[PATCH v4 21/23] trace-cmd: Get current clock for host-guest tracing session

["Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com>]

In host-guest tracing session, all peers should use the same tracing
clock. If there is no user configured trace clock, the current logic
assumes "local" clock for the session. This could be wrong, as other
clock than "local" could be already configured on the host, before
running trace-cmd. The default clock for host-guest tracing session
should be rertieved from the "trace_clock" file of the first host trace
instance, used in the tracing session.

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 tracecmd/trace-record.c | 49 ++++++++++++++++++++++++++++++++---------
 1 file changed, 39 insertions(+), 10 deletions(-)

diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index d794f1af..4f412e8d 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -4128,6 +4128,23 @@ static void print_stat(struct buffer_instance *instance)
 		trace_seq_do_printf(&instance->s_print[cpu]);
 }
 
+static char *get_trace_clock(bool selected)
+{
+	struct buffer_instance *instance;
+
+	for_all_instances(instance) {
+		if (is_guest(instance))
+			continue;
+		break;
+	}
+
+	if (selected)
+		return tracefs_get_clock(instance ? instance->tracefs : NULL);
+	else
+		return tracefs_instance_file_read(instance ? instance->tracefs : NULL,
+						  "trace_clock", NULL);
+}
+
 enum {
 	DATA_FL_NONE		= 0,
 	DATA_FL_DATE		= 1,
@@ -6460,11 +6477,12 @@ static void get_tsc_offset(struct common_record_context *ctx)
 
 static void set_tsync_params(struct common_record_context *ctx)
 {
-	const char *clock = ctx->clock;
 	struct buffer_instance *instance;
 	int shift, mult;
 	bool force_tsc = false;
+	char *clock = NULL;
 
+	if (!ctx->clock) {
 	/*
 	 * If no clock is configured &&
 	 * KVM time sync protocol is available &&
@@ -6473,18 +6491,27 @@ static void set_tsync_params(struct common_record_context *ctx)
 	 * force using the x86-tsc clock for this host-guest tracing session
 	 * and store TSC to nsec multiplier and shift.
 	 */
-	if (!clock && tsync_proto_is_supported("kvm") &&
-	    clock_is_supported(NULL, TSC_CLOCK) &&
-	    !get_tsc_nsec(&shift, &mult) && mult) {
-		clock = TSC_CLOCK;
-		ctx->tsc2nsec.mult = mult;
-		ctx->tsc2nsec.shift = shift;
-		ctx->tsc2nsec.offset = get_clock_now(TSC_CLOCK);
-		force_tsc = true;
+		if (tsync_proto_is_supported("kvm") &&
+		    clock_is_supported(NULL, TSC_CLOCK) &&
+		    !get_tsc_nsec(&shift, &mult) && mult) {
+			clock = strdup(TSC_CLOCK);
+			if (!clock)
+				die("Cannot not allocate clock");
+			ctx->tsc2nsec.mult = mult;
+			ctx->tsc2nsec.shift = shift;
+			ctx->tsc2nsec.offset = get_clock_now(TSC_CLOCK);
+			force_tsc = true;
+		} else { /* Use the current clock of the first host instance */
+			clock = get_trace_clock(true);
+		}
+	} else {
+		clock = strdup(ctx->clock);
+		if (!clock)
+			die("Cannot not allocate clock");
 	}
 
 	if (!clock && !ctx->tsync_loop_interval)
-		return;
+		goto out;
 	for_all_instances(instance) {
 		if (clock && !(instance->flags & BUFFER_FL_HAS_CLOCK)) {
 			/* use the same clock in all tracing peers */
@@ -6506,6 +6533,8 @@ static void set_tsync_params(struct common_record_context *ctx)
 		}
 		instance->tsync_loop_interval = ctx->tsync_loop_interval;
 	}
+out:
+	free(clock);
 }
 
 /*
-- 
2.30.2