Re: [Qemu-devel] [PATCH v2] wdt_i6300esb: fix vmstate versioning

[Anthony Liguori <aliguori@us.ibm.com>]

mdroth <mdroth@linux.vnet.ibm.com> writes:

> On Tue, Jun 11, 2013 at 04:53:51PM -0500, mdroth wrote:
>> On Wed, May 22, 2013 at 11:32:51AM -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>
>> 
>> Ping, looking to pull this in for 1.5.1
>
> Anthony, Juan? Not sure if this is on your radar. Looking to get it
> applied prior to stable freeze tomorrow.

I'll pick it up.

Regards,

Anthony Liguori

>
>> 
>> > ---
>> > v2:
>> >  * Fixed s/except/accept/ typo (Laszlo)
>> > 
>> >  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..05af0b1 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 accept 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
>> >