trace: add "-trace help"

Print a list of trace points

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-id: 1452174932-28657-7-git-send-email-den@openvz.org
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

qemu-options.hx

@@ -3564,6 +3564,8 @@ available if QEMU has been compiled with the @var{simple}, @var{stderr}
 or @var{ftrace} tracing backend.  To specify multiple events or patterns,
 specify the @option{-trace} option multiple times.
 
+Use @code{-trace help} to print a list of names of trace points.
+
 @item events=@var{file}
 Immediately enable events listed in @var{file}.
 The file must contain one event name (as listed in the @file{trace-events} file)

trace/control.c

@@ -88,7 +88,16 @@ TraceEvent *trace_event_pattern(const char *pat, TraceEvent *ev)
     return NULL;
 }
 
-void trace_enable_events(const char *line_buf)
+void trace_list_events(void)
+{
+    int i;
+    for (i = 0; i < trace_event_count(); i++) {
+        TraceEvent *res = trace_event_id(i);
+        fprintf(stderr, "%s\n", trace_event_get_name(res));
+    }
+}
+
+static void do_trace_enable_events(const char *line_buf)
 {
     const bool enable = ('-' != line_buf[0]);
     const char *line_ptr = enable ? line_buf : line_buf + 1;
@@ -114,6 +123,16 @@ void trace_enable_events(const char *line_buf)
     }
 }
 
+void trace_enable_events(const char *line_buf)
+{
+    if (is_help_option(line_buf)) {
+        trace_list_events();
+        exit(0);
+    } else {
+        do_trace_enable_events(line_buf);
+    }
+}
+
 void trace_init_events(const char *fname)
 {
     Location loc;

trace/control.h

@@ -181,6 +181,13 @@ void trace_init_events(const char *file);
  */
 void trace_init_file(const char *file);
 
+/**
+ * trace_list_events:
+ *
+ * List all available events.
+ */
+void trace_list_events(void);
+
 /**
  * trace_enable_events:
  * @line_buf: A string with a glob pattern of events to be enabled or,