From mboxrd@z Thu Jan  1 00:00:00 1970
From: "J. Bruce Fields" <bfields@fieldses.org>
Subject: Re: [patch 4/8] fs, exportfs: Add export_encode_inode_fh helper
Date: Mon, 20 Aug 2012 15:32:04 -0400
Message-ID: <20120820193204.GD5779@fieldses.org>
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 <20120820183225.GB4911@fieldses.org>
 <20120820190606.GE27443@moon>
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Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	Al Viro <viro@zeniv.linux.org.uk>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Pavel Emelyanov <xemul@parallels.com>,
	James Bottomley <jbottomley@parallels.com>,
	Matthew Helsley <matt.helsley@gmail.com>
To: Cyrill Gorcunov <gorcunov@openvz.org>
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On Mon, Aug 20, 2012 at 11:06:06PM +0400, Cyrill Gorcunov wrote:
> On Mon, Aug 20, 2012 at 02:32:25PM -0400, J. Bruce Fields wrote:
> > On Mon, Aug 20, 2012 at 08:33:38PM +0400, Cyrill Gorcunov wrote:
> > > On Mon, Aug 20, 2012 at 07:49:23PM +0530, Aneesh Kumar K.V wrote:
> > > > Cyrill Gorcunov <gorcunov@openvz.org> writes:
> > > > 
> > > > > To provide fsnotify object inodes being watched without
> > > > > binding to alphabetical path we need to encode them with
> > > > > exportfs help. This patch adds a helper which operates
> > > > > with plain inodes directly.
> > > > 
> > > > doesn't name_to_handle_at()  work for you ? It also allows to get a file
> > > > handle using file descriptor.
> > > 
> > > Hi, sorry for dealy. Well, the last idea is to get rid of this helper,
> > > I've sent out an updated version where ino+dev is only printed.
> > 
> > I don't understand how ino and dev are useful to you, though, if you're
> > still hoping to be able to look up inodes using this information later
> > on.
> 
> Hi Bruce, I believe having ino+dev is better than nothing. Otherwise we
> simply have no clue which targets are bound to inotify mark. Sometime
> (!) we can try to generate fhandle in userspace from this ino+dev bundle
> and then open the target file.

That's insufficient to generate a filehandle in general.

(Also: there's the usual inode-number aliasing problem: the inode number
could get reused by another file.  Unless you know the file is being
held open the whole time.)

--b.