Date: Sat, 24 Sep 2011 07:36:10 -0400
From: Jeff Layton <jlayton@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ian Kent <raven@themaw.net>, Miklos Szeredi <miklos@szeredi.hu>,
        David Howells <dhowells@redhat.com>,
        Trond Myklebust <Trond.Myklebust@netapp.com>, viro@zeniv.linux.org.uk,
        gregkh@suse.de, linux-nfs@vger.kernel.org, leonardo.lists@gmail.com
Subject: Re: [PATCH] VFS: Suppress automount on [l]stat, [l]getxattr, etc.
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On Fri, 23 Sep 2011 18:44:59 -0700
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Fri, Sep 23, 2011 at 6:30 PM, Ian Kent <raven@themaw.net> wrote:
> >
> > Perhaps, but that allows modules to circumvent VFS policy which is what
> > allowed this situation to come up in the first place.
> 
> So, realistically, what's the downside of just adding LOOKUP_DIRECTORY
> (or LOOKUP_OPEN) to the nfs_follow_remote_path() case?
> 

There's certainly no danger in adding LOOKUP_DIRECTORY to that call. We
are, after all, looking for a directory there.

The problem is that that does not fully fix the NFS regression. NFS
(and CIFS) has always allowed the automounting of submounts to trigger
on stat() -- this is both before and after the d_automount patches went
in. Miklos' patch changes this.

The problem really boils down to this:

The d_automount patches changed autofs' automount trigger behavior to
be like that of NFS and CIFS. Miklos' patch reverts the behavior of
autofs to pre-2.6.38 behavior, but it also changes NFS and CIFS in the
same way, which is also a regression.

If you want to go back to pre-2.6.38 behavior, then you really have no
choice but to do re-introduce filesystem-specific behavior for
automounting. The behavior of autofs was different from that of
NFS and CIFS in earlier kernels.

-- 
Jeff Layton <jlayton@redhat.com>