linux-kernel - Re: [PATCH 3/7] nfsd: remove redundant i

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Date:	Sun, 24 Jul 2016 15:23:07 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	"J. Bruce Fields" <bfields@...hat.com>,
	Oleg Drokin <green@...uxhacker.ru>,
	Jeff Layton <jlayton@...chiereds.net>,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] nfsd: remove redundant i_lookup check

On Sun, Jul 24, 2016 at 08:10:14AM -0400, J. Bruce Fields wrote:
> On Sun, Jul 24, 2016 at 01:22:06AM +0100, Al Viro wrote:
> > On Fri, Jul 22, 2016 at 01:48:52PM -0400, J. Bruce Fields wrote:
> > > From: "J. Bruce Fields" <bfields@...hat.com>
> > > 
> > > I'm not sure why this was added.  It doesn't seem necessary, and no
> > > other caller does this.
> > 
> > lookup_one_len() will explode if you call it for non-directory (==
> > !d_can_lookup(), i.e. something without ->lookup()).  So unless the callers
> > do guarantee that check being true, it *is* needed.
> 
> Both callers call fh_verify(.,.,S_IFDIR,.), so at this point we know
> that i_mode & S_IFMT == S_IFDIR.  Is there some odd case where that's
> insufficient?  If so, I think there may be bugs elsewhere in nfsd.  If
> not, I'll add a note to the changelog.

First of all, such objects do exist; they probably won't be encountered by
nfsd and all instances I can think of are not writable, but...

> Thanks for reminding me to check this, I hadn't thought of that as an
> "is this a directory" check, it makes more sense now.

I'd have turned that into d_can_lookup(fhp->fh_dentry), actually.