Determine autoremovable kernels at run-time

Our kernel autoremoval helper script protects the currently booted
kernel, but it only runs whenever we install or remove a kernel,
causing it to protect the kernel that was booted at that point in time,
which is not necessarily the same kernel as the one that is running
right now.

Reimplement the logic in C++ such that we can calculate it at run-time:
Provide a function to produce a regular expression that matches all
kernels that need protecting, and by changing the default root set
function in the DepCache to make use of that expression.

Note that the code groups the kernels by versions as before, and then
marks all kernel packages with the same version.

This optimized version inserts a virtual package $kernel into the cache
when building it to avoid having to iterate over all packages in the
cache to find the installed ones, significantly improving performance at
a minor cost when building the cache.

LP: #1615381

1 files changed, 1 insertions, 68 deletions

diff --git a/debian/apt.auto-removal.sh b/debian/apt.auto-removal.sh
index 2c32b0c9d..eef550a53 100644
--- a/debian/apt.auto-removal.sh
+++ b/debian/apt.auto-removal.sh
@@ -1,82 +1,15 @@
 #!/bin/sh
 set -e
-# Mark as not-for-autoremoval those kernel packages that are:
-#  - the currently booted version
-#  - the kernel version we've been called for
-#  - the latest kernel version (as determined by debian version number)
-#  - the second-latest kernel version
-#
-# In the common case this results in two kernels saved (booted into the
-# second-latest kernel, we install the latest kernel in an upgrade), but
-# can save up to four. Kernel refers here to a distinct release, which can
-# potentially be installed in multiple flavours counting as one kernel.
 
 eval $(apt-config shell APT_CONF_D Dir::Etc::parts/d)
 test -n "${APT_CONF_D}" || APT_CONF_D="/etc/apt/apt.conf.d"
 config_file="${APT_CONF_D}/01autoremove-kernels"
 
-eval $(apt-config shell DPKG Dir::bin::dpkg/f)
-test -n "$DPKG" || DPKG="/usr/bin/dpkg"
-
-list="$("${DPKG}" -l | awk '/^[ih][^nc][ ]+(linux|kfreebsd|gnumach)-image-[0-9]+\./ && $2 !~ /-dbg(:.*)?$/ && $2 !~ /-dbgsym(:.*)?$/ { print $2,$3; }' \
-   | sed -e 's#^\(linux\|kfreebsd\|gnumach\)-image-##' -e 's#:[^:]\+ # #')"
-debverlist="$(echo "$list" | cut -d' ' -f 2 | sort --unique --reverse --version-sort)"
-
-if [ -n "$1" ]; then
-	installed_version="$(echo "$list" | awk "\$1 == \"$1\" { print \$2;exit; }")"
-fi
-unamer="$(uname -r | tr '[A-Z]' '[a-z]')"
-if [ -n "$unamer" ]; then
-	running_version="$(echo "$list" | awk "\$1 == \"$unamer\" { print \$2;exit; }")"
-fi
-# ignore the currently running version if attempting a reproducible build
-if [ -n "${SOURCE_DATE_EPOCH}" ]; then
-	unamer=""
-	running_version=""
-fi
-latest_version="$(echo "$debverlist" | sed -n 1p)"
-previous_version="$(echo "$debverlist" | sed -n 2p)"
-
-debkernels="$(echo "$latest_version
-$installed_version
-$running_version
-$previous_version" | sort -u | sed -e '/^$/ d')"
-kernels="$( (echo "$1
-$unamer"; for deb in $debkernels; do echo "$list" | awk "\$2 == \"$deb\" { print \$1; }"; done; ) \
-   | sed -e 's#\([\.\+]\)#\\\1#g' -e '/^$/ d' | sort -u)"
-
 generateconfig() {
 	cat <<EOF
 // DO NOT EDIT! File autogenerated by $0
-APT::NeverAutoRemove
-{
-EOF
-	for package in $(apt-config dump --no-empty --format '%v%n' 'APT::VersionedKernelPackages'); do
-		for kernel in $kernels; do
-			echo "   \"^${package}-${kernel}$\";"
-		done
-	done
-	echo '};'
-	if [ "${APT_AUTO_REMOVAL_KERNELS_DEBUG:-true}" = 'true' ]; then
-		cat <<EOF
-/* Debug information:
-# dpkg list:
-$(dpkg -l | grep '\(linux\|kfreebsd\|gnumach\)-image-')
-# list of installed kernel packages:
-$list
-# list of different kernel versions:
-$debverlist
-# Installing kernel: $installed_version ($1)
-# Running kernel: ${running_version:-ignored} (${unamer:-ignored})
-# Last kernel: $latest_version
-# Previous kernel: $previous_version
-# Kernel versions list to keep:
-$debkernels
-# Kernel packages (version part) to protect:
-$kernels
-*/
+APT::LastInstalledKernel "$1";
 EOF
-	fi
 }
 generateconfig "$@" > "${config_file}.dpkg-new"
 mv -f "${config_file}.dpkg-new" "$config_file"