tests/qemu-iotests/085


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--- a/include/applets.h
+++ b/include/applets.h
@@ -223,6 +223,7 @@ USE_LN(APPLET_NOEXEC(ln, ln, _BB_DIR_BIN
 USE_LOAD_POLICY(APPLET(load_policy, _BB_DIR_USR_SBIN, _BB_SUID_NEVER))
 USE_LOADFONT(APPLET(loadfont, _BB_DIR_USR_SBIN, _BB_SUID_NEVER))
 USE_LOADKMAP(APPLET(loadkmap, _BB_DIR_SBIN, _BB_SUID_NEVER))
+USE_LOCK(APPLET(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))
--- a/include/usage.h
+++ b/include/usage.h
@@ -2150,6 +2150,9 @@
 #define loadkmap_example_usage \
        "$ loadkmap < /etc/i18n/lang-keymap\n"
 
+#define lock_trivial_usage NOUSAGE_STR
+#define lock_full_usage ""
+
 #define logger_trivial_usage \
        "[OPTION]... [MESSAGE]"
 #define logger_full_usage "\n\n" \
--- a/miscutils/Config.in
+++ b/miscutils/Config.in
@@ -395,6 +395,12 @@ config FEATURE_HDPARM_HDIO_GETSET_DMA
 	  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
--- a/miscutils/Kbuild
+++ b/miscutils/Kbuild
@@ -21,6 +21,7 @@ lib-$(CONFIG_INOTIFYD)    += inotifyd.o
 lib-$(CONFIG_FEATURE_LAST_SMALL)+= last.o
 lib-$(CONFIG_FEATURE_LAST_FANCY)+= last_fancy.o
 lib-$(CONFIG_LESS)        += less.o
+lib-$(CONFIG_LOCK)        += lock.o
 lib-$(CONFIG_MAKEDEVS)    += makedevs.o
 lib-$(CONFIG_MAN)         += man.o
 lib-$(CONFIG_MICROCOM)    += microcom.o
--- /dev/null
+++ b/miscutils/lock.c
@@ -0,0 +1,132 @@
+/*
+ * 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;
+}
+
+int lock_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int lock_main(int argc, char **argv)
+{
+	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();
+}