This small project provides a couple of useful utilities for
validating lock support on an OCFS2 filesystem. Historically, OCFS2
supported only advisory locks using the flock(2) system call as
documented in [1] section III, item 10, page 12.
OCFS2 supports POSIX style locks (see lockf(3) and fcntl(2))
but only when using a userspace cluster stack. This is documented
in [2] in the section entitled Cluster aware POSIX file locks. The
feature is supported in Linux Kernel 2.6.28 and higher. Apparently, the
default O2CB cluster stack is a kernel-based cluster stack not a
userspace cluster stack.
POSIX locks are used internally by Java's FileChannel.lock method.
Thus, lock support on OCFS2 is relevant to anyone trying to use file
locks in Java to support synchronization between Java processes running
on different cluster nodes. This is one of the [supported HA solutions]
(http://activemq.apache.com/shared-file-system-master-slave.html) for
[Apache Active MQ] (http://activemq.apache.com).
Using the utilities in this project, you can quickly assess what you're working with in your OCFS2 configuration.
This project includes a simple utility written in C as well as a
simple Java program (for those of you needing to test locks acquired
using Java's FileChannel class).
The project's Makefile will build both utilities by default by simply running
make
If you don't have Java or simply don't want to build the Java program, you can build just the C-based utility using
make locktest
The locktest utility provided in this project is a C program that
can acquire a lock using either flock, lockf, or fcntl.
Using this utility on two different cluster nodes, you can attempt to
obtain a lock on a given file using any of these mechanisms, and see for
yourself whether what should be an exclusive lock is actually an
exclusive lock.
Run locktest with no arguments to see the command line syntax.
Example -- acquire a lock on a file named LOCK using flock:
./locktest flock LOCK
This example uses the default ten second delay after acquiring the lock before releasing it.
The LockTest.class is a Java program that acquires a lock using
the FileChannel.lock method.
Run java LockTest to see the command line syntax.
Example --- acquire a lock on a file named LOCK
java LockTest LOCK