linux-kernel - Re: Q: (stupid) can't we "fix" hlist_for_each

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Message-ID: <20080312125348.GA1487@linux.vnet.ibm.com>
Date:	Wed, 12 Mar 2008 05:53:48 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org
Subject: Re: Q: (stupid) can't we "fix" hlist_for_each_entry() ?

On Wed, Mar 12, 2008 at 11:12:01AM +0300, Oleg Nesterov wrote:
> hlist_for_each_entry/hlist_for_each_entry_rcu doesn't actually need 4
> arguments, it could be
> 
> #define hlist_for_each_entry_rcu(pos, head, member)		 			\
> 	for (pos = hlist_entry((head)->first, typeof(*(pos)), member);			\
> 	     rcu_dereference(pos) != hlist_entry(NULL, typeof(*(pos)), member) &&	\
> 		({ prefetch((pos)->member.next); 1; });					\
> 	     (pos) = hlist_entry((pos)->member.next, typeof(*(pos)), member))
> 
> Or,
> 
> #define hlist_for_each_entry_rcu(pos, head, member)		 			\
> 	for (pos = (void*)(head)->first;						\
> 	     rcu_dereference(pos) && ({ prefetch(((hlist_node*)pos)->next); 1; }) &&	\
> 		({ (pos) = hlist_entry((void*)(pos), typeof(*(pos)), member)); 1; });	\
> 	     (pos) = (void*)(pos)->member.next)
> 
> Q: is it worth "fixing" ?

I have already come out in favor: http://lwn.net/Articles/262464/
answer to Quick Quiz 3.  ;-)

The first option above looks more straightforward to me.

> If yes, what is the "right" way to do this? These macros are spread all over
> the kernel...

Peter's approach looked reasonable to me.

							Thanx, Paul
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