Enabling Kernel Settings in Debian

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This time it’s about enabling new kernel config options in the official Debian kernel packages. A few dependencies are needed to run the various scripts used by the Debian kernel folks, as well as to build the kernel itself:

apt install git gpg python3-debian python3-dacite
apt build-dep linux

With that in place, fetch the linux and kernel-team repos:

git clone --depth 1 https://salsa.debian.org/kernel-team/linux
git clone --depth 1 https://salsa.debian.org/kernel-team/kernel-team

So far you’ve only got the Debian-specific bits. Fetch the actual kernel sources now. In the likely case that you’re building a stable kernel, run the following from within the linux directory:

debian/bin/genorig.py https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git

Use the torvalds repo if you’re building an RC version instead:

debian/bin/genorig.py https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

Now generate the upstream tarball as well as debian/control. The first command will take a bit, and the second command will fail: but that’s success — just as the output says.

debian/rules orig
debian/rules debian/control

Now generate patched sources with:

debian/rules source

Time to edit the Kconfig and enable/disable whatever setting you wanted to change. Take a look around the files under debian/config/ to see where your changes should go. If it’s a setting shared among multiple architectures that may be debian/config/config. For x86-specific things, the file is debian/config/amd64/config. On aarch64 debian/config/arm64/config. If in doubt, you could try asking #debian-kernel on IRC.

It may look like you need to figure out where exactly in the file the setting should be placed. That is not the case. There’s a helpful script fixing things up for you:

../kernel-team/utils/kconfigeditor2/process.py .

The above will fail if you forgot to run debian/rules source. The debian/build/source_rt/Kconfig file is needed by the script:

Traceback (most recent call last):
  File "/tmp/linux/../kernel-team/utils/kconfigeditor2/process.py", line 19, in __init__
    menu = fs_menu[featureset or 'none']
KeyError: 'rt'

During handling of the above exception, another exception occurred:
FileNotFoundError: [Errno 2] No such file or directory: './debian/build/source_rt/Kconfig'

If that happens, run:

debian/rules source

Now process.py should work fine and fix your config file.

Excellent, now the config is updated and we’re ready to build the kernel. Off we go:

export MAKEFLAGS=-j$(nproc)
export DEB_BUILD_PROFILES='pkg.linux.nokerneldbg pkg.linux.nokerneldbginfo pkg.linux.notools nodoc'
dpkg-buildpackage -b -nc -uc