zed: Prevent special vdev to be replaced by hot spare

Special vdevs should not be replaced by a hot spare.
Log vdevs already support this, extending the
functionality for special vdevs.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ameer Hamza <ahamza@ixsystems.com>
Closes #14129

module/zfs/spa.c

@@ -6819,10 +6819,12 @@ spa_vdev_attach(spa_t *spa, uint64_t guid, nvlist_t *nvroot, int replacing,
 		return (spa_vdev_exit(spa, newrootvd, txg, error));
 
 	/*
-	 * Spares can't replace logs
+	 * log, dedup and special vdevs should not be replaced by spares.
 	 */
-	if (oldvd->vdev_top->vdev_islog && newvd->vdev_isspare)
+	if ((oldvd->vdev_top->vdev_alloc_bias != VDEV_BIAS_NONE ||
+	    oldvd->vdev_top->vdev_islog) && newvd->vdev_isspare) {
 		return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));
+	}
 
 	/*
 	 * A dRAID spare can only replace a child of its parent dRAID vdev.

tests/zfs-tests/tests/functional/fault/auto_offline_001_pos.ksh

@@ -121,6 +121,11 @@ done
 #    the removed data device
 for conf in "${poolconfs[@]}"
 do
+	# special vdev can not be replaced by a hot spare
+	if [[ $conf = *"special mirror"* ]]; then
+		continue
+	fi
+
 	# 1. Create a pool with a spare
 	log_must zpool create -f $TESTPOOL $conf
 	block_device_wait ${DEV_DSKDIR}/${removedev}