From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932702AbZHDJU3 (ORCPT ); Tue, 4 Aug 2009 05:20:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932650AbZHDJU2 (ORCPT ); Tue, 4 Aug 2009 05:20:28 -0400 Received: from mx2.redhat.com ([66.187.237.31]:38845 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932527AbZHDJU2 (ORCPT ); Tue, 4 Aug 2009 05:20:28 -0400 Message-ID: <4A77FE9D.3020505@redhat.com> Date: Tue, 04 Aug 2009 12:25:49 +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> In-Reply-To: <20090804091755.GD4764@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 12:17 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. The "last read value" needs to be maintained for each reader, which is not possible with read(). -- error compiling committee.c: too many arguments to function