busybox: lock: implement -n "Fail rather than wait"

lock -n is similiar to flock -n. If the lock was already taken,
fail with exit code = 1 and write error message to stderr.

example:
if ! lock -n /tmp/foo ; then
	echo lock exits.
else
	echo lock was free. But is locked now.
fi
> lock was free. But is locked now.
> lock exists.

Signed-off-by: Alexander Couzens <lynxis@fe80.eu>
SVN-Revision: 46836

diff --git a/package/utils/busybox/patches/220-add_lock_util.patch b/package/utils/busybox/patches/220-add_lock_util.patch
index 5c7ca26da8b373c59d8a71b5247ef58ae64e3adb..9cac9e6219548253e9559f561e065369f6325793 100644 (file)
--- a/package/utils/busybox/patches/220-add_lock_util.patch
+++ b/package/utils/busybox/patches/220-add_lock_util.patch
@@ -35,7 +35,7 @@
  lib-$(CONFIG_MICROCOM)    += microcom.o
 --- /dev/null
 +++ b/miscutils/lock.c
-@@ -0,0 +1,135 @@
+@@ -0,0 +1,144 @@
 +/*
 + * Copyright (C) 2006 Felix Fietkau <nbd@openwrt.org>
 + *
@@ -56,6 +56,7 @@
 +static int unlock = 0;
 +static int shared = 0;
 +static int waitonly = 0;
++static int try_lock = 0;
 +static int fd;
 +static char *file;
 +
@@ -65,6 +66,7 @@
 +                      "       -s      Use shared locking\n"
 +                      "       -u      Unlock\n"
 +                      "       -w      Wait for the lock to become free, don't acquire lock\n"
++                      "       -n      Don't wait for the lock to become free. Fail with exit code\n"
 +                                      "\n", name);
 +      exit(1);
 +}
@@ -95,6 +97,7 @@
 +static int do_lock(void)
 +{
 +      int pid;
++      int flags;
 +      char pidstr[8];
 +
 +      if ((fd = open(file, O_RDWR | O_CREAT | O_EXCL, 0700)) < 0) {
@@ -104,7 +107,10 @@
 +              }
 +      }
 +
-+      if (flock(fd, (shared ? LOCK_SH : LOCK_EX)) < 0) {
++      flags = shared ? LOCK_SH : LOCK_EX;
++      flags |= try_lock ? LOCK_NB : 0;
++
++      if (flock(fd, flags) < 0) {
 +              fprintf(stderr, "Can't lock %s\n", file);
 +              return 1;
 +      }
@@ -156,6 +162,9 @@
 +                              case 'u':
 +                                      unlock = 1;
 +                                      break;
++                              case 'n':
++                                      try_lock = 1;
++                                      break;
 +                      }
 +              }
 +              c--;