From 027ffc9d1553dc4263fda2fdcee5acc33f08d819 Mon Sep 17 00:00:00 2001 From: Pierre-Marc Fournier Date: Fri, 15 Jan 2010 18:04:25 -0500 Subject: [PATCH] Add comment on manual registration of "ust" channel --- libust/tracectl.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) diff --git a/libust/tracectl.c b/libust/tracectl.c index 873b0f6..f9312b4 100644 --- a/libust/tracectl.c +++ b/libust/tracectl.c @@ -949,7 +949,24 @@ static void __attribute__((constructor)) init() /* Ensure markers are initialized */ init_markers(); - /* In case. */ + /* FIXME: When starting early tracing (here), depending on the + * order of constructors, it is very well possible some marker + * sections are not yet registered. Because of this, some + * channels may not be registered. Yet, we are about to ask the + * daemon to collect the channels. Channels which are not yet + * registered will not be collected. + * + * Currently, in LTTng, there is no way to add a channel after + * trace start. The reason for this is that it induces complex + * concurrency issues on the trace structures, which can only + * be resolved using RCU. This has not been done yet. As a + * workaround, we are forcing the registration of the "ust" + * channel here. This is the only channel (apart from metadata) + * that can be reliably used in early tracing. + * + * Non-early tracing does not have this problem and can use + * arbitrary channel names. + */ ltt_channels_register("ust"); result = ltt_trace_setup(trace_name); -- 2.34.1