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

[Michael S. Tsirkin]

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.

> 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?

> On 07/05/2013 12:22, Michael S. Tsirkin wrote:
> >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[] = {