[PATCH kernel-helper v2] kernel hooks: flag pending reboot after installing a new kernel

[Jonas Theisen <j.theisen@proxmox.com>]

Ship a postinst.d hook that writes /run/reboot-required and records
the kernel package in /run/reboot-required.pkgs, similar to
the hooks shipped by unattended-upgrades on Debian and
update-notifier on Ubuntu. Tools like update-notifier or monitoring checks
can then notice that the newly installed kernel is not running yet
by checking the existance of this file.
See f.ex.: https://github.com/mvo5/unattended-upgrades/blob/master/unattended-upgrade#L867
and: https://git.launchpad.net/ubuntu/+source/update-notifier/tree/data/update-motd-reboot-required

Skip this when configuring the currently running kernel, as no reboot
is needed then.

Came up in https://forum.proxmox.com/threads/156352/

Signed-off-by: Jonas Theisen <j.theisen@proxmox.com>
---
 src/proxmox-boot/Makefile                |  2 ++
 src/proxmox-boot/proxmox-reboot-required | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100755 src/proxmox-boot/proxmox-reboot-required

diff --git a/src/proxmox-boot/Makefile b/src/proxmox-boot/Makefile
index 044a024..d9e1c3d 100644
--- a/src/proxmox-boot/Makefile
+++ b/src/proxmox-boot/Makefile
@@ -1,4 +1,5 @@
 KERNEL_HOOKSCRIPTS = proxmox-auto-removal zz-proxmox-boot
+KERNEL_POSTINST_HOOKSCRIPTS = proxmox-reboot-required
 INITRAMFS_HOOKSCRIPTS = proxmox-boot-sync
 SHARE_FILES = functions
 GRUB_CFG_SNIPPET = 000_proxmox_boot_header
@@ -17,6 +18,7 @@ all:
 install:
 	install -d $(POSTINSTHOOKDIR)
 	install -m 0755 $(KERNEL_HOOKSCRIPTS) $(POSTINSTHOOKDIR)
+	install -m 0755 $(KERNEL_POSTINST_HOOKSCRIPTS) $(POSTINSTHOOKDIR)
 	install -d $(POSTRMHOOKDIR)
 	install -m 0755 $(KERNEL_HOOKSCRIPTS) $(POSTRMHOOKDIR)
 	install -d $(POSTINITRAMFSHOOKDIR)
diff --git a/src/proxmox-boot/proxmox-reboot-required b/src/proxmox-boot/proxmox-reboot-required
new file mode 100755
index 0000000..c645914
--- /dev/null
+++ b/src/proxmox-boot/proxmox-reboot-required
@@ -0,0 +1,19 @@
+#! /bin/sh
+set -e
+
+# Flag that a reboot is needed to boot the newly installed kernel, following the convention used by
+# update-notifier and unattended-upgrades, so that tools like update-notifier or monitoring checks
+# notice it. Reconfiguring the currently running kernel does not require a reboot.
+
+version="$1"
+
+[ -n "$version" ] || exit 0
+[ "$version" != "$(uname -r)" ] || exit 0
+[ -d /run ] || exit 0
+
+pkg="${DPKG_MAINTSCRIPT_PACKAGE:-proxmox-kernel-$version}"
+
+printf "*** System restart required ***\n" > /run/reboot-required
+if ! grep -qxF "$pkg" /run/reboot-required.pkgs 2>/dev/null; then
+	printf "%s\n" "$pkg" >> /run/reboot-required.pkgs
+fi
-- 
2.47.3