[Devel] Re: [PATCH][NETNS] Use list_for_each_entry_continue_reverse in setup_net

[Eric W. Biederman]

Pavel Emelyanov <xemul at openvz.org> writes:

> I proposed introducing a list_for_each_entry_continue_reverse
> macro to be used in setup_net() when unrolling the failed
> ->init callback.
>
> Here is the macro and some more cleanup in the setup_net() itself
> to remove one variable from the stack :) Minor, but the code
> looks nicer.
>
> Signed-off-by: Pavel Emelyanov <xemul at openvz.org>
> Acked-by: "Eric W. Biederman" <ebiederm at xmission.com>

Pavel if you are going down this route.  Could you look at
cleanup_net as well.  The reverse walk there could probably
benefit from being list_for_each_entry_reverse.

Eric


>
> ---
>
>  include/linux/list.h     |   14 ++++++++++++++
>  net/core/net_namespace.c |    8 +++-----
>  2 files changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/list.h b/include/linux/list.h
> index f29fc9c..ad9dcb9 100644
> --- a/include/linux/list.h
> +++ b/include/linux/list.h
> @@ -525,6 +525,20 @@ static inline void list_splice_init_rcu(
>  	     pos = list_entry(pos->member.next, typeof(*pos), member))
>  
>  /**
> + * list_for_each_entry_continue_reverse - iterate backwards from the given
> point
> + * @pos:	the type * to use as a loop cursor.
> + * @head:	the head for your list.
> + * @member:	the name of the list_struct within the struct.
> + *
> + * Start to iterate over list of given type backwards, continuing after
> + * the current position.
> + */
> +#define list_for_each_entry_continue_reverse(pos, head, member) \
> +	for (pos = list_entry(pos->member.prev, typeof(*pos), member);	\
> +	     prefetch(pos->member.prev), &pos->member != (head);	\
> +	     pos = list_entry(pos->member.prev, typeof(*pos), member))
> +
> +/**
>   * list_for_each_entry_from - iterate over list of given type from the current
> point
>   * @pos:	the type * to use as a loop cursor.
>   * @head:	the head for your list.
> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
> index 1fc513c..a9dd261 100644
> --- a/net/core/net_namespace.c
> +++ b/net/core/net_namespace.c
> @@ -102,7 +102,6 @@ static int setup_net(struct net *net)
>  {
>  	/* Must be called with net_mutex held */
>  	struct pernet_operations *ops;
> -	struct list_head *ptr;
>  	int error;
>  
>  	memset(net, 0, sizeof(struct net));
> @@ -110,8 +109,7 @@ static int setup_net(struct net *net)
>  	atomic_set(&net->use_count, 0);
>  
>  	error = 0;
> -	list_for_each(ptr, &pernet_list) {
> -		ops = list_entry(ptr, struct pernet_operations, list);
> +	list_for_each_entry(ops, &pernet_list, list) {
>  		if (ops->init) {
>  			error = ops->init(net);
>  			if (error < 0)
> @@ -120,12 +118,12 @@ static int setup_net(struct net *net)
>  	}
>  out:
>  	return error;
> +
>  out_undo:
>  	/* Walk through the list backwards calling the exit functions
>  	 * for the pernet modules whose init functions did not fail.
>  	 */
> -	for (ptr = ptr->prev; ptr != &pernet_list; ptr = ptr->prev) {
> -		ops = list_entry(ptr, struct pernet_operations, list);
> +	list_for_each_entry_continue_reverse(ops, &pernet_list, list) {
>  		if (ops->exit)
>  			ops->exit(net);
>  	}