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.

v6:
Moved creating new volume label dentry out of
exfat_get_volume_label_ptrs.
Use exfat_find_empty_entry to allocate new volume label dentry.
Better usage of hint_femp.
Use ALLOC_FAT_CHAIN in root directory.
Only allocate new volume label dentry when the label length > 0.
v5:
Change behavior to only allocate new cluster when no useable dentries
exist.
Leverage exfat_find_empty_entry to handle this behavior, and to set
inode size.
Update inode hint_femp to speed up later search efforts.
Link: https://lore.kernel.org/all/20250903183322.191136-1-ethan.ferguson@zetier.com/
v4:
Implement allocating a new cluster when the current dentry cluster would
be full as a result of inserting a volume label dentry.
Link: https://lore.kernel.org/all/20250822202010.232922-1-ethan.ferguson@zetier.com/
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.
Link: https://lore.kernel.org/all/20250821150926.1025302-1-ethan.ferguson@zetier.com/
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/dir.c       | 162 +++++++++++++++++++++++++++++++++++++++++++
 fs/exfat/exfat_fs.h  |   7 ++
 fs/exfat/exfat_raw.h |   6 ++
 fs/exfat/file.c      |  80 +++++++++++++++++++++
 fs/exfat/namei.c     |   2 +-
 5 files changed, 256 insertions(+), 1 deletion(-)

-- 
2.34.1