[PATCH v3 7/7] RTC:Allow to migrate from old version

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

The new logic is compatible with old. So it should not block to migrate
from old version. But new version cannot migrate to old.

Signed-off-by: Yang Zhang <yang.z.zhang@xxxxxxxxx>
---
 hw/mc146818rtc.c |   48 ++++++++++++++++++++++++++++++++++++++++++++----
 1 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/hw/mc146818rtc.c b/hw/mc146818rtc.c
index 384bdc1..02f7ea0 100644
--- a/hw/mc146818rtc.c
+++ b/hw/mc146818rtc.c
@@ -635,11 +635,51 @@ static int rtc_post_load(void *opaque, int version_id)
     return 0;
 }

+static int rtc_load_old(QEMUFile *f, void *opaque, int version_id)
+{
+    RTCState *s = opaque;
+
+    if (version_id > 2) {
+        return -EINVAL;
+    }
+
+    qemu_get_buffer(f, s->cmos_data, sizeof(s->cmos_data));
+    /* dummy load for compatibility */
+    qemu_get_byte(f); /* cmos_index */
+    qemu_get_be32(f); /* tm_sec */
+    qemu_get_be32(f); /* tm_min */
+    qemu_get_be32(f); /* tm_hour */
+    qemu_get_be32(f); /* tm_wday */
+    qemu_get_be32(f); /* tm_mday */
+    qemu_get_be32(f); /* tm_mon */
+    qemu_get_be32(f); /* tm_year */
+    qemu_get_be64(f); /* periodic_timer */
+    qemu_get_be64(f); /* next_periodic_time */
+    qemu_get_be64(f); /* next_second_time */
+    qemu_get_be64(f); /* second_timer */
+    qemu_get_be64(f); /* second_timer2 */
+    qemu_get_be32(f); /* irq_coalesced */
+    qemu_get_be32(f); /* period */
+
+
+    rtc_set_date_from_host(&s->dev);
+    periodic_timer_update(s,  qemu_get_clock_ns(rtc_clock));
+    check_update_timer(s);
+
+#ifdef TARGET_I386
+    if (s->lost_tick_policy == LOST_TICK_SLEW) {
+        rtc_coalesced_timer_update(s);
+    }
+#endif
+    return 0;
+}
+
 static const VMStateDescription vmstate_rtc = {
     .name = "mc146818rtc",
-    .version_id = 2,
-    .minimum_version_id = 1,
-    .minimum_version_id_old = 1,
+    .version_id = 3,
+    .minimum_version_id = 3,
+    .minimum_version_id_old = 2,
+    .load_state_old = rtc_load_old,
     .post_load = rtc_post_load,
     .fields      = (VMStateField []) {
         VMSTATE_BUFFER(cmos_data, RTCState),
@@ -777,7 +817,7 @@ static int rtc_initfn(ISADevice *dev)
     memory_region_init_io(&s->io, &cmos_ops, s, "rtc", 2);
     isa_register_ioport(dev, &s->io, base);

-    qdev_set_legacy_instance_id(&dev->qdev, base, 2);
+    qdev_set_legacy_instance_id(&dev->qdev, base, 3);
     qemu_register_reset(rtc_reset, s);

     object_property_add(OBJECT(s), "date", "struct tm",
--
1.7.1
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