I need to add a kernel module to the kernel snap of an Ubuntu core image. I first tried to do this using insmod, but this failed because the filesystem is read-only. Now, I am trying to add the module to the kernel snap itself. I downloaded the pc-kernel snap (22/stable) and unsquashfs’ed it. Before trying to add my own module, I first wanted to see if I could successfully build it. For reference, here is the snapcraft.yaml file associated with this snap:
name: pc-kernel
adopt-info: kernel
grade: stable
summary: generic linux kernel
description: The generic Ubuntu kernel package as a snap
type: kernel
confinement: strict
build-base: core22
# In addition to these repositories, the /+snap/ page on launchpad may
# also build with ESM repositories enabled, or built in a particular
# PPA, which will also be used.
package-repositories:
- type: apt
ppa: canonical-kernel-team/uc20-release
parts:
kernel:
source: https://git.launchpad.net/~canonical-kernel-snaps/+git/kernel-snaps-uc22
source-type: git
source-branch: main
plugin: nil
# Set this snap version to the meta version of the package used to
# provide kernel.efi / vmlinuz
override-pull: |
snapcraftctl pull
snapcraftctl set-version "$(apt show linux-image-uc22-generic 2>/dev/null | sed -n 's/^Version: //p' | head -n1)"
build-packages:
- kmod
stage-packages:
- linux-image-uc22-generic
- on amd64:
- firmware-sof-signed
organize:
boot: ./
lib/firmware: firmware
lib/modules: modules
usr/share/doc: doc
override-build: |
if [ -e "$SNAPCRAFT_PART_INSTALL"/usr/share/doc/linux-image-uc22-generic/kernelefi.stamp ]; then
rm -vf "$SNAPCRAFT_PART_INSTALL"/boot/vmlinuz-*
else
mv "$SNAPCRAFT_PART_INSTALL"/boot/vmlinuz-* "$SNAPCRAFT_PART_INSTALL"/boot/vmlinuz
fi
if [ -d "$SNAPCRAFT_PART_INSTALL"/usr/share/doc/linux-signatures-nvidia-*-generic ]; then
cd $(dirname "$SNAPCRAFT_PART_INSTALL"/lib/modules/*/kernel/nvidia-*/bits/SHA256SUMS)
sh BUILD
# Remove nouveau
rm -rf "$SNAPCRAFT_PART_INSTALL"/lib/modules/*/kernel/drivers/gpu/drm/nouveau
# Update depmod
depmod -b "$SNAPCRAFT_PART_INSTALL" $(basename "$SNAPCRAFT_PART_INSTALL"/lib/modules/*)
# Trim firmware
"$SNAPCRAFT_PART_SRC"/trim-firmware "$SNAPCRAFT_PART_INSTALL"/lib
# Clean nvidia modules
sh CLEAN
# Fake the nvidia.ko modules pointing at an nvidia assemble location
cd ../
for module in nvidia-drm.ko nvidia-modeset.ko nvidia-peermem.ko nvidia-uvm.ko nvidia.ko
do
ln -s /var/snap/nvidia-assemble/common/nvidia-driver/$module $module
done
else
# Update depmod
depmod -b "$SNAPCRAFT_PART_INSTALL" $(basename "$SNAPCRAFT_PART_INSTALL"/lib/modules/*)
# Trim firmware
"$SNAPCRAFT_PART_SRC"/trim-firmware "$SNAPCRAFT_PART_INSTALL"/lib
fi
snapcraftctl build
# Exclude transitive dependencies of userspace stage-packages that
# do not make sense in the kernel snap. E.g. iw tool is shipped in
# base snap, but kernel needs to ship regulatory-db datafiles
# alone.
stage:
- -etc
- -lib
- -usr
- -sbin
- -bin
- -var
- -lib64
- -doc/linux-base
- -doc/binutils*
- -doc/debconf
- -doc/dpkg
- -doc/gcc-*
- -doc/kmod*
- -doc/lib*
- -doc/lsb-base
- -doc/perl*
- -doc/tar
- -doc/zlib1g
override-stage: |
snapcraftctl stage
# Check that only one nvidia series got shipped
if [ "$SNAPCRAFT_TARGET_ARCH" != "armhf" ]; then
[ $(ls "$SNAPCRAFT_STAGE"/modules/*/kernel/nvidia-*/bits/SHA256SUMS | wc -l) -eq 1 ]
fi
Building the kernel snap with snapcraft fails because a dependency linux-objects-nvidia-525-server-5.15.0-86-generic for the package: linux-image-uc22-generic can not be resolved. After some digging, it appears as though linux-image-uc22-generic requires linux-objects-nvidia-525-server-5.15.0-86-generic=5.15.0-88.98, but the only available version is linux-objects-nvidia-525-server-5.15.0-86-generic=5.15.0-88.98+1.
How can I get around this issue to build the kernel snap? I’m assuming it’s possible because it had to have been built at some point - unless I am missing something about how unsquashfs works on snaps.