Add the EV_DISPATCH flag to kevents.

When the EV_DISPATCH flag is used the event source will be disabled
immediately after the delivery of an event.   This is similar to the
EV_ONESHOT flag but it doesn't delete the event.

Approved by:	rwatson (co-mentor)

3 files changed, 11 insertions, 2 deletions

diff --git a/lib/libc/sys/kqueue.2 b/lib/libc/sys/kqueue.2
index 1e5e2b5..63f5a4d 100644
--- a/lib/libc/sys/kqueue.2
+++ b/lib/libc/sys/kqueue.2
@@ -201,6 +201,11 @@ Disable the event so
 .Fn kevent
 will not return it.
 The filter itself is not disabled.
+.It EV_DISPATCH
+Disable the event source immediately after delivery of an event.
+See 
+.Dv EV_DISABLE
+above.
 .It EV_DELETE
 Removes the event from the kqueue.
 Events which are attached to
diff --git a/sys/kern/kern_event.c b/sys/kern/kern_event.c
index 92afec2..2630894 100644
--- a/sys/kern/kern_event.c
+++ b/sys/kern/kern_event.c
@@ -1445,15 +1445,17 @@ start:
 				*kevp = kn->kn_kevent;
 			KQ_LOCK(kq);
 			KQ_GLOBAL_UNLOCK(&kq_global, haskqglobal);
-			if (kn->kn_flags & EV_CLEAR) {
+			if (kn->kn_flags & (EV_CLEAR |  EV_DISPATCH)) {
 				/* 
 				 * Manually clear knotes who weren't 
 				 * 'touch'ed.
 				 */
-				if (touch == 0) {
+				if (touch == 0 && kn->kn_flags & EV_CLEAR) {
 					kn->kn_data = 0;
 					kn->kn_fflags = 0;
 				}
+				if (kn->kn_flags & EV_DISPATCH)
+					kn->kn_status |= KN_DISABLED;
 				kn->kn_status &= ~(KN_QUEUED | KN_ACTIVE);
 				kq->kq_count--;
 			} else
diff --git a/sys/sys/event.h b/sys/sys/event.h
index eb0fefd..2934b7b 100644
--- a/sys/sys/event.h
+++ b/sys/sys/event.h
@@ -72,6 +72,8 @@ struct kevent {
 /* flags */
 #define EV_ONESHOT	0x0010		/* only report one occurrence */
 #define EV_CLEAR	0x0020		/* clear event state after reporting */
+					/* 0x0040 reserved for EV_RECEIPT */
+#define EV_DISPATCH	0x0080		/* disable event after reporting */
 
 #define EV_SYSFLAGS	0xF000		/* reserved by system */
 #define EV_FLAG1	0x2000		/* filter-specific flag */