From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=47033 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Q2R3K-00076x-Q9 for qemu-devel@nongnu.org; Wed, 23 Mar 2011 12:36:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Q2R3J-0004u2-IL for qemu-devel@nongnu.org; Wed, 23 Mar 2011 12:36:58 -0400 Received: from thoth.sbs.de ([192.35.17.2]:24264) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Q2R3J-0004tR-7K for qemu-devel@nongnu.org; Wed, 23 Mar 2011 12:36:57 -0400 Message-ID: <4D8A21A4.3040404@siemens.com> Date: Wed, 23 Mar 2011 17:36:52 +0100 From: Jan Kiszka MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: [PATCH 11/11] test-vmstate: add test case to verify we don't change VMState References: <1300839376-22520-1-git-send-email-aliguori@us.ibm.com> <1300839376-22520-12-git-send-email-aliguori@us.ibm.com> <4D89EABE.50204@codemonkey.ws> <4D8A0947.5080809@codemonkey.ws> <4D8A1F6F.8060003@codemonkey.ws> In-Reply-To: <4D8A1F6F.8060003@codemonkey.ws> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: Peter Maydell , "qemu-devel@nongnu.org" , "quintela@redhat.com" On 2011-03-23 17:27, Anthony Liguori wrote: > On 03/23/2011 10:00 AM, Peter Maydell wrote: >> On 23 March 2011 14:52, Anthony Liguori wrote: >>> I think we ought to merge VMStateDescription into DeviceInfo. For >>> compatibility, we probably need a vmstate_alias name since the device names >>> don't always map 1-1 with the qdev names. But this should eliminate the >>> problem of reusing VMStateDescriptions for multiple devices. >> That's a feature, not a bug. Consider eg hw/pl110.c -- there >> are two different DeviceInfo devices but since the underlying >> implementation is the same you definitely don't want to have >> two separate VMStateDescription structures to get out of sync. > > No, it's a bug. > > Migration uses the VMStateDescription name as a section identifier. The > section identifiers MUST be unique for a given device. Otherwise, if > both devices are present, migration fails miserably. It also means that > if the wrong devices are created on the destination, instead of > predictable failure, you get unpredictable guest corruption. This is true for incompatible devices, but not for those that are perfectly exchangeable (like in-kernel vs. user-space irqchip). Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux