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

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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
This commit is contained in:
Felix Fietkau 2015-09-09 20:36:10 +00:00
parent 5fcafa319d
commit 3670f4128d
1 changed files with 11 additions and 2 deletions
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13
package/utils/busybox/patches/220-add_lock_util.patch
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@ -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--;