Message-ID: <49DE26EE.9030402@novell.com>
Date: Thu, 09 Apr 2009 12:48:46 -0400
From: Gregory Haskins <ghaskins@novell.com>
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To: avi@redhat.com
CC: linux-kernel@vger.kernel.org, agraf@suse.de, pmullaney@novell.com,
       pmorreale@novell.com, anthony@codemonkey.ws, rusty@rustcorp.com.au,
       netdev@vger.kernel.org, kvm@vger.kernel.org, bhutchings@solarflare.com,
       andi@firstfloor.org, gregkh@suse.de, herber@gondor.apana.org.au,
       chrisw@sous-sol.org, shemminger@vyatta.com
Subject: Re: [RFC PATCH v2 00/19] virtual-bus
References: <20090409155200.32740.19358.stgit@dev.haskins.net>
In-Reply-To: <20090409155200.32740.19358.stgit@dev.haskins.net>
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Avi,

Gregory Haskins wrote:
>
> Todo:
> *) Develop some kind of hypercall registration mechanism for KVM so tha=
t
>    we can use that as an integration point instead of directly hooking
>    kvm hypercalls
>  =20

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 ;)

So, one thing we could do is use a string-identifier to discover
hypercall resources.  In this model, we would have one additional
hypercall registered with kvm (in addition to the mmu-ops, etc) called
KVM_HC_DYNHC or something like that.  The support for DYNHC could be
indicated in the cpuid (much like I do with the RESET, DYNIRQ, and VBUS
support today.   When hypercall provides register, the could provide a
string such as "vbus", and they would be allocated a hypercall id.=20
Likewise, the HC_DYNHC interface would allow a guest to query the cpuid
for the DYNHC feature, and then query the HC_DYNHC vector for a string
to hc# translation.  If the provider is not present, we return -1 for
the hc#, otherwise we return the one that was allocated.

I know how you feel about string-ids in general, but I am not quite sure
how to design this otherwise without it looking eerily similar to what I
already have (which is registering a new HC vector in kvm_para.h)

Thoughts?

-Greg


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