linux/debian

Checklist for uploaders
=======================

There is a checklist in the kernel-team.git repository; see
<https://salsa.debian.org/kernel-team/kernel-team/-/blob/master/docs/kernel-upload-checklist.md>.

Updating the upstream source
============================

In addition to the build-dependencies, you will need the rsync package
installed.

1) Run: uscan --download-current-version --vcs-export-uncompressed

   This will produce ../linux-<version>.tar (e.g. linux-6.11.tar) and
   ../linux_<version>.orig.tar.xz (e.g. linux_6.11.orig.tar.xz).  You
   can delete the first of these.

   It involves deleting files for DFSG compliance, as listed in the
   Files-Excluded field in debian/copyright.

2) Run: make -f debian/rules orig

   This will apply the main quilt series to the upstream source, which
   will usually fail due to conflicts with upstream changes.  You need
   to resolve those by dropping or refreshing patches.

Recording updates in the changelog
----------------------------------

Upstream commits that we already cherry-picked and included in a
previous package upload should not be mentioned, since they don't make
any difference to the package.  Any other commits that fix a Debian
bug report and/or a security issue with a CVE ID should always be
listed, along with the (Closes: #nnnnnn) and/or (CVE-yyyy-nnnn)
reference.

Aside from those general rules:

* For an upstream release candidate, don't attempt to list the changes

* For a stable release by Linus, refer to the summary at
  kernelnewbies.org, e.g. https://kernelnewbies.org/Linux_4.5

* For a stable update, refer to the changelog on kernel.org, e.g.
  https://www.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.5.1, and
  list all changes that are relevant to our package and that fix bugs
  that we would consider 'important' or higher severity

  - The script debian/bin/stable-update updates the changelog
    version and inserts the list of changes.  It doesn't attempt to
    filter out irrelevant or unimportant changes.

  - If you have time, please delete irrelevant changes such as:
    + Fixes for architectures not supported by the package
    + Fixes for drivers that aren't enabled in any of our configurations
    + Build fixes for configurations that we don't use
    + Fixes for lockdep false positives

If you have time, please add bracketted prefixes to the upstream
change list as described below under "Changelog conventions".

Applying patches to the Debian kernel tree
==========================================

The Debian kernel packaging uses the quilt patch system, but with
multiple series to allow for featuresets.

Patches are stored below debian/patches, loosely sorted in bugfix/,
features/ and debian/. Patches are in the standard kernel patch
format (unified diff to be applied with patch -p1) and generally have
DEP-3 headers.

For each optional featureset there is an additional patch directory
debian/patches-<featureset>.

If you want to generate a source tree with all patches applied, run
make -f debian/rules source

The resulting source can be found below debian/build.

Changelog conventions
=====================

If a change only affects some architectures, flavours or featuresets,
this should be noted with a bracketted prefix on the changelog line:

* [<fset>] Change to featureset <fset>
* [<arch>] Change that affects Debian architecture <arch>
* [<arch1>,<arch2>...] Change that affects Debian architectures
  <arch1>, <arch2>, ...
* [<arch>/<flavour>] Change that affects kernel flavour <flavour>
  on Debian architecture <arch>
* [<arch>/{<flavour1>,<flavour2>...}] Change that affects kernel
  flavours <flavour1>, <flavour2>, ... on Debian architecture <arch>

You can use wildcards to cover multiple values, e.g. 'arm*' for armel,
armhf and arm64 architectures.  Also 'x86' is used to cover the Debian
architectures amd64, i386 and x32.

Kernel config files
===================

Each kernel configuration file is constructed dynamically from a
number of files under debian/config and (if it exists)
debian/config.local.  They are read in the following order, such that
files later on the list can override settings from earlier files.
Files in debian/config.local can also override settings from the
corresponding file in debian/config.

1. Common:
   - Default filename: config
   - Filename list: [build.config]
2. Per kernel architecture:
   - Default filename: kernelarch-<karch>/config
   - Filename list: [kernelarch.build.config]
3. Per Debian architecture:
   - Default filename: <arch>/config
   - Filename list: [kernelarch.debianarch.build.config]
4. Per Debian architecture and flavour:
   - Default filename: <arch>/config.<flavour>
   - Filename list: [kernelarch.debianarch.flavour.build.config]
5. Per featureset:
   - Default filename: featureset-<fset>/config
   - Filename list: [featureset.build.config]
6. Per Debian architecture and featureset:
   - Default filename: <arch>/<fset>/config
   - Filename list: [kernelarch.debianarch.featureset.build.config]
7. Per Debian architecture, featureset, and flavour:
   - Default filename: <arch>/<fset>/config.<flavour>
   - Filename list:
     [kernelarch.debianarch.featureset.flavour.build.config]

You can check the final list of configuration files by reading
debian/rules.gen.  Each binary-arch_<arch>_<fset>_<flavour>_image
rule passes the list to debian/rules.real as the KCONFIG variable.

These files should be kept in order using the kconfigeditor2
utility from <https://salsa.debian.org/kernel-team/kernel-team>.
With this source package as your working directory, run:

    debian/rules source
    .../kernel-team/utils/kconfigeditor2/process.py .

This will also warn about any symbols that no longer exist, or
cannot be explicitly configured.

