linux-kernel - Re: [PATCH] VFS: fix recent breakage of FS_REVAL

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Message-ID: <20100525015822.GV31073@ZenIV.linux.org.uk>
Date:	Tue, 25 May 2010 02:58:22 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Neil Brown <neilb@...e.de>
Cc:	Trond Myklebust <trond.myklebust@....uio.no>,
	Chuck Lever <chuck.lever@...cle.com>,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] VFS: fix recent breakage of FS_REVAL_DOT

On Tue, May 25, 2010 at 11:14:05AM +1000, Neil Brown wrote:

> I must confess though that I don't feel I understand VFS name lookup properly
> any more.  Since intents were added it seems to have become much more obscure
> and complex.  I cannot help thinking that there must be a better way:
> distinguish between the various cases at a higher level so we don't need as
> many flags being passed around and interpreted by widely separate pieces of
> code.  I don't have a concrete proposal but I would certainly be interested
> to work on one if there were any hope of real change.
> Thoughts?

Intents are vile crap that has been introduced by the nfs folks to start
with...  I've been trying to localize the mess and it's got a _lot_ better
than it used to be a year ago, but they are still not gone.  And yes, I
plan to kill that crap.  Basically, most of the do_last() guts will become
a method that would get struct file *explicitly* and ask the fs to do
(possibly atomic) open.  With normal filesystems defaulting to what's there
right now.

The main obstacle at the moment is in ->d_revalidate() abuses.  NFS, CIFS
*and* autofs, the last one in a way that isn't really compatible with what
NFS et.al. are trying to do.  Overloading of ->d_revalidate() and ->lookup()
to do the work of open() doesn't help, and the horrors nfs4 piles on top
of that are even scarier.

_Another_ fine piece of something is ->follow_link() abuses, including
referrals' treatment.  Also tied to the previous messes.

We definitely will need to get VFS-to-fs APIs in that area changed; most of
the mess has been created by the deeply misguided efforts to keep the API
changes minimal.

As for the flags, quite a few will be gone once we split "opening the final
component" from the normal cases.  Google for lookup_instantiate_filp+shit
for details of these plans...
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