Index: busybox-1.7.2/include/applets.h
===================================================================
--- busybox-1.7.2.orig/include/applets.h	2007-10-30 15:35:03.000000000 -0500
+++ busybox-1.7.2/include/applets.h	2007-10-30 15:35:03.000000000 -0500
@@ -209,6 +209,7 @@
 USE_LOAD_POLICY(APPLET(load_policy, _BB_DIR_USR_SBIN, _BB_SUID_NEVER))
 USE_LOADFONT(APPLET(loadfont, _BB_DIR_USR_BIN, _BB_SUID_NEVER))
 USE_LOADKMAP(APPLET(loadkmap, _BB_DIR_SBIN, _BB_SUID_NEVER))
+USE_LOCK(APPLET_NOUSAGE(lock, lock, _BB_DIR_BIN, _BB_SUID_NEVER))
 USE_LOGGER(APPLET(logger, _BB_DIR_USR_BIN, _BB_SUID_NEVER))
 USE_LOGIN(APPLET(login, _BB_DIR_BIN, _BB_SUID_ALWAYS))
 USE_LOGNAME(APPLET_NOFORK(logname, logname, _BB_DIR_USR_BIN, _BB_SUID_NEVER, logname))
Index: busybox-1.7.2/miscutils/Config.in
===================================================================
--- busybox-1.7.2.orig/miscutils/Config.in	2007-10-30 15:34:59.000000000 -0500
+++ busybox-1.7.2/miscutils/Config.in	2007-10-30 15:35:03.000000000 -0500
@@ -244,6 +244,12 @@
 	  Enables the 'hdparm -d' option to get/set using_dma flag.
 	  This is dangerous stuff, so you should probably say N.
 
+config LOCK
+	bool "lock"
+	default y
+	help
+	  Small utility for using locks in scripts
+
 config MAKEDEVS
 	bool "makedevs"
 	default n
Index: busybox-1.7.2/miscutils/Kbuild
===================================================================
--- busybox-1.7.2.orig/miscutils/Kbuild	2007-10-30 15:34:59.000000000 -0500
+++ busybox-1.7.2/miscutils/Kbuild	2007-10-30 15:35:03.000000000 -0500
@@ -16,6 +16,7 @@
 lib-$(CONFIG_HDPARM)      += hdparm.o
 lib-$(CONFIG_LAST)        += last.o
 lib-$(CONFIG_LESS)        += less.o
+lib-$(CONFIG_LOCK)        += lock.o
 lib-$(CONFIG_MAKEDEVS)    += makedevs.o
 lib-$(CONFIG_MOUNTPOINT)  += mountpoint.o
 lib-$(CONFIG_MT)          += mt.o
Index: busybox-1.7.2/miscutils/lock.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ busybox-1.7.2/miscutils/lock.c	2007-10-30 15:35:03.000000000 -0500
@@ -0,0 +1,135 @@
+/*
+ * Copyright (C) 2006 Felix Fietkau <nbd@openwrt.org>
+ *
+ * This is free software, licensed under the GNU General Public License v2.
+ */
+#include <sys/types.h>
+#include <sys/file.h>
+#include <sys/stat.h>
+#include <signal.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <stdio.h>
+#include "busybox.h" 
+
+static int unlock = 0;
+static int shared = 0;
+static int waitonly = 0;
+static int fd;
+static char *file;
+
+static void usage(char *name)
+{
+	fprintf(stderr, "Usage: %s [-suw] <filename>\n"
+	                "	-s	Use shared locking\n"
+	                "	-u	Unlock\n"
+	                "	-w	Wait for the lock to become free, don't acquire lock\n"
+					"\n", name);
+	exit(1);
+}
+
+static void exit_unlock(int sig)
+{
+	flock(fd, LOCK_UN);
+	exit(0);
+}
+
+static int do_unlock(void)
+{
+	FILE *f;
+	int i;
+	
+	if ((f = fopen(file, "r")) == NULL)
+		return 0;
+	
+	fscanf(f, "%d", &i);
+	if (i > 0)
+		kill(i, SIGTERM);
+	
+	fclose(f);
+
+	return 0;
+}
+		
+static int do_lock(void)
+{
+	int pid;
+	char pidstr[8];
+
+	if ((fd = open(file, O_RDWR | O_CREAT | O_EXCL, 0700)) < 0) {
+		if ((fd = open(file, O_RDWR)) < 0) {
+			fprintf(stderr, "Can't open %s\n", file);
+			return 1;
+		}
+	}
+
+	if (flock(fd, (shared ? LOCK_SH : LOCK_EX)) < 0) {
+		fprintf(stderr, "Can't lock %s\n", file);
+		return 1;
+	}
+
+	pid = fork();
+
+	if (pid < 0)
+		return -1;
+	
+	if (pid == 0) {
+		signal(SIGKILL, exit_unlock);
+		signal(SIGTERM, exit_unlock);
+		signal(SIGINT, exit_unlock);
+		if (waitonly)
+			exit_unlock(0);
+		else
+			while (1)
+				sleep(1);
+	} else {
+		if (!waitonly) {
+			lseek(fd, 0, SEEK_SET);
+			ftruncate(fd, 0);
+			sprintf(pidstr, "%d\n", pid);
+			write(fd, pidstr, strlen(pidstr));
+			close(fd);
+		}
+
+		return 0;
+	}
+	return 0;
+}
+
+#ifndef CONFIG_LOCK
+int main(int argc, char **argv)
+#else
+int lock_main(int argc, char **argv)
+#endif
+{
+	char **args = &argv[1];
+	int c = argc - 1;
+
+	while ((*args != NULL) && (*args)[0] == '-') {
+		char *ch = *args;
+		while (*(++ch) > 0) {
+			switch(*ch) {
+				case 'w':
+					waitonly = 1;
+					break;
+				case 's':
+					shared = 1;
+					break;
+				case 'u':
+					unlock = 1;
+					break;
+			}
+		}
+		c--;
+		args++;
+	}
+
+	if (c != 1)
+		usage(argv[0]);
+
+	file = *args;
+	if (unlock)
+		return do_unlock();
+	else
+		return do_lock();
+}