Add path handling for aux vdevs in label_path

If the AUX vdev is added using UUID, importing the pool falls back AUX
vdev to open it with disk name instead of UUID due to the absence of
path information for AUX vdevs. Since AUX label now have path
information, this PR adds path handling for it in `label_path`.

Reviewed-by: Umer Saleem <[email protected]>
Reviewed-by: Alexander Motin <[email protected]>
Signed-off-by: Ameer Hamza <[email protected]>
Closes openzfs#15737

lib/libzutil/zutil_import.c

@@ -1194,13 +1194,26 @@ label_paths(libpc_handle_t *hdl, nvlist_t *label, char **path, char **devid)
 	nvlist_t *nvroot;
 	uint64_t pool_guid;
 	uint64_t vdev_guid;
+	uint64_t state;
 
 	*path = NULL;
 	*devid = NULL;
+	if (nvlist_lookup_uint64(label, ZPOOL_CONFIG_GUID, &vdev_guid) != 0)
+		return (ENOENT);
+
+	/*
+	 * In case of spare or l2cache, we directly return path/devid from the
+	 * label.
+	 */
+	if (!(nvlist_lookup_uint64(label, ZPOOL_CONFIG_POOL_STATE, &state)) &&
+	    (state == POOL_STATE_SPARE || state == POOL_STATE_L2CACHE)) {
+		(void) nvlist_lookup_string(label, ZPOOL_CONFIG_PATH, path);
+		(void) nvlist_lookup_string(label, ZPOOL_CONFIG_DEVID, devid);
+		return (0);
+	}
 
 	if (nvlist_lookup_nvlist(label, ZPOOL_CONFIG_VDEV_TREE, &nvroot) ||
-	    nvlist_lookup_uint64(label, ZPOOL_CONFIG_POOL_GUID, &pool_guid) ||
-	    nvlist_lookup_uint64(label, ZPOOL_CONFIG_GUID, &vdev_guid))
+	    nvlist_lookup_uint64(label, ZPOOL_CONFIG_POOL_GUID, &pool_guid))
 		return (ENOENT);
 
 	return (label_paths_impl(hdl, nvroot, pool_guid, vdev_guid, path,