linux-kernel - Re: [patch 4/8] fs, exportfs: Add export_encode_inode

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Date:	Mon, 20 Aug 2012 15:32:04 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	James Bottomley <jbottomley@...allels.com>,
	Matthew Helsley <matt.helsley@...il.com>
Subject: Re: [patch 4/8] fs, exportfs: Add export_encode_inode_fh helper

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@...nvz.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.
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