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, 31 deletions

diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index 9268592..c12c965 100644
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -65,6 +65,8 @@
 
 #include <sys/user.h>
 
+static MALLOC_DEFINE(M_ATFORK, "atfork", "atfork callback");
+
 static int	fast_vfork = 1;
 SYSCTL_INT(_kern, OID_AUTO, fast_vfork, CTLFLAG_RW, &fast_vfork, 0, "");
 
@@ -72,12 +74,13 @@ SYSCTL_INT(_kern, OID_AUTO, fast_vfork, CTLFLAG_RW, &fast_vfork, 0, "");
  * These are the stuctures used to create a callout list for things to do
  * when forking a process
  */
-typedef struct fork_list_element {
-	struct fork_list_element *next;
+struct forklist {
 	forklist_fn function;
-} *fle_p;
+	TAILQ_ENTRY(forklist) next;
+};
 
-static fle_p	fork_list;
+TAILQ_HEAD(forklist_head, forklist);
+static struct forklist_head fork_list = TAILQ_HEAD_INITIALIZER(fork_list);
 
 #ifndef _SYS_SYSPROTO_H_
 struct fork_args {
@@ -150,9 +153,7 @@ fork1(p1, flags, procp)
 	struct proc *newproc;
 	int count;
 	static int pidchecked = 0;
-	fle_p ep ;
-
-	ep = fork_list;
+	struct forklist *ep;
 
 	if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
 		return (EINVAL);
@@ -461,9 +462,8 @@ again:
 	 * to adjust anything.
 	 *   What if they have an error? XXX
 	 */
-	while (ep) {
+	TAILQ_FOREACH(ep, &fork_list, next) {
 		(*ep->function)(p1, p2, flags);
-		ep = ep->next;
 	}
 
 	/*
@@ -505,48 +505,44 @@ again:
  * However first make sure that it's not already there.
  * Returns 0 on success or a standard error number.
  */
+
 int
 at_fork(function)
 	forklist_fn function;
 {
-	fle_p ep;
+	struct forklist *ep;
 
+#ifdef INVARIANTS
 	/* let the programmer know if he's been stupid */
 	if (rm_at_fork(function)) 
-		printf("fork callout entry already present\n");
-	ep = malloc(sizeof(*ep), M_TEMP, M_NOWAIT);
+		printf("WARNING: fork callout entry (%p) already present\n",
+		    function);
+#endif
+	ep = malloc(sizeof(*ep), M_ATFORK, M_NOWAIT);
 	if (ep == NULL)
 		return (ENOMEM);
-	ep->next = fork_list;
 	ep->function = function;
-	fork_list = ep;
+	TAILQ_INSERT_TAIL(&fork_list, ep, next);
 	return (0);
 }
 
 /*
- * Scan the exit callout list for the given items and remove them.
- * Returns the number of items removed.
- * Theoretically this value 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_fork(function)
 	forklist_fn function;
 {
-	fle_p *epp, ep;
-	int count;
+	struct forklist *ep;
 
-	count= 0;
-	epp = &fork_list;
-	ep = *epp;
-	while (ep) {
+	TAILQ_FOREACH(ep, &fork_list, next) {
 		if (ep->function == function) {
-			*epp = ep->next;
-			free(ep, M_TEMP);
-			count++;
-		} else {
-			epp = &ep->next;
+			TAILQ_REMOVE(&fork_list, ep, next);
+			free(ep, M_ATFORK);
+			return(1);
 		}
-		ep = *epp;
-	}
-	return (count);
+	}	
+	return (0);
 }