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

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Message-ID: <adak5uppqft.fsf@cisco.com>
Date:	Wed, 30 May 2007 21:28:22 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	Pete Zaitcev <zaitcev@...hat.com>
Cc:	"Satyam Sharma" <satyam.sharma@...il.com>,
	"Matthias Kaehlcke" <matthias.kaehlcke@...il.com>,
	linux-usb-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/block/ub.c: use list_for_each_entry()

 > > If I just see
 > > 
 > > 	for (pos = list_entry((head)->next, typeof(*pos), member),
 > > 		n = list_entry(pos->member.next, typeof(*pos), member);
 > > 	     &pos->member != (head);
 > > 	     pos = n, n = list_entry(n->member.next, typeof(*n), member))
 > > 
 > > then what am I to think?
 > 
 > You won't catch me writing this kind of crap, so the question is moot.
 > Seriously, a comma operator? Admit it, you just expanded a marcro from
 > list.h by hand. Real people cannot write like that.

Of course I admit it, that is a copy of the definition of list_for_each_safe()
(with just the '/'s removed).  But the point is, if you are writing
something that iterates through a list and deletes entries, you
basically have to write equivalent code.

Just think about how many silly bugs you've written in your life when
(re)implementing linked lists.  By using <linux/list.h>, you avoid all
that, and as a code reviewer that makes my life easier.  It's the same
theory as <linux/kref.h> -- the code is rather trivial (although as
"git log lib/kref.c" shows, not entirely trivial).  But if I see
someone using struct kref, all I have to check is whether she used it
correctly.  I don't have to worry about whether she screwed up the
implementation.

 - R.
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