libzfs: FreeBSD doesn't resize partitions for you

This code can be failure prone on FreeBSD, where zfsd will pass a guid
as the vdev path to online.  The guid causes zfs_resolve_shortname to
fail because it expects a path.  We can just skip the whole ordeal.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@ixsystems.com>
Closes openzfs#12083

lib/libzfs/libzfs_pool.c

@@ -3137,11 +3137,9 @@ zpool_vdev_online(zpool_handle_t *zhp, const char *path, int flags,
 {
 	zfs_cmd_t zc = {"\0"};
 	char msg[1024];
-	char *pathname;
 	nvlist_t *tgt;
 	boolean_t avail_spare, l2cache, islog;
 	libzfs_handle_t *hdl = zhp->zpool_hdl;
-	int error;
 
 	if (flags & ZFS_ONLINE_EXPAND) {
 		(void) snprintf(msg, sizeof (msg),
@@ -3161,6 +3159,8 @@ zpool_vdev_online(zpool_handle_t *zhp, const char *path, int flags,
 	if (avail_spare)
 		return (zfs_error(hdl, EZFS_ISSPARE, msg));
 
+#ifndef __FreeBSD__
+	char *pathname;
 	if ((flags & ZFS_ONLINE_EXPAND ||
 	    zpool_get_prop_int(zhp, ZPOOL_PROP_AUTOEXPAND, NULL)) &&
 	    nvlist_lookup_string(tgt, ZPOOL_CONFIG_PATH, &pathname) == 0) {
@@ -3181,6 +3181,7 @@ zpool_vdev_online(zpool_handle_t *zhp, const char *path, int flags,
 		if (wholedisk) {
 			const char *fullpath = path;
 			char buf[MAXPATHLEN];
+			int error;
 
 			if (path[0] != '/') {
 				error = zfs_resolve_shortname(path, buf,
@@ -3197,6 +3198,7 @@ zpool_vdev_online(zpool_handle_t *zhp, const char *path, int flags,
 				return (error);
 		}
 	}
+#endif
 
 	zc.zc_cookie = VDEV_STATE_ONLINE;
 	zc.zc_obj = flags;