From d2693dbbc4a50cadea996cfa60f52b91c9d39e4c Mon Sep 17 00:00:00 2001
From: Jonathan Lemon <jlemon@FreeBSD.org>
Date: Thu, 22 Jun 2000 18:39:31 +0000
Subject: [PATCH] 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
---
 sys/kern/kern_event.c | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/sys/kern/kern_event.c b/sys/kern/kern_event.c
index eca90dfee9e..e1c2ca71546 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);