Control file
============
The master control file debian/control must be generated before the package is
uploaded. debian/rules contains various targets to facilitate this task:

debian/control  Generates the control file by invoking the
                debian/bin/gencontrol.py script, which combines the templates
                from the templates directory and architecture-specific
                defines.toml file to produce the debian/control file. Note that
                this target is intentionally made to fail with a non-zero exit
                code to make sure that it is never run during an automatic
                build.

orig            Populate the current directory with all files from the unpacked
                upstream tarball in ../orig/linux_${ver} and apply the Debian
                quilt patch stack.

clean-generated Clean up all auto-generated files inside the ./debian directory

maintainerclean What clean-generated does and additionally also cleans up all
                files other than the ./debian and ./.git directories.

The following variables are substituted into the templates:

@version@      Upstream kernel version, for example 2.6.11.
@arch@         The Debian arch name, such as powerpc or amd64.
@flavour@      The build flavour, such as cloud-amd64.
@class@        The CPU/architecture class; displayed in synopsis.  It should
               be fairly short, as the synopsis is supposed to be <80 chars.
               It should be in the form "foo class", and will show up in the
	       description as "foo class machines".
@longclass@    The CPU/architecture class; displayed in the extended
               description.  The same rules apply as in @class@.  If
	       this is unset, it will default to @class@.
@desc@         (Potentially) multi-line verbiage that's appended to
               -image descriptions.

Normally, the arch-specific contents should be controlled by
adjusting the corresponding defines.toml file.

Build-dependencies that relate to specific binary packages can be
specified in a Build-Depends field in the template for that binary
package.  gencontrol.py will append the value to the source package's
Build-Depends-Arch or Build-Depends-Indep field, as appropriate.  It
will also use the binary package's Architecture and Build-Profile as
the architecture-qualification and/or restriction for each build-
dependency that doesn't already have them.

TODO:
- Patches applied to the upstream source
- How to define a flavour
- More detail on generation of debian/control and configs

Running tests
=============

linux supports autopkgtest and should be able to run most of the
kernel's self-tests on any architecture where kexec is supported,
but it has higher resource requirements than most packages:

- A VM with plenty of disk space (10GB is enough), RAM (1GB is
  probably enough) and at least 2 CPUs
- The temporary directory for adt-virt-qemu (-o option) will need
  several GB of space, so a tmpfs may not be suitable

Note that if you tell adt-run to use an 'unbuilt tree' (i.e. an
unpacked source package) it does not exclude VCS directories such as
.git.  Either use a packed source package or copy the working tree
elsewhere excluding .git.

Example invocation:

    adt-run -B ../linux-image-4.2.0-rc6-amd64_4.2~rc6-1~exp2_amd64.deb \
        ../linux_4.2~rc6-1~exp2.dsc \
	--timeout-test=1200 \
        --- adt-virt-qemu /var/cache/autopkgtest/adt-sid.img -o /var/tmp -c 2

Build profiles
==============

Several build profiles are understood and supported:

- nodoc: Exclude most documentation
- noudeb: Exclude installer udeb packages
- pkg.linux.notools: Exclude userland tool packages (linux-kbuild-<version>,
  linux-perf, etc.)
- pkg.linux.mintools: Build minimal set of userland tool packages
  (linux-kbuild-<version>)
- pkg.linux.nokernel: Exclude kernel image and header packages
- pkg.linux.nokerneldbg: Exclude kernel debug packages
- pkg.linux.nokerneldbginfo: Build kernel without debug symbols (also disables
  BTF)
- pkg.linux.nosource: Exclude source binary package (linux-source-<version>)
- cross: Needed when cross-building.
- nopython: Disable Python bindings.  This currently disables building the
  linux-perf-<version> package, as the perf program embeds Python.
- pkg.linux.nometa: Exclude most meta-packages.  The linux-headers-*-all*
  packages can still be built.
- pkg.linux.quick: Perform a limited build that should provide good
  coverage yet be quick enough for use in CI.

Build rules
===========

The Debian build rules are split across multiple makefiles:

- debian/rules: Standard top-level makefile for Debian package build.
- debian/rules.gen: Intermediate makefile between debian/rules and
  debian/rules.real.  This is generated by gencontrol.py based on
  the configuration under debian/config.
- debian/rules.real: Makefile for building a single kernel flavour
  or other group of binary packages.
- debian/rules.d: Makefiles for building userland code from specific
  source directories.  The directory structure mirrors the kernel
  source directories.  debian/rules.real uses the "make-tools" to
  invoke these makefiles.

All builds *must* be done out-of-tree in a subdirectory of
debian/build, so that the output files do not end up in the
linux-source-<version> binary package.  Currently kernel builds use
debian/build/build_<arch>_<featureset>_<flavour>, userland code uses
debian/build/build-tools/<source-dir> and documentation uses
debian/build/build-doc.

Code signing
============

The kernel image and modules may be signed after building, to support
a Secure Boot or Trusted Boot policy.  In Debian, this is performed by
a "code signing service" that is separate from the normal package
build process.

The initial package build generates binary packages named
linux-image-<arch>-signed-template, that contain a source package
template and metadata about the files to be signed.  The code signing
service will download this and the linux-image packages to be signed.
It will add detached signatures to the source package, then upload it
(without ever running debian/rules).

The source package template is generated by
debian/bin/gencontrol_signed.py and debian/rules.real with files from
debian/signing_templates and debian/templates.  To test changes to
these:

1. Build the linux source package.
2. Generate the signed source package by running the script
   "debian-test-sign" from the kernel-team.git repository.  It is
   also possible to set up a development configuration of the
   official code signing service, but this is more complicated.
3. Build the signed source package.