Merge branch 'flock' of https://github.com/lynxeye-dev/microcom into HEAD

While some tools still use uucp style locking (e.g. minicom) there isn't
much much breakage exprected by dropping it.

This only hurts if microcom (or another terminal program that relies on
flock() only (e.g. picocom)) and a uucp-locking program are used on the
same device, which should be rare.

Also swiching completely away from uucp (instead of doing both uucp
and flock() for some time) might give some incentive to other terminal
programs to do the same move and maybe eventually get rid of
uucp-locking completely.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

Author: Uwe Kleine-König

serial.c

@@ -21,13 +21,13 @@
 ****************************************************************************/
 
 #include <limits.h>
+#include <sys/file.h>
 #include <sys/ioctl.h>
 #include <arpa/telnet.h>
 
 #include "microcom.h"
 
 static struct termios pots;		/* old port termios settings to restore */
-static char *lockfile;
 
 static void init_comm(struct termios *pts)
 {
@@ -134,39 +134,23 @@ static int serial_send_break(struct ios_ops *ios)
 	return 0;
 }
 
-/* unlink the lockfile */
-static void serial_unlock()
-{
-	if (lockfile)
-		unlink(lockfile);
-}
-
 /* restore original terminal settings on exit */
 static void serial_exit(struct ios_ops *ios)
 {
 	tcsetattr(ios->fd, TCSANOW, &pots);
 	close(ios->fd);
 	free(ios);
-	serial_unlock();
 }
 
-#define BUFLEN 512
-
 struct ios_ops * serial_init(char *device)
 {
 	struct termios pts;	/* termios settings on port */
 	struct ios_ops *ops;
-	int fd;
-	char *substring;
-	long pid;
-	int ret;
+	int fd, ret;
 
 	ops = malloc(sizeof(*ops));
 	if (!ops)
 		return NULL;
-	lockfile = malloc(BUFLEN);
-	if (!lockfile)
-		return NULL;
 
 	ops->write = serial_write;
 	ops->read = serial_read;
@@ -177,51 +161,20 @@ struct ios_ops * serial_init(char *device)
 	ops->exit = serial_exit;
 	ops->istelnet = false;
 
-	/* check lockfile */
-	substring = strrchr(device, '/');
-	if (substring)
-		substring++;
-	else
-		substring = device;
-
-	ret = snprintf(lockfile, BUFLEN, "/var/lock/LCK..%s", substring);
-	if (ret >= BUFLEN) {
-		printf("path to lockfile too long\n");
-		exit(1);
-	}
-
-	fd = open(lockfile, O_RDONLY);
-	if (fd >= 0 && !opt_force) {
-		close(fd);
-		main_usage(3, "lockfile for port exists", device);
-	}
-
-	if (fd >= 0 && opt_force) {
-		close(fd);
-		printf("lockfile for port exists, ignoring\n");
-		serial_unlock();
-	}
-
-	fd = open(lockfile, O_RDWR | O_CREAT, 0444);
-	if (fd < 0 && opt_force) {
-		printf("cannot create lockfile. ignoring\n");
-		lockfile = NULL;
-		goto force;
-	}
-	if (fd < 0)
-		main_usage(3, "cannot create lockfile", device);
-	/* Kermit wants binary pid */
-	pid = getpid();
-	write(fd, &pid, sizeof(long));
-	close(fd);
-force:
 	/* open the device */
 	fd = open(device, O_RDWR | O_NONBLOCK);
 	ops->fd = fd;
 
-	if (fd < 0) {
-		serial_unlock();
+	if (fd < 0)
 		main_usage(2, "cannot open device", device);
+
+	/* try to lock the device */
+	ret = flock(fd, LOCK_EX | LOCK_NB);
+	if (ret) {
+		if (!opt_force)
+			main_usage(3, "could not lock port", device);
+		else
+			printf("could not lock port, ignoring\n");
 	}
 
 	/* modify the port configuration */