From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnaldo Carvalho de Melo Subject: Re: [PATCH 1/3] net: sendmmsg should only return an error if no messages were sent Date: Fri, 5 Aug 2011 11:40:27 -0300 Message-ID: <20110805144027.GA7560@ghostprotocols.net> References: <20110805000737.743684961@samba.org> <20110805000822.240895823@samba.org> <201108050357.p753vtpO022773@www262.sakura.ne.jp> <1312532408.2762.4.camel@menhir> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Tetsuo Handa , rdenis@simphalempin.com, netdev@vger.kernel.org To: Steven Whitehouse Return-path: Received: from mx1.redhat.com ([209.132.183.28]:37947 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756648Ab1HEOke (ORCPT ); Fri, 5 Aug 2011 10:40:34 -0400 Content-Disposition: inline In-Reply-To: <1312532408.2762.4.camel@menhir> Sender: netdev-owner@vger.kernel.org List-ID: Em Fri, Aug 05, 2011 at 09:20:08AM +0100, Steven Whitehouse escreveu: > On Fri, 2011-08-05 at 12:57 +0900, Tetsuo Handa wrote: > > Anton Blanchard wrote: > > > sendmmsg uses a similar error return strategy as recvmmsg but it > > > turns out to be a confusing way to communicate errors. > > > > > > The current code stores the error code away and returns it on the next > > > sendmmsg call. This means a call with completely valid arguments could > > > get an error from a previous call. > > > > > > Change things so we only return an error if no datagrams could be sent. > > > If less than the requested number of messages were sent, the application > > > must retry starting at the first failed one and if the problem is > > > persistent the error will be returned. > > > > > > This matches the behaviour of other syscalls like read/write - it > > > is not an error if less than the requested number of elements are sent. > > > > OK. David S. Miller suggested this behavior and Anton Blanchard agreed with > > this behavior. > > > > Quoting from commit a2e27255 "net: Introduce recvmmsg socket syscall": > > | . R?mi Denis-Courmont & Steven Whitehouse: If we receive N < vlen > > | datagrams and then recvmsg returns an error, recvmmsg will return > > | the successfully received datagrams, store the error and return it > > | in the next call. > > > > R?mi Denis-Courmont, Steven Whitehouse and Arnaldo Carvalho de Melo, do you > > want to change recvmmsg()'s behaviour as well? > > Since I've joined this part way through it seems, I'm assuming that if > something was sent/received then that will be returned and the error > stored until the next call. If nothing was sent/received then the error > can be returned immediately. > > That is what I'd expect to be the case, since otherwise it is impossible > to know how much has been successfully sent/received in the partial > failure case, I think. Also it means that sendmmesg/recvmmsg matches > sendmsg/recvmsg in terms of expected return values and thus the > principle of least surprise. > > So if thats what is being proposed, then it sounds good to me, Sounds sane to me too. - Arnaldo