Introduce REMOVE_NEXT() macro's for SLIST and STAILQ.

Even though single linked lists allow items to be removed at constant time
(when the previous element is known), the queue macro's don't allow this.
Implement new REMOVE_NEXT() macro's. Because the REMOVE() macro's also
contain the same code, make it call REMOVE_NEXT().

The OpenBSD version of SLIST_REMOVE_NEXT() needs a reference to the list
head, even though it is unused. We'd better mimic this. The STAILQ version
also needs a reference to the list. This means the prototypes of both
macro's are the same.

Approved by:	philip (mentor)
PR:		kern/121117

1 files changed, 14 insertions, 5 deletions

diff --git a/sys/sys/queue.h b/sys/sys/queue.h
index eefd620..3a0a354 100644
--- a/sys/sys/queue.h
+++ b/sys/sys/queue.h
@@ -97,6 +97,7 @@
  * _INSERT_TAIL			-	-	+	+
  * _CONCAT			-	-	+	+
  * _REMOVE_HEAD			+	-	+	-
+ * _REMOVE_NEXT			+	-	+	-
  * _REMOVE			+	+	+	+
  *
  */
@@ -195,12 +196,16 @@ struct {								\
 		struct type *curelm = SLIST_FIRST((head));		\
 		while (SLIST_NEXT(curelm, field) != (elm))		\
 			curelm = SLIST_NEXT(curelm, field);		\
-		SLIST_NEXT(curelm, field) =				\
-		    SLIST_NEXT(SLIST_NEXT(curelm, field), field);	\
+		SLIST_REMOVE_NEXT(head, curelm, field);			\
 	}								\
 	TRASHIT((elm)->field.sle_next);					\
 } while (0)
 
+#define SLIST_REMOVE_NEXT(head, elm, field) do {				\
+	SLIST_NEXT(elm, field) =					\
+	    SLIST_NEXT(SLIST_NEXT(elm, field), field);			\
+} while (0)
+
 #define	SLIST_REMOVE_HEAD(head, field) do {				\
 	SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);	\
 } while (0)
@@ -287,9 +292,7 @@ struct {								\
 		struct type *curelm = STAILQ_FIRST((head));		\
 		while (STAILQ_NEXT(curelm, field) != (elm))		\
 			curelm = STAILQ_NEXT(curelm, field);		\
-		if ((STAILQ_NEXT(curelm, field) =			\
-		     STAILQ_NEXT(STAILQ_NEXT(curelm, field), field)) == NULL)\
-			(head)->stqh_last = &STAILQ_NEXT((curelm), field);\
+		STAILQ_REMOVE_NEXT(head, curelm, field);		\
 	}								\
 	TRASHIT((elm)->field.stqe_next);				\
 } while (0)
@@ -300,6 +303,12 @@ struct {								\
 		(head)->stqh_last = &STAILQ_FIRST((head));		\
 } while (0)
 
+#define STAILQ_REMOVE_NEXT(head, elm, field) do {			\
+	if ((STAILQ_NEXT(elm, field) =					\
+	     STAILQ_NEXT(STAILQ_NEXT(elm, field), field)) == NULL)	\
+		(head)->stqh_last = &STAILQ_NEXT((elm), field);		\
+} while (0)
+
 /*
  * List declarations.
  */