Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S270512AbTGNDOd (ORCPT ); Sun, 13 Jul 2003 23:14:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S270513AbTGNDOd (ORCPT ); Sun, 13 Jul 2003 23:14:33 -0400 Received: from x35.xmailserver.org ([208.129.208.51]:18313 "EHLO x35.xmailserver.org") by vger.kernel.org with ESMTP id S270512AbTGNDO0 (ORCPT ); Sun, 13 Jul 2003 23:14:26 -0400 X-AuthUser: davidel@xmailserver.org Date: Sun, 13 Jul 2003 20:21:49 -0700 (PDT) From: Davide Libenzi X-X-Sender: davide@bigblue.dev.mcafeelabs.com To: Jamie Lokier cc: "David S. Miller" , Eric Varsanyi , Linux Kernel Mailing List , kuznet@ms2.inr.ac.ru Subject: Re: POLLRDONCE optimisation for epoll users (was: epoll and half closed TCP connections) In-Reply-To: <20030714031614.GD23110@mail.jlokier.co.uk> Message-ID: References: <20030712222457.3d132897.davem@redhat.com> <20030713140758.GF19132@mail.jlokier.co.uk> <20030713191559.GA20573@mail.jlokier.co.uk> <20030714014135.GA22769@mail.jlokier.co.uk> <20030714022412.GD22769@mail.jlokier.co.uk> <20030714025644.GA23110@mail.jlokier.co.uk> <20030714031614.GD23110@mail.jlokier.co.uk> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1317 Lines: 38 On Mon, 14 Jul 2003, Jamie Lokier wrote: > Davide Libenzi wrote: > > > > Where this will break by using a POLLRDHUP ? > > > > > > It will break if > > > > > > (a) fd isn't a socket > > > (b) fd isn't a TCP socket > > > (c) kernel version <= 2.5.75 > > > (d) SO_RCVLOWAT < s > > > (e) there is urgent data with OOBINLINE (I think) > > > Jamie, did you smoke that stuff again ? :) > > With Eric patch in the proper places it is just fine. You just make > > f_op->poll() to report the extra flag other that POLLIN. What's the problem ? > > The problem in cases (a)-(e) is your loop will call read() just once > when it needs to call read() until it sees EAGAIN. > > What's wrong is the behaviour of your program when the extra flag > _isn't_ set. Jamie, the loop will call read(2) until data is available. With the trick of checking the returned number of bytes you can avoid the extra EAGAIN read(2). That's the point of the read(2) trick. The final check for RDHUP will tell that it has no more to wait for POLLINs since there's no more someone sending. - Davide - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/