refactor: faster kernel installation with a shim (#2926)

This is taken from [1]. We were for no good reason regenerating the initramfs
here. We can also install the kmods with the kernel in one step so I
don't see why we shouldn't just do that. It reduces the amount of time
needed to run this script (on my machine) from 49s to 28s.

I'm not sure if this is an oversight in rpm-ostree, we could technically
use the initramfs that is built during this stage, however, we lose
quite a bit of control, which we definitively want to have.

Also it should generally be noticable when the v4l2 and xone kmods fail
to install. There also haven't been problem regarding that in quite a
while.

[1] 5441c76f1f

build_scripts/base/02-install-common-kernel-akmods.sh

@@ -4,29 +4,52 @@ echo "::group:: ===$(basename "$0")==="
 
 set -eoux pipefail
 
-# Remove Existing Kernel
-for pkg in kernel kernel{-core,-modules,-modules-core,-modules-extra,-tools-libs,-tools}; do
-    rpm --erase "${pkg}" --nodeps
+KERNEL_PKGS_ORIG=(kernel kernel-{core,modules,modules-core,modules-extra,tools-libs,tools})
+
+# removing them all at once is slower
+for pkg in "${KERNEL_PKGS_ORIG[@]}"; do
+  rpm --erase "${pkg}" --nodeps
 done
 
 # cleanup leftovers that are not covered by kernel-* packages for some reason
 rm -rf /usr/lib/modules
 
-# Install Kernel
-dnf5 -y install \
-    /tmp/kernel-rpms/kernel-[0-9]*.rpm \
-    /tmp/kernel-rpms/kernel-core-*.rpm \
-    /tmp/kernel-rpms/kernel-modules-*.rpm
+KERNEL_PKGS=(
+  /tmp/kernel-rpms/kernel-[0-9]*.rpm
+  /tmp/kernel-rpms/kernel-core-*.rpm
+  /tmp/kernel-rpms/kernel-modules-*.rpm
+)
+
+KMODS=(
+  /tmp/rpms/{common,kmods}/*xone*.rpm
+  /tmp/rpms/{common,kmods}/*v4l2loopback*.rpm
+)
 
 if [[ "${IMAGE_FLAVOR}" == "dx" ]]; then
-  dnf -y install /tmp/kernel-rpms/kernel-devel-*.rpm
+  KERNEL_PKGS+=(/tmp/kernel-rpms/kernel-devel-*.rpm)
 fi
 
-dnf5 versionlock add kernel kernel-devel kernel-devel-matched kernel-core kernel-modules kernel-modules-core kernel-modules-extra
+KERNEL_PKGS_ALL=( "${KERNEL_PKGS[@]}" "${KMODS[@]}" )
 
-dnf -y install /tmp/rpms/{common,kmods}/*xone*.rpm || true
+# shims to bypass kernel install triggering dracut/rpm-ostree
+# this is really ugly, skipping scriplets might be not a good idea
+cd /usr/lib/kernel/install.d \
+&& mv 05-rpmostree.install 05-rpmostree.install.bak \
+&& mv 50-dracut.install 50-dracut.install.bak \
+&& printf '%s\n' '#!/bin/sh' 'exit 0' > 05-rpmostree.install \
+&& printf '%s\n' '#!/bin/sh' 'exit 0' > 50-dracut.install \
+&& chmod +x  05-rpmostree.install 50-dracut.install
 
-dnf -y install /tmp/rpms/{kmods,common}/*v4l2loopback*.rpm || true
+dnf -y install "${KERNEL_PKGS_ALL[@]}"
+
+# restore original kernel install
+mv -f 05-rpmostree.install.bak 05-rpmostree.install \
+&& mv -f 50-dracut.install.bak 50-dracut.install
+cd -
+
+KERNEL_VERSIONLOCK=( "${KERNEL_PKGS_ORIG[@]}" kernel-devel{-matched,} )
+
+dnf versionlock add "${KERNEL_VERSIONLOCK[@]}"
 
 mkdir -p /etc/pki/akmods/certs
 ghcurl "https://github.com/ublue-os/akmods/raw/refs/heads/main/certs/public_key.der" --retry 3 -Lo /etc/pki/akmods/certs/akmods-ublue.der