From: Larry McVoy <lm@bitmover.com>
Date: Sun, 14 Oct 2001 11:11:04 -0700
Message-Id: <200110141811.f9EIB4823631@work.bitmover.com>
To: linux-kernel@vger.kernel.org
Subject: NFS file locking?
Sender: linux-kernel-owner@vger.kernel.org

Hi, the open(2) man page says:

       O_EXCL When  used with O_CREAT, if the file already exists
              it is an error and the open will fail.   O_EXCL  is
              broken  on NFS file systems, programs which rely on
              it for performing locking tasks will contain a race
              condition.  The solution for performing atomic file
              locking using a lockfile is to create a unique file
              on  the  same  fs (e.g., incorporating hostname and
              pid), use link(2) to make a link to  the  lockfile.
              If  link() returns 0, the lock is successful.  Oth?
              erwise, use stat(2) on the unique file to check  if
              its  link  count  has increased to 2, in which case
              the lock is also successful.

I coded this up and tried it here on a cluster of different operating
systems (Linux 2.4.5 server, linux, freebsd, solaris, aix, hpux, irix
clients) and it doesn't work.

2 questions:

a) is it the belief of folks here that this should work?

b) if performance isn't a big issue, is there any portable way to do
   locking over NFS with just files?

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