netdev - Re: [RFC PATCH v2 00/19] virtual-bus

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Date:	Thu, 04 Jun 2009 14:49:17 -0400
From:	Gregory Haskins <gregory.haskins@...il.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Avi Kivity <avi@...hat.com>, Gregory Haskins <ghaskins@...ell.com>,
	linux-kernel@...r.kernel.org, agraf@...e.de, pmullaney@...ell.com,
	pmorreale@...ell.com, anthony@...emonkey.ws, rusty@...tcorp.com.au,
	netdev@...r.kernel.org, kvm@...r.kernel.org,
	bhutchings@...arflare.com, andi@...stfloor.org, gregkh@...e.de,
	herber@...dor.apana.org.au, chrisw@...s-sol.org,
	shemminger@...tta.com
Subject: Re: [RFC PATCH v2 00/19] virtual-bus

Avi Kivity wrote:
> Gregory Haskins wrote:
>> Avi,
>>
>> Gregory Haskins wrote:
>>  
>>> Todo:
>>> *) Develop some kind of hypercall registration mechanism for KVM so
>>> that
>>>    we can use that as an integration point instead of directly hooking
>>>    kvm hypercalls
>>>       
>>
>> What would you like to see here?  I now remember why I removed the
>> original patch I had for registration...it requires some kind of
>> discovery mechanism on its own.  Note that this is hard, but I figured
>> it would make the overall series simpler if I didn't go this route and
>> instead just integrated with a statically allocated vector.  That being
>> said, I have no problem adding this back in but figure we should discuss
>> the approach so I don't go down a rat-hole ;)
>>
>>   
>
>
> One idea is similar to signalfd() or eventfd().  Provide a kvm ioctl
> that takes a gsi and returns an fd.  Writes to the fd change the state
> of the line, possible triggering an interrupt.  Another ioctl takes a
> hypercall number or pio port as well as an existing fd.  Invocations
> of the hypercall or writes to the port write to the fd (using the same
> protocol as eventfd), so the other end can respond.
>
> The nice thing is that this can be used by both kernel and userspace
> components, and for kernel components, hypercalls can be either
> buffered or unbuffered.


And thus the "kvm-eventfd" (irqfd/iosignalfd) interface project was born. ;)

(Michael FYI: so I will be pushing a vbus-v4 series at some point in the
near future that is expressed in terms of irqfd/iosignalfd, per the
conversation above.  The patches in v3 and earlier are more intrusive to
the KVM core than they will be in final form)

-Greg



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