From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263568AbUBFJJ6 (ORCPT ); Fri, 6 Feb 2004 04:09:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S265291AbUBFJJ6 (ORCPT ); Fri, 6 Feb 2004 04:09:58 -0500 Received: from mta05-svc.ntlworld.com ([62.253.162.45]:4641 "EHLO mta05-svc.ntlworld.com") by vger.kernel.org with ESMTP id S263568AbUBFJJz (ORCPT ); Fri, 6 Feb 2004 04:09:55 -0500 Message-ID: <402359E1.6000007@ntlworld.com> Date: Fri, 06 Feb 2004 09:09:53 +0000 From: Matt User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.6) Gecko/20040122 Debian/1.4-6 StumbleUpon/1.87 X-Accept-Language: en, en-gb, ja MIME-Version: 1.0 To: Andrew Morton , Linux Kernel Mailing List Subject: Re: VFS locking: f_pos thread-safe ? Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > Werner Almesberger wrote: >> >> "[...] read( ) [...] shall be atomic with respect to each other >> in the effects specified in IEEE Std. 1003.1-200x when they >> operate on regular files. If two threads each call one of these >> functions, each call shall either see all of the specified >> effects of the other call, or none of them." > Whichever thread finishes its read last gets to update f_pos. > I'm struggling a bit to understand what they're calling for there. If > thread A enters a read and then shortly afterwards thread B enters the > read, does thread B see an f_pos which starts out at the beginning of A's > read, or the end of it? > Similar questions apply as the threads exit their read()s. > Either way, there's no way in which we should serialise concurrent readers. > That would really suck for sensible apps which are using pread64(). Surely, we can just serialise read() (and related) calls that modify f_pos? Since pread() doesn't modify f_pos we shouldn't need to serialise those calls no? Also doesn't spec make the same claims about other calls that modify f_pos such as write()? Matt