation/dev-tools/container.rst diff --git a/Documentation/dev-tools/container.rst b/Documentation/dev-tools/container.rst new file mode 100644 index 000000000000..2a56f256f648 --- /dev/null +++ b/Documentation/dev-tools/container.rst @@ -0,0 +1,175 @@ +.. SPDX-License-Identifier: GPL-2.0-only +.. Copyright (C) 2025 Guillaume Tucker + +==================== +Containerized Builds +==================== + +The ``container`` tool can be used to run any command in the kernel source tree +from within a container. Doing so facilitates reproducing builds across +various platforms, for example when a test bot has reported an issue which +requires a specific version of a compiler or an external test suite. While +this can already be done by users who are familiar with containers, having a +dedicated tool in the kernel tree lowers the barrier to entry by solving common +problems once and for all (e.g. user id management). It also makes it easier +to share an exact command line leading to a particular result. The main use +case is likely to be kernel builds but virtually anything can be run: KUnit, +checkpatch etc. provided a suitable image is available. + + +Options +======= + +Command line syntax:: + + scripts/container [OPTION]... CMD... + +Available options: + +``-e, --env-file ENV_FILE`` + + Path to an environment file to load in the container. + +``-g, --gid GID`` + + Group id to use inside the container. + +``-i, --image IMAGE`` + + Container image, default is ``gcc``. + +``-r, --runtime RUNTIME`` + + Container runtime, default is ``docker``. Supported runtimes: ``docker``, + ``podman``. + +``-u, --uid UID`` + + User id to use inside the container. If the ``-g`` option is not + specified, the user id will also be used for the group id. + +``-v, --verbose`` + + Enable verbose output. + +``-h, --help`` + + Show the help message and exit. + + +Usage +===== + +It's entirely up to the user to choose which image to use and the ``CMD`` +arguments are passed directly as an arbitrary command line to run in the +container. The tool will take care of mounting the source tree as the current +working directory and adjust the user and group id as needed. + +The container images are provided by the user and selected via the ``-i`` +option. They will typically include a compiler toolchain to build the kernel +and as such, the default image tag is set to ``gcc`` to give a convenient way +of running builds. Any local image with a GCC compiler toolchain could be +tagged as ``gcc`` to make it point to it. For example:: + + docker tag my-user/gcc:15 gcc + +The container runtime can be selected with the ``-r`` option, which can be +either Docker or Podman. Support for other runtimes may be added later +depending on their popularity among users. + + +Environment Variables +===================== + +Environment variables are not propagated to the container so they have to be +either defined in the image itself or via the ``-e`` option using an +environment file. In some cases it makes more sense to have them defined in +the Containerfile used to create the image. For example, a Clang-only compiler +toolchain image would most likely have ``LLVM=1`` defined. The local +environment file is more useful for user-specific variables during development. + +Please note that ``make`` options can still be passed on the command line, so +while this can't be done as the first argument needs to be the executable:: + + scripts/container INSTALL_MOD_STRIP=1 make modules_install + +this will work:: + + scripts/container make modules_install INSTALL_MOD_STRIP=1 + + +User IDs +======== + +This is an area where the behaviour will vary slightly depending on the +container runtime. The goal is to run commands as the user invoking the tool. +With Podman, a namespace is created to map the current user id to a different +one in the container (1000 by default). With Docker, while this is also +possible with recent versions it requires a special feature to be enabled in +the daemon so it's not used here for simplicity. Instead, the container is run +with the current user id directly. In both cases, this will provide the same +file permissions for the kernel source tree mounted as a volume. The only +difference is that when using Docker without a namespace, the user id may not +be the same as the default one set in the image. + +Say, we're using an image which sets up a default user with id 1000 and the +current user calling the ``container`` tool has id 1234. The kernel source +tree was checked out by this same user so the files belong to user 1234. With +Podman, the container will be running as user id 1000 with a mapping to id 1234 +so that the files from the mounted volume appear to belong to id 1000 inside +the container. With Docker and no namespace, the container will be running +with user id 1234 which can access the files in the volume but not in the user +1000 home directory. This shouldn't be an issue when running commands only in +the kernel tree but it is worth highlighting here as it might matter for +special corner cases. + + +Examples +======== + +The shortest example is to run a basic kernel build using Docker and the +default ``gcc`` image:: + + scripts/container -- make defconfig + scripts/container -- make -j$(nproc) + +.. note:: + + When running a command with options within the container, it should be + separated with a double dash ``--`` to not confuse them with the + ``container`` tool options. Simple make targets with no options don't + strictly require the double dashes e.g.:: + + scripts/container make mrproper + +To run ``checkpatch.pl`` in a ``patches`` directory with a generic image:: + + scripts/container -i perl:slim-trixie scripts/checkpatch.pl patches/* + +To build using the TuxMake Clang image:: + + scripts/container -i tuxmake/x86_64_korg-clang -- make LLVM=1 -j$(nproc) + +The examples below refer to ``kernel.org`` images which are based on the +`kernel.org compiler toolchains +<https://mirrors.edge.kernel.org/pub/tools/>`__. These aren't (yet) available +in any public registry but users can build their own locally instead using this +`experimental repository <https://gitlab.com/gtucker/korg-containers>`__ by +running ``make PREFIX=kernel.org/``. + +To build just ``bzImage`` using Clang:: + + scripts/container -i kernel.org/clang -- make bzImage -j$(nproc) + +To run KUnit:: + + scripts/container -i kernel.org/gcc:kunit -- \ + tools/testing/kunit/kunit.py \ + run \ + --arch=x86_64 \ + --cross_compile=x86_64-linux- + +To build the HTML documentation, which requires the ``kdocs`` image built with +``make PREFIX=kernel.org/ extra`` as it's not a compiler toolchain:: + + scripts/container -i kernel.org/kdocs make htmldocs diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst index 4b8425e348ab..527a0e4cf2ed 100644 --- a/Documentation/dev-tools/index.rst +++ b/Documentation/dev-tools/index.rst @@ -38,6 +38,7 @@ Documentation/process/debugging/index.rst gpio-sloppy-logic-analyzer autofdo propeller + container .. only:: subproject and html -- 2.47.3
