Add 'zfs rename -u' to rename without remounting

Allow to rename file systems without remounting if it is possible.
It is possible for file systems with 'mountpoint' property set to
'legacy' or 'none' - we don't have to change mount directory for them.
Currently such file systems are unmounted on rename and not even
mounted back.

This introduces layering violation, as we need to update
'f_mntfromname' field in statfs structure related to mountpoint (for
the dataset we are renaming and all its children).

In my opinion it is worth it, as it allow to update FreeBSD in even
cleaner way - in ZFS-only configuration root file system is ZFS file
system with 'mountpoint' property set to 'legacy'. If root dataset is
named system/rootfs, we can snapshot it (system/rootfs@upgrade), clone
it (system/oldrootfs), update FreeBSD and if it doesn't boot we can
boot back from system/oldrootfs and rename it back to system/rootfs
while it is mounted as /. Before it was not possible, because
unmounting / was not possible.

Authored by: Pawel Jakub Dawidek <[email protected]>
Reviewed-by: Allan Jude <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Ported by: Matt Macy <[email protected]>
Signed-off-by: Ryan Moeller <[email protected]>
Closes #10839 

1 files changed, 23 insertions, 9 deletions

diff --git a/lib/libzfs/libzfs_dataset.c b/lib/libzfs/libzfs_dataset.c
index d548cc0ec..2c707f23f 100644
--- a/lib/libzfs/libzfs_dataset.c
+++ b/lib/libzfs/libzfs_dataset.c
@@ -4370,14 +4370,14 @@ zfs_rollback(zfs_handle_t *zhp, zfs_handle_t *snap, boolean_t force)
  * Renames the given dataset.
  */
 int
-zfs_rename(zfs_handle_t *zhp, const char *target, boolean_t recursive,
-    boolean_t force_unmount)
+zfs_rename(zfs_handle_t *zhp, const char *target, renameflags_t flags)
 {
 	int ret = 0;
 	zfs_cmd_t zc = {"\0"};
 	char *delim;
 	prop_changelist_t *cl = NULL;
 	char parent[ZFS_MAX_DATASET_NAME_LEN];
+	char property[ZFS_MAXPROPLEN];
 	libzfs_handle_t *hdl = zhp->zfs_hdl;
 	char errbuf[1024];
 
@@ -4429,7 +4429,7 @@ zfs_rename(zfs_handle_t *zhp, const char *target, boolean_t recursive,
 		if (!zfs_validate_name(hdl, target, zhp->zfs_type, B_TRUE))
 			return (zfs_error(hdl, EZFS_INVALIDNAME, errbuf));
 	} else {
-		if (recursive) {
+		if (flags.recursive) {
 			zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
 			    "recursive rename must be a snapshot"));
 			return (zfs_error(hdl, EZFS_BADTYPE, errbuf));
@@ -4470,8 +4470,19 @@ zfs_rename(zfs_handle_t *zhp, const char *target, boolean_t recursive,
 		return (zfs_error(hdl, EZFS_ZONED, errbuf));
 	}
 
-	if (recursive) {
-		zfs_handle_t *zhrp;
+	/*
+	 * Avoid unmounting file systems with mountpoint property set to
+	 * 'legacy' or 'none' even if -u option is not given.
+	 */
+	if (zhp->zfs_type == ZFS_TYPE_FILESYSTEM &&
+	    !flags.recursive && !flags.nounmount &&
+	    zfs_prop_get(zhp, ZFS_PROP_MOUNTPOINT, property,
+	    sizeof (property), NULL, NULL, 0, B_FALSE) == 0 &&
+	    (strcmp(property, "legacy") == 0 ||
+	    strcmp(property, "none") == 0)) {
+		flags.nounmount = B_TRUE;
+	}
+	if (flags.recursive) {
 		char *parentname = zfs_strdup(zhp->zfs_hdl, zhp->zfs_name);
 		if (parentname == NULL) {
 			ret = -1;
@@ -4479,7 +4490,8 @@ zfs_rename(zfs_handle_t *zhp, const char *target, boolean_t recursive,
 		}
 		delim = strchr(parentname, '@');
 		*delim = '\0';
-		zhrp = zfs_open(zhp->zfs_hdl, parentname, ZFS_TYPE_DATASET);
+		zfs_handle_t *zhrp = zfs_open(zhp->zfs_hdl, parentname,
+		    ZFS_TYPE_DATASET);
 		free(parentname);
 		if (zhrp == NULL) {
 			ret = -1;
@@ -4488,8 +4500,9 @@ zfs_rename(zfs_handle_t *zhp, const char *target, boolean_t recursive,
 		zfs_close(zhrp);
 	} else if (zhp->zfs_type != ZFS_TYPE_SNAPSHOT) {
 		if ((cl = changelist_gather(zhp, ZFS_PROP_NAME,
+		    flags.nounmount ? CL_GATHER_DONT_UNMOUNT :
 		    CL_GATHER_ITER_MOUNTED,
-		    force_unmount ? MS_FORCE : 0)) == NULL)
+		    flags.forceunmount ? MS_FORCE : 0)) == NULL)
 			return (-1);
 
 		if (changelist_haszonedchild(cl)) {
@@ -4513,7 +4526,8 @@ zfs_rename(zfs_handle_t *zhp, const char *target, boolean_t recursive,
 	(void) strlcpy(zc.zc_name, zhp->zfs_name, sizeof (zc.zc_name));
 	(void) strlcpy(zc.zc_value, target, sizeof (zc.zc_value));
 
-	zc.zc_cookie = recursive;
+	zc.zc_cookie = !!flags.recursive;
+	zc.zc_cookie |= (!!flags.nounmount) << 1;
 
 	if ((ret = zfs_ioctl(zhp->zfs_hdl, ZFS_IOC_RENAME, &zc)) != 0) {
 		/*
@@ -4523,7 +4537,7 @@ zfs_rename(zfs_handle_t *zhp, const char *target, boolean_t recursive,
 		(void) snprintf(errbuf, sizeof (errbuf), dgettext(TEXT_DOMAIN,
 		    "cannot rename '%s'"), zc.zc_name);
 
-		if (recursive && errno == EEXIST) {
+		if (flags.recursive && errno == EEXIST) {
 			zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
 			    "a child dataset already has a snapshot "
 			    "with the new name"));