Re: [PATCH v11 00/15] Exposing case folding behavior

["Chuck Lever" <cel@kernel.org>]

On Mon, Apr 27, 2026, at 6:55 AM, Jan Kara wrote:
> On Fri 24-04-26 21:53:02, Chuck Lever wrote:
>> Changes since v10:
>> - cifs: Source case-handling flags from the server's cached
>>   FS_ATTRIBUTE_INFORMATION reply instead of the nocase mount
>>   option, with a nocase fallback when the reply is absent
>> - Address findings from sashiko(gemini-3) and gpt-5.5:
>>   - nfs: Skip pathconf case bits on NFSv4 (set via FATTR4_CASE_*
>>     instead)
>>   - xfs: Hide FS_CASEFOLD_FL from the legacy flags view so
>>     chattr round-trips do not hit the setflags whitelist
>>   - ext4, f2fs: Drop redundant fileattr_get patches; the
>>     FS_CASEFOLD_FL translation in fileattr_fill_flags() already
>>     reports FS_XFLAG_CASEFOLD for casefolded directories
>
> Err, how is this supposed to work? I wasn't able to find any code
> transforming S_CASEFOLDED inode flag into FS_CASEFOLD_FL on fileattr_get
> path. Sure, fileattr_fill_flags() takes care of setting FS_XFLAG_CASEFOLD
> once FS_CASEFOLD_FL is set. What am I missing?

Agreed, that is a little surprising.

The path does not go through S_CASEFOLD.  Both filesystems
report FS_CASEFOLD_FL straight from their on-disk flag word.

For ext4, EXT4_CASEFOLD_FL is 0x40000000, the same bit value
as FS_CASEFOLD_FL, and it is included in EXT4_FL_USER_VISIBLE.
ext4_iget() loads it into ei->i_flags directly from
raw_inode->i_flags (fs/ext4/inode.c:5358). ext4_fileattr_get()
then masks with EXT4_FL_USER_VISIBLE and hands the result to
fileattr_fill_flags(), which translates FS_CASEFOLD_FL into
FS_XFLAG_CASEFOLD on the way out.

For f2fs, f2fs_fileattr_get() runs fi->i_flags through
f2fs_iflags_to_fsflags(), whose mapping table has an explicit
{ F2FS_CASEFOLD_FL, FS_CASEFOLD_FL } entry (fs/f2fs/file.c:2205).
F2FS_GETTABLE_FS_FL includes FS_CASEFOLD_FL, so
fileattr_fill_flags() again lights up FS_XFLAG_CASEFOLD.

S_CASEFOLD is a separate VFS-level cache that
ext4_set_inode_flags() and f2fs's equivalent set at iget
time; nothing on the fileattr_get path consults it.

For reference, the original observation about the manual
assignment being redundant came from sashiko's review of v10:

  https://sashiko.dev/#/patchset/20260423-case-sensitivity-v10-0-c385d674a6cf%40oracle.com?part=8                                             
  https://sashiko.dev/#/patchset/20260423-case-sensitivity-v10-0-c385d674a6cf%40oracle.com?part=12  


-- 
Chuck Lever