Delete lock file if contained pid is stale

Fixes #2.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

Author: a3f

serial.c

@@ -22,6 +22,8 @@
 
 #include <limits.h>
 #include <sys/ioctl.h>
+#include <signal.h>
+#include <errno.h>
 #include <arpa/telnet.h>
 
 #include "microcom.h"
@@ -178,15 +180,18 @@ struct ios_ops * serial_init(char *device)
 	}
 
 	fd = open(lockfile, O_RDONLY);
-	if (fd >= 0 && !opt_force) {
+	if (fd >= 0) {
+		read(fd, &pid, sizeof(long));
 		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();
+		if (kill(pid, 0) < 0 && errno == ESRCH) {
+			printf("lockfile contains stale pid, ignoring\n");
+			serial_unlock();
+		} else if (opt_force) {
+			printf("lockfile for port exists, ignoring\n");
+			serial_unlock();
+		} else {
+			main_usage(3, "lockfile for port exists", device);
+		}
 	}
 
 	fd = open(lockfile, O_RDWR | O_CREAT, 0444);