Message-ID: <97fb956ee0d303c8e41f4266f25ebadc9ce295d7.1765374789.git.gtucker@gtucker.io>
Date: Wed, 10 Dec 2025 14:58:29 +0100
From: Guillaume Tucker <gtucker@...cker.io>
To: Nathan Chancellor <nathan@...nel.org>,
	Miguel Ojeda <ojeda@...nel.org>
Cc: linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org,
	linux-kbuild@...r.kernel.org,
	automated-testing@...ts.yoctoproject.org,
	workflows@...r.kernel.org,
	llvm@...ts.linux.dev,
	Arnd Bergmann <arnd@...db.de>,
	Guillaume Tucker <gtucker@...cker.io>
Subject: [PATCH v1 2/2] Documentation: dev-tools: add container.rst page

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 <nathan@...nel.org>
Cc: Miguel Ojeda <ojeda@...nel.org>
Signed-off-by: Guillaume Tucker <gtucker@...cker.io>
---
 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

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