Subject: Re: [Alacrityvm-devel] [PATCH v3 3/6] vbus: add a "vbus-proxy" bus model for vbus_driver objects

From: Avi Kivity <[email-masked]>
Date: Tue, 18 Aug 2009 19:51:21 +0300

On 08/18/2009 06:53 PM, Ira W. Snyder wrote:
> So, in my system, copy_(to|from)_user() is completely wrong. There is no
> userspace, only a physical system. In fact, because normal x86 computers
> do not have DMA controllers, the host system doesn't actually handle any
> data transfer!
>    

In fact, modern x86s do have dma engines these days (google for Intel 
I/OAT), and one of our plans for vhost-net is to allow their use for 
packets above a certain size.  So a patch allowing vhost-net to 
optionally use a dma engine is a good thing.

> I used virtio-net in both the guest and host systems in my example
> virtio-over-PCI patch, and succeeded in getting them to communicate.
> However, the lack of any setup interface means that the devices must be
> hardcoded into both drivers, when the decision could be up to userspace.
> I think this is a problem that vbus could solve.
>    

Exposing a knob to userspace is not an insurmountable problem; vhost-net 
already allows changing the memory layout, for example.

-- 
error compiling committee.c: too many arguments to function