Again, thank you all for your valuable comments! There were quite a lot of
suggestions, so I briefly gathered all of them.
Feature bits
------------
VIRTIO_SND_F_PCM_OUTPUT
VIRTIO_SND_F_PCM_INPUT
and new ones would be
VIRTIO_SND_F_PCM_EVT_PERIOD - support elapsed period notifications
VIRTIO_SND_F_PCM_EVT_XRUN - support underrun/overrun notifications
VIRTIO_SND_F_PCM_MSG - support message-based data transport
VIRTIO_SND_F_PCM_HOST_MEM - support sharing host memory with guest
VIRTIO_SND_F_PCM_GUEST_MEM - support sharing guest memory with host
Not sure about correct naming here.
