From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MQ4kX-0000xq-GR for qemu-devel@nongnu.org; Sun, 12 Jul 2009 15:30:13 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MQ4kS-0000vm-Mr for qemu-devel@nongnu.org; Sun, 12 Jul 2009 15:30:12 -0400 Received: from [199.232.76.173] (port=58935 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MQ4kS-0000ve-Cd for qemu-devel@nongnu.org; Sun, 12 Jul 2009 15:30:08 -0400 Received: from mx2.redhat.com ([66.187.237.31]:41338) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1MQ4kR-0002WC-VZ for qemu-devel@nongnu.org; Sun, 12 Jul 2009 15:30:08 -0400 Message-ID: <4A5A39CA.5000306@redhat.com> Date: Sun, 12 Jul 2009 22:30:18 +0300 From: Avi Kivity MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH 2/3] move vm stop/start to migrate_set_state References: <1247140059-5034-1-git-send-email-pbonzini@redhat.com> <1247140059-5034-3-git-send-email-pbonzini@redhat.com> <4A55F46F.6060705@codemonkey.ws> <4A55F510.5090801@redhat.com> <4A55F641.6000701@codemonkey.ws> <20090710231424.GD30322@shareable.org> <4A57E3AA.5020305@codemonkey.ws> <20090711014207.GM30322@shareable.org> <4A5958F8.3090306@codemonkey.ws> <4A59F1AC.9070401@redhat.com> <4A5A3533.7040107@codemonkey.ws> In-Reply-To: <4A5A3533.7040107@codemonkey.ws> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: Paolo Bonzini , qemu-devel@nongnu.org On 07/12/2009 10:10 PM, Anthony Liguori wrote: >> It's actually a common scenario for block devices. I don't know >> about networking, but for disks a write can be completed and then >> report an error if the cable or power was disconnected before the >> acknowledge could arrive. > > > Is it common that a disk cable is yanked out before the ack arrives? It was common when I was doing filesystems. > Are their gremlins in your servers :-) Worse, QA. > >> It could conceivably happen with networking if the device reports an >> error when it isn't sure if the data was sent out or not (but it >> actually was), or if some path after the transmission required a >> memory allocation, which failed. > > But does this actually happen or is this all theoretical? With block devices, my experience indicates that the probability of something happening is proportional to the damage it will cause. With networking, it may be theoretical or practical, I suggest we don't rely on it either way. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.