Add a configuration file option for the extra sync-fup check.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>

config.c

@@ -301,6 +301,12 @@ static enum parser_result parse_global_setting(const char *option,
 			return r;
 		*cfg->tx_timestamp_timeout = val;
 
+	} else if (!strcmp(option, "check_fup_sync")) {
+		r = get_ranged_int(value, &val, 0, 1);
+		if (r != PARSED_OK)
+			return r;
+		*cfg->check_fup_sync = val;
+
 	} else if (!strcmp(option, "pi_proportional_const")) {
 		r = get_ranged_double(value, &df, 0.0, DBL_MAX);
 		if (r != PARSED_OK)

config.h

@@ -70,6 +70,7 @@ struct config {
 	struct port_defaults pod;
 	int *assume_two_step;
 	int *tx_timestamp_timeout;
+	int *check_fup_sync;
 
 	enum servo_type clock_servo;
 

default.cfg

@@ -36,6 +36,7 @@ use_syslog		1
 verbose			0
 summary_interval	0
 kernel_leap		1
+check_fup_sync		0
 #
 # Servo Options
 #

gPTP.cfg

@@ -35,6 +35,7 @@ use_syslog		1
 verbose			0
 summary_interval	0
 kernel_leap		1
+check_fup_sync		0
 #
 # Servo options
 #

ptp4l.8

@@ -255,6 +255,18 @@ The number of milliseconds to poll waiting for the tx time stamp from the kernel
 when a message has recently been sent.
 The default is 1.
 .TP
+.B check_fup_sync
+Because of packet reordering that can occur in the network, in the
+hardware, or in the networking stack, a follow up message can appear
+to arrive in the application before the matching sync message. As this
+is a normal occurrence, and the sequenceID message field ensures
+proper matching, the ptp4l program accepts out of order packets. This
+option adds an additional check using the software time stamps from
+the networking stack to verify that the sync message did arrive
+first. This option is only useful if you do not trust the sequence IDs
+generated by the master.
+The default is 0 (disabled).
+.TP
 .B clock_servo
 The servo which is used to synchronize the local clock. Currently only one
 servo is implemented, a PI controller.

ptp4l.c

@@ -92,6 +92,7 @@ static struct config cfg_settings = {
 
 	.assume_two_step = &assume_two_step,
 	.tx_timestamp_timeout = &sk_tx_timeout,
+	.check_fup_sync = &sk_check_fupsync,
 
 	.clock_servo = CLOCK_SERVO_PI,