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

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Message-ID: <20100524115903.GP31073@ZenIV.linux.org.uk>
Date:	Mon, 24 May 2010 12:59:03 +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 Mon, May 24, 2010 at 04:57:56PM +1000, Neil Brown wrote:
> 
> Commit 1f36f774b22a0ceb7dd33eca626746c81a97b6a5 broke FS_REVAL_DOT semantics.
> 
> In particular, before this patch, the command
>    ls -l
> in an NFS mounted directory would always check if the directory on the server
> had changed and if so would flush and refill the pagecache for the dir.
> After this patch, the same "ls -l" will repeatedly return stale date until
> the cached attributes for the directory time out.
> 
> The following patch fixes this by ensuring the d_revalidate is called by
> do_last when "." is being looked-up.
> link_path_walk has already called d_revalidate, but in that case LOOKUP_OPEN
> is not set so nfs_lookup_verify_inode chooses not to do any validation.
> 
> The following patch restores the original behaviour.
> 
> Cc: stable@...nel.org
> Signed-off-by: NeilBrown <neilb@...e.de>

Applied, but I really don't like the way you do it; note that e.g. foo/bar/.
gets that revalidation as well, for no good reason.  If anything, shouldn't
we handle that thing in the _beginning_ of pathname resolution, not in
the end?  For now it'd do, and it's a genuine regression, but...

BTW, here's a question for nfs client folks: is it true that for any two
pathnames on _client_ resolving to pairs (mnt1, dentry) and (mnt2, dentry)
resp., nfs_devname(mnt1, dentry, ...) and nfs_devname(mnt2, dentry, ...)
should yield the strings that do not differ past the ':' (i.e. that the
only possible difference is going to be in spelling the server name)?
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