nilfs2: add support for FS_IOC_GETUUID

nilfs2: add support for FS_IOC_GETUUID

Patch series "nilfs2: add support for some common ioctls".

This series adds support for common ioctls to nilfs2 for getting the
volume UUID and the relative path of an FS instance within the sysfs
namespace, and also implements ioctls for nilfs2 to get and set the volume
label.

This patch (of 2):

Expose the UUID of a file system instance using the super_set_uuid helper
and support the FS_IOC_GETUUID ioctl.

Link: https://lkml.kernel.org/r/20240815074408.5550-1-konishi.ryusuke@gmail.com
Link: https://lkml.kernel.org/r/20240815074408.5550-2-konishi.ryusuke@gmail.com
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>