lkml.org 
[lkml]   [2022]   [Jul]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH] ovl: Handle ENOSYS when fileattr support is missing in lower/upper fs
On Mon, 18 Jul 2022 at 12:10, Christian Kohlschütter
<christian@kohlschutter.com> wrote:
>
> > Am 18.07.2022 um 11:14 schrieb Miklos Szeredi <miklos@szeredi.hu>:
> >
> > On Mon, 4 Jul 2022 at 20:36, Christian Kohlschütter
> > <christian@kohlschutter.com> wrote:
> >>
> >> overlayfs may fail to complete updates when a filesystem lacks
> >> fileattr/xattr syscall support and responds with an ENOSYS error code,
> >> resulting in an unexpected "Function not implemented" error.
> >
> > Issue seems to be with fuse: nothing should be returning ENOSYS to
> > userspace except the syscall lookup code itself. ENOSYS means that
> > the syscall does not exist.
> >
> > Fuse uses ENOSYS in the protocol to indicate that the filesystem does
> > not support that operation, but that's not the value that the
> > filesystem should be returning to userspace.
> >
> > The getxattr/setxattr implementations already translate ENOSYS to
> > EOPNOTSUPP, but ioctl doesn't.
> >
> > The attached patch (untested) should do this. Can you please give it a try?
> >
> > Thanks,
> > Miklos
> > <fuse-ioctl-translate-enosys.patch>
>
> Yes, that change basically has the same effect for the demo use case,.
>
> However: it will change (and potentially) break assumptions in user space. We should never break user space.
>
> Example: lsattr /test/lower
> Currently, fuse returns ENOSYS, e.g.
> > lsattr: reading ./lost+found: Function not implemented
> With your change, it would return ENOTTY
> > lsattr: reading ./lost+found: Not a tty

No, it would return success.

> I also tried the setup (without patches) on a very old 4.4.176 system, and everything works fine. ovl introduced the regression, so it should also be fixed there.
> It may affect other filing systems as well (I see some other fs also return ENOSYS on occasion).
>
> It's safe to say that adding the ENOSYS to the ovl code is probably the best move. Besides, you already have a workaround for ntfs-3g there as well.

Flawed arguments. The change in overlayfs just made the preexisting
bug in fuse visible. The bug should still be fixed in fuse.

Thanks,
Miklos

\
 
 \ /
  Last update: 2022-07-18 12:33    [W:2.053 / U:0.344 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site