Fix: don't enable a channel if a session was already started

This removes also the check done to start the session if it was started
before.

Signed-off-by: David Goulet <dgoulet@efficios.com>

diff --git a/doc/man/lttng.1 b/doc/man/lttng.1
index e650d24264c27e50b65d59973c26c5935fc69e4f..72454f0d3e85ad0f1c6ffeb8e4221e8251a03a07 100644 (file)
--- a/doc/man/lttng.1
+++ b/doc/man/lttng.1
@@ -312,8 +312,8 @@ It is important to note that if a certain type of buffers is used, the session
 will be set with that type and all other subsequent channel needs to have the
 same type.
 
-For the kernel tracer (\-k), once the session is started at least once, it's
-not possible anymore to enable new channel for that session.
+Note that once the session has been started and enabled on the tracer side,
+it's not possible anymore to enable a new channel for that session.
 .fi
 
 .B OPTIONS:

diff --git a/src/bin/lttng-sessiond/cmd.c b/src/bin/lttng-sessiond/cmd.c
index a23a2b761eac462a4b48869a36b5138a3b71413f..bba77023a6415ff0b52e9f0dcfde6729c5a0856f 100644 (file)
--- a/src/bin/lttng-sessiond/cmd.c
+++ b/src/bin/lttng-sessiond/cmd.c
@@ -856,6 +856,15 @@ int cmd_enable_channel(struct ltt_session *session,
 
        DBG("Enabling channel %s for session %s", attr->name, session->name);
 
+       /*
+        * Don't try to enable a channel if the session has been started at
+        * some point in time before. The tracer does not allow it.
+        */
+       if (session->started) {
+               ret = LTTNG_ERR_TRACE_ALREADY_STARTED;
+               goto error;
+       }
+
        rcu_read_lock();
 
        switch (domain->type) {
@@ -876,18 +885,6 @@ int cmd_enable_channel(struct ltt_session *session,
                }
 
                kernel_wait_quiescent(kernel_tracer_fd);
-
-               /*
-                * If the session was previously started, start as well this newly
-                * created kernel session so the events/channels enabled *after* the
-                * start actually work.
-                */
-               if (session->started && !session->kernel_session->started) {
-                       ret = start_kernel_session(session->kernel_session, wpipe);
-                       if (ret != LTTNG_OK) {
-                               goto error;
-                       }
-               }
                break;
        }
        case LTTNG_DOMAIN_UST:
@@ -902,17 +899,6 @@ int cmd_enable_channel(struct ltt_session *session,
                } else {
                        ret = channel_ust_enable(usess, uchan);
                }
-
-               /* Start the UST session if the session was already started. */
-               if (session->started && !usess->start_trace) {
-                       ret = ust_app_start_trace_all(usess);
-                       if (ret < 0) {
-                               ret = LTTNG_ERR_UST_START_FAIL;
-                               goto error;
-                       }
-                       ret = LTTNG_OK;
-                       usess->start_trace = 1;
-               }
                break;
        }
        default:
@@ -1616,8 +1602,6 @@ int cmd_stop_trace(struct ltt_session *session)
                }
        }
 
-       session->started = 0;
-
        ret = LTTNG_OK;
 
 error: