Add support for reading / writing to the exfat volume label from the
FS_IOC_GETFSLABEL and FS_IOC_SETFSLABEL ioctls.

Implemented in similar ways to other fs drivers, namely btrfs and ext4,
where the ioctls are performed on file inodes.

NOTE: I have not implemented allocating a new cluster in this patch.
This is because I am having trouble with using exfat_alloc_cluster.
I have submitted this patch so that while I debug this error, I can
receive comments on the rest of my changes. Any pointers in the right
direction would be appreciated!

v3:
Add lazy-loading of volume label into superblock.
Use better UTF-16 conversions to detect invalid characters.
If no volume label entry exists, overwrite a deleted dentry,
or create a new dentry if the cluster has space.
v2:
Fix endianness conversion as reported by kernel test robot
Link: https://lore.kernel.org/all/20250817003046.313497-1-ethan.ferguson@zetier.com/
v1:
Link: https://lore.kernel.org/all/20250815171056.103751-1-ethan.ferguson@zetier.com/

Ethan Ferguson (1):
  exfat: Add support for FS_IOC_{GET,SET}FSLABEL

 fs/exfat/exfat_fs.h  |   3 +
 fs/exfat/exfat_raw.h |   6 ++
 fs/exfat/file.c      |  78 ++++++++++++++++++
 fs/exfat/super.c     | 190 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 277 insertions(+)

-- 
2.34.1