linux-kernel - Re: [RFD 1/4] Pass no useless nameidata to the create, lookup, and permission IOPs

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Date:	Sat, 30 Jun 2007 10:13:02 +0100
From:	Christoph Hellwig <hch@...radead.org>
To:	jjohansen@...e.de
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, Andreas Gruenbacher <agruen@...e.de>
Subject: Re: [RFD 1/4] Pass no useless nameidata to the create, lookup, and permission IOPs

On Tue, Jun 26, 2007 at 04:15:11PM -0700, jjohansen@...e.de wrote:
> The create, lookup, and permission inode operations are all passed a
> full nameidata.  This is unfortunate because in nfsd and the mqueue
> filesystem, we must instantiate a struct nameidata but cannot provide
> all of the same information that a regular lookup would provide.  The
> unused fields take up space on the stack, but more importantly, it is
> not obvious which fields have meaningful values and which don't, and so
> things might easily break.
> 
> This patch introduces struct nameidata2 with only the fields that make
> sense independent of an actual lookup, and uses that struct in those
> places where a full nameidat is not needed.

We need something like this, but I don't quite like the way you've done
it.  First the name is wrong, it's not a nameidata anymore but a lookup
intent, so it should be named that way, struct lookup_intent.  Second
the macro hackery is more than ugly,  please keep the structures separate.
With modern gcc it might be possible to embed the lookup_intent into
the nameidata anonymously.  Also please either remove the dentry from
struct lookup_entry or from the direct argument list of the functions
and methods - there is no need to pass this one twice.

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