From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:51693) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TjVnb-0000IM-RE for qemu-devel@nongnu.org; Fri, 14 Dec 2012 08:59:36 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TjVna-0003PC-MG for qemu-devel@nongnu.org; Fri, 14 Dec 2012 08:59:35 -0500 Received: from mail-ia0-f173.google.com ([209.85.210.173]:50507) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TjVna-0003Op-0T for qemu-devel@nongnu.org; Fri, 14 Dec 2012 08:59:34 -0500 Received: by mail-ia0-f173.google.com with SMTP id w21so3155185iac.4 for ; Fri, 14 Dec 2012 05:59:33 -0800 (PST) From: Anthony Liguori In-Reply-To: <50CB126C.6030408@redhat.com> References: <1355149790-8125-1-git-send-email-aliguori@us.ibm.com> <1355149790-8125-4-git-send-email-aliguori@us.ibm.com> <87d2yhcttd.fsf@rustcorp.com.au> <87y5h5xvbk.fsf@codemonkey.ws> <87bodx4fj5.fsf@rustcorp.com.au> <50CB126C.6030408@redhat.com> Date: Fri, 14 Dec 2012 07:59:29 -0600 Message-ID: <87vcc4pwe6.fsf@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Subject: Re: [Qemu-devel] [PATCH 3/4] virtio: modify savevm to have a stable wire format List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini , Rusty Russell Cc: "Michael S. Tsirkin" , qemu-devel@nongnu.org, David Gibson Paolo Bonzini writes: > Il 14/12/2012 01:57, Rusty Russell ha scritto: >> With the new code we only need the head from that structure. > > We also need to do again all validation of the elements if we fetch it > back from the data. Sometimes the parsed data is saved elsewhere (e.g. > in a SCSIRequest struct that is serialized by the SCSI subsystem) and > that data may be inconsistent with whatever you read from guest memory. > It's a can of worms. > >>> I'm certainly in favor of cleaning up the savevm format and probably >>> leaving the existing load/save functions as-is for legacy purposes. >>> I'll leave that as an exercise for someone else though :-) >> >> What is the rule about new versions? Can we introduce a new save >> version at any time, or only at major qemu version changes? > > Any time, but we provide a backwards-compatible loader for older > versions. Well.. if we can avoid bumping the version, we should. Bumping the version breaks migration from new -> old so it's preferrable that we don't do it unless it's absolutely required. Regards, Anthony Liguori > > Paolo