wdt_i6300esb: fix vmstate versioning

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>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
(cherry picked from commit c1990468d5a13c8f1d9111fcca0a78a6adad062b)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

diff --git a/hw/watchdog/wdt_i6300esb.c b/hw/watchdog/wdt_i6300esb.c
index 1407fbadb2ea9874cc51b5f9dad924e95e9457f1..05af0b1b683fb6c473e017bd96cf02c30f82188b 100644 (file)
--- 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),