Re: [Qemu-devel] [PATCH] virtio-net: require that config size is initialized

[KONRAD Frédéric]

On 07/05/2013 16:00, Michael S. Tsirkin wrote:
> On Tue, May 07, 2013 at 02:54:38PM +0200, KONRAD Frédéric wrote:
> > On 07/05/2013 14:33, Michael S. Tsirkin wrote:
> > > On Tue, May 07, 2013 at 02:29:38PM +0200, KONRAD Frédéric wrote:
> > > > Hi,
> > > >
> > > > I think it is not a good idea, as we wanted to make VirtIODevice
> > > > hot-pluggable for virtio-mmio.
> > > And then this hack will break cross version migration.
> > Why?
> >
> > virtio_net_set_config_size is called by each "proxy" devices no?
> If it's called then there's no need for a default,
> so this patch should be fine.

True but as I told you, we made this refactoring to be able to hot-plug
VirtIODevice on a virtio-bus, so calling this function won't be possible.

But you are right this must be fixed.

> > > > Maybe we can use a callback which is called by virtio-bus before
> > > > plugging, to ensure that this
> > > > config size is computed?
> > > OK, will you post such a patch?
> > The issue is as we said in the last thread, host_feature is part of
> > the proxy.
> Maybe you could add documentation on how initialization works?
> If I could fiure it out I would maybe suggest some solutions.

Yes, where do you think I can add this?

> > And if we want to move it to the devices, we must have a kind of
> > property forwarding mechanism.
> >
> > Anthony said he had something about that.
> > > > > All buses do this, and if they don't they get subtle
> > > > > bugs related to cross version migration.
> > > > > Let's add an assert to catch these bugs early.
> > > > >
> > > > > Signed-off-by: Michael S. Tsirkin <address@hidden>
> > > > > ---
> > > > >
> > > > > Just a cleanup so not 1.5 material.
> > > > > Seems to work fine here - any opinions?
> > > > >
> > > > >   hw/net/virtio-net.c | 7 ++++---
> > > > >   1 file changed, 4 insertions(+), 3 deletions(-)
> > > > >
> > > > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> > > > > index 908e7b8..f0a9272 100644
> > > > > --- a/hw/net/virtio-net.c
> > > > > +++ b/hw/net/virtio-net.c
> > > > > @@ -1282,6 +1282,8 @@ static int virtio_net_device_init(VirtIODevice *vdev)
> > > > >       DeviceState *qdev = DEVICE(vdev);
> > > > >       VirtIONet *n = VIRTIO_NET(vdev);
> > > > > +    /* Verify that config size has been initialized */
> > > > > +    assert(n->config_size != (size_t)-1);
> > > > >       virtio_init(VIRTIO_DEVICE(n), "virtio-net", VIRTIO_ID_NET,
> > > > >                                     n->config_size);
> > > > > @@ -1386,10 +1388,9 @@ static void virtio_net_instance_init(Object *obj)
> > > > >       VirtIONet *n = VIRTIO_NET(obj);
> > > > >       /*
> > > > > -     * The default config_size is sizeof(struct virtio_net_config).
> > > > > -     * Can be overriden with virtio_net_set_config_size.
> > > > > +     * The config_size must be set later with virtio_net_set_config_size.
> > > > >        */
> > > > > -    n->config_size = sizeof(struct virtio_net_config);
> > > > > +    n->config_size = (size_t)-1;
> > > > >   }
> > > > >   static Property virtio_net_properties[] = {