From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932719AbZHDJZK (ORCPT ); Tue, 4 Aug 2009 05:25:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755287AbZHDJZJ (ORCPT ); Tue, 4 Aug 2009 05:25:09 -0400 Received: from mx2.redhat.com ([66.187.237.31]:40779 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754773AbZHDJZI (ORCPT ); Tue, 4 Aug 2009 05:25:08 -0400 Message-ID: <4A77FFB5.4060201@redhat.com> Date: Tue, 04 Aug 2009 12:30:29 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1b3pre) Gecko/20090513 Fedora/3.0-2.3.beta2.fc11 Lightning/1.0pre Thunderbird/3.0b2 MIME-Version: 1.0 To: Gleb Natapov CC: "Michael S. Tsirkin" , davidel@xmailserver.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH-RFC 2/2] eventfd: EFD_STATE flag References: <20090728175538.GC21549@redhat.com> <4A76FDB2.7080706@redhat.com> <20090803151426.GA3630@redhat.com> <4A770260.5000507@redhat.com> <20090803165708.GB3630@redhat.com> <4A77F6EF.8010002@redhat.com> <20090804085406.GA3311@redhat.com> <4A77FCB8.1000205@redhat.com> <20090804091755.GD4764@redhat.com> <4A77FE9D.3020505@redhat.com> <20090804092342.GE4764@redhat.com> In-Reply-To: <20090804092342.GE4764@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/04/2009 12:23 PM, Gleb Natapov wrote: > On Tue, Aug 04, 2009 at 12:25:49PM +0300, Avi Kivity wrote: > >> On 08/04/2009 12:17 PM, Gleb Natapov wrote: >> >>>> If a different read comes after the write but after our read, it will >>>> have transferred the value, resulting in the same situation. >>>> >>>> I think reads should never block with a state based mechanism. >>>> >>>> >>>> >>> Reader may want to poll for the status change. >>> >>> >> Without epoll(), it's inherently racy since reads from other processes >> can clear the status. >> >> > This is correct for any file descriptor. Multiple readers shouldn't > simultaneously read from the same files descriptor if they expect to > make any sense from a result. > I think counting eventfd is an exception, but in general you are right. -- error compiling committee.c: too many arguments to function