Re: btrfs+overlayfs: upper fs does not support xattr, falling back to index=off and metacopy=off.

[Chris Murphy <lists@colorremedies.com>]

On Sat, Apr 10, 2021 at 11:55 AM Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Sat, Apr 10, 2021 at 8:36 PM Chris Murphy <lists@colorremedies.com> wrote:
> >
> > I can reproduce the bolt testcase problem in a podman container, with
> > overlay driver, using ext4, xfs, and btrfs. So I think I can drop
> > linux-btrfs@ from this thread.
> >
> > Also I can reproduce the title of this thread simply by 'podman system
> > reset' and see the kernel messages before doing the actual reset. I
> > have a strace here of what it's doing:
> >
> > https://drive.google.com/file/d/1L9lEm5n4-d9qemgCq3ijqoBstM-PP1By/view?usp=sharing
> >
>
> I'm confused. The error in the title of the page is from overlayfs mount().
> I see no mount in the strace.
> I feel that I am missing some info.
> Can you provide the overlayfs mount arguments
> and more information about the underlying layers?

Not really? There are none if a container isn't running, and in this
case no containers are running, in fact there are no upper or lower
dirs because I had already reset podman before doing 'strace podman
system reset' - I get the kernel message twice every time I merely do
'podman system reset'

overlayfs: upper fs does not support xattr, falling back to index=off
and metacopy=off
overlayfs: upper fs does not support xattr, falling back to index=off
and metacopy=off

This part of the issue might be something of a goose chase. I don't
know if it's relevant or distracting.


> > Yep. I think tmpfs supports xattr but not user xattr? And this example
> > is rootless podman, so it's all unprivileged.
> >
>
> OK, so unprivileged overlayfs mount support was added in v5.11
> and it requires opt-in with mount option "userxattr", which could
> explain the problem if tmpfs is used as upper layer.
>
> Do you know if that is the case?
> I sounds to me like it may not be a kernel regression per-se,
> but a regression in the container runtime that started to use
> a new kernel feature?
> Need more context to understand.
>
> Perhaps the solution will be to add user xattr support to tmpfs..

$ sudo mount -o remount,userxattr /home
mount: /home: mount point not mounted or bad option.

[   92.573364] BTRFS error (device sda6): unrecognized mount option 'userxattr'

/home is effectively a bind mount because it is backed by a btrfs subvolume...

/dev/sda6 on /home type btrfs
(rw,noatime,seclabel,compress=zstd:1,ssd,space_cache=v2,subvolid=586,subvol=/home)

...which is mounted via fstab using -o subvol=home

Is it supported to remount,userxattr? If not then maybe this is needed:

rootflags=subvol=root,userxattr


-- 
Chris Murphy