[Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector

[Cornelia Huck <cornelia.huck@de.ibm.com>]

Currently, config_vector is managed in VirtIODevice, but migration is
handled by the transport; this led to one transport using config_vector
migrating correctly (pci), while the other forgot it (ccw).

Let's have the core handle migration of config_vector in a vmstate
subsection instead, so that we can keep it backwards compatible and
no additional code is needed if config_vector is not used at all. Also
provide a callback for virtio-pci so they can avoid introducing a
subsection that is not needed and still be compatible in both directions.

Reported-by: "Jason J. Herne" <jjherne@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
---
 hw/virtio/virtio-pci.c         | 14 ++++++++++++++
 hw/virtio/virtio.c             | 25 +++++++++++++++++++++++++
 include/hw/virtio/virtio-bus.h |  5 +++++
 3 files changed, 44 insertions(+)

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 867c9d1..4959b7d 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -971,6 +971,19 @@ static void virtio_pci_device_unplugged(DeviceState *d)
     virtio_pci_stop_ioeventfd(proxy);
 }
 
+static bool virtio_pci_needs_confvec(DeviceState *d)
+{
+    VirtIOPCIProxy *proxy = VIRTIO_PCI(d);
+    VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
+
+    /*
+     * We don't want the core to create an unneeded vmstate subsection
+     * when we already migrate the config vector ourselves.
+     */
+    return (vdev->config_vector != VIRTIO_NO_VECTOR) &&
+        !msix_present(&proxy->pci_dev);
+}
+
 static void virtio_pci_realize(PCIDevice *pci_dev, Error **errp)
 {
     VirtIOPCIProxy *dev = VIRTIO_PCI(pci_dev);
@@ -1505,6 +1518,7 @@ static void virtio_pci_bus_class_init(ObjectClass *klass, void *data)
     k->device_plugged = virtio_pci_device_plugged;
     k->device_unplugged = virtio_pci_device_unplugged;
     k->query_nvectors = virtio_pci_query_nvectors;
+    k->needs_confvec = virtio_pci_needs_confvec;
 }
 
 static const TypeInfo virtio_pci_bus_info = {
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 6985e76..3af530e 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -903,6 +903,27 @@ static const VMStateDescription vmstate_virtio_device_endian = {
     }
 };
 
+static bool virtio_device_confvec_needed(void *opaque)
+{
+    VirtIODevice *vdev = opaque;
+    BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
+
+    return k->needs_confvec ?
+        k->needs_confvec(qbus->parent) :
+        (vdev->config_vector != VIRTIO_NO_VECTOR);
+}
+
+static const VMStateDescription vmstate_virtio_device_confvec = {
+    .name = "virtio/config_vector",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT16(config_vector, VirtIODevice),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 static const VMStateDescription vmstate_virtio = {
     .name = "virtio",
     .version_id = 1,
@@ -916,6 +937,10 @@ static const VMStateDescription vmstate_virtio = {
             .vmsd = &vmstate_virtio_device_endian,
             .needed = &virtio_device_endian_needed
         },
+        {
+            .vmsd = &vmstate_virtio_device_confvec,
+            .needed = &virtio_device_confvec_needed,
+        },
         { 0 }
     }
 };
diff --git a/include/hw/virtio/virtio-bus.h b/include/hw/virtio/virtio-bus.h
index a4588ca..79e6e8b 100644
--- a/include/hw/virtio/virtio-bus.h
+++ b/include/hw/virtio/virtio-bus.h
@@ -69,6 +69,11 @@ typedef struct VirtioBusClass {
      * Note that changing this will break migration for this transport.
      */
     bool has_variable_vring_alignment;
+    /*
+     * (optional) Does the bus want the core to handle config_vector
+     * migration? This is for backwards compatibility only.
+     */
+    bool (*needs_confvec)(DeviceState *d);
 } VirtioBusClass;
 
 struct VirtioBusState {
-- 
2.1.4