From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47203) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VZTXG-0004Hp-Rg for qemu-devel@nongnu.org; Thu, 24 Oct 2013 18:37:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VZTXB-0005ur-VU for qemu-devel@nongnu.org; Thu, 24 Oct 2013 18:37:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44631) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VZTXB-0005uj-N1 for qemu-devel@nongnu.org; Thu, 24 Oct 2013 18:37:41 -0400 From: Juan Quintela In-Reply-To: <5269694B.2030106@kamp.de> (Peter Lieven's message of "Thu, 24 Oct 2013 20:39:07 +0200") References: <5269694B.2030106@kamp.de> Date: Fri, 25 Oct 2013 00:37:23 +0100 Message-ID: <877gd21brg.fsf@elfo.elfo> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [RFC] Migration capability negotation Reply-To: quintela@redhat.com List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Lieven Cc: Paolo Bonzini , "qemu-devel@nongnu.org" Peter Lieven wrote: > Hi, > > I was thinking that it would be great to have the source and > destination during migration negoatiate > migration capabilities e.g. something like this: > > User wants to use a feature e.g. 'zero_blocks'. He switches it to 'on' > or maybe a new state 'auto' on the source VM. > > If the migration is started the source hypervisor sends a set of all > desired features. The destination hypervisor > answers with a subset of all features it supports and automatically > enables them on its side. Depending on the returned > subset the source disables all features the destination does not support. > > This would also allow us also to introduce new features which we would > like to enable by default, but we cannot > because we do not know if the destination will support it. > > Is there any way to add this without breaking backwards compability? > > Comments welcome. As said by Eric, comunications goes only in one direction (think that we are migrating to a file, A.K.A. savevm). Anthony basically forbides them. You can do the equivalent thing from the management application.