From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH-RFC 2/2] eventfd: EFD_STATE flag Date: Tue, 04 Aug 2009 12:30:29 +0300 Message-ID: <4A77FFB5.4060201@redhat.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "Michael S. Tsirkin" , davidel@xmailserver.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: Gleb Natapov Return-path: In-Reply-To: <20090804092342.GE4764@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.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