[Midnightbsd-cvs] src [8372] trunk: implement LIST_PREV

[laffer1 at midnightbsd.org]

Revision: 8372
          http://svnweb.midnightbsd.org/src/?rev=8372
Author:   laffer1
Date:     2016-09-18 15:05:19 -0400 (Sun, 18 Sep 2016)
Log Message:
-----------
implement LIST_PREV

Modified Paths:
--------------
    trunk/share/man/man3/Makefile
    trunk/share/man/man3/queue.3
    trunk/sys/sys/param.h
    trunk/sys/sys/queue.h

Modified: trunk/share/man/man3/Makefile
===================================================================
--- trunk/share/man/man3/Makefile	2016-09-18 19:04:32 UTC (rev 8371)
+++ trunk/share/man/man3/Makefile	2016-09-18 19:05:19 UTC (rev 8372)
@@ -52,6 +52,7 @@
 		queue.3 LIST_INSERT_BEFORE.3 \
 		queue.3 LIST_INSERT_HEAD.3 \
 		queue.3 LIST_NEXT.3 \
+		queue.3 LIST_PREV.3 \
 		queue.3 LIST_REMOVE.3 \
 		queue.3 LIST_SWAP.3 \
 		queue.3 SLIST_EMPTY.3 \

Modified: trunk/share/man/man3/queue.3
===================================================================
--- trunk/share/man/man3/queue.3	2016-09-18 19:04:32 UTC (rev 8371)
+++ trunk/share/man/man3/queue.3	2016-09-18 19:05:19 UTC (rev 8372)
@@ -32,7 +32,7 @@
 .\"	@(#)queue.3	8.2 (Berkeley) 1/24/94
 .\" $MidnightBSD$
 .\"
-.Dd May 13, 2011
+.Dd Sep 12, 2012
 .Dt QUEUE 3
 .Os
 .Sh NAME
@@ -81,6 +81,7 @@
 .Nm LIST_INSERT_BEFORE ,
 .Nm LIST_INSERT_HEAD ,
 .Nm LIST_NEXT ,
+.Nm LIST_PREV ,
 .Nm LIST_REMOVE ,
 .Nm LIST_SWAP ,
 .Nm TAILQ_CONCAT ,
@@ -155,6 +156,7 @@
 .Fn LIST_INSERT_BEFORE "TYPE *listelm" "TYPE *elm" "LIST_ENTRY NAME"
 .Fn LIST_INSERT_HEAD "LIST_HEAD *head" "TYPE *elm" "LIST_ENTRY NAME"
 .Fn LIST_NEXT "TYPE *elm" "LIST_ENTRY NAME"
+.Fn LIST_PREV "TYPE *elm" "LIST_HEAD *head" "TYPE" "LIST_ENTRY NAME"
 .Fn LIST_REMOVE "TYPE *elm" "LIST_ENTRY NAME"
 .Fn LIST_SWAP "LIST_HEAD *head1" "LIST_HEAD *head2" "TYPE" "LIST_ENTRY NAME"
 .\"
@@ -248,8 +250,18 @@
 twice that of the singly-linked data-structures.
 .El
 .Pp
-Linked lists are the simplest of the doubly linked data structures and support
-only the above functionality over singly-linked lists.
+Linked lists are the simplest of the doubly linked data structures.
+They add the following functionality over the above:
+.Bl -enum -compact -offset indent
+.It
+They may be traversed backwards.
+.El
+However:
+.Bl -enum -compact -offset indent
+.It
+To traverse backwards, an entry to begin the traversal and the list in
+which it is contained must be specified.
+.El
 .Pp
 Tail queues add the following functionality:
 .Bl -enum -compact -offset indent
@@ -763,6 +775,14 @@
 returns the next element in the list, or NULL if this is the last.
 .Pp
 The macro
+.Nm LIST_PREV
+returns the previous element in the list, or NULL if this is the first.
+List
+.Fa head
+must contain element
+.Fa elm .
+.Pp
+The macro
 .Nm LIST_REMOVE
 removes the element
 .Fa elm

Modified: trunk/sys/sys/param.h
===================================================================
--- trunk/sys/sys/param.h	2016-09-18 19:04:32 UTC (rev 8371)
+++ trunk/sys/sys/param.h	2016-09-18 19:05:19 UTC (rev 8372)
@@ -324,8 +324,7 @@
 	((db) << (PAGE_SHIFT - DEV_BSHIFT))
 
 /*
- * Given the pointer x to the member m of the struct s, return
- * a pointer to the containing structure.
+ * Old spelling of __containerof().
  */
 #define	member2struct(s, m, x)						\
 	((struct s *)(void *)((char *)(x) - offsetof(struct s, m)))

Modified: trunk/sys/sys/queue.h
===================================================================
--- trunk/sys/sys/queue.h	2016-09-18 19:04:32 UTC (rev 8371)
+++ trunk/sys/sys/queue.h	2016-09-18 19:05:19 UTC (rev 8372)
@@ -65,7 +65,7 @@
  * so that an arbitrary element can be removed without a need to
  * traverse the list. New elements can be added to the list before
  * or after an existing element or at the head of the list. A list
- * may only be traversed in the forward direction.
+ * may be traversed in either direction.
  *
  * A tail queue is headed by a pair of pointers, one to the head of the
  * list and the other to the tail of the list. The elements are doubly
@@ -85,7 +85,7 @@
  * _EMPTY			+	+	+	+
  * _FIRST			+	+	+	+
  * _NEXT			+	+	+	+
- * _PREV			-	-	-	+
+ * _PREV			-	+	-	+
  * _LAST			-	-	+	+
  * _FOREACH			+	+	+	+
  * _FOREACH_SAFE		+	+	+	+
@@ -287,10 +287,8 @@
 } while (0)
 
 #define	STAILQ_LAST(head, type, field)					\
-	(STAILQ_EMPTY((head)) ?						\
-		NULL :							\
-	        ((struct type *)(void *)				\
-		((char *)((head)->stqh_last) - __offsetof(struct type, field))))
+	(STAILQ_EMPTY((head)) ? NULL :					\
+	    __containerof((head)->stqh_last, struct type, field.stqe_next))
 
 #define	STAILQ_NEXT(elm, field)	((elm)->field.stqe_next)
 
@@ -425,6 +423,10 @@
 
 #define	LIST_NEXT(elm, field)	((elm)->field.le_next)
 
+#define	LIST_PREV(elm, head, type, field)				\
+	((elm)->field.le_prev == &LIST_FIRST((head)) ? NULL :		\
+	    __containerof((elm)->field.le_prev, struct type, field.le_next))
+
 #define	LIST_REMOVE(elm, field) do {					\
 	QMD_SAVELINK(oldnext, (elm)->field.le_next);			\
 	QMD_SAVELINK(oldprev, (elm)->field.le_prev);			\