Subject: Re: [PATCH] VFS: Suppress automount on [l]stat, [l]getxattr, etc.
From: Ian Kent <raven@themaw.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Howells <dhowells@redhat.com>, miklos@szeredi.hu,
        viro@zeniv.linux.org.uk, jlayton@redhat.com, gregkh@suse.de,
        linux-nfs@vger.kernel.org, leonardo.lists@gmail.com
In-Reply-To: <CA+55aFxGxv5DGAQcgn1avwUcW1xZVvz1VEajF6zT5HHiVEsJ2w@mail.gmail.com>
References: <20110922134510.24683.14576.stgit@warthog.procyon.org.uk>
	 <1316707443.3346.44.camel@perseus.themaw.net>
	 <CA+55aFxGxv5DGAQcgn1avwUcW1xZVvz1VEajF6zT5HHiVEsJ2w@mail.gmail.com>
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Date: Fri, 23 Sep 2011 00:45:35 +0800
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Sender: linux-nfs-owner@vger.kernel.org
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On Thu, 2011-09-22 at 09:30 -0700, Linus Torvalds wrote:
> On Thu, Sep 22, 2011 at 9:04 AM, Ian Kent <raven@themaw.net> wrote:
> >
> > I haven't checked what the side effects would be but using the
> > LOOKUP_DIRECTORY flag in walks that get caught by the removal of the
> > LOOKUP_FOLLOW test in follow_automount() and retaining Miklos's original
> > patch is probably a more natural solution IMO.
> 
> Ok, I do have to agree with that.
> 
> So instead of adding a new flag, let's just document a few *logical*
> rules for what causes auto-mounting:
> 
>  - opening the mount-point itself with LOOKUP_DIRECTORY does so
> 
>    Logic: when you use LOOKUP_DIRECTORY, you expect to see the
> *contents* of the mount-point.
> 
>  - looking something up *under* the mount-point does so.
> 
>    This may be obvious, but it actually has a non-obvious special
> case: what about the pathname "mountpoint" vs "mountpoint/"
> 
> And I think the "LOOKUP_DIRECTORY" rule ends up automatically also
> resolving that special case: when we have a slash at the end of the
> last component, it not only implies that we care about the contents,
> it will also automatically set LOOKUP_DIRECTORY.
> 
> So I'm getting more and more convinced that LOOKUP_DIRECTORY is
> actually the right thing to trigger on. It automatically means that
> "opendir()" on the mountpoint will do the right thing (because
> O_DIRECTORY results in LOOKUP_DIRECTORY), and it automatically - and
> very naturally - gives user processes the ability to choose whether
> they want to see auto-monting or not ("path" doesn't get auto-mounted,
> but "path/" does).
> 
> Yet at the same time it keeps the "stupid default behavior for
> processes that only look at each directory entry and don't even think
> about automounting" be the "don't auto-mount when not necessary"
> behavior.
> 
> So: no new flag. Just make nfs4 use LOOKUP_DIRECTORY, and let's add
> big documentation notes about this.

Yes, that's what I think is best.

It's late here so I'll survey the code and see if I can find any other
instances of this and post a patch, tomorrow.

Jeff, could you test adding LOOKUP_DIRECTORY to the walk in
nfs_follow_remote_path() please, just in case I've got this all wrong.

> 
> Ok?
> 
>                      Linus