tests: better handling for dmeventd restart

Handle the case, where we  'kill -9' running dmeventd,
and restarting 'dmeventd -R' manages to still contact this
'zombie' damone and manages to get list of monitored devices
out of this and eventually 'run' new and in this case
unexpected instance of dmeventd.

test/shell/dmeventd-restart.sh

@@ -20,21 +20,22 @@ _restart_dmeventd() {
 	#rm -f debug.log*
 
 	dmeventd -R -fldddd -e "$PWD/test_nologin" > debug.log_DMEVENTD_$RANDOM 2>&1 &
-	echo $! >LOCAL_DMEVENTD
+	local local=$!
+	echo "$local" >LOCAL_DMEVENTD
 
-	for i in {1..10}; do
+	for i in {1..50}; do
-		pid=$(pgrep -o dmeventd || true)
+		pid=$(pgrep -o dmeventd) || break
-		test -n "$pid" || break; # no dmeventd running
+		# Check pid and dmeventd readiness to communicate
-		test "$pid" = "$(< LOCAL_DMEVENTD)" && break
+		test "$pid" = "$local" && dmeventd -i && break
 		sleep .2
 	done
 
-	# wait a bit, so we talk to the new dmeventd later
+	if [ "$i" -eq 50 ]; then
-	if test -n "$pid" ; then
+		# Unexpected - we waited over 10 seconds and
-		for i in {1..10}; do
+		# dmeventd has not managed to restart
-			dmeventd  -i && break;
+		cat /run/dmeventd.pid || true
-			sleep .1
+		pgrep dmeventd || true
-		done
+		die "dmeventd restart is too slow"
 	fi
 }
 
@@ -61,7 +62,20 @@ lvchange --monitor y --verbose $vg/4way 2>&1 | tee lvchange.out
 test -e LOCAL_CLVMD || grep 'already monitored' lvchange.out
 
 # now try what happens if no dmeventd is running
-kill -9 "$(< LOCAL_DMEVENTD)"
+pid=$(< LOCAL_DMEVENTD)
+kill -9 "$pid"
+# TODO/FIXME: it would be surely better, if the wait loop bellow would
+# not be need however ATM the API for communication is not welldetecting
+# this highly unusual race case - and things will simply timeout on
+# reading failure within 4 seconds.
+# Fixing would require to add some handling for losing FIFO connection
+for i in {1..10}; do
+	# wait here for a while until dmeventd dies....
+	# suprisingly it's not instant and we can actually
+	# obtain list of monitored devices...
+	test -z $(ps -p "$pid" -o comm=) && break
+	sleep .1
+done
 rm LOCAL_DMEVENTD debug.log*
 
 _restart_dmeventd