Re: [Qemu-devel] [PATCH 0/4] virtio: Move host features to backends

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Fri, 17 Apr 2015 20:13:42 +0800
Shannon Zhao <shannon.zhao@linaro.org> wrote:

[Some questions may be silly, but I'm not familiar with the virtio-mmio
code]

> The reason to do this is that the virtio-net-device can't expose host
> features to guest while using virtio-mmio. So the performance is low.

So how does virtio-mmio expose any host features?

> 
> The virtio-*-pci, virtio-*-s390, and virtio-*-ccw already have the ability
> to forward property accesses to the backend child, by calling 
> *_virtio_*_instance_init -> qdev_alias_all_properties.

Is there a way virtio-mmio could make use of instance_init?

> 
> Here we move the host features to backends, involving
> DEFINE_VIRTIO_NET_FEATURES, DEFINE_VIRTIO_SCSI_FEATURES. So the virtio-mmio
> devices could have the host freatures, and this has a great performance
> improvement to virtio-mmio.
> 
> This is also backward compatible for s390 and x86.
> 
> Shannon Zhao (4):
>   hw/s390x/virtio-ccw: Add virtio_ccw_device_plugged for virtio-ccw
>   hw/s390x/s390-virtio-bus: Add virtio_s390_device_plugged for
>     s390-virtio
>   hw/net/virtio-net: Move DEFINE_VIRTIO_NET_FEATURES to virtio-net
>   virtio-scsi: Move DEFINE_VIRTIO_SCSI_FEATURES to virtio-scsi
> 
>  hw/net/virtio-net.c             |  4 ++++
>  hw/s390x/s390-virtio-bus.c      | 12 ++++++++++--
>  hw/s390x/virtio-ccw.c           | 13 +++++++++++--
>  hw/scsi/virtio-scsi.c           |  5 +++++
>  hw/virtio/virtio-pci.c          |  2 --
>  include/hw/virtio/virtio-net.h  |  1 +
>  include/hw/virtio/virtio-scsi.h |  1 +
>  7 files changed, 32 insertions(+), 6 deletions(-)
>