zed: Add synchronous zedlets

Historically, ZED has blindly spawned off zedlets in parallel and never
worried about their completion order.  This means that you can
potentially have zedlets for event number 2 starting before zedlets for
event number 1 had finished.  Most of the time this is fine, and it
actually helps a lot when the system is getting spammed with hundreds
of events.

However, there are times when you want your zedlets to be executed
in sequence with the event ID.  That is where synchronous zedlets
come in.

ZED will wait for all previously spawned zedlets to finish before
running a synchronous zedlet.  Synchronous zedlets are guaranteed to be
the only zedlet running.  No other zedlets may run in parallel with a
synchronous zedlet.  Users should be careful to only use synchronous
zedlets when needed, since they decrease parallelism.

To make a zedlet synchronous, simply add a "-sync-" immediately
following the event name in the zedlet's file name:

	EVENT_NAME-sync-ZEDLETNAME.sh

For example, if you wanted a synchronous statechange script:

	statechange-sync-myzedlet.sh

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #17335

Author: tonyhutter

cmd/zed/zed.d/Makefile.am

@@ -9,18 +9,18 @@ dist_zedexec_SCRIPTS = \
 	%D%/all-debug.sh \
 	%D%/all-syslog.sh \
 	%D%/data-notify.sh \
-	%D%/deadman-slot_off.sh \
+	%D%/deadman-sync-slot_off.sh \
 	%D%/generic-notify.sh \
-	%D%/pool_import-led.sh \
+	%D%/pool_import-sync-led.sh \
 	%D%/resilver_finish-notify.sh \
 	%D%/resilver_finish-start-scrub.sh \
 	%D%/scrub_finish-notify.sh \
-	%D%/statechange-led.sh \
+	%D%/statechange-sync-led.sh \
 	%D%/statechange-notify.sh \
-	%D%/statechange-slot_off.sh \
+	%D%/statechange-sync-slot_off.sh \
 	%D%/trim_finish-notify.sh \
-	%D%/vdev_attach-led.sh \
-	%D%/vdev_clear-led.sh
+	%D%/vdev_attach-sync-led.sh \
+	%D%/vdev_clear-sync-led.sh
 
 nodist_zedexec_SCRIPTS = \
 	%D%/history_event-zfs-list-cacher.sh
@@ -30,17 +30,17 @@ SUBSTFILES += $(nodist_zedexec_SCRIPTS)
 zedconfdefaults = \
 	all-syslog.sh \
 	data-notify.sh \
-	deadman-slot_off.sh \
+	deadman-sync-slot_off.sh \
 	history_event-zfs-list-cacher.sh \
-	pool_import-led.sh \
+	pool_import-sync-led.sh \
 	resilver_finish-notify.sh \
 	resilver_finish-start-scrub.sh \
 	scrub_finish-notify.sh \
-	statechange-led.sh \
+	statechange-sync-led.sh \
 	statechange-notify.sh \
-	statechange-slot_off.sh \
-	vdev_attach-led.sh \
-	vdev_clear-led.sh
+	statechange-sync-slot_off.sh \
+	vdev_attach-sync-led.sh \
+	vdev_clear-sync-led.sh
 
 dist_noinst_DATA += %D%/README
 

cmd/zed/zed.d/deadman-slot_off.sh renamed to cmd/zed/zed.d/deadman-sync-slot_off.sh

@@ -0,0 +1 @@
+statechange-sync-led.sh

cmd/zed/zed.d/pool_import-led.sh

@@ -0,0 +1 @@
+statechange-sync-led.sh

cmd/zed/zed.d/pool_import-sync-led.sh

@@ -0,0 +1 @@
+statechange-sync-led.sh