Only print relevant session statistics in channel listing

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

diff --git a/src/bin/lttng/commands/list.c b/src/bin/lttng/commands/list.c
index 8705a4446ae7c446959e3dbc107245601d5c9e94..8f07bb2da253e8de18c7aff280e5b472294f8112 100644 (file)
--- a/src/bin/lttng/commands/list.c
+++ b/src/bin/lttng/commands/list.c
@@ -57,6 +57,9 @@ enum {
 static struct lttng_handle *handle;
 static struct mi_writer *writer;
 
+/* Only set when listing a single session. */
+static struct lttng_session listed_session;
+
 static struct poptOption long_options[] = {
        /* longName, shortName, argInfo, argPtr, value, descrip, argDesc */
        {"help",        'h', POPT_ARG_NONE, 0, OPT_HELP, 0, 0},
@@ -1215,8 +1218,6 @@ static void print_channel(struct lttng_channel *channel)
        MSG("%sblocking timeout: %" PRId64 " µs", indent6, blocking_timeout);
        MSG("%strace file count: %" PRIu64, indent6, channel->attr.tracefile_count);
        MSG("%strace file size: %" PRIu64 " bytes", indent6, channel->attr.tracefile_size);
-       MSG("%sdiscarded events: %" PRIu64, indent6, discarded_events);
-       MSG("%slost packets: %" PRIu64, indent6, lost_packets);
        switch (channel->attr.output) {
                case LTTNG_EVENT_SPLICE:
                        MSG("%soutput: splice()", indent6);
@@ -1225,6 +1226,31 @@ static void print_channel(struct lttng_channel *channel)
                        MSG("%soutput: mmap()", indent6);
                        break;
        }
+
+       if (!listed_session.snapshot_mode) {
+               /*
+                * The lost packet count is omitted for sessions in snapshot
+                * mode as it is misleading: it would indicate the number of
+                * packets that the consumer could not extract during the
+                * course of recording the snapshot. It does not have the
+                * same meaning as the "regular" lost packet count that
+                * would result from the consumer not keeping up with
+                * event production in an overwrite-mode channel.
+                *
+                * A more interesting statistic would be the number of
+                * packets lost between the first and last extracted
+                * packets of a given snapshot (which prevents most analyses).
+                */
+               goto skip_stats_printing;
+       }
+
+       if (!channel->attr.overwrite) {
+               MSG("%sdiscarded events: %" PRIu64, indent6, discarded_events);
+       } else {
+               MSG("%slost packets: %" PRIu64, indent6, lost_packets);
+       }
+skip_stats_printing:
+       return;
 }
 
 /*
@@ -1584,6 +1610,8 @@ static int list_sessions(const char *session_name)
                                                        active_string(sessions[i].enabled),
                                                        snapshot_string(sessions[i].snapshot_mode));
                                        MSG("%sTrace path: %s\n", indent4, sessions[i].path);
+                                       memcpy(&listed_session, &sessions[i],
+                                                       sizeof(listed_session));
                                        break;
                                }
                        } else {
@@ -1593,7 +1621,7 @@ static int list_sessions(const char *session_name)
                                                snapshot_string(sessions[i].snapshot_mode));
                                MSG("%sTrace path: %s", indent4, sessions[i].path);
                                if (sessions[i].live_timer_interval != 0) {
-                                       MSG("%sLive timer interval (usec): %u", indent4,
+                                       MSG("%sLive timer interval: %u µs", indent4,
                                                        sessions[i].live_timer_interval);
                                }
                                MSG("");