Use pipe instead of eventfd() for notification command queue

Signed-off-by: Jonathan Rajotte <[email protected]>
Signed-off-by: Jérémie Galarneau <[email protected]>

src/bin/lttng-sessiond/notification-thread-commands.c

@@ -44,7 +44,7 @@ int run_command_wait(struct notification_thread_handle *handle,
 	cds_list_add_tail(&cmd->cmd_list_node,
 			&handle->cmd_queue.list);
 	/* Wake-up thread. */
-	ret = write(handle->cmd_queue.event_fd,
+	ret = write(lttng_pipe_get_writefd(handle->cmd_queue.event_pipe),
 			&notification_counter, sizeof(notification_counter));
 	if (ret < 0) {
 		PERROR("write to notification thread's queue event fd");

src/bin/lttng-sessiond/notification-thread-events.c

@@ -1275,7 +1275,7 @@ int handle_notification_thread_command(
 	struct notification_thread_command *cmd;
 
 	/* Read event_fd to put it back into a quiescent state. */
-	ret = read(handle->cmd_queue.event_fd, &counter, sizeof(counter));
+	ret = read(lttng_pipe_get_readfd(handle->cmd_queue.event_pipe), &counter, sizeof(counter));
 	if (ret == -1) {
 		goto error;
 	}

src/bin/lttng-sessiond/notification-thread.c

@@ -54,17 +54,12 @@ void notification_thread_handle_destroy(
 		goto end;
 	}
 
-	if (handle->cmd_queue.event_fd < 0) {
-		goto end;
-	}
-	ret = close(handle->cmd_queue.event_fd);
-	if (ret < 0) {
-		PERROR("close notification command queue event_fd");
-	}
-
 	assert(cds_list_empty(&handle->cmd_queue.list));
 	pthread_mutex_destroy(&handle->cmd_queue.lock);
 
+	if (handle->cmd_queue.event_pipe) {
+		lttng_pipe_destroy(handle->cmd_queue.event_pipe);
+	}
 	if (handle->channel_monitoring_pipes.ust32_consumer >= 0) {
 		ret = close(handle->channel_monitoring_pipes.ust32_consumer);
 		if (ret) {
@@ -94,18 +89,22 @@ struct notification_thread_handle *notification_thread_handle_create(
 {
 	int ret;
 	struct notification_thread_handle *handle;
+	struct lttng_pipe *event_pipe = NULL;
 
 	handle = zmalloc(sizeof(*handle));
 	if (!handle) {
 		goto end;
 	}
 
-	/* FIXME Replace eventfd by a pipe to support older kernels. */
-	handle->cmd_queue.event_fd = eventfd(0, EFD_CLOEXEC | EFD_SEMAPHORE);
-	if (handle->cmd_queue.event_fd < 0) {
-		PERROR("eventfd notification command queue");
+	event_pipe = lttng_pipe_open(O_CLOEXEC);
+	if (!event_pipe) {
+		ERR("event_pipe creation");
 		goto error;
 	}
+
+	handle->cmd_queue.event_pipe = event_pipe;
+	event_pipe = NULL;
+
 	CDS_INIT_LIST_HEAD(&handle->cmd_queue.list);
 	ret = pthread_mutex_init(&handle->cmd_queue.lock, NULL);
 	if (ret) {
@@ -145,6 +144,7 @@ struct notification_thread_handle *notification_thread_handle_create(
 end:
 	return handle;
 error:
+	lttng_pipe_destroy(event_pipe);
 	notification_thread_handle_destroy(handle);
 	return NULL;
 }
@@ -282,7 +282,7 @@ int init_poll_set(struct lttng_poll_event *poll_set,
 		ERR("[notification-thread] Failed to add notification channel socket to pollset");
 		goto error;
 	}
-	ret = lttng_poll_add(poll_set, handle->cmd_queue.event_fd,
+	ret = lttng_poll_add(poll_set, lttng_pipe_get_readfd(handle->cmd_queue.event_pipe),
 			LPOLLIN | LPOLLERR);
 	if (ret < 0) {
 		ERR("[notification-thread] Failed to add notification command queue event fd to pollset");
@@ -544,7 +544,7 @@ void *thread_notification(void *data)
 					ERR("[notification-thread] Unexpected poll events %u for notification socket %i", revents, fd);
 					goto error;
 				}
-			} else if (fd == handle->cmd_queue.event_fd) {
+			} else if (fd == lttng_pipe_get_readfd(handle->cmd_queue.event_pipe)) {
 				ret = handle_notification_thread_command(handle,
 						&state);
 				if (ret < 0) {

src/bin/lttng-sessiond/notification-thread.h

@@ -30,11 +30,11 @@
 struct notification_thread_handle {
 	/*
 	 * Queue of struct notification command.
-	 * event_fd must be WRITE(2) to signal that a new command
+	 * event_pipe must be WRITE(2) to signal that a new command
 	 * has been enqueued.
 	 */
 	struct {
-		int event_fd;
+		struct lttng_pipe *event_pipe;
 		struct cds_list_head list;
 		pthread_mutex_t lock;
 	} cmd_queue;