netdev - Re: [PATCH] list.h: add list_for_each_struct

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Message-Id: <1263835033.3667.23.camel@achroite.uk.solarflarecom.com>
Date:	Mon, 18 Jan 2010 17:17:13 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Jiri Pirko <jpirko@...hat.com>
Cc:	linux-kernel@...r.kernel.org, davem@...emloft.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH] list.h: add list_for_each_struct_entry macro

On Mon, 2010-01-18 at 17:23 +0100, Jiri Pirko wrote:
> When preparing to upcoming migration of mc_list (list of multicast MACs)
> to list_head, the need of traversing the list over one structure member
> appeared. I thought I'll do it locally but I decided that an intruduction
> the macro in list.h would be much clearer. Please kindly for a review.
> 
> Jirka
> 
> Signed-off-by: Jiri Pirko <jpirko@...hat.com>
> 
> diff --git a/include/linux/list.h b/include/linux/list.h
> index 969f6e9..8350a94 100644
> --- a/include/linux/list.h
> +++ b/include/linux/list.h
> @@ -420,6 +420,22 @@ static inline void list_splice_tail_init(struct list_head *list,
>  	     pos = list_entry(pos->member.prev, typeof(*pos), member))
>  
>  /**
> + * list_for_each_struct_entry  -       iterate over list of given type using
> + *                                     the struct member.
> + * @pos:       the type * to use as a loop cursor.
> + * @head:      the head for your list.
> + * @type:      the type of the struct.
> + * @posmember: the name ot the loop cursor within the struct.
> + * @member:    the name of the list_struct within the struct.
> + */
> +#define list_for_each_struct_entry(pos, head, type, posmember, member)		\
> +	for (pos = list_entry((head)->next, type, member)->posmember;		\

Surely &list_entry(...)->posmember ?

> +	     prefetch(container_of(pos, type, posmember)->member.next),		\
> +	     &container_of(pos, type, posmember)->member != (head);		\

It seems a bit dodgy to do this pointer arithmetic on a list node which
might be the list head.

> +	     pos = list_entry(container_of(pos, type, posmember)->member.next,	\
> +	     type, member)->posmember)

My version:

#define list_for_each_struct_entry(pos, head, type, posmember, member)	     \
	for (pos = list_empty(head) ? NULL :				     \
		&list_first_entry(head, type, member)->posmember;	     \
	     prefetch(container_of(pos, type, posmember)->member.next), pos; \
	     pos = list_is_last(&container_of(pos, type, posmember)->member, \
				head) ?	NULL :				     \
		&list_entry(container_of(pos, type, posmember)->member.next, \
			    type, member)->posmember)

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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