linux-kernel - Re: [PATCH 1/4] list: introduce list_is

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Message-ID: <20151210152357.GG29872@treble.redhat.com>
Date:	Thu, 10 Dec 2015 09:23:57 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Geliang Tang <geliangtang@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jan Kara <jack@...e.cz>, Josef Bacik <jbacik@...com>,
	Josh Triplett <josh@...htriplett.org>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Patrick McHardy <kaber@...sh.net>,
	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
	"David S. Miller" <davem@...emloft.net>,
	live-patching@...r.kernel.org, netfilter-devel@...r.kernel.org,
	coreteam@...filter.org, netdev@...r.kernel.org,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] list: introduce list_is_first()

On Thu, Dec 10, 2015 at 08:10:34AM -0700, Jens Axboe wrote:
> On 12/10/2015 07:17 AM, Geliang Tang wrote:
> >We already have list_is_last(), it makes sense to also add
> >list_is_first() for consistency. This list utility function
> >to check for first element in a list.
> 
> Honestly, I think we already have way too many of these kind of helpers.
> IMHO they don't really help, they hurt readability. You should know how the
> list works anyway, and if you do, then it's a no-brainer what's first and
> last. If you don't, then you are bound to screw up in other ways.
> 
> Just my 2 cents.

Personally I would disagree.  Something like:

  if (list_is_first(&rq->queuelist, &nd->queue))

is much more readable to me than:

  if (rq->queuelist.prev == &nd->queue)

The first one takes no effort for me -- it's almost English.  While the
second one takes me a few seconds (and some precious brain cycles) to
decipher.

Maybe whether it's readable depends on how many years you've been
looking at the pattern.  But IMHO we shouldn't make "having x # of years
staring at kernel code" a prerequisite for being able to read kernel
code.

-- 
Josh
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