linux-kernel - Re: 45aebeaf4f67 "ovl: Ensure upper filesystem supports d

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Message-ID: <20160516130727.GA26411@redhat.com>
Date:	Mon, 16 May 2016 09:07:27 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Daniel Axtens <dja@...ens.net>
Cc:	linux-fsdevel@...r.kernel.org, linux-unionfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, mpe@...erman.id.au,
	mszeredi@...hat.com, dchinner@...hat.com
Subject: Re: 45aebeaf4f67 "ovl: Ensure upper filesystem supports d_type"
 breaking Docker

On Mon, May 16, 2016 at 04:45:09PM +1000, Daniel Axtens wrote:
> Hi,
> 
> I installed a fresh 4.6.0 kernel on my ppc64le system, and tried to run
> a docker container. It failed.
> 
> Docker gave me errors like this:
> 
> docker: Error response from daemon: error creating overlay mount to /var/lib/docker/overlay/2bc07cedad2770da2f384d5c1e81a6f45fa3c44a7658f10d02e5973ef76620fc-init/merged: invalid argument.
> 
> In dmesg, I'm seeing:
> 
> overlayfs: upper fs needs to support d_type.
> 

Hi Daniel,

What't the underlying fs you are using. overlayfs requires underlying
filesystem to support d_type and there were cases where xfs was
built with ftype=0 and in that case xfs does not support d_type. That
means it led to issues like whiteouts not being recognized and being
left behind during various operations.

So it became clear that we need a check at mount time to make sure
d_type is supported otherwise error out. This will require users to
do mkfs.xfs with ftype=1 to make progress.

I think new defaults for mkfs.xfs are such that ftype=1 is set. I am
not sure which version that change was made in.

Thanks
Vivek

> Reverting 45aebeaf4f67 ("ovl: Ensure upper filesystem supports d_type")
> fixes the issue for me. I haven't investigated the root cause yet - at a
> guess I'd say either Docker's layering system, or some weird interaction
> with namespacing, maybe? I'll have a look when I get a spare moment.
> 
> For reference, I'm using docker 1.11.0-dev.
> 
> Regards,
> Daniel Axtens