linux-kernel - Re: [PATCH] vhost: introduce mdev based hardware backend

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Date:   Thu, 26 Sep 2019 21:14:39 +0800
From:   Tiwei Bie <tiwei.bie@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     jasowang@...hat.com, alex.williamson@...hat.com,
        maxime.coquelin@...hat.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, dan.daly@...el.com,
        cunming.liang@...el.com, zhihong.wang@...el.com,
        lingshan.zhu@...el.com
Subject: Re: [PATCH] vhost: introduce mdev based hardware backend

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.

> 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.

Thanks!
Tiwei


> 
> -- 
> MST