Fix: channels can be _enabled_ after tracing is started, but not created

Fixes #619

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/src/bin/lttng-sessiond/cmd.c b/src/bin/lttng-sessiond/cmd.c
index e9fa3b462d29d533583815296d3ed20c6723ce8e..f2043df9cb9c25bf364fb96b08b86340cadc7b1a 100644 (file)
--- a/src/bin/lttng-sessiond/cmd.c
+++ b/src/bin/lttng-sessiond/cmd.c
@@ -859,15 +859,6 @@ int cmd_enable_channel(struct ltt_session *session,
 
        rcu_read_lock();
 
-       /*
-        * 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;
-       }
-
        switch (domain->type) {
        case LTTNG_DOMAIN_KERNEL:
        {
@@ -876,6 +867,15 @@ int cmd_enable_channel(struct ltt_session *session,
                kchan = trace_kernel_get_channel_by_name(attr->name,
                                session->kernel_session);
                if (kchan == NULL) {
+                       /*
+                        * Don't try to create 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;
+                       }
                        ret = channel_kernel_create(session->kernel_session, attr, wpipe);
                        if (attr->name[0] != '\0') {
                                session->kernel_session->has_non_default_channel = 1;
@@ -899,6 +899,15 @@ int cmd_enable_channel(struct ltt_session *session,
 
                uchan = trace_ust_find_channel_by_name(chan_ht, attr->name);
                if (uchan == NULL) {
+                       /*
+                        * Don't try to create 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;
+                       }
                        ret = channel_ust_create(usess, attr, domain->buf_type);
                        if (attr->name[0] != '\0') {
                                usess->has_non_default_channel = 1;