Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755277AbaFPJ7P (ORCPT ); Mon, 16 Jun 2014 05:59:15 -0400 Received: from mail-qa0-f54.google.com ([209.85.216.54]:48555 "EHLO mail-qa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754820AbaFPJ7N (ORCPT ); Mon, 16 Jun 2014 05:59:13 -0400 MIME-Version: 1.0 Reply-To: mtk.manpages@gmail.com In-Reply-To: <20140529141705.GI2764@kernel.org> References: <20140527192115.GD25474@kernel.org> <20140527203010.GA2764@kernel.org> <5385D47A.3070401@gmail.com> <20140528150720.GB2764@kernel.org> <063D6719AE5E284EB5DD2968C1650D6D1724F2A0@AcuExch.aculab.com> <20140528195004.GD2764@kernel.org> <063D6719AE5E284EB5DD2968C1650D6D1724FB67@AcuExch.aculab.com> <20140529135547.GG2764@kernel.org> <063D6719AE5E284EB5DD2968C1650D6D1724FC78@AcuExch.aculab.com> <20140529141705.GI2764@kernel.org> From: "Michael Kerrisk (man-pages)" Date: Mon, 16 Jun 2014 11:58:51 +0200 Message-ID: Subject: Re: [PATCH/RFC] Re: recvmmsg() timeout behavior strangeness [RESEND] To: Arnaldo Carvalho de Melo Cc: David Laight , lkml , "linux-man@vger.kernel.org" , netdev , =?UTF-8?Q?Ondrej_B=C3=ADlka?= , Caitlin Bestler , Neil Horman , Elie De Brauwer , David Miller , Steven Whitehouse , =?UTF-8?Q?R=C3=A9mi_Denis=2DCourmont?= , Paul Moore , Chris Friesen Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Arnaldo, Things have gone quiet ;-). What's the current state of this patch? Thanks, Michael On Thu, May 29, 2014 at 4:17 PM, Arnaldo Carvalho de Melo wrote: > Em Thu, May 29, 2014 at 02:06:04PM +0000, David Laight escreveu: >> From: 'Arnaldo Carvalho de Melo' >> ... >> > > I remember some discussions from an XNET standards meeting (I've forgotten >> > > exactly which errors on which calls were being discussed). >> > > My recollection is that you return success with a partial transfer >> > > count for ANY error that happens after some data has been transferred. >> > > The actual error will be returned when it happens again on the next >> > > system call - Note the AGAIN, not a saved error. > >> > A saved error, for the right entity, in the recvmmsg case, that >> > basically is batching multiple recvmsg syscalls, doesn't sound like a >> > problem, i.e. the idea is to, as much as possible, mimic what multiple >> > recvmsg calls would do, but reduce its in/out kernel (and inside kernel >> > subsystems) overhead. > >> > Perhaps we can have something in between, i.e. for things like EFAULT, >> > we should report straight away, effectively dropping whatever datagrams >> > successfully received in the current batch, do you agree? > >> Not unreasonable - EFAULT shouldn't happen unless the application >> is buggy. > > Ok. > >> > For transient errors the existing mechanism, fixed so that only per >> > socket errors are saved for later, as today, could be kept? > >> I don't think it is ever necessary to save an errno value for the >> next system call at all. >> Just process the next system call and see what happens. > >> If the call returns with less than the maximum number of datagrams >> and with a non-zero timeout left - then the application can infer >> that it was terminated by an abnormal event of some kind. >> This might be a signal. > > Then it could use getsockopt(SO_ERROR) perhaps? I.e. we don't return the > error on the next call, but we provide a way for the app to retrieve the > reason for the smaller than expected batch? > >> I'm not sure if an icmp error on a connected datagram socket could >> generate a 'disconnect'. It might happen if the interface is being >> used for something like SCTP. >> In either case the next call will detect the error. > > - Arnaldo -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- 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/