From: Miklos Szeredi <miklos@szeredi.hu>
Subject: Re: xattr hash error in 4.13-rc with overlayfs over ext4
Date: Thu, 27 Jul 2017 21:36:20 +0200
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Cc: "Theodore Ts'o" <tytso@mit.edu>,
        "linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>,
        linux-fsdevel@vger.kernel.org, lkml <linux-kernel@vger.kernel.org>,
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To: Tahsin Erdogan <tahsin@google.com>
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On Thu, Jul 27, 2017 at 9:28 PM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> On Thu, Jul 27, 2017 at 8:20 PM, Tahsin Erdogan <tahsin@google.com> wrote:
>> Hi Miklos,
>> I made a first attempt to reproduce the failure but did not get lucky.
>>
>>> Inode 3093, i_blocks is 16, should be 8.  Fix<y>? yes
>> Does this inode correspond to foo, bar or a preexisting file?

The inode in question corresponds to the copy-up of bar into upper.

There's quite a lot overlayfs does in this apparently simple
operation, and that's probably why I've not been able to reproduce
without overlayfs (although admittedly I didn't try very hard).

It's basically the following:

 - create tempfile
 - copy data from lower/bar to work/index/XXX  using reflink
 - copy metadata
 - set trusted.overlay.origin xattr
 - set trusted.overlay.nlink xattr
 - hardlink index file to upper/bar
 - overwrite trusted.overlay.nlink with different value

And ther's also some attr and xattr setting going on for the upper directory.

Thanks,
Miklos