Add code so that the udata field is preserved across a TRACK event.

When re-adding an event, do not reset the event state.  If the event was
pending, it will remain pending.  This allows the user to change the udata
field after the event was registered, while not losing any events which
have already occurred.

Reported by:   jmg

1 files changed, 18 insertions, 9 deletions

diff --git a/sys/kern/kern_event.c b/sys/kern/kern_event.c
index eca90df..e1c2ca7 100644
--- a/sys/kern/kern_event.c
+++ b/sys/kern/kern_event.c
@@ -283,6 +283,7 @@ filt_proc(struct knote *kn, long hint)
 		kev.flags = kn->kn_flags | EV_ADD | EV_ENABLE | EV_FLAG1;
 		kev.fflags = kn->kn_sfflags;
 		kev.data = kn->kn_id;			/* parent */
+		kev.udata = kn->kn_kevent.udata;	/* preserve udata */
 		error = kqueue_register(kn->kn_kq, &kev, NULL);
 		if (error)
 			kn->kn_fflags |= NOTE_TRACKERR;
@@ -447,7 +448,6 @@ kqueue_register(struct kqueue *kq, struct kevent *kev, struct proc *p)
 	 * kn now contains the matching knote, or NULL if no match
 	 */
 	if (kev->flags & EV_ADD) {
-		int attach = 0;
 
 		if (kn == NULL) {
 			kn = knote_alloc();
@@ -458,25 +458,34 @@ kqueue_register(struct kqueue *kq, struct kevent *kev, struct proc *p)
 			kn->kn_fp = fp;
 			kn->kn_kq = kq;
 			kn->kn_fop = fops;
-			attach = 1;
-		}
-		kn->kn_sfflags = kev->fflags;
-		kn->kn_sdata = kev->data;
-		kev->fflags = 0;
-		kev->data = 0;
-		kn->kn_kevent = *kev;
 
-		if (attach) {
+			kn->kn_sfflags = kev->fflags;
+			kn->kn_sdata = kev->data;
+			kev->fflags = 0;
+			kev->data = 0;
+			kn->kn_kevent = *kev;
+
 			knote_attach(kn, fdp);
 			if ((error = fops->f_attach(kn)) != 0) {
 				knote_drop(kn, p);
 				goto done;
 			}
+		} else {
+			/*
+			 * The user may change some filter values after the
+			 * initial EV_ADD, but doing so will not reset any 
+			 * filter which have already been triggered.
+			 */
+			kn->kn_sfflags = kev->fflags;
+			kn->kn_sdata = kev->data;
+			kn->kn_kevent.udata = kev->udata;
 		}
+
 		s = splhigh();
 		if (kn->kn_fop->f_event(kn, 0))
 			KNOTE_ACTIVATE(kn);
 		splx(s);
+
 	} else if (kev->flags & EV_DELETE) {
 		kn->kn_fop->f_detach(kn);
 		knote_drop(kn, p);