[pve-devel] [PATCH pve-kernel-meta v3 2/4] proxmox-boot: fix #3671 add pin/unpin for kernel-version

[Stoiko Ivanov <s.ivanov@proxmox.com>]

The 2 commands follow the mechanics of p-b-t kernel add/remove in
writing the desired abi-version to a config-file in /etc/kernel and
actually modifying the boot-loader configuration upon p-b-t refresh.

A dedicated new file is used instead of writing the version (with some
kind of annotation) to the manual kernel list to keep parsing the file
simple (and hopefully also cause fewer problems with manually edited
files)

For systemd-boot we write the entry into the loader.conf on the ESP(s)
instead of relying on the `bootctl set-default` mechanics (bootctl(1))
which write the entry in an EFI-var. This was preferred, because of a
few reports of unwriteable EFI-vars on some systems (e.g. DELL servers
have a setting preventing writing EFI-vars from the OS). The rationale
in `Why not simply rely on the EFI boot menu logic?` from [0] also
makes a few points in that direction.

For grub the following choices were made:
* write the pinned version (or actually the menu-path leading to it)
  to a snippet in /etc/default/grub.d instead of editing the grub.cfg
  files on the partition. Mostly to divert as little as possible from
  the grub-workflow I assume people are used to.
* the 'root-device-id' part of the menu-entries is parsed from
  /boot/grub/grug.cfg since it was stable (the same on all ESPs and in
  /boot/grub), saves us from copying the part of "find device behind
  /, mangle it if zfs/btrfs, call grub_probe a few times" part of
  grub-mkconfig - and seems a bit more robust

Tested with a BIOS and an UEFI VM with / on ZFS.

[0] https://systemd.io/BOOT_LOADER_SPECIFICATION/

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
---
 bin/proxmox-boot-tool        | 48 ++++++++++++++++++++++++++++++++++++
 proxmox-boot/functions       | 37 +++++++++++++++++++++++++++
 proxmox-boot/zz-proxmox-boot |  5 ++++
 3 files changed, 90 insertions(+)

diff --git a/bin/proxmox-boot-tool b/bin/proxmox-boot-tool
index 93760fb..329df42 100755
--- a/bin/proxmox-boot-tool
+++ b/bin/proxmox-boot-tool
@@ -286,6 +286,13 @@ list_kernels() {
 	echo ""
 	echo "Automatically selected kernels:"
 	echo "$boot_kernels"
+
+	pinned_kernel="$(get_first_line "$PINNED_KERNEL_CONF")"
+	if [ -n "$pinned_kernel" ]; then
+		echo ""
+		echo "Pinned kernel:"
+		echo "${pinned_kernel}"
+	fi
 }
 
 usage() {
@@ -296,6 +303,8 @@ usage() {
 	warn "       $0 clean [--dry-run]"
 	warn "       $0 refresh [--hook <name>]"
 	warn "       $0 kernel <add|remove> <kernel-version>"
+	warn "       $0 kernel pin <kernel-version>"
+	warn "       $0 kernel unpin"
 	warn "       $0 kernel list"
 	warn "       $0 status [--quiet]"
 	warn "       $0 help"
@@ -323,6 +332,15 @@ help() {
 	echo "    add/remove pve-kernel with ABI <kernel-version> to list of synced kernels, in addition to automatically selected ones."
 	echo "    NOTE: you need to manually run 'refresh' once you're finished with adding/removing kernels from the list"
 	echo ""
+	echo "USAGE: $0 kernel pin <kernel-version>"
+	echo ""
+	echo "    pin pve-kernel with ABI <kernel-version> as the default entry to be booted."
+	echo "    NOTE: you need to manually run 'refresh' once you're finished with pinning kernels"
+	echo ""
+	echo "USAGE: $0 kernel unpin"
+	echo ""
+	echo "    unpin sets the latest kernel as the default entry (undoes a previous pin)"
+	echo ""
 	echo "USAGE: $0 kernel list"
 	echo ""
 	echo "    list kernel versions currently selected for inclusion on ESPs."
@@ -392,6 +410,28 @@ status() {
 	fi
 }
 
+pin_kernel() {
+	ver="$1"
+
+	if [ -z "$ver" ]; then
+		warn "E: <kernel-version> is mandatory"
+		warn ""
+		exit 1
+	fi
+
+	if [ ! -e "/boot/vmlinuz-$ver" ]; then
+		warn "E: no kernel image found in /boot for '$ver', not setting default."
+		exit 1
+	fi
+	echo "$ver" > "$PINNED_KERNEL_CONF"
+	echo "Set kernel '$ver' $PINNED_KERNEL_CONF. Use the 'refresh' command to update the ESPs."
+}
+
+unpin_kernel() {
+	rm -f "$PINNED_KERNEL_CONF"
+	echo "Removed $PINNED_KERNEL_CONF. Use the 'refresh' command to update the ESPs."
+}
+
 if [ -z "$1" ]; then
     usage
     exit 0
@@ -460,6 +500,14 @@ case "$1" in
 				list_kernels
 				exit 0
 			;;
+			'pin')
+				pin_kernel "$2"
+				exit 0
+			;;
+			'unpin')
+				unpin_kernel "$2"
+				exit 0
+			;;
 			*)
 				warn "E: invalid 'kernel' subcommand '$cmd'."
 				warn ""
diff --git a/proxmox-boot/functions b/proxmox-boot/functions
index 27da363..5a56b74 100755
--- a/proxmox-boot/functions
+++ b/proxmox-boot/functions
@@ -5,11 +5,13 @@ ESP_LIST="/etc/kernel/proxmox-boot-uuids"
 ESPTYPE='c12a7328-f81f-11d2-ba4b-00a0c93ec93b'
 
 MANUAL_KERNEL_LIST="/etc/kernel/pve-efiboot-manual-kernels"
+PINNED_KERNEL_CONF="/etc/kernel/proxmox-boot-pin"
 
 MOUNTROOT="${TMPDIR:-/var/tmp}/espmounts"
 # relative to the ESP mountpoint
 PMX_ESP_DIR="EFI/proxmox"
 PMX_LOADER_CONF="loader/loader.conf"
+GRUB_PIN_SNIPPET="/etc/default/grub.d/proxmox-kernel-pin.cfg"
 
 # adapted from /etc/kernel/postinst.d/apt-auto-removal as present in
 # debian's apt package:
@@ -21,6 +23,7 @@ PMX_LOADER_CONF="loader/loader.conf"
 #  - the second-latest kernel version
 #  - the latest kernel version of each series (e.g. 4.13, 4.15, 5.0) by
 #    marking the meta-packages
+#  - the currently pinned kernel if any
 
 kernel_keep_versions() {
 	eval "$(apt-config shell DPKG Dir::bin::dpkg/f)"
@@ -56,6 +59,8 @@ kernel_keep_versions() {
 		manual_kernels="$(cat "$MANUAL_KERNEL_LIST")"
 	fi
 
+	pinned_kernel="$(get_first_line "$PINNED_KERNEL_CONF")"
+
 	kernels="$(cat <<-EOF
 		$running_version
 		$install_version
@@ -63,6 +68,7 @@ kernel_keep_versions() {
 		$latest_2_versions
 		$series_metapackages
 		$oldseries_latest_kernel
+		$pinned_kernel
 		EOF
 	)"
 
@@ -114,3 +120,34 @@ get_first_line() {
 	done < "${file}"
 	echo "$line"
 }
+
+set_grub_default() {
+	kver="$1"
+
+	if [ -z "${kver}" ]; then
+		rm -f "${GRUB_PIN_SNIPPET}"
+	else
+		# grub menu entry ids contain the internal root-device id (e.g. for zfs the GUID of
+		# the pool printed in hex) as this is independent of the ESP (or grub location)
+		# take it from /boot/grub/grub.cfg
+		root_devid=$(sed -rn "s/.*gnulinux-advanced-(.+)['] \{$/\1/p" \
+			/boot/grub/grub.cfg)
+		entry="gnulinux-advanced-${root_devid}>gnulinux-${kver}-advanced-${root_devid}"
+		echo "GRUB_DEFAULT=\"${entry}\"" > "${GRUB_PIN_SNIPPET}"
+	fi
+}
+
+set_systemd_boot_default() {
+	mountpoint="$1"
+	kver="$2"
+	if [ -z "${kver}" ]; then
+		entry="proxmox-*"
+	else
+		entry="proxmox-${kver}.conf"
+	fi
+
+	# replaces the current default entry, if one exists else append it at the end of the file
+	sed -ri "/^default /{h;s/ .*\$/ ${entry}/};\${x;/^$/{s//default ${entry}/;H};x}" \
+		"${mountpoint}/$PMX_LOADER_CONF"
+
+}
diff --git a/proxmox-boot/zz-proxmox-boot b/proxmox-boot/zz-proxmox-boot
index db73166..7958a5d 100755
--- a/proxmox-boot/zz-proxmox-boot
+++ b/proxmox-boot/zz-proxmox-boot
@@ -90,9 +90,14 @@ update_esp_func() {
 	fi
 	warn "Copying and configuring kernels on ${path}"
 	copy_and_config_kernels "${mountpoint}"
+
+	pinned_kernel=$(get_first_line "${PINNED_KERNEL_CONF}")
+
 	if [ -d /sys/firmware/efi ]; then
+		set_systemd_boot_default "${mountpoint}" "${pinned_kernel}"
 		remove_old_kernels_efi "${mountpoint}"
 	else
+		set_grub_default "${pinned_kernel}"
 		remove_old_kernels_legacy "${mountpoint}"
 		mount --bind "${mountpoint}" "/boot"
 		update-grub
-- 
2.30.2