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

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Message-ID: <87eg906nwm.fsf@gamma.ozlabs.ibm.com>
Date:	Wed, 18 May 2016 13:33:13 +1000
From:	Daniel Axtens <dja@...ens.net>
To:	Vivek Goyal <vgoyal@...hat.com>,
	Miklos Szeredi <mszeredi@...hat.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-unionfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	mpe@...erman.id.au, dchinner@...hat.com
Subject: Re: 45aebeaf4f67 "ovl: Ensure upper filesystem supports d_type" breaking Docker

Hi Vivek,

My sincere apologies - it turns out I *was* running on xfs with
ftype=0. Someone in the office had moved docker's storage without
me noticing.

Apologies to all whose time I wasted.

Regards,
Daniel

Vivek Goyal <vgoyal@...hat.com> writes:

> On Tue, May 17, 2016 at 10:15:21AM +0200, Miklos Szeredi wrote:
>> On Tue, May 17, 2016 at 8:28 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
>> > On Mon, May 16, 2016 at 09:07:27AM -0400, Vivek Goyal wrote:
>> >> 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.
>> >
>> > Dumb question - can we end up with empty workdir at that point?  Because
>> > if we do, the check would appear to return a false negative, no matter
>> > what fs supports...
>> 
>> ovl_workdir_create() creates a subdirectory of workdir ("work") so
>> workdir itself won't be empty after that.  If somebody else messes
>> with workdir, then we are screwed anyway.
>
> Right. Initially I was creating a directory of my own and later realized
> that ovl_workdir_create() already creates one.
>
> Having said that, what happens when ovl_workdir_create() fails and we
> mount overlayfs read only. In that case I think we will conclude that
> underlying fs does not support d_type and mounting will fail.
>
> Any thoughts, on how to handle this failure path better?
>
> Daniel,
>
> Yesterday Eric Sandeen told me that I can run "xfs_info <mount-point>" to
> figure out if ftype is 0 or 1. You might want to run "xfs_info /" and 
> ensure ftype=0 in your case and overlay is not detecting it wrong.
>
> Thanks
> Vivek