linux-kernel - Re: [PATCH] vfs: return EOPNOTSUPP when ioctl

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Message-ID: <CAG27Bk0qp_+eF5u6zXBBqgWXd8f48RYJOPJ88mTRigWEmsedNA@mail.gmail.com>
Date:   Mon, 19 Dec 2016 22:33:13 +0000
From:   Sami Kerola <kerolasa@....fi>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfs: return EOPNOTSUPP when ioctl_fsthaw() is not supported

On 19 December 2016 at 10:24, Christoph Hellwig <hch@...radead.org> wrote:
> On Sun, Dec 18, 2016 at 06:57:27PM +0000, Sami Kerola wrote:
>> An attempt to freeze a filesystem that does not support such operation is
>> reported as EOPNOTSUPP to user.  Running unfreeze to the same filesystem
>> returns EINVAL.  Later is a little misleading, users can mix that message
>> with return value from unfreezing when filesystem is not frozen.
>
> This is going to break gfs2 with it's odd ->that_super method.

Thank you for feedback, there's just one small problem with it.  I don't
quite understand the breakage.

Proposed change uses similar logic as ioctl_fsfreeze()[1] and it works fine.
If I am not entirely mistaking freeze and thaw hooks where added[2] to avoid
issues with gfs2.  And looking gfs2 super_operations init[3] does not make
me any wiser what might be wrong.

Maybe feedback had typo s/that_super/thaw_super/[4].  But even then it is
unclear to me how a null could cause breakage.

[1] https://github.com/torvalds/linux/blob/master/fs/ioctl.c#L553
[2] https://github.com/torvalds/linux/commit/48b6bca6b7b8309697fc8a101793befe92d249d9
[3] https://github.com/torvalds/linux/blob/master/fs/gfs2/super.c#L1683
[4] https://github.com/torvalds/linux/blob/master/fs/super.c#L1446

-- 
Sami Kerola
http://www.iki.fi/kerolasa/