The at_exit and at_fork functions currently use a 'roll your own'

linked list to store the callbak routines.  The patch converts the
lists to queue(3) TAILQs, making the code slightly clearer and ensuring
that callbacks are executed in FIFO order.

Man page also updated as necesary.

(discontinued use of M_TEMP malloc type while here anyway /phk)

Submitted by:   Jake Burkholder jake@checker.org
PR:             14912

1 files changed, 27 insertions, 30 deletions

diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
index 6c00e43..abbe9de 100644
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -75,17 +75,20 @@
 /* Required to be non-static for SysVR4 emulator */
 MALLOC_DEFINE(M_ZOMBIE, "zombie", "zombie proc status");
 
+static MALLOC_DEFINE(M_ATEXIT, "atexit", "atexit callback");
+
 static int wait1 __P((struct proc *, struct wait_args *, int));
 
 /*
  * callout list for things to do at exit time
  */
-typedef struct exit_list_element {
-	struct exit_list_element *next;
+struct exitlist {
 	exitlist_fn function;
-} *ele_p;
+	TAILQ_ENTRY(exitlist) next;
+};
 
-static ele_p exit_list;
+TAILQ_HEAD(exit_list_head, exitlist);
+static struct exit_list_head exit_list = TAILQ_HEAD_INITIALIZER(exit_list);
 
 /*
  * exit --
@@ -115,7 +118,7 @@ exit1(p, rv)
 {
 	register struct proc *q, *nq;
 	register struct vmspace *vm;
-	ele_p ep = exit_list;
+	struct exitlist *ep;
 
 	if (p->p_pid == 1) {
 		printf("init died (signal %d, exit %d)\n",
@@ -154,10 +157,8 @@ exit1(p, rv)
 	 * e.g. SYSV IPC stuff
 	 * XXX what if one of these generates an error?
 	 */
-	while (ep) {
+	TAILQ_FOREACH(ep, &exit_list, next) 
 		(*ep->function)(p);
-		ep = ep->next;
-	}
 
 	if (p->p_flag & P_PROFIL)
 		stopprofclock(p);
@@ -580,49 +581,45 @@ proc_reparent(child, parent)
  * However first make sure that it's not already there.
  * returns 0 on success.
  */
+
 int
 at_exit(function)
 	exitlist_fn function;
 {
-	ele_p ep;
+	struct exitlist *ep;
 
+#ifdef INVARIANTS
 	/* Be noisy if the programmer has lost track of things */
 	if (rm_at_exit(function)) 
-		printf("exit callout entry already present\n");
-	ep = malloc(sizeof(*ep), M_TEMP, M_NOWAIT);
+		printf("WARNING: exit callout entry (%p) already present\n",
+		    function);
+#endif
+	ep = malloc(sizeof(*ep), M_ATEXIT, M_NOWAIT);
 	if (ep == NULL)
 		return (ENOMEM);
-	ep->next = exit_list;
 	ep->function = function;
-	exit_list = ep;
+	TAILQ_INSERT_TAIL(&exit_list, ep, next);
 	return (0);
 }
+
 /*
- * Scan the exit callout list for the given items and remove them.
- * Returns the number of items removed.
- * Logically this can only be 0 or 1.
+ * Scan the exit callout list for the given item and remove it.
+ * Returns the number of items removed (0 or 1)
  */
 int
 rm_at_exit(function)
 	exitlist_fn function;
 {
-	ele_p *epp, ep;
-	int count;
+	struct exitlist *ep;
 
-	count = 0;
-	epp = &exit_list;
-	ep = *epp;
-	while (ep) {
+	TAILQ_FOREACH(ep, &exit_list, next) {
 		if (ep->function == function) {
-			*epp = ep->next;
-			free(ep, M_TEMP);
-			count++;
-		} else {
-			epp = &ep->next;
+			TAILQ_REMOVE(&exit_list, ep, next);
+			free(ep, M_ATEXIT);
+			return(1);
 		}
-		ep = *epp;
-	}
-	return (count);
+	}	
+	return (0);
 }
 
 void check_sigacts (void)