On Wed, 13 May 2015 16:58:58 +0200
"Michael S. Tsirkin" <m...@redhat.com> wrote:
> On Wed, May 13, 2015 at 04:42:02PM +0200, Cornelia Huck wrote:
> > 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" <jjhe...@linux.vnet.ibm.com>
> > Signed-off-by: Cornelia Huck <cornelia.h...@de.ibm.com>
>
> I'm inclined to say just fix ccw, don't touch core.
> queue vectors are still saved by transports, why special-case
> config_vector?
- config_vector is in the common VirtIODevice structure, not in
transport-specific code
- new transports may make the same mistake
- AFAICS, there's no easy way to add transport-specific subsections -
and simply adding config_vector in ccw would break compatibility
>
> > ---
> > 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);
>
> As config_vector is ignored without msix,
> why is it a good idea to break migration if it's wrong?
This should be covered by the first check, no?
>
> > +}
> > +
> > 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
>
