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Re: [Qemu-devel] [PATCH 2/5] Migration: Defined VMStateDescription struc

From: Jianjun Duan
Subject: Re: [Qemu-devel] [PATCH 2/5] Migration: Defined VMStateDescription struct for spapr_drc
Date: Thu, 21 Apr 2016 10:03:56 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0

On 04/19/2016 09:32 PM, David Gibson wrote:
On Fri, Apr 15, 2016 at 01:33:02PM -0700, Jianjun Duan wrote:
To manage hotplug/unplug of dynamic resources such as PCI cards,
memory, and CPU on sPAPR guests, a firmware abstraction known as
a Dynamic Resource Connector (DRC) is used to assign a particular
dynamic resource to the guest, and provide an interface for the
guest to manage configuration/removal of the resource associated
with it.

To migrate the hotplugged resources in migration, the
associated DRC state need be migrated. To migrate the DRC state,
we defined the VMStateDescription struct for spapr_drc to enable
the transmission of spapr_drc state in migration.

Not all the elements in the DRC state are migrated. Only those
ones modifiable by guest actions or device add/remove operation
are migrated.

Signed-off-by: Jianjun Duan <address@hidden>
Urgh.  It would be really nice if we could avoid this and instead
calculate these states from other information.  I hate migrating
what's essentially transitory state if we can possibly avoid it - is
there any way to defer or retry hotplug operations to make this

Even if we have to migrate some state here, I'm a bit dubious about
whether directly migrating the PAPR indicator states is the best way.
It does have the advantage of having a spec, on the other hand the
PAPR indicators are really weird and hard to understand the meaning
I don't think we can avoid this. I would think migrating the machine state is
actually a clean approach, as you said it does have PAPR spec.
  hw/ppc/spapr_drc.c | 15 +++++++++++++++
  1 file changed, 15 insertions(+)

diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
index 3173940..5f7a25f 100644
--- a/hw/ppc/spapr_drc.c
+++ b/hw/ppc/spapr_drc.c
@@ -610,6 +610,20 @@ static void spapr_dr_connector_instance_init(Object *obj)
                          NULL, NULL, NULL, NULL);
+static const VMStateDescription vmstate_spapr_drc = {
+    .name = "spapr_drc",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .fields  = (VMStateField []) {
+        VMSTATE_UINT32(isolation_state, sPAPRDRConnector),
+        VMSTATE_UINT32(allocation_state, sPAPRDRConnector),
+        VMSTATE_UINT32(indicator_state, sPAPRDRConnector),
+        VMSTATE_BOOL(configured, sPAPRDRConnector),
+        VMSTATE_BOOL(awaiting_release, sPAPRDRConnector),
+    }
  static void spapr_dr_connector_class_init(ObjectClass *k, void *data)
      DeviceClass *dk = DEVICE_CLASS(k);
@@ -618,6 +632,7 @@ static void spapr_dr_connector_class_init(ObjectClass *k, 
void *data)
      dk->reset = reset;
      dk->realize = realize;
      dk->unrealize = unrealize;
+    dk->vmsd = &vmstate_spapr_drc;
      drck->set_isolation_state = set_isolation_state;
      drck->set_indicator_state = set_indicator_state;
      drck->set_allocation_state = set_allocation_state;

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