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

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Date:	Sun, 24 Jul 2016 08:10:14 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Al Viro <viro@...IV.linux.org.uk>
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 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.

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.

--b.