linux-kernel - Re: [PATCH] UBIFS: fill f

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Date:	Tue, 02 Sep 2008 22:26:09 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Andreas Dilger <adilger@....com>,
	Artem Bityutskiy <dedekind@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Adrian Hunter <ext-adrian.hunter@...ia.com>
Subject: Re: [PATCH] UBIFS: fill f_fsid

On Tue, 2008-09-02 at 17:02 -0400, Christoph Hellwig wrote:
> On Tue, Sep 02, 2008 at 11:09:54AM -0600, Andreas Dilger wrote:
> > The fsid is supposed to be a persistent, unique identifier for the
> > filesystem, used by NFS in file handles.  Using st_dev is unsafe,
> > because that may change from one server boot to the next, because
> > of device probing order, driver changes, etc.  Also, not all filesystems
> > HAVE a valid st_dev in the first place, which is the whole reason
> > for this thread.
> > 
> > I think a ->get_fsid() export method would be preferable.
> 
> Umm, different things.  f_fsid in stat(v)fs is just a cookie exported to
> userspac that has never really been documented.
> 
> We also called the filesystem part of the NFS filehandle in a few
> places, and for those it's correct that it should be stable.  Currently
> the fsid is either created from the dev_t in kernelspace or from
> uuids extracted through libuuid in userspace.

Or from the f_fsid returned in statfs(), as of a week or so ago.

> I can't see anything in the message that started this thread that
> mentions NFS, btw.

That was Artem's motivation for filling in f_fsid in the first place.
Does anything else even _care_ about f_fsid? 

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@...el.com                              Intel Corporation



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