add callout lists for exit() and fork()

I've been meaning to do this for AGES as I keep having to patch those routines
whenever I write a proprietary package or similar..

any module that assigns resources to processes needs to know when
these events occur. there are existsing modules that should be modified
to take advantage of these.. e.g. SYSV IPC primatives
presently have #ifdef entries in exit()


this also helps with making LKMs out of such things..

(see the man pages at_exit(9) and at_fork(9))

1 files changed, 72 insertions, 1 deletions

diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index 2ac1849..f6bb284 100644
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -36,7 +36,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)kern_fork.c	8.6 (Berkeley) 4/8/94
- * $Id: kern_fork.c,v 1.22 1996/06/12 05:07:30 gpalmer Exp $
+ * $Id: kern_fork.c,v 1.23 1996/07/31 09:26:34 davidg Exp $
  */
 
 #include "opt_ktrace.h"
@@ -64,6 +64,16 @@
 
 static int fork1 __P((struct proc *p, int flags, int *retval));
 
+/*
+ * callout list for things to do at fork time
+ */
+typedef struct fork_list_element {
+	struct fork_list_element *next;
+	forklist_fn function;
+} *fle_p;
+
+static fle_p fork_list;
+
 #ifndef _SYS_SYSPROTO_H_
 struct fork_args {
         int     dummy;
@@ -114,6 +124,7 @@ fork1(p1, flags, retval)
 	struct proc *newproc;
 	int count;
 	static int nextpid, pidchecked = 0;
+	fle_p ep = fork_list;
 
 	if ((flags & RFPROC) == 0)
 		return (EINVAL);
@@ -335,6 +346,16 @@ again:
 	}
 
 	/*
+	 * Both processes are set up, 
+	 * check if any LKMs want to adjust anything
+	 * What if they have an error? XXX
+	 */
+        while(ep) {
+                (*ep->function)(p1,p2,flags);
+                ep = ep->next;
+        }
+
+	/*
 	 * Make child runnable and add to run queue.
 	 */
 	(void) splhigh();
@@ -363,3 +384,53 @@ again:
 	retval[1] = 0;
 	return (0);
 }
+
+
+/*********************************************************
+ * general routines to handle adding/deleting items on the
+ * fork callout list
+ *****
+ * Take the arguments given and put them onto the fork callout list.
+ * However first make sure that it's not already there.
+ * returns 0 on success.
+ */
+int
+at_fork(forklist_fn function)
+{
+	fle_p ep;
+	if(rm_at_fork(function)) {
+		printf("fork callout entry already present\n");
+	}
+	ep = malloc(sizeof(*ep),M_TEMP,M_NOWAIT);
+	if(!ep) return ENOMEM;
+	ep->next = fork_list;
+	ep->function = function;
+	fork_list = ep;
+	return 0;
+}
+/*
+ * Scan the exit callout list for the given items and remove them.
+ * Returns the number of items removed.
+ */
+int
+rm_at_fork(forklist_fn function)
+{
+	fle_p *epp,ep;
+	int count = 0;
+
+	epp = &fork_list;
+	ep = *epp;
+	while(ep) {
+		if(ep->function == function) {
+			*epp = ep->next;
+			free(ep,M_TEMP);
+			count++;
+		} else {
+			epp = &ep->next;
+		}
+		ep = *epp;
+	}
+	return count;
+}
+
+