Re: [Qemu-devel] [PATCH for-2.3] virtio-serial: fix virtio config size

[Cole Robinson]

On 03/25/2015 07:41 AM, Michael S. Tsirkin wrote:
> commit 9b70c1790acacae54d559d38ca69186a85040bb8
>     virtio-serial: switch to standard-headers
> 
> changes virtio_console_config size from 8 to 12 bytes:
> it adds an optional 4 byte emerg_wr field.
> 
> As this crosses a power of two boundary, this changes the PCI BAR size,
> which breaks migration compatibility with old qemu machine types.
> It's probably a problem for other transports as well.
> 
> As a temporary fix, as we don't yet support this new field anyway,
> simply make the config size smaller at init time.
> 
> Long terms we probably want something along the lines
> of virtio_net_set_config_size.
> 
> Reported-by: Cole Robinson <address@hidden>
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> ---
> 
> Cole, could you pls confirm the following fixes the
> issue that you reported?
> 
> Thanks!
> 
>  hw/char/virtio-serial-bus.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
> index 9a029d2..d05473f 100644
> --- a/hw/char/virtio-serial-bus.c
> +++ b/hw/char/virtio-serial-bus.c
> @@ -949,8 +949,10 @@ static void virtio_serial_device_realize(DeviceState 
> *dev, Error **errp)
>          return;
>      }
>  
> +    /* We don't support emergency write, skip it for now. */
> +    /* TODO: cleaner fix, depending on host features. */
>      virtio_init(vdev, "virtio-serial", VIRTIO_ID_CONSOLE,
> -                sizeof(struct virtio_console_config));
> +                offsetof(struct virtio_console_config, emerg_wr));
>  
>      /* Spawn a new virtio-serial bus on which the ports will ride as devices 
> */
>      qbus_create_inplace(&vser->bus, sizeof(vser->bus), 
> TYPE_VIRTIO_SERIAL_BUS,
> 

Fixes the migration failure for me, thanks!

Tested-by: Cole Robinson <address@hidden>

- Cole