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

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jun 03, 2015 at 01:59:15PM +0200, Christian Borntraeger wrote:
> Am 18.05.2015 um 17:29 schrieb Cornelia Huck:
> > On Mon, 18 May 2015 13:26:35 +0200
> > Cornelia Huck <cornelia.huck@de.ibm.com> wrote:
> 
> Had a discussion with Juan in irc regarding compatibility. As v2.3.0 is still
> on v2 for the machine and v2.4.0 will have v4 we could simply go with Jasons
> first approach that boild down to 
> 
> diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
> index 9ef1059..13d9dda 100644
> --- a/hw/s390x/virtio-ccw.c
> +++ b/hw/s390x/virtio-ccw.c
> @@ -1332,6 +1332,7 @@ static void virtio_ccw_save_config(DeviceState *d, QEMUFile *f)
>  {
>      VirtioCcwDevice *dev = VIRTIO_CCW_DEVICE(d);
>      SubchDev *s = dev->sch;
> +    VirtIODevice *vdev = virtio_ccw_get_vdev(s);
> 
>      subch_device_save(s, f);
>      if (dev->indicators != NULL) {
> @@ -1355,6 +1356,7 @@ static void virtio_ccw_save_config(DeviceState *d, QEMUFile *f)
>          qemu_put_be32(f, 0);
>          qemu_put_be64(f, 0UL);
>      }
> +    qemu_put_be16(f, vdev->config_vector);
>      qemu_put_be64(f, dev->routes.adapter.ind_offset);
>      qemu_put_byte(f, dev->thinint_isc);
>  }
> @@ -1363,6 +1365,7 @@ static int virtio_ccw_load_config(DeviceState *d, QEMUFile *f)
>  {
>      VirtioCcwDevice *dev = VIRTIO_CCW_DEVICE(d);
>      SubchDev *s = dev->sch;
> +    VirtIODevice *vdev = virtio_ccw_get_vdev(s);
>      int len;
> 
>      s->driver_data = dev;
> @@ -1388,6 +1391,7 @@ static int virtio_ccw_load_config(DeviceState *d, QEMUFile *f)
>          qemu_get_be64(f);
>          dev->summary_indicator = NULL;
>      }
> +    qemu_get_be16s(f, &vdev->config_vector);
>      dev->routes.adapter.ind_offset = qemu_get_be64(f);
>      dev->thinint_isc = qemu_get_byte(f);
>      if (s->thinint_active) {
> 
> 
> we only have to provide compatibility checks between releases. As there is no
> production envrionment yet we can break compatibility and the migration code will
> reject 2.3->2.4 and vice versa. 

Let's do this for now.


> In the future we have to be more careful, though.
> Juan, Conny virtio-ccw has no version as virtio has no vmstate.
> I am tempted to convert subch_device_save to use a vmstate_save_state 
> instead of qemu_put*.... This would allow us to have a version for
> the virtio-ccw stuff only. 
> This would be an incompatible change, though. Maybe we should continue
> to bump the machine version even if only the virtio migration format 
> changes (which should rarely  happen).
> 
> Christian
> 
> 

I discussed another idea on IRC, which is to add section length
at the beginning of each section. Will simplify debugging as well.
Juan, you agreed with this idea, right?


> 
> 
> 
> 
> > 
> >> Would the subsection approach be more acceptable if I default needed to
> >> false and have only virtio-ccw override it in a callback?
> > 
> > Smth like the following:
> > 
> > From 773a753475d9c89fb8dc789005a694d07b0cfac2 Mon Sep 17 00:00:00 2001
> > From: Cornelia Huck <cornelia.huck@de.ibm.com>
> > Date: Tue, 12 May 2015 09:14:45 +0200
> > Subject: [PATCH] virtio: migrate config_vector
> > 
> > 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).
> > 
> > We don't want to simply add a value to the virtio-ccw save data (it
> > may make migration failures hard to debug), and unfortunately we can't
> > add optional vmstate subsections to a transport only. So let's add
> > a new subsection for config_vector to the core and only let virtio-ccw
> > signal via an optional callback that it wants the config_vector to be
> > saved.
> > 
> > Reported-by: "Jason J. Herne" <jjherne@linux.vnet.ibm.com>
> > Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> > ---
> >  hw/s390x/virtio-ccw.c          | 10 ++++++++++
> >  hw/virtio/virtio.c             | 24 ++++++++++++++++++++++++
> >  include/hw/virtio/virtio-bus.h |  5 +++++
> >  3 files changed, 39 insertions(+)
> > 
> > diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
> > index c96101a..dfb4514 100644
> > --- a/hw/s390x/virtio-ccw.c
> > +++ b/hw/s390x/virtio-ccw.c
> > @@ -1436,6 +1436,15 @@ static void virtio_ccw_device_unplugged(DeviceState *d)
> >  
> >      virtio_ccw_stop_ioeventfd(dev);
> >  }
> > +
> > +static bool virtio_ccw_needs_confvec(DeviceState *d)
> > +{
> > +    VirtioCcwDevice *dev = VIRTIO_CCW_DEVICE(d);
> > +    VirtIODevice *vdev = virtio_bus_get_device(&dev->bus);
> > +
> > +    return vdev && (vdev->config_vector != VIRTIO_NO_VECTOR);
> > +}
> > +
> >  /**************** Virtio-ccw Bus Device Descriptions *******************/
> >  
> >  static Property virtio_ccw_net_properties[] = {
> > @@ -1760,6 +1769,7 @@ static void virtio_ccw_bus_class_init(ObjectClass *klass, void *data)
> >      k->load_config = virtio_ccw_load_config;
> >      k->device_plugged = virtio_ccw_device_plugged;
> >      k->device_unplugged = virtio_ccw_device_unplugged;
> > +    k->needs_confvec = virtio_ccw_needs_confvec;
> >  }
> >  
> >  static const TypeInfo virtio_ccw_bus_info = {
> > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > index 6985e76..627be0d 100644
> > --- a/hw/virtio/virtio.c
> > +++ b/hw/virtio/virtio.c
> > @@ -903,6 +903,26 @@ 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 && k->needs_confvec ?
> > +        k->needs_confvec(qbus->parent) : false;
> > +}
> > +
> > +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 +936,10 @@ 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 {
> > 
> 
> 
>