Add SLIST_FOREACH_PREVPTR and SLIST_REMOVE_NEXT. SLIST_FOREACH_PREVPTR

is like SLIST_FOREACH but it saves a pointer to the previous element.
SLIST_REMOVE_NEXT will remove the element *after* the one passed in.
SLIST_FOREACH_PREVPTR is from FreeBSD; SLIST_REMOVE_NEXT was suggested
by canacar@; man page additions by yours truly.  OK deraadt@ (grudgingly)
and man page changes OK jmc@.

2 files changed, 30 insertions, 2 deletions

diff --git a/share/man/man3/queue.3 b/share/man/man3/queue.3
index b739e762944..b9d5832bb6b 100644
--- a/share/man/man3/queue.3
+++ b/share/man/man3/queue.3
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: queue.3,v 1.32 2003/12/05 21:55:29 millert Exp $
+.\"	$OpenBSD: queue.3,v 1.33 2003/12/16 21:08:20 millert Exp $
 .\"	$NetBSD: queue.3,v 1.4 1995/07/03 00:25:36 mycroft Exp $
 .\"
 .\" Copyright (c) 1993 The Regents of the University of California.
@@ -42,10 +42,12 @@
 .Nm SLIST_END ,
 .Nm SLIST_EMPTY ,
 .Nm SLIST_FOREACH ,
+.Nm SLIST_FOREACH_PREVPTR ,
 .Nm SLIST_INIT ,
 .Nm SLIST_INSERT_AFTER ,
 .Nm SLIST_INSERT_HEAD ,
 .Nm SLIST_REMOVE_HEAD ,
+.Nm SLIST_REMOVE_NEXT ,
 .Nm SLIST_REMOVE ,
 .Nm LIST_ENTRY ,
 .Nm LIST_HEAD ,
@@ -124,6 +126,7 @@
 .Ft "bool"
 .Fn SLIST_EMPTY "SLIST_HEAD *head"
 .Fn SLIST_FOREACH "VARNAME" "SLIST_HEAD *head" "SLIST_ENTRY NAME"
+.Fn SLIST_FOREACH_PREVPTR "VARNAME" "VARNAMEP" "SLIST_HEAD *head" "SLIST_ENTRY NAME"
 .Ft void
 .Fn SLIST_INIT "SLIST_HEAD *head"
 .Ft void
@@ -133,6 +136,8 @@
 .Ft void
 .Fn SLIST_REMOVE_HEAD "SLIST_HEAD *head" "SLIST_ENTRY NAME"
 .Ft void
+.Fn SLIST_REMOVE_NEXT "SLIST_HEAD *head" "struct TYPE *elm" "SLIST_ENTRY NAME"
+.Ft void
 .Fn SLIST_REMOVE "SLIST_HEAD *head" "struct TYPE *elm" "TYPE" "SLIST_ENTRY NAME"
 .Pp
 .Fn LIST_ENTRY "TYPE"
@@ -443,6 +448,11 @@ macro removes the first element of the list pointed by
 .Fa head .
 .Pp
 The
+.Fn SLIST_REMOVE_NEXT
+macro removes the list element immediately following
+.Fa elm .
+.Pp
+The
 .Fn SLIST_REMOVE
 macro removes the element
 .Fa elm
@@ -466,6 +476,15 @@ SLIST_FOREACH(np, head, NAME)
 .Ed
 .Pp
 The
+.Fn SLIST_FOREACH_PREVPTR
+macro is similar to
+.Fn SLIST_FOREACH
+except that it stores a pointer to the previous element in
+.Fa VARNAMEP .
+This provides access to the previous element while traversing the list,
+as one would have with a doubly-linked list.
+.Pp
+The
 .Fn SLIST_EMPTY
 macro should be used to check whether a simple list is empty.
 .Sh LISTS
diff --git a/sys/sys/queue.h b/sys/sys/queue.h
index 9b2b8dd5788..7d5fb83c455 100644
--- a/sys/sys/queue.h
+++ b/sys/sys/queue.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: queue.h,v 1.23 2003/06/02 23:28:21 millert Exp $	*/
+/*	$OpenBSD: queue.h,v 1.24 2003/12/16 21:08:20 millert Exp $	*/
 /*	$NetBSD: queue.h,v 1.11 1996/05/16 05:17:14 mycroft Exp $	*/
 
 /*
@@ -111,6 +111,11 @@ struct {								\
 	    (var) != SLIST_END(head);					\
 	    (var) = SLIST_NEXT(var, field))
 
+#define	SLIST_FOREACH_PREVPTR(var, varp, head, field)			\
+	for ((varp) = &SLIST_FIRST((head));				\
+	    ((var) = *(varp)) != SLIST_END(head);			\
+	    (varp) = &SLIST_NEXT((var), field))
+
 /*
  * Singly-linked List functions.
  */
@@ -128,6 +133,10 @@ struct {								\
 	(head)->slh_first = (elm);					\
 } while (0)
 
+#define	SLIST_REMOVE_NEXT(head, elm, field) do {			\
+	(elm)->field.sle_next = (elm)->field.sle_next->field.sle_next;	\
+} while (0)
+
 #define	SLIST_REMOVE_HEAD(head, field) do {				\
 	(head)->slh_first = (head)->slh_first->field.sle_next;		\
 } while (0)