linux-kernel - Re: [PATCH -V14 04/11] vfs: Allow handle based open on symlinks

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Date:	Thu, 8 Jul 2010 02:57:19 +1000
From:	Nick Piggin <npiggin@...e.de>
To:	"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	hch@...radead.org, viro@...iv.linux.org.uk, adilger@....com,
	corbet@....net, serue@...ibm.com, neilb@...e.de,
	hooanon05@...oo.co.jp, bfields@...ldses.org,
	linux-fsdevel@...r.kernel.org, sfrench@...ibm.com,
	philippe.deniel@....FR, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V14 04/11] vfs: Allow handle based open on symlinks

On Wed, Jul 07, 2010 at 09:54:52PM +0530, Aneesh Kumar K. V wrote:
> On Thu, 8 Jul 2010 01:23:03 +1000, Nick Piggin <npiggin@...e.de> wrote:
> > On Tue, Jun 15, 2010 at 10:42:54PM +0530, Aneesh Kumar K.V wrote:
> > > The patch update may_open to allow handle based open on symlinks.
> > > The file handle based API use file descritor returned from open_by_handle_at
> > > to do different file system operations. To find the link target name we
> > > need to get a file descriptor on symlinks.
> > 
> > This is a pretty big change, isn't it?
> 
> Yes
> 
> > Have you looked through vfs to
> > ensure this is actually OK? I was just looking at remount,ro code, for
> > example, and it seems to assume only writable open files on ISREG
> > files.
> 
> I verified that write and read returns an error on that descriptor. I
> will look at rest of code to ensure the it doesn't break assumptions in
> the rest of VFS.
> 
> > 
> > Is this restricted to RDONLY? Really, it should be O_NONE...
> > 
> > 
> 
> we need the interface so that we can do fstat(lstat) and readlink using the
> handle. If we are against the idea of allowing an fd on symlink, how about
> adding stat_by_handle and readlink_by_handle syscall ? That way we can
> drop "vfs: Support null pathname in readlink" patch 

It would be nice to avoid introducing open files to symlinks, but
I don't know about really the *right* thing to do though. I think
avoiding adding any by-handle syscalls except for open by handle
may be a good idea... OTOH if this is really a special case for
handles...

I haven't followed this thread closely, so can you just go back
and explain to me why you need this? Ie. that you can't achieve with
a path-to-handle follow/nofollow option.


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