Re: [PATCH] vhost: introduce mdev based hardware backend

[Jason Wang]

On 2019/9/26 äå9:14, Tiwei Bie wrote:
> On Thu, Sep 26, 2019 at 04:35:18AM -0400, Michael S. Tsirkin wrote:
> > On Thu, Sep 26, 2019 at 12:54:27PM +0800, Tiwei Bie wrote:
> [...]
> > > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> > > index 40d028eed645..5afbc2f08fa3 100644
> > > --- a/include/uapi/linux/vhost.h
> > > +++ b/include/uapi/linux/vhost.h
> > > @@ -116,4 +116,12 @@
> > >   #define VHOST_VSOCK_SET_GUEST_CID	_IOW(VHOST_VIRTIO, 0x60, __u64)
> > >   #define VHOST_VSOCK_SET_RUNNING		_IOW(VHOST_VIRTIO, 0x61, int)
> > >   
> > > +/* VHOST_MDEV specific defines */
> > > +
> > > +#define VHOST_MDEV_SET_STATE	_IOW(VHOST_VIRTIO, 0x70, __u64)
> > > +
> > > +#define VHOST_MDEV_S_STOPPED	0
> > > +#define VHOST_MDEV_S_RUNNING	1
> > > +#define VHOST_MDEV_S_MAX	2
> > > +
> > >   #endif
> > So assuming we have an underlying device that behaves like virtio:
> I think they are really good questions/suggestions. Thanks!
>
> > 1. Should we use SET_STATUS maybe?
> I like this idea. I will give it a try.
>
> > 2. Do we want a reset ioctl?
> I think it is helpful. If we use SET_STATUS, maybe we
> can use it to support the reset.
>
> > 3. Do we want ability to enable rings individually?
> I will make it possible at least in the vhost layer.


Note the API support e.g set_vq_ready().


> > 4. Does device need to limit max ring size?
> > 5. Does device need to limit max number of queues?
> I think so. It's helpful to have ioctls to report the max
> ring size and max number of queues.


An issue is the max number of queues is done through a device specific 
way, usually device configuration space. This is supported by the 
transport API, but how to expose it to userspace may need more thought.

Thanks


> Thanks!