Re: [PATCH 4/4] ovl: Expose the filesystem encoding through sysfs

[Gabriel Krisman Bertazi <krisman@suse.de>]

Amir Goldstein <amir73il@gmail.com> writes:

> On Mon, Sep 28, 2026 at 11:32 PM Gabriel Krisman Bertazi
> <krisman@suse.de> wrote:

> I am not ok with this API.
> It is wrong in several ways.
> It is not generic, we have already file_getattr() to get casefold status.
> There was a suggestion by Pali [1] to get the supported xflags - statx style,
> which can be a way to say if a fs could return FS_XFLAG_CASEFOLD.
> In Chuck's v2 [2] FILEATTR_CASEFOLD_TYPE was already suggested
> as an extension to file_getattr(). I think we can still do that if we include
> proper versioning in the casefold type.

Ok. I'm not fond of the overlay part of this series at all, in
particular due to the major:minor design.  I was looking for an
alternative way to do it and didn't find it, thus /sys/fs.

> TBH, I don't think anyone requested this - you only mentioned
> the need to know if tmpfs was mounted with casefold on and that
> doesn't mean that etx4/ovl patches are justified, but ext4 can decide
> for themselves.

There is a need for a proper probing API when deciding to fallback to
userspace casefolding workarounds, and that is not shmem specific at
all.  I'm sure the Wine folks that right now use ext4/overlayfs will
also benefit from a smarter way to fetch the information.

> The point is that this sysfs is not going to be the standard for all the
> fs that can return the FS_XFLAG_CASEFOLD, so I see no reason
> to add this sysfs interface to ovl.

Ack.  I'll drop patches 3 and 4 and wait on ext4 people to see if they want
patch 2 to match f2fs. Will also keep an eye on FS_XFLAG_CASEFOLD.

> Thanks,
> Amir.
>
> [1] https://lore.kernel.org/linux-fsdevel/20250216164029.20673-4-pali@kernel.org/
> [2] https://lore.kernel.org/linux-fsdevel/20251211152116.480799-2-cel@kernel.org/

-- 
Gabriel Krisman Bertazi