From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39937) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aTyBf-0005Lh-D4 for qemu-devel@nongnu.org; Thu, 11 Feb 2016 15:50:04 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aTyBb-0002lO-By for qemu-devel@nongnu.org; Thu, 11 Feb 2016 15:50:03 -0500 Received: from mail-wm0-x242.google.com ([2a00:1450:400c:c09::242]:34506) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aTyBb-0002lJ-58 for qemu-devel@nongnu.org; Thu, 11 Feb 2016 15:49:59 -0500 Received: by mail-wm0-x242.google.com with SMTP id p63so12738438wmp.1 for ; Thu, 11 Feb 2016 12:49:58 -0800 (PST) Sender: Paolo Bonzini References: <1453564933-29638-1-git-send-email-ehabkost@redhat.com> <20160204180024-mutt-send-email-mst@redhat.com> <20160204171617.GM26314@thinpad.lan.raisama.net> <20160204195522-mutt-send-email-mst@redhat.com> <20160204190944.GO26314@thinpad.lan.raisama.net> <20160204221416.GA21272@redhat.com> <20160205144611.GQ26314@thinpad.lan.raisama.net> <20160206201057-mutt-send-email-mst@redhat.com> <20160211155130.GA6239@thinpad.lan.raisama.net> <20160211183032-mutt-send-email-mst@redhat.com> From: Paolo Bonzini Message-ID: <56BCF3F1.9080807@redhat.com> Date: Thu, 11 Feb 2016 21:49:53 +0100 MIME-Version: 1.0 In-Reply-To: <20160211183032-mutt-send-email-mst@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v2 0/5] q35: Remove old machines and unused compat code List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" , Eduardo Habkost Cc: Marcel Apfelbaum , Laszlo Ersek , qemu-devel@nongnu.org, Markus Armbruster , Igor Mammedov , John Snow On 11/02/2016 17:33, Michael S. Tsirkin wrote: >> They won't start unless the QEMU command-line is changed, because >> they are using a feature QEMU won't support anymore. Why is that >> a problem? > > We don't support installing one machine type, then switching. Uhm, we definitely support people using qemu directly with no -M option at all with installed VMs. That's the same as switching machine types every time a new QEMU is released. At least RHEV supports switching machine types, even RHEL6->RHEL7. There are constraints on when to do that because it affects the whole datacenter, but it is done routinely because each RHEV release only supports two machine types IIRC. Paolo