Ensure that we test the event condition when a disabled kevent is enabled.

r274560 modified kqueue_register() to only test the event condition if the
corresponding knote is not disabled. However, this check takes place before
the EV_ENABLE flag is used to clear the KN_DISABLED flag on the knote, so
enabling a previously-disabled kevent would not result in a notification for
a triggered event. This change fixes the problem by testing for EV_ENABLED
before possibly checking the event condition.

This change also updates a kqueue regression test to exercise this case.

PR:		206368
Reviewed by:	kib
Sponsored by:	EMC / Isilon Storage Division
Differential Revision:	https://reviews.freebsd.org/D5307

1 files changed, 8 insertions, 6 deletions

diff --git a/tests/sys/kqueue/read.c b/tests/sys/kqueue/read.c
index cc65427..2837144 100644
--- a/tests/sys/kqueue/read.c
+++ b/tests/sys/kqueue/read.c
@@ -124,15 +124,17 @@ test_kevent_socket_disable_and_enable(void)
 
     test_begin(test_id);
 
-    /* Add an event, then disable it. */
-    EV_SET(&kev, sockfd[0], EVFILT_READ, EV_ADD, 0, 0, &sockfd[0]);
-    if (kevent(kqfd, &kev, 1, NULL, 0, NULL) < 0)
-        err(1, "%s", test_id);
-    EV_SET(&kev, sockfd[0], EVFILT_READ, EV_DISABLE, 0, 0, &sockfd[0]);
+    /*
+     * Write to the socket before adding the event. This way we can verify that
+     * enabling a triggered kevent causes the event to be returned immediately.
+     */
+    kevent_socket_fill();
+
+    /* Add a disabled event. */
+    EV_SET(&kev, sockfd[0], EVFILT_READ, EV_ADD | EV_DISABLE, 0, 0, &sockfd[0]);
     if (kevent(kqfd, &kev, 1, NULL, 0, NULL) < 0)
         err(1, "%s", test_id);
 
-    kevent_socket_fill();
     test_no_kevents();
 
     /* Re-enable the knote, then see if an event is generated */