From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=56903 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PfXn7-0006Ro-3t for qemu-devel@nongnu.org; Wed, 19 Jan 2011 08:09:39 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PfXn0-0001Ls-Vn for qemu-devel@nongnu.org; Wed, 19 Jan 2011 08:09:33 -0500 Received: from mx1.redhat.com ([209.132.183.28]:33767) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PfXn0-0001Kt-Ok for qemu-devel@nongnu.org; Wed, 19 Jan 2011 08:09:30 -0500 From: Markus Armbruster Subject: Re: [Qemu-devel] [PATCH 28/35] kvm: x86: Introduce kvmclock device to save/restore its state References: <4D2B6CB5.9050602@codemonkey.ws> <4D2B74D8.4080309@web.de> <4D2B8662.9060909@web.de> <4D2C60FB.7030009@linux.vnet.ibm.com> <4D2D80ED.8030405@redhat.com> <4D2D82EE.20002@siemens.com> <4D35A39A.8000801@siemens.com> <4D35ABF8.9050700@linux.vnet.ibm.com> <4D35B521.3090601@siemens.com> <4D35B6DD.1020005@linux.vnet.ibm.com> <4D35B963.7000605@siemens.com> <4D35BA22.7060602@linux.vnet.ibm.com> <4D35BD30.1060900@siemens.com> <4D35C1CE.10509@linux.vnet.ibm.com> <4D35C648.7050809@siemens.com> <4D35C92D.7030000@linux.vnet.ibm.com> Date: Wed, 19 Jan 2011 14:09:15 +0100 In-Reply-To: <4D35C92D.7030000@linux.vnet.ibm.com> (Anthony Liguori's message of "Tue, 18 Jan 2011 11:09:01 -0600") Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: "kvm@vger.kernel.org" , Jan Kiszka , Glauber Costa , Marcelo Tosatti , "qemu-devel@nongnu.org" , Avi Kivity Anthony Liguori writes: > On 01/18/2011 10:56 AM, Jan Kiszka wrote: >> >>> The device model topology is 100% a hidden architectural detail. >>> >> This is true for the sysbus, it is obviously not the case for PCI and >> similarly discoverable buses. There we have a guest-explorable topology >> that is currently equivalent to the the qdev layout. >> > > But we also don't do PCI passthrough so we really haven't even > explored how that maps in qdev. I don't know if qemu-kvm has > attempted to qdev-ify it. > >>>> Management and analysis tools must be able to traverse the system buses >>>> and find guest devices this way. >>>> >>> We need to provide a compatible interface to the guest. If you agree >>> with my above statements, then you'll also agree that we can do this >>> without keeping the device model topology stable. >>> >>> But we also need to provide a compatible interface to management tools. >>> Exposing the device model topology as a compatible interface >>> artificially limits us. It's far better to provide higher level >>> supported interfaces to give us the flexibility to change the device >>> model as we need to. >>> >> How do you want to change qdev to keep the guest and management tool >> view stable while branching off kvm sub-buses? > > The qdev device model is not a stable interface. I think that's been > clear from the very beginning. > >> Please propose such >> extensions so that they can be discussed. IIUC, that would be second >> relation between qdev and qbus instances besides the physical topology. >> What further use cases (besides passing kvm_state around) do you have in >> mind? >> > > The -device interface is a stable interface. Right now, you don't > specify any type of identifier of the pci bus when you create a PCI > device. It's implied in the interface. Now I'm confused. Isn't "-device FOO,bus=pci.0" specifying the PCI bus? [...]