Fix: lttng-list: don't warn when the kernel domain has no channels

Some commands beside lttng-enable-channel have the side-effect of
creating a domain. For instance, the lttng-track and lttng-untrack
commands will implicitly create their target domains if they don't
exist. Thus, it is not unexpected for a domain to exist without
channels.

Currently, tracking process attributes in the user space and kernel
domains will result in a warning being printed when lttng-status
(or lttng-list `the_session`) is invoked.

Example output:
Tracing session arielle_bolduc: [inactive]
    Trace output: /home/jgalar/lttng-traces/arielle_bolduc-20200323-191128

=== Domain: Linux kernel ===

Tracked process attributes
  Process IDs: all
  Virtual Process IDs: 12365, 526, 41
  User IDs: all
  Virtual User IDs: all
  Group IDs: all
  Virtual Group IDs: all

Warning: No kernel channel
=== Domain: User space ===

Buffering scheme: per-user

Tracked process attributes
  Virtual Process IDs: 12365, 526, 41
  Virtual User IDs: all
  Virtual Group IDs: all

The warning is removed since it can only confuse users.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I733ee6c3d8c1d297194842c7bdbdf3f237661e51

diff --git a/src/bin/lttng/commands/list.c b/src/bin/lttng/commands/list.c
index 70dc99b0afc55801067e6b224481977d597ba471..372a71dad1d2579f4cd329f9cd97180c867d52f7 100644 (file)
--- a/src/bin/lttng/commands/list.c
+++ b/src/bin/lttng/commands/list.c
@@ -1446,7 +1446,6 @@ static int list_channels(const char *channel_name)
                                count = 0;
                        } else {
                                ret = CMD_SUCCESS;
-                               WARN("No kernel channel");
                                goto error_channels;
                        }
                        break;