vdev_id: Fix partition regular expression

Given a DM device name, the old vdev_id script would extract any text
after a 'p' as the partition number.  It then appends "-part" + the
partition number to the name, giving a by-vdev name like "L0-part5".

This works fine if the DM name is like 'dm-2p5', but doesn't work if
the DM name is a multipath name like "mpatha".  In those cases it
incorrectly matches the 'p' in "mpatha", giving by-vdev names like
"L0-partatha".

This patch fixes the issue by making the partition regex match stricter.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #11637 

cmd/vdev_id/vdev_id

@@ -285,7 +285,9 @@ sas_handler() {
 		# we have to append the -part suffix directly in the
 		# helper.
 		if [ "$DEVTYPE" != "partition" ] ; then
-			PART=$(echo "$DM_NAME" | awk -Fp '/p/{print "-part"$2}')
+			# Match p[number], remove the 'p' and prepend "-part"
+			PART=$(echo "$DM_NAME" |
+				awk 'match($0,/p[0-9]+$/) {print "-part"substr($0,RSTART+1,RLENGTH-1)}')
 		fi
 
 		# Strip off partition information.
@@ -499,7 +501,9 @@ scsi_handler() {
 		# we have to append the -part suffix directly in the
 		# helper.
 		if [ "$DEVTYPE" != "partition" ] ; then
-			PART=$(echo "$DM_NAME" | awk -Fp '/p/{print "-part"$2}')
+			# Match p[number], remove the 'p' and prepend "-part"
+			PART=$(echo "$DM_NAME" |
+			    awk 'match($0,/p[0-9]+$/) {print "-part"substr($0,RSTART+1,RLENGTH-1)}')
 		fi
 
 		# Strip off partition information.
@@ -648,7 +652,9 @@ alias_handler () {
 	DM_PART=
 	if echo "$DM_NAME" | grep -q -E 'p[0-9][0-9]*$' ; then
 		if [ "$DEVTYPE" != "partition" ] ; then
-			DM_PART=$(echo "$DM_NAME" | awk -Fp '/p/{print "-part"$2}')
+			# Match p[number], remove the 'p' and prepend "-part"
+			DM_PART=$(echo "$DM_NAME" |
+			    awk 'match($0,/p[0-9]+$/) {print "-part"substr($0,RSTART+1,RLENGTH-1)}')
 		fi
 	fi