[PATCH kernel-helper] 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 needrestart or monitoring checks
can then notice that the newly installed kernel is not running yet,
without requiring one of those packages to be installed.

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..ccb01cd
--- /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 needrestart 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}"
+
+echo "*** System restart required ***" > /run/reboot-required
+if ! grep -qxF "$pkg" /run/reboot-required.pkgs 2>/dev/null; then
+	echo "$pkg" >> /run/reboot-required.pkgs
+fi
-- 
2.47.3