From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:50297) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Uf4KJ-0003QD-2H for qemu-devel@nongnu.org; Wed, 22 May 2013 04:23:21 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Uf4KC-0004Od-JR for qemu-devel@nongnu.org; Wed, 22 May 2013 04:23:15 -0400 Message-ID: <519C80DE.7090203@redhat.com> Date: Wed, 22 May 2013 10:25:02 +0200 From: Laszlo Ersek MIME-Version: 1.0 References: <1369175577-18130-1-git-send-email-mdroth@linux.vnet.ibm.com> In-Reply-To: <1369175577-18130-1-git-send-email-mdroth@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] wdt_i6300esb: fix vmstate versioning List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Michael Roth Cc: peter.maydell@linaro.org, nick@bytemark.co.uk, qemu-devel@nongnu.org, qemu-stable@nongnu.org On 05/22/13 00:32, Michael Roth wrote: > When this VMSD was introduced it's version fields were set to > sizeof(I6300State), making them essentially random from build to build, > version to version. > > To fix this, we lock in a high version id and low minimum version id to > support old->new migration from all prior versions of this device's > state. This should work since the device state has not changed since > its introduction. > > The potentially breaks migration from 1.5+ to 1.5, but since the > versioning was essentially random prior to this patch, new->old > migration was not consistently functional to begin with. > > Reported-by: Nicholas Thomas > Suggested-by: Peter Maydell > Cc: qemu-stable@nongnu.org > Signed-off-by: Michael Roth > --- > hw/watchdog/wdt_i6300esb.c | 19 ++++++++++++++++--- > 1 file changed, 16 insertions(+), 3 deletions(-) > > diff --git a/hw/watchdog/wdt_i6300esb.c b/hw/watchdog/wdt_i6300esb.c > index 1407fba..851b664 100644 > --- a/hw/watchdog/wdt_i6300esb.c > +++ b/hw/watchdog/wdt_i6300esb.c > @@ -374,9 +374,22 @@ static const MemoryRegionOps i6300esb_ops = { > > static const VMStateDescription vmstate_i6300esb = { > .name = "i6300esb_wdt", > - .version_id = sizeof(I6300State), > - .minimum_version_id = sizeof(I6300State), > - .minimum_version_id_old = sizeof(I6300State), > + /* With this VMSD's introduction, version_id/minimum_version_id were > + * erroneously set to sizeof(I6300State), causing a somewhat random > + * version_id to be set for every build. This eventually broke > + * migration. > + * > + * To correct this without breaking old->new migration for older versions > + * of QEMU, we've set version_id to a value high enough to exceed all past > + * values of sizeof(I6300State) across various build environments, and have > + * reset minimum_version_id_old/minimum_version_id to 1, since this VMSD > + * has never changed and thus can except all past versions. As a non-native speaker I think you mean "accept". > + * > + * For future changes we can treat these values as we normally would. > + */ > + .version_id = 10000, > + .minimum_version_id = 1, > + .minimum_version_id_old = 1, > .fields = (VMStateField []) { > VMSTATE_PCI_DEVICE(dev, I6300State), > VMSTATE_INT32(reboot_enabled, I6300State), > Otherwise looks good to me (which may not mean much :)) Laszlo