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

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Date:	Tue, 17 May 2016 10:15:21 +0200
From:	Miklos Szeredi <mszeredi@...hat.com>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Vivek Goyal <vgoyal@...hat.com>, Daniel Axtens <dja@...ens.net>,
	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

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.

Thanks,
Miklos