linux-kernel - Re: [PATCH -V18 04/13] vfs: Allow handle based open on symlinks

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Message-ID: <m3lj7wjo3r.fsf@linux.vnet.ibm.com>
Date:	Tue, 24 Aug 2010 16:04:32 +0530
From:	"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Nick Piggin <npiggin@...nel.dk>
Cc:	Nick Piggin <npiggin@...nel.dk>, Neil Brown <neilb@...e.de>,
	Al Viro <viro@...IV.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>, adilger@....com,
	corbet@....net, hooanon05@...oo.co.jp, bfields@...ldses.org,
	miklos@...redi.hu, linux-fsdevel@...r.kernel.org,
	sfrench@...ibm.com, philippe.deniel@....FR,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V18 04/13] vfs: Allow handle based open on symlinks

On Tue, 24 Aug 2010 17:21:55 +1000, Nick Piggin <npiggin@...nel.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@...nel.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

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