Combining list_for_each and list_entry

[Kristian Hogsberg]

Hi,

Everywhere in the kernel where list_for_each is used, you typically
find a list_entry as the first statement in the loop body, e.g.:

	list_for_each(tmp, &runqueue_head) {
		p = list_entry(tmp, struct task_struct, run_list);
		if (can_schedule(p, this_cpu)) {
			int weight = goodness(p, this_cpu, prev->active_mm);
			if (weight > c)
				c = weight, next = p;
		}
	}

I came up with the following idea to combine the two:

#define list_iterate(lh, head, elm, link)				     \
	for (lh = (head)->next;						     \
	     lh != (head) &&						     \
	       (elm = list_entry(lh, typeof(*elm), link), lh = lh->next, 1);)

Now you can say

	list_iterate(tmp, &runqueue_head, p, run_list) {
		if (can_schedule(p, this_cpu)) {
			int weight = goodness(p, this_cpu, prev->active_mm);
			if (weight > c)
				c = weight, next = p;
		}
	}

and since lh is update at the beginning of the loop, list_iterate is
automatically safe, i.e. you can remove the current element while
looping.

How about it?

regards,
Kristian