Fix: Revert of 814b4934e2604a419bcb8eec57c0450dbb47e2c3

[lttng-tools.git] / src / bin / lttng-sessiond / notification-thread-events.cpp

diff --git a/src/bin/lttng-sessiond/notification-thread-events.cpp b/src/bin/lttng-sessiond/notification-thread-events.cpp
index 279bc7c5a26aa797c08d800b38b16ae98aa04627..da4f8a4b2ad515f601b90435fe696acde129beb0 100644 (file)
--- a/src/bin/lttng-sessiond/notification-thread-events.cpp
+++ b/src/bin/lttng-sessiond/notification-thread-events.cpp
@@ -3123,28 +3123,55 @@ end:
        return 0;
 }
 
+static
+int pop_cmd_queue(struct notification_thread_handle *handle,
+               struct notification_thread_command **cmd)
+{
+       int ret;
+       uint64_t counter;
+
+       pthread_mutex_lock(&handle->cmd_queue.lock);
+       ret = lttng_read(handle->cmd_queue.event_fd, &counter, sizeof(counter));
+       if (ret != sizeof(counter)) {
+               ret = -1;
+               goto error_unlock;
+       }
+
+       /* Simulate behaviour of EFD_SEMAPHORE for older kernels. */
+       counter -= 1;
+       if (counter != 0) {
+               ret = lttng_write(handle->cmd_queue.event_fd, &counter,
+                               sizeof(counter));
+               if (ret != sizeof(counter)) {
+                       PERROR("Failed to write back to event_fd for EFD_SEMAPHORE emulation");
+                       ret = -1;
+                       goto error_unlock;
+               }
+       }
+
+       *cmd = cds_list_first_entry(&handle->cmd_queue.list,
+                       struct notification_thread_command, cmd_list_node);
+       cds_list_del(&((*cmd)->cmd_list_node));
+       ret = 0;
+
+error_unlock:
+       pthread_mutex_unlock(&handle->cmd_queue.lock);
+       return ret;
+}
+
 /* Returns 0 on success, 1 on exit requested, negative value on error. */
 int handle_notification_thread_command(
                struct notification_thread_handle *handle,
                struct notification_thread_state *state)
 {
        int ret;
-       uint64_t counter;
        struct notification_thread_command *cmd;
 
-       /* Read the event pipe to put it back into a quiescent state. */
-       ret = lttng_read(lttng_pipe_get_readfd(handle->cmd_queue.event_pipe), &counter,
-                       sizeof(counter));
-       if (ret != sizeof(counter)) {
+       ret = pop_cmd_queue(handle, &cmd);
+       if (ret) {
                goto error;
        }
 
-       pthread_mutex_lock(&handle->cmd_queue.lock);
-       cmd = cds_list_first_entry(&handle->cmd_queue.list,
-                       struct notification_thread_command, cmd_list_node);
-       cds_list_del(&cmd->cmd_list_node);
-       pthread_mutex_unlock(&handle->cmd_queue.lock);
-
        DBG("Received `%s` command",
                        notification_command_type_str(cmd->type));
        switch (cmd->type) {