From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:46043) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QcFAh-0004zd-6j for qemu-devel@nongnu.org; Thu, 30 Jun 2011 07:12:36 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QcFAf-0005vl-BT for qemu-devel@nongnu.org; Thu, 30 Jun 2011 07:12:34 -0400 Received: from cantor2.suse.de ([195.135.220.15]:36612 helo=mx2.suse.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QcFAe-0005vS-Oe for qemu-devel@nongnu.org; Thu, 30 Jun 2011 07:12:33 -0400 Message-ID: <4E0C5A1E.3030806@suse.de> Date: Thu, 30 Jun 2011 13:12:30 +0200 From: Alexander Graf MIME-Version: 1.0 References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] Questions on DeviceState and Virtio infrