slcan_attach: added '-f' commandline option to read status flags.

In the case of pending bus errors on some slcan adapters the read of the
status flags resets the adapter and clears the error LED.

This patch adds the commandline option to send the status read command to the
adapter as suggested by Thorsten Godau.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>

slcan_attach.c

@@ -61,13 +61,14 @@ void print_usage(char *prg)
 	fprintf(stderr, "\nUsage: %s [options] tty\n\n", prg);
 	fprintf(stderr, "Options: -o         (send open command 'O\\r')\n");
 	fprintf(stderr, "         -c         (send close command 'C\\r')\n");
+	fprintf(stderr, "         -f         (read status flags with 'F\\r' to reset error states)\n");
 	fprintf(stderr, "         -s <speed> (set CAN speed 0..8)\n");
 	fprintf(stderr, "         -b <btr>   (set bit time register value)\n");
 	fprintf(stderr, "         -d         (only detach line discipline)\n");
 	fprintf(stderr, "         -w         (attach - wait for keypess - detach)\n");
 	fprintf(stderr, "         -n <name>  (assign created netdevice name)\n");
 	fprintf(stderr, "\nExamples:\n");
-	fprintf(stderr, "slcan_attach -w -o -s6 -c /dev/ttyS1\n");
+	fprintf(stderr, "slcan_attach -w -o -f -s6 -c /dev/ttyS1\n");
 	fprintf(stderr, "slcan_attach /dev/ttyS1\n");
 	fprintf(stderr, "slcan_attach -d /dev/ttyS1\n");
 	fprintf(stderr, "slcan_attach -w -n can15 /dev/ttyS1\n");
@@ -83,14 +84,15 @@ int main(int argc, char **argv)
 	int waitkey = 0;
 	int send_open = 0;
 	int send_close = 0;
+	int send_read_status_flags = 0;
 	char *speed = NULL;
 	char *btr = NULL;
 	char buf[IFNAMSIZ+1];
 	char *tty;
 	char *name = NULL;
 	int opt;
 
-	while ((opt = getopt(argc, argv, "l:dwocs:b:n:?")) != -1) {
+	while ((opt = getopt(argc, argv, "l:dwocfs:b:n:?")) != -1) {
 		switch (opt) {
 		case 'l':
 			fprintf(stderr, "Ignored option '-l'\n");
@@ -112,6 +114,10 @@ int main(int argc, char **argv)
 			send_close = 1;
 			break;
 
+		case 'f':
+			send_read_status_flags = 1;
+			break;
+
 		case 's':
 			speed = optarg;
 			if (strlen(speed) > 1)
@@ -159,6 +165,11 @@ int main(int argc, char **argv)
 			write(fd, buf, strlen(buf));
 		}
 
+		if (send_read_status_flags) {
+			sprintf(buf, "F\r");
+			write(fd, buf, strlen(buf));
+		}
+
 		if (send_open) {
 			sprintf(buf, "O\r");
 			write(fd, buf, strlen(buf));