Missing LIST_PREV() ?

[Giorgos Keramidas]

On 2007-05-05 16:17, Hans Petter Selasky <hselasky at c2i.net> wrote:
> Hi,
> 
> Why should LISTs only be forward traversable? The following piece of code make 
> lists backward traversable:
> 
> /sys/sys/queue.h:
> 
> +#define LIST_PREV(head,elm,field) \
> +  (((elm) == LIST_FIRST(head)) ? ((__typeof(elm))0) : \
> +   ((__typeof(elm))(((uint8_t *)((elm)->field.le_prev)) - \
> +                   ((uint8_t *)&LIST_NEXT((__typeof(elm))0,field)))))
> 
> Any comments?

1. The use of (uint8_t *) casts is relatively ugly.

2. What does LIST_PREV give us that cannot be done with TAILQ_PREV()
   already?