Issue: With an OverlayFS that has Btrfs as the upper layer, removal of directories silently fails

Issue: With an OverlayFS that has Btrfs as the upper layer, removal of directories silently fails

[Neal Gompa]

Hello,

For those who have received this message twice already, I sincerely apologize.

Yesterday I filed an issue in the CentOS bug tracker (#9297[1]) and
the Red Hat Bugzilla (#1255512[2]) about OverlayFS with Btrfs as the
upper layer.

The issue was discovered by a colleague of mine, and we verified the
issue exists in the EL7 kernel and mainline kernels (tested on Arch
Linux). I additionally verified the problem exists in Fedora kernels.

Rather than quoting the issue, I'll just note that the issue is
described quite well in the filed bugs noted earlier. In the linked
bugs, there's a simple Bash script that will reliably reproduce the
problem. While the script uses tmpfs at the lower layer, we originally
discovered the problem with ext4 as the lower layer and verified that
it doesn't matter which lower layer filesystem it is, the problem
exists. Additionally, the problem doesn't exist when using ext4 as the
upper layer.

I was advised by Josh Boyer to email you guys (and the mailing lists,
to be sure to get everyone a chance to look over it) about the
problem, since it affects mainline.

[1]: https://bugs.centos.org/view.php?id=9297
[2]: https://bugzilla.redhat.com/show_bug.cgi?id=1255512

-- 
Neal Gompa (FAS: ngompa)

Re: Issue: With an OverlayFS that has Btrfs as the upper layer, removal of directories silently fails

[Miklos Szeredi]

On Fri, Aug 21, 2015 at 9:23 PM, Neal Gompa <ngompa@fedoraproject.org> wrote:
> Hello,
>
> For those who have received this message twice already, I sincerely apologize.
>
> Yesterday I filed an issue in the CentOS bug tracker (#9297[1]) and
> the Red Hat Bugzilla (#1255512[2]) about OverlayFS with Btrfs as the
> upper layer.
>
> The issue was discovered by a colleague of mine, and we verified the
> issue exists in the EL7 kernel and mainline kernels (tested on Arch
> Linux). I additionally verified the problem exists in Fedora kernels.
>
> Rather than quoting the issue, I'll just note that the issue is
> described quite well in the filed bugs noted earlier. In the linked
> bugs, there's a simple Bash script that will reliably reproduce the
> problem. While the script uses tmpfs at the lower layer, we originally
> discovered the problem with ext4 as the lower layer and verified that
> it doesn't matter which lower layer filesystem it is, the problem
> exists. Additionally, the problem doesn't exist when using ext4 as the
> upper layer.
>
> I was advised by Josh Boyer to email you guys (and the mailing lists,
> to be sure to get everyone a chance to look over it) about the
> problem, since it affects mainline.
>
> [1]: https://bugs.centos.org/view.php?id=9297
> [2]: https://bugzilla.redhat.com/show_bug.cgi?id=1255512

AFAICS btrfs doesn't support RENAME_EXCHANGE and RENAME_WHITEOUT.
These flags are needed for any filesystem that wants to be a fully
functional  overlayfs upper layer.

Thanks,
Miklos

Issue: With an OverlayFS that has Btrfs as the upper layer, removal of directories silently fails

[Neal Gompa]

[-- Attachment #1: Type: text/plain, Size: 1152 bytes --]

Hello,

Yesterday I filed an issue in the CentOS bug tracker (#9297
<https://bugs.centos.org/view.php?id=9297>) and the Red Hat Bugzilla (
#1255512 <https://bugzilla.redhat.com/show_bug.cgi?id=1255512>) about
OverlayFS with Btrfs as the upper layer.

The issue was discovered by a colleague of mine, and we verified the issue
exists in the EL7 kernel and mainline kernels (tested on Arch Linux). I
additionally verified the problem exists in Fedora kernels.

Rather than quoting the issue, I'll just note that the issue is described
quite well in the filed bugs linked earlier. In the linked bugs, there's a
simple Bash script that will reliably reproduce the problem. While the
script uses tmpfs at the lower layer, we originally discovered the problem
with ext4 as the lower layer and verified that it doesn't matter which
lower layer filesystem it is, the problem exists. Additionally, the problem
doesn't exist when using ext4 as the upper layer.

I was advised by Josh Boyer to email you guys (and the mailing lists, to be
sure to get everyone a chance to look over it) about the problem, since it
affects mainline.


-- 
Neal Gompa (FAS: ngompa)

[-- Attachment #2: Type: text/html, Size: 1853 bytes --]