From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Aneesh Kumar K. V" <aneesh.kumar@linux.vnet.ibm.com>
Subject: Re: [PATCH -V18 04/13] vfs: Allow handle based open on symlinks
Date: Tue, 24 Aug 2010 16:04:32 +0530
Message-ID: <m3lj7wjo3r.fsf@linux.vnet.ibm.com>
References: <1282269097-26166-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1282269097-26166-5-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <20100820083057.GA10039@infradead.org> <20100820195303.20b17210@notabene> <20100820115135.GQ31363@ZenIV.linux.org.uk> <20100821100900.4b15fe08@notabene> <20100821083024.GB3448@amd> <m3zkwgqp3c.fsf@linux.vnet.ibm.com> <20100824072155.GA3948@amd>
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Cc: Nick Piggin <npiggin@kernel.dk>, Neil Brown <neilb@suse.de>,
	Al Viro <viro@ZenIV.linux.org.uk>,
	Christoph Hellwig <hch@infradead.org>, adilger@sun.com,
	corbet@lwn.net, hooanon05@yahoo.co.jp, bfields@fieldses.org,
	miklos@szeredi.hu, linux-fsdevel@vger.kernel.org,
	sfrench@us.ibm.com, philippe.deniel@CEA.FR,
	linux-kernel@vger.kernel.org
To: Nick Piggin <npiggin@kernel.dk>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <20100824072155.GA3948@amd>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: linux-fsdevel.vger.kernel.org

On Tue, 24 Aug 2010 17:21:55 +1000, Nick Piggin <npiggin@kernel.dk> wrote:
> On Sat, Aug 21, 2010 at 03:12:15PM +0530, Aneesh Kumar K. V wrote:
> > On Sat, 21 Aug 2010 18:30:24 +1000, Nick Piggin <npiggin@kernel.dk> wrote:
> > > Thanks, I had both of the same concerns as Christoph with API
> > > change and exposing symlink fds last time I looked at the patces,
> > > actually.
> > > 
> > > But they can probably be worked around or avoided. I think the more
> > > important thing is whether it is worth supporting. This is
> > > all restricted to root (or CAP_DAC_READ_SEARCH) only, right, and
> > > what exact semantics they want. I would like to see more discussion
> > > of what this enables and some results.
> > > 
> > > For the case of avoiding expensive network revalidations in path name
> > > lookup, do we even need to open symlinks? Could the security issues be
> > > avoided by always having handle attached to an open fd?
> > > 
> > 
> > For implementing a userspace file server that use handle for
> > representing files (like NFS) we would require to have the ability to do
> > different file system operations that can operate on symlink to work on
> > handle too. 
> 
> Right. Is this a really important goal, I'm wondering? Is it realistic
> (ie. to be able to remove the nfs server from the kernel)?
> 

The feature is also needed to implement a 9p virtio pass through file
system in Qemu http://thread.gmane.org/gmane.comp.emulators.qemu/68992

-aneesh