[PATCH v2] trace-cmd: Add record --clock option to specify a trace clock

[Ian Webster <ian@planetaryresources.com>]

This change adds a --clock option to trace-cmd record. It simply writes
trace_clock on debugfs. Examples of valid choices on most systems are: local,
global, counter, and any other choice compatible with ftrace.

This complements Yoshihiro Yunomae's change 8c9867c (trace-cmd: Add support for
extracting trace_clock in report).

Signed-off-by: Ian Webster <ian@planetaryresources.com>

---
Changes per Steven's comments:
  * add missing const
  * preserve tab whitespace

 Documentation/trace-cmd-record.1.txt |    5 +++++
 trace-record.c                       |   19 +++++++++++++++++++
 trace-usage.c                        |    1 +
 3 files changed, 25 insertions(+)

diff --git a/Documentation/trace-cmd-record.1.txt b/Documentation/trace-cmd-record.1.txt
index 832a257..5e83454 100644
--- a/Documentation/trace-cmd-record.1.txt
+++ b/Documentation/trace-cmd-record.1.txt
@@ -240,6 +240,11 @@ OPTIONS
     timestamp to gettimeofday which will allow wall time output from the
     timestamps reading the created 'trace.dat' file.

+*--clock* 'clock_name'::
+    When an event is recorded into the ring buffer, a timestamp is added. This
+    stamp comes from the specified clock. Ftrace uses the "local" clock by
+    default. Other common clocks include: global, counter, uptime, perf, x86-tsc.
+
 EXAMPLES
 --------

diff --git a/trace-record.c b/trace-record.c
index 0199627..2143080 100644
--- a/trace-record.c
+++ b/trace-record.c
@@ -399,6 +399,20 @@ static int set_ftrace(int set, int use_proc)
 	return 0;
 }

+static void set_trace_clock(const char *clock_choice)
+{
+	FILE *fp;
+	char *path;
+
+	path = tracecmd_get_tracing_file("trace_clock");
+	fp = fopen(path, "w");
+	if (!fp)
+		die("writing to '%s'", path);
+	tracecmd_put_tracing_file(path);
+	fwrite(clock_choice, 1, strlen(clock_choice), fp);
+	fclose(fp);
+}
+
 static char *
 get_instance_file(struct buffer_instance *instance, const char *file)
 {
@@ -2279,6 +2293,7 @@ static void record_all_events(void)
 }

 enum {
+	OPT_clock = 252,
 	OPT_nosplice	= 253,
 	OPT_funcstack	= 254,
 	OPT_date	= 255,
@@ -2351,6 +2366,7 @@ void trace_record (int argc, char **argv)
 			{"func-stack", no_argument, NULL, OPT_funcstack},
 			{"nosplice", no_argument, NULL, OPT_nosplice},
 			{"help", no_argument, NULL, '?'},
+			{"clock", required_argument, NULL, OPT_clock},
 			{NULL, 0, NULL, 0}
 		};

@@ -2530,6 +2546,9 @@ void trace_record (int argc, char **argv)
 		case OPT_nosplice:
 			recorder_flags |= TRACECMD_RECORD_NOSPLICE;
 			break;
+		case OPT_clock:
+			set_trace_clock(optarg);
+			break;
 		default:
 			usage(argv);
 		}
diff --git a/trace-usage.c b/trace-usage.c
index b8f26e6..54dbb85 100644
--- a/trace-usage.c
+++ b/trace-usage.c
@@ -46,6 +46,7 @@ static struct usage_help usage_help[] = {
 		"          -i do not fail if an event is not found\n"
 		"          --func-stack perform a stack trace for function tracer\n"
 		"             (use with caution)\n"
+		"          --clock change the method used to produce trace timestamps\n"
 	},
 	{
 		"start",
--
1.7.9.5