Subject: Re: [PATCH] VFS: Suppress automount on [l]stat, [l]getxattr, etc.
From: Ian Kent <raven@themaw.net>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jeff Layton <jlayton@redhat.com>, David Howells <dhowells@redhat.com>,
        viro@zeniv.linux.org.uk, gregkh@suse.de, linux-nfs@vger.kernel.org,
        leonardo.lists@gmail.com
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Date: Fri, 23 Sep 2011 18:57:09 +0800
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Sender: linux-nfs-owner@vger.kernel.org
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On Fri, 2011-09-23 at 09:25 +0200, Miklos Szeredi wrote:
> Trond Myklebust <Trond.Myklebust@netapp.com> writes:
> 
> > On Thu, 2011-09-22 at 18:04 -0700, Linus Torvalds wrote: 
> >> On Thu, Sep 22, 2011 at 5:56 PM, Myklebust, Trond
> >> <Trond.Myklebust@netapp.com> wrote:
> >> >
> >> > Your assumption is that in the majority of cases, we do _not_ want to
> >> > automount the final directory unless we know that we are expecting a
> >> > directory.
> >> 
> >> Umm. That is the assumption yes, BUT THAT IS ALSO THE CURRENT STATE.
> >> 
> >> So it's more than an assumption. It's a fact.
> >> 
> >> So when you call it "assumption", you are basically ignoring and
> >> trying to belittle current reality. Why?
> >
> > AFAICR, the whole point of doing the ->automount() stuff was to fix what
> > was perceived to be a broken situation in which the application was more
> > often than not seeing the properties of a directory which it would
> > _never_ directly access.
> 
> We are pitting one set of applications against another.  There's no
> Right(TM) behavior here.  In any case there will be applications which
> will behave strangely, be extremely slow, etc...
> 
> Changing the behavior of stat will cause regressions.  Period.  If we
> just fixed up those apps which behave badly with the old kernels, there
> wouldn't be any regressions.

That's the point isn't it.

Your patch changes the pre-exiting behavior of NFS and probably CIFS and
AFS, but restores the pre-existing behavior of autofs, which is
something I've wanted to change for years.

My suggestion of using LOOKUP_DIRECTORY at path walk sites that need it
is still a possibility. I'm still looking through path walk call sites.
But that resolution will still leave NFS et.al. with LOOKUP_FOLLOW only
calls having changed semantic behavior.

There is no resolution to this that will satisfy everyone. Passing on
the lookup flags is, I think, the only way to segregate the sub system
behaviors and I'm not in favor of that either.

Ian