Force fault a vdev with 'zpool offline -f'

This patch adds a '-f' option to 'zpool offline' to fault a vdev
instead of bringing it offline.  Unlike the OFFLINE state, the
FAULTED state will trigger the FMA code, allowing for things like
autoreplace and triggering the slot fault LED.  The -f faults
persist across imports, unless they were set with the temporary
(-t) flag.  Both persistent and temporary faults can be cleared
with zpool clear.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #6094

include/libzfs.h

@@ -284,6 +284,7 @@ extern nvlist_t *zpool_find_vdev_by_physpath(zpool_handle_t *, const char *,
     boolean_t *, boolean_t *, boolean_t *);
 extern int zpool_label_disk_wait(char *, int);
 extern int zpool_label_disk(libzfs_handle_t *, zpool_handle_t *, char *);
+extern uint64_t zpool_vdev_path_to_guid(zpool_handle_t *zhp, const char *path);
 
 int zfs_dev_is_dm(char *dev_name);
 int zfs_dev_is_whole_disk(char *dev_name);

include/sys/fs/zfs.h

@@ -731,9 +731,10 @@ typedef enum vdev_aux {
 	VDEV_AUX_ERR_EXCEEDED,	/* too many errors			*/
 	VDEV_AUX_IO_FAILURE,	/* experienced I/O failure		*/
 	VDEV_AUX_BAD_LOG,	/* cannot read log chain(s)		*/
-	VDEV_AUX_EXTERNAL,	/* external diagnosis			*/
+	VDEV_AUX_EXTERNAL,	/* external diagnosis or forced fault	*/
 	VDEV_AUX_SPLIT_POOL,	/* vdev was split off into another pool	*/
-	VDEV_AUX_BAD_ASHIFT	/* vdev ashift is invalid		*/
+	VDEV_AUX_BAD_ASHIFT,	/* vdev ashift is invalid		*/
+	VDEV_AUX_EXTERNAL_PERSIST	/* persistent forced fault	*/
 } vdev_aux_t;
 
 /*