linux-kernel - Re: [PATCH 05/16] nfs: don't open in ->d

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Date:	Wed, 28 Mar 2012 21:45:18 +0000
From:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
To:	Miklos Szeredi <miklos@...redi.hu>
CC:	"viro@...IV.linux.org.uk" <viro@...IV.linux.org.uk>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hch@...radead.org" <hch@...radead.org>,
	"sfrench@...ba.org" <sfrench@...ba.org>,
	"sage@...dream.net" <sage@...dream.net>,
	"ericvh@...il.com" <ericvh@...il.com>,
	"mszeredi@...e.cz" <mszeredi@...e.cz>
Subject: Re: [PATCH 05/16] nfs: don't open in ->d_revalidate

On Wed, 2012-03-28 at 22:24 +0200, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@...e.cz>
> 
> NFSv4 can't do reliable opens in d_revalidate, since it cannot know whether a
> mount needs to be followed or not.  It does check d_mountpoint() on the dentry,
> which can result in a weird error if the VFS found that the mount does not in
> fact need to be followed, e.g.:
> 
>   # mount --bind /mnt/nfs /mnt/nfs-clone
>   # echo something > /mnt/nfs/tmp/bar
>   # echo x > /tmp/file
>   # mount --bind /tmp/file /mnt/nfs-clone/tmp/bar
>   # cat  /mnt/nfs/tmp/bar
>   cat: /mnt/nfs/tmp/bar: Not a directory
> 
> Which should, by any sane filesystem, result in "something" being printed.
> 
> So instead do the open in f_op->open() and in the unlikely case that the cached
> dentry turned out to be invalid, drop the dentry and return ESTALE to let the
> VFS retry.


Just one comment. Would it now make sense for NFSv4 to just skip
->d_revalidate() if LOOKUP_OPEN is set, and LOOKUP_EXCL is not set? We
will in any case be doing a revalidation in nfs4_file_open.

Otherwise, the rest all looks good to me.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com