feat(os-update): add generic 'os_update' pre-reboot event for plugins (OS-486)

emhttp/plugins/unRAIDServer/unRAIDServer.plg

@@ -366,6 +366,22 @@ rm -f /boot/config/plugins/dynamix.plg
 if [[ -x /usr/local/emhttp/plugins/unraid.patch/scripts/patch.php ]]; then
   /usr/local/emhttp/plugins/unraid.patch/scripts/patch.php check &version;
 fi
+# Fire the generic 'os_update' event: a pre-reboot hook for an OS update that
+# any plugin can register for (config migration, backups, compatibility checks
+# and - for out-of-tree driver plugins - staging a build matching the INCOMING
+# kernel so a reboot never lands on a kernel without its driver). The new release
+# files - including changes.txt - are already on the flash here; pass the
+# incoming Unraid version and kernel release as context (consumers ignore what
+# they do not need). Hooks run synchronously, so the reboot prompt below only
+# appears once they have finished. Self-registering: a plugin just installs an
+# executable at its event/os_update path - no hardcoded list.
+new_kernel=$(awk '/[Ll]inux kernel/{f=3} f>0{if(match($0,/[0-9]+(\.[0-9]+)+/)){print substr($0,RSTART,RLENGTH);exit}f--}' /boot/changes.txt 2>/dev/null | head -1)
+if [ -n "$new_kernel" ]; then new_kernel="${new_kernel}-Unraid"; fi
+if [ -x /usr/local/sbin/emhttp_event ]; then
+  # Bound the whole dispatch so a wedged hook cannot stall the update forever;
+  # a hook that needs longer should background itself and notify (see emhttp_event).
+  timeout 300 /usr/local/sbin/emhttp_event os_update "&version;" "$new_kernel"
+fi
 # ensure writes to USB flash boot device have completed
 sync -f /boot
 if [ -z "${plg_update_helper}" ]; then

sbin/emhttp_event

@@ -79,6 +79,22 @@
 #   Note that if array is not Started, emhttpd will not spin down any disk, but emhttpd will
 #   still poll SMART data (for spun-up devices) and generate this event.
 
+# os_update
+#   Occurs during an Unraid OS update, after the new release files (including
+#   /boot/changes.txt) have been written to the flash but BEFORE the user reboots.
+#   Fired by the unRAIDServer plugin, not by emhttpd. A general pre-reboot hook
+#   for an OS update: any plugin can run work that must happen before rebooting
+#   into the new release - e.g. migrate/convert config, back something up, warn
+#   about an incompatibility, or (for out-of-tree driver plugins) stage a build
+#   matching the incoming kernel so the reboot never lands on a kernel without it.
+#   Extra arguments, passed as context (ignore if not needed): $2 = incoming
+#   Unraid version, $3 = incoming kernel release (uname -r form, e.g.
+#   6.18.33-Unraid; empty if it could not be determined).
+#   Hooks run synchronously and the whole dispatch is bounded by a timeout, so
+#   keep them quick and use network timeouts. A hook that genuinely needs long
+#   or async work should fork itself, return promptly, and surface its own result
+#   via notify - rather than blocking the OS update.
+
 # Invoke all 'any_event' scripts that might exist
 for Dir in /usr/local/emhttp/plugins/* ; do
   if [ -d $Dir/event/any_event ]; then