From mboxrd@z Thu Jan 1 00:00:00 1970 From: Evgeniy Polyakov Subject: Re: [PATCH] tcp: do not promote SPLICE_F_NONBLOCK to socket O_NONBLOCK Date: Thu, 17 Jul 2008 21:41:56 +0400 Message-ID: <20080717174150.GA24002@2ka.mipt.ru> References: <200807171633.49791.opurdila@ixiacom.com> <20080717142132.GA11702@2ka.mipt.ru> <200807171747.27775.opurdila@ixiacom.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Octavian Purdila Return-path: Received: from relay.2ka.mipt.ru ([194.85.80.65]:50961 "EHLO 2ka.mipt.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756077AbYGQRmQ (ORCPT ); Thu, 17 Jul 2008 13:42:16 -0400 Content-Disposition: inline In-Reply-To: <200807171747.27775.opurdila@ixiacom.com> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, Jul 17, 2008 at 05:47:27PM +0300, Octavian Purdila (opurdila@ixiacom.com) wrote: > > Existing behaviour was selected to be able to have a progress if socket > > does not have enough data to fill the pipe. With your change if socket > > is not opened with non-blocking mode reading will block not matter if > > SPLICE_F_NONBLOCK is set or not. > > I am probably missing some usecases here, but usually if you want to use > non-blocking I/O you need to use special approach anyway (e.g. code the > poll/epoll/select bits) so then you could open the socket with O_NONBLOCK. It depends. Splice clearly states that it tries to be nonblocking with given flag being set, and its reading will be non-blocking indeed. > > This is a quite serious break of the > > overall idea behind SPLICE_F_NONBLOCK. > > > > I don't know... the man page explicitly says that even when you use > SPLICE_F_NONBLOCK splice may block because of the underlying fd blocking. Yes, but reading from the network will not. > But more importantly, how can we solve the deadlock issue described in the > patch? Do we need all of the complications of async I/O for such a simple and > common usecase? I'm not sure I understand how it can deadlock, please explain it in more details. -- Evgeniy Polyakov