linux-kernel - Re: [PATCH] drivers/block/ub.c: use list_for_each

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Message-Id: <20070530160850.0c536d55.zaitcev@redhat.com>
Date:	Wed, 30 May 2007 16:08:50 -0700
From:	Pete Zaitcev <zaitcev@...hat.com>
To:	"Satyam Sharma" <satyam.sharma@...il.com>
Cc:	"Matthias Kaehlcke" <matthias.kaehlcke@...il.com>, axboe@...nel.dk,
	linux-usb-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] drivers/block/ub.c: use list_for_each_entry()

On Thu, 31 May 2007 02:44:17 +0530, "Satyam Sharma" <satyam.sharma@...il.com> wrote:

> > > -     list_for_each(p, &sc->luns) {
> > > -             lun = list_entry(p, struct ub_lun, link);
> > > +     list_for_each_entry(lun, &sc->luns, link) {

> > This patch straddles the border of acceptable. The pointless obfuscation
> > is balanced against the removal of explicit type in list_entry() and thus
> > a possible mismatched struct. I'm not acking nor naking this.
> 
> A list_for_each() followed by list_entry() ---> list_for_each_entry()
> conversion is a pretty harmless (and desirable) conversion, IMO.
> In fact list_for_each_entry() itself uses list_entry(..., typeof(*p), ...)
> which seems to be a safer way to use list_entry() than specifying
> the type explicity/manually in its arguments, no?

I believe I have mentioned the type safety as a positive, and in fact
it's quoted above. I just didn't think it necessary to use quite as
many words explaining it until now.

The negative is the sheer number of helper functions in list.h. Personally,
I find it difficult to retain a working knowledge of them. Iterators are
particularly nasty that way. I'm thinking about dropping all of these
list_for_each_with_murky_argument_requirements_and_odd_side_effects()
and use plain for(;;), as a courtesy to someone who has to read the
code years down the road.

-- Pete
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