From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [Qemu-devel] [PATCH v5 06/16] apic: Introduce backend/frontend infrastructure for KVM reuse Date: Tue, 20 Dec 2011 07:54:05 -0600 Message-ID: <4EF0937D.3090207@codemonkey.ws> References: <4EEFB72E.7030508@codemonkey.ws> <4EEFC970.9030205@web.de> <4EEFD69F.6080700@codemonkey.ws> <4EEFD786.8030609@web.de> <4EEFD90A.1000204@codemonkey.ws> <4EF05BC4.8010905@redhat.com> <4EF09078.2030508@codemonkey.ws> <4EF092D2.6080009@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, "Michael S. Tsirkin" , Marcelo Tosatti , qemu-devel , Blue Swirl , Jan Kiszka , Avi Kivity To: Paolo Bonzini Return-path: Received: from mail-gy0-f174.google.com ([209.85.160.174]:64277 "EHLO mail-gy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751514Ab1LTNyI (ORCPT ); Tue, 20 Dec 2011 08:54:08 -0500 Received: by ghbz12 with SMTP id z12so4143631ghb.19 for ; Tue, 20 Dec 2011 05:54:07 -0800 (PST) In-Reply-To: <4EF092D2.6080009@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 12/20/2011 07:51 AM, Paolo Bonzini wrote: > On 12/20/2011 02:41 PM, Anthony Liguori wrote: >> On 12/20/2011 03:56 AM, Avi Kivity wrote: >>> On 12/20/2011 02:38 AM, Anthony Liguori wrote: >>>>> That was v1 of my patches. Avi didn't like it, I tried it like this, >>>>> and >>>>> in the end I had to agree. So, no, I don't think we want such a model. >>>> >>>> >>>> Yes, we do :-) >>>> >>>> The in-kernel APIC is a different implementation of the APIC device. >>>> It's not an "accelerator" for the userspace APIC. >>> >>> A different implementation but not a different device. Device == spec. >> >> If it was hardware, it'd be a fully compatible clone. The way we would >> model this is via inheritance. > > I see your fully compatible clone, and I raise my bridge with a different > implementation underneath. It's the same old debate on is-a vs has-a. > > In QOM parlance Jan implemented this: > > abstract class Object > abstract class Device > class APIC: { backend: link } > abstract class APICBackend > class QEMU_APICBackend > class KVM_APICBackend I don't fundamentally object to modeling it like this provided that it's modeled (and visible) through qdev and not done through a one-off infrastructure. But yes, you are exactly correct in your observation (and that both can be right). Regards, Anthony Liguori > > and you're proposing this: > > abstract class Object > abstract class Device > abstract class APIC > class QEMU_APIC > class KVM_APIC > > Both can be right, both can be wrong. > > Paolo > >