linux-kernel - Re: [PATCH] [REGRESSION] ovl: Handle ENOSYS when fileattr support is missing in lower/upper fs

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Date:   Mon, 18 Jul 2022 19:23:11 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Christian Kohlschütter 
        <christian@...lschutter.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        overlayfs <linux-unionfs@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] [REGRESSION] ovl: Handle ENOSYS when fileattr support is
 missing in lower/upper fs

On Mon, 18 Jul 2022 at 16:25, Christian Kohlschütter
<christian@...lschutter.com> wrote:
>
> > Am 18.07.2022 um 15:13 schrieb Miklos Szeredi <miklos@...redi.hu>:

> > Correct.  The question is whether any application would break in this
> > case.  I think not, but you are free to prove otherwise.
> >
> > Thanks,
> > Miklos
>
> I'm not going to do that since I expect any answer I give would not change your position here. All I know is there is a non-zero chance such programs exist.

If you (or anyone) gave a real life example of an application relying
on e.g. ioctl(..., FS_IOC_SETFLAGS) returning ENOSYS, then I would
have no choice but to revert this change.

However I think that's highly unlikely given that such an application
would only have been tested on fuse filesystems and also given that
very few (if any) fuse filesystems support these ioctls in the first
place.

Thanks,
Miklos