From mboxrd@z Thu Jan 1 00:00:00 1970 From: Trond Myklebust Subject: Re: Propagation of changes in shared mmap()ed NFS files Date: Sat, 21 Jun 2008 17:43:44 -0400 Message-ID: <1214084624.7493.0.camel@localhost> References: <1214075120367@dmwebmail.dmwebmail.chezphil.org> Mime-Version: 1.0 Content-Type: text/plain Cc: linux-nfs@vger.kernel.org To: Phil Endecott Return-path: Received: from mail-out1.uio.no ([129.240.10.57]:41033 "EHLO mail-out1.uio.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753145AbYFUVnt (ORCPT ); Sat, 21 Jun 2008 17:43:49 -0400 In-Reply-To: <1214075120367-YnoLgZYwwYuCbKHnblo0pmrPP3OPMK55cpQHUIT47Ck@public.gmane.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Sat, 2008-06-21 at 20:05 +0100, Phil Endecott wrote: > Dear Experts, > > I have a program which uses an mmap()ed read-mostly data file. When > not using NFS, each instance of the program can use inotify to detect > when other instances have made changes to the data file. Since inotify > doesn't work with NFS, I have now implemented a scheme using network > broadcasts to announce changes. At present it works like this: > > All instances of the program mmap(MAP_SHARED) the data file. > > One instance stores some new data at the end of the file and calls > msync(MS_SYNC) on the affected pages. It then "atomically commits" the > new data by write()ing a new header at the start of the file with an > "end of data" field advanced to include the new data. It then calls > fdatasync(). Then it transmits a broadcast packet. > > The other instance(s) of the program receive the broadcast packet and > read() the header at the start of the file. My hope was that they > would see the new value, but they don't; they continue to see the old value. open(O_DIRECT) is your friend. Cheers Trond