lib/tevent: Add trace point callback

Set/get a single callback function to be invoked at various trace
points.  Define "before wait" and "after wait" trace points - more
trace points can be added later if required.

CTDB wants this to log long waits and events.

Pair-programmed-with: Amitay Isaacs <amitay@gmail.com>
Signed-off-by: Martin Schwenke <martin@meltin.net>
Signed-off-by: Stefan Metzmacher <metze@samba.org>

8 files changed, 82 insertions, 0 deletions

diff --git a/lib/tevent/tevent.h b/lib/tevent/tevent.h
index c38f7c36e1..c8719fa4f1 100644
--- a/lib/tevent/tevent.h
+++ b/lib/tevent/tevent.h
@@ -501,6 +501,49 @@ int tevent_set_debug(struct tevent_context *ev,
  */
 int tevent_set_debug_stderr(struct tevent_context *ev);
 
+enum tevent_trace_point {
+	/**
+	 * Corresponds to a trace point just before waiting
+	 */
+	TEVENT_TRACE_BEFORE_WAIT,
+	/**
+	 * Corresponds to a trace point just after waiting
+	 */
+	TEVENT_TRACE_AFTER_WAIT,
+};
+
+typedef void (*tevent_trace_callback_t)(enum tevent_trace_point,
+					void *private_data);
+
+/**
+ * Register a callback to be called at certain trace points
+ *
+ * @param[in] ev             Event context
+ * @param[in] cb             Trace callback
+ * @param[in] private_data   Data to be passed to callback
+ *
+ * @note The callback will be called at trace points defined by
+ * tevent_trace_point.  Call with NULL to reset.
+ */
+void tevent_set_trace_callback(struct tevent_context *ev,
+			       tevent_trace_callback_t cb,
+			       void *private_data);
+
+/**
+ * Retrieve the current trace callback
+ *
+ * @param[in] ev             Event context
+ * @param[out] cb            Registered trace callback
+ * @param[out] private_data  Registered data to be passed to callback
+ *
+ * @note This can be used to allow one component that wants to
+ * register a callback to respect the callback that another component
+ * has already registered.
+ */
+void tevent_get_trace_callback(struct tevent_context *ev,
+			       tevent_trace_callback_t *cb,
+			       void *private_data);
+
 /**
  * @}
  */
diff --git a/lib/tevent/tevent_debug.c b/lib/tevent/tevent_debug.c
index 3f4112831a..31da7b9683 100644
--- a/lib/tevent/tevent_debug.c
+++ b/lib/tevent/tevent_debug.c
@@ -94,3 +94,26 @@ void tevent_debug(struct tevent_context *ev, enum tevent_debug_level level,
 	va_end(ap);
 }
 
+void tevent_set_trace_callback(struct tevent_context *ev,
+			       tevent_trace_callback_t cb,
+			       void *private_data)
+{
+	ev->tracing.callback = cb;
+	ev->tracing.private_data = private_data;
+}
+
+void tevent_get_trace_callback(struct tevent_context *ev,
+			       tevent_trace_callback_t *cb,
+			       void *private_data)
+{
+	*cb = ev->tracing.callback;
+	*(void**)private_data = ev->tracing.private_data;
+}
+
+void tevent_trace_point_callback(struct tevent_context *ev,
+				 enum tevent_trace_point tp)
+{
+	if (ev->tracing.callback != NULL) {
+		ev->tracing.callback(tp, ev->tracing.private_data);
+	}
+}
diff --git a/lib/tevent/tevent_epoll.c b/lib/tevent/tevent_epoll.c
index 33e1d3f20f..5f93de2c57 100644
--- a/lib/tevent/tevent_epoll.c
+++ b/lib/tevent/tevent_epoll.c
@@ -264,7 +264,9 @@ static int epoll_event_loop(struct epoll_event_context *epoll_ev, struct timeval
 		return 0;
 	}
 
+	tevent_trace_point_callback(epoll_ev->ev, TEVENT_TRACE_BEFORE_WAIT);
 	ret = epoll_wait(epoll_ev->epoll_fd, events, MAXEVENTS, timeout);
+	tevent_trace_point_callback(epoll_ev->ev, TEVENT_TRACE_AFTER_WAIT);
 
 	if (ret == -1 && errno == EINTR && epoll_ev->ev->signal_events) {
 		if (tevent_common_check_signal(epoll_ev->ev)) {
diff --git a/lib/tevent/tevent_internal.h b/lib/tevent/tevent_internal.h
index 472beb5c94..877510f9f4 100644
--- a/lib/tevent/tevent_internal.h
+++ b/lib/tevent/tevent_internal.h
@@ -258,6 +258,11 @@ struct tevent_context {
 		tevent_nesting_hook hook_fn;
 		void *hook_private;
 	} nesting;
+
+	struct {
+		tevent_trace_callback_t callback;
+		void *private_data;
+	} tracing;
 };
 
 
@@ -313,3 +318,6 @@ bool tevent_poll_init(void);
 #ifdef HAVE_EPOLL
 bool tevent_epoll_init(void);
 #endif
+
+void tevent_trace_point_callback(struct tevent_context *ev,
+				 enum tevent_trace_point);
diff --git a/lib/tevent/tevent_poll.c b/lib/tevent/tevent_poll.c
index 2e202aa7ec..7ae3c42188 100644
--- a/lib/tevent/tevent_poll.c
+++ b/lib/tevent/tevent_poll.c
@@ -201,7 +201,9 @@ static int poll_event_loop_poll(struct tevent_context *ev,
 		timeout += (tvalp->tv_usec + 999) / 1000;
 	}
 
+	tevent_trace_point_callback(poll_ev->ev, TEVENT_TRACE_BEFORE_WAIT);
 	pollrtn = poll(poll_ev->fds, poll_ev->num_fds, timeout);
+	tevent_trace_point_callback(poll_ev->ev, TEVENT_TRACE_AFTER_WAIT);
 
 	if (pollrtn == -1 && errno == EINTR && ev->signal_events) {
 		tevent_common_check_signal(ev);
diff --git a/lib/tevent/tevent_select.c b/lib/tevent/tevent_select.c
index 94faa86593..c11f0e8324 100644
--- a/lib/tevent/tevent_select.c
+++ b/lib/tevent/tevent_select.c
@@ -167,7 +167,9 @@ static int select_event_loop_select(struct select_event_context *select_ev, stru
 		return 0;
 	}
 
+	tevent_trace_point_callback(select_ev->ev, TEVENT_TRACE_BEFORE_WAIT);
 	selrtn = select(select_ev->maxfd+1, &r_fds, &w_fds, NULL, tvalp);
+	tevent_trace_point_callback(select_ev->ev, TEVENT_TRACE_AFTER_WAIT);
 
 	if (selrtn == -1 && errno == EINTR && 
 	    select_ev->ev->signal_events) {
diff --git a/lib/tevent/tevent_standard.c b/lib/tevent/tevent_standard.c
index e2ca44f9c2..1e33720f70 100644
--- a/lib/tevent/tevent_standard.c
+++ b/lib/tevent/tevent_standard.c
@@ -278,7 +278,9 @@ static int epoll_event_loop(struct std_event_context *std_ev, struct timeval *tv
 		return 0;
 	}
 
+	tevent_trace_point_callback(std_ev->ev, TEVENT_TRACE_BEFORE_WAIT);
 	ret = epoll_wait(std_ev->epoll_fd, events, MAXEVENTS, timeout);
+	tevent_trace_point_callback(std_ev->ev, TEVENT_TRACE_AFTER_WAIT);
 
 	if (ret == -1 && errno == EINTR && std_ev->ev->signal_events) {
 		if (tevent_common_check_signal(std_ev->ev)) {
diff --git a/lib/tevent/wscript b/lib/tevent/wscript
index 2e6c2a6e6e..2e6c2a6e6e 100644..100755
--- a/lib/tevent/wscript
+++ b/lib/tevent/wscript