Creating subvolumes and snapshots is one of the core features of btrfs and is even available to unprivileged users. Make it possible to use subvolume and snapshot creation on idmapped mounts. This is a fairly straightforward operation since all the permission checking helpers are already capable of handling idmapped mounts. So we just need to pass down the mount's userns. Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>