Re: [Qemu-devel] [PATCH] wdt_i6300esb: fix vmstate versioning

[mdroth <mdroth@linux.vnet.ibm.com>]

On Wed, Jun 12, 2013 at 04:17:53PM -0500, Anthony Liguori wrote:
> mdroth <mdroth@linux.vnet.ibm.com> writes:
> 
> > On Tue, May 21, 2013 at 05:32:57PM -0500, 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 <nick@bytemark.co.uk>
> >> Suggested-by: Peter Maydell <peter.maydell@linaro.org>
> >> Cc: qemu-stable@nongnu.org
> >> Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
> >
> > CC'ing qemu-trivial. Looking to get this in for 1.5.1
> 
> v2?  There were some review comments that haven't been addressed.

Sorry, pinged the wrong email. v2 is to the latest:

http://lists.nongnu.org/archive/html/qemu-devel/2013-05/msg02991.html

> 
> Regards,
> 
> Anthony Liguori
> 
> >
> >> ---
> >>  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.
> >> +     *
> >> +     * 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),
> >> -- 
> >> 1.7.9.5
> >> 
>