Store the L2ARC device ashift in the vdev label

If this is not done, and the pool has an ashift other than the default
(at the moment 9) then the following happens:

1) vdev_alloc() assigns the ashift of the pool to L2ARC device, but
   upon export it is not stored anywhere
2) at the first import, vdev_open() sees an vdev_ashift() of 0 and
   assigns the logical_ashift, which is 9
3) reading the contents of L2ARC, including the header fails
4) L2ARC buffers are not restored in ARC.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: George Amanakis <[email protected]>
Closes openzfs#14313 
Closes openzfs#14963

Author: gamanakis

module/zfs/vdev_label.c

@@ -486,6 +486,9 @@ vdev_config_generate(spa_t *spa, vdev_t *vd, boolean_t getstats,
 	if (vd->vdev_isspare)
 		fnvlist_add_uint64(nv, ZPOOL_CONFIG_IS_SPARE, 1);
 
+	if (flags & VDEV_CONFIG_L2CACHE)
+		fnvlist_add_uint64(nv, ZPOOL_CONFIG_ASHIFT, vd->vdev_ashift);
+
 	if (!(flags & (VDEV_CONFIG_SPARE | VDEV_CONFIG_L2CACHE)) &&
 	    vd == vd->vdev_top) {
 		fnvlist_add_uint64(nv, ZPOOL_CONFIG_METASLAB_ARRAY,

tests/zfs-tests/tests/functional/l2arc/persist_l2arc_001_pos.ksh

@@ -27,15 +27,14 @@
 #
 # STRATEGY:
 #	1. Create pool with a cache device.
-#	2. Export and re-import pool without writing any data.
-#	3. Create a random file in that pool and random read for 10 sec.
-#	4. Export pool.
-#	5. Read the amount of log blocks written from the header of the
+#	2. Create a random file in that pool and random read for 10 sec.
+#	3. Export pool.
+#	4. Read the amount of log blocks written from the header of the
 #		L2ARC device.
-#	6. Import pool.
-#	7. Read the amount of log blocks rebuilt in arcstats and compare to
+#	5. Import pool.
+#	6. Read the amount of log blocks rebuilt in arcstats and compare to
 #		(5).
-#	8. Check if the labels of the L2ARC device are intact.
+#	7. Check if the labels of the L2ARC device are intact.
 #
 #	* We can predict the minimum bytes of L2ARC restored if we subtract
 #	from the effective size of the cache device the bytes l2arc_evict()
@@ -77,10 +76,8 @@ export FILE_SIZE=$(( floor($fill_mb / $NUMJOBS) ))M
 
 log_must truncate -s ${cache_sz}M $VDEV_CACHE
 
-log_must zpool create -f $TESTPOOL $VDEV cache $VDEV_CACHE
-
-log_must zpool export $TESTPOOL
-log_must zpool import -d $VDIR $TESTPOOL
+log_must zpool create -f -o ashift=12 $TESTPOOL $VDEV
+log_must zpool add $TESTPOOL cache $VDEV_CACHE
 
 log_must fio $FIO_SCRIPTS/mkfiles.fio
 log_must fio $FIO_SCRIPTS/random_reads.fio