Docs: document the meaning of a ust app channel key set to 0

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

diff --git a/src/bin/lttng-sessiond/ust-app.h b/src/bin/lttng-sessiond/ust-app.h
index c3e37e0712b69b49274c1d6b6b16df30785d7343..7cc0d10aad3eeea499a23da90eefee78374b7a29 100644 (file)
--- a/src/bin/lttng-sessiond/ust-app.h
+++ b/src/bin/lttng-sessiond/ust-app.h
@@ -137,7 +137,11 @@ struct ust_app_channel {
        int handle;
        /* Channel and streams were sent to the UST tracer. */
        int is_sent;
-       /* Unique key used to identify the channel on the consumer side. */
+       /*
+        * Unique key used to identify the channel on the consumer side.
+        * 0 is a reserved 'invalid' value used to indicate that the consumer
+        * does not know about this channel (i.e. an error occured).
+        */
        uint64_t key;
        /* Id of the tracing channel set on creation. */
        uint64_t tracing_channel_id;