Merge tag 'fs.move_mount.move_mount_set_group.v5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

Pull move_mount updates from Christian Brauner:
 "This contains an extension to the move_mount() syscall making it
  possible to add a single private mount into an existing propagation
  tree.

  The use-case comes from the criu folks which have been struggling with
  restoring complex mount trees for a long time. Variations of this work
  have been discussed at Plumbers before, e.g.

      https://www.linuxplumbersconf.org/event/7/contributions/640/

  The extension to move_mount() enables criu to restore any set of mount
  namespaces, mount trees and sharing group trees without introducing
  yet more complexity into mount propagation itself.

  The changes required to criu to make use of this and restore complex
  propagation trees are available at

      https://github.com/Snorch/criu/commits/mount-v2-poc

  A cleaned-up version of this will go up for merging into the main criu
  repo after this lands"

* tag 'fs.move_mount.move_mount_set_group.v5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  tests: add move_mount(MOVE_MOUNT_SET_GROUP) selftest
  move_mount: allow to add a mount into an existing group

include/uapi/linux/mount.h

@@ -73,7 +73,8 @@
 #define MOVE_MOUNT_T_SYMLINKS		0x00000010 /* Follow symlinks on to path */
 #define MOVE_MOUNT_T_AUTOMOUNTS		0x00000020 /* Follow automounts on to path */
 #define MOVE_MOUNT_T_EMPTY_PATH		0x00000040 /* Empty to path permitted */
-#define MOVE_MOUNT__MASK		0x00000077
+#define MOVE_MOUNT_SET_GROUP		0x00000100 /* Set sharing group instead */
+#define MOVE_MOUNT__MASK		0x00000177
 
 /*
  * fsopen() flags.