[paging] Simplify the last request and treat llist as a queue

The current code was overly complex. It tried to iterate over
the list in a round robin and we had to keep track of the last
element, see if we remove that one, check if the list becomes
empty... This can all replaced by treating the double linked
list as a queue. We take the item at the front, do something
on it and then and then put it back to the list at the end.

2 files changed, 9 insertions, 35 deletions

diff --git a/openbsc/include/openbsc/gsm_data.h b/openbsc/include/openbsc/gsm_data.h
index 8dfa5886b..ef0b50768 100644
--- a/openbsc/include/openbsc/gsm_data.h
+++ b/openbsc/include/openbsc/gsm_data.h
@@ -368,7 +368,6 @@ struct gsm_paging_request {
 struct gsm_bts_paging_state {
 	/* pending requests */
 	struct llist_head pending_requests;
-	struct gsm_paging_request *last_request;
 	struct gsm_bts *bts;
 
 	struct timer_list work_timer;
diff --git a/openbsc/src/paging.c b/openbsc/src/paging.c
index 2ae3fc6bf..ece71ca7f 100644
--- a/openbsc/src/paging.c
+++ b/openbsc/src/paging.c
@@ -70,14 +70,6 @@ static unsigned int calculate_group(struct gsm_bts *bts, struct gsm_subscriber *
 static void paging_remove_request(struct gsm_bts_paging_state *paging_bts,
 				struct gsm_paging_request *to_be_deleted)
 {
-	/* Update the last_request if that is necessary */
-	if (to_be_deleted == paging_bts->last_request) {
-		paging_bts->last_request =
-			(struct gsm_paging_request *)paging_bts->last_request->entry.next;
-		if (&to_be_deleted->entry == &paging_bts->pending_requests)
-			paging_bts->last_request = NULL;
-	}
-
 	bsc_del_timer(&to_be_deleted->T3113);
 	llist_del(&to_be_deleted->entry);
 	subscr_put(to_be_deleted->subscr);
@@ -103,14 +95,6 @@ static void page_ms(struct gsm_paging_request *request)
 			request->chan_type);
 }
 
-static void paging_move_to_next(struct gsm_bts_paging_state *paging_bts)
-{
-	paging_bts->last_request =
-		(struct gsm_paging_request *)paging_bts->last_request->entry.next;
-	if (&paging_bts->last_request->entry == &paging_bts->pending_requests)
-		paging_bts->last_request = NULL;
-}
-
 /*
  * This is kicked by the periodic PAGING LOAD Indicator
  * coming from abis_rsl.c
@@ -128,7 +112,6 @@ static void paging_handle_pending_requests(struct gsm_bts_paging_state *paging_b
 	 * return then.
 	 */
 	if (llist_empty(&paging_bts->pending_requests)) {
-		paging_bts->last_request = NULL;
 		/* since the list is empty, no need to reschedule the timer */
 		return;
 	}
@@ -147,12 +130,8 @@ static void paging_handle_pending_requests(struct gsm_bts_paging_state *paging_b
 		paging_bts->available_slots = 20;
 	}
 
-	if (!paging_bts->last_request)
-		paging_bts->last_request =
-			(struct gsm_paging_request *)paging_bts->pending_requests.next;
-
-	assert(paging_bts->last_request);
-	initial_request = paging_bts->last_request;
+	initial_request = llist_entry(paging_bts->pending_requests.next,
+				      struct gsm_paging_request, entry);
 	current_request = initial_request;
 
 	do {
@@ -160,17 +139,13 @@ static void paging_handle_pending_requests(struct gsm_bts_paging_state *paging_b
 		page_ms(current_request);
 		paging_bts->available_slots--;
 
-		/*
-		 * move to the next item. We might wrap around
-		 * this means last_request will be NULL and we just
-		 * call paging_page_to_next again. It it guranteed
-		 * that the list is not empty.
-		 */
-		paging_move_to_next(paging_bts);
-		if (!paging_bts->last_request)
-			paging_bts->last_request =
-				(struct gsm_paging_request *)paging_bts->pending_requests.next;
-		current_request = paging_bts->last_request;
+		/* take the current and add it to the back */
+		llist_del(&current_request->entry);
+		llist_add_tail(&current_request->entry, &paging_bts->pending_requests);
+
+		/* take the next request */
+		current_request = llist_entry(paging_bts->pending_requests.next,
+					      struct gsm_paging_request, entry);
 	} while (paging_bts->available_slots > 0
 		    &&  initial_request != current_request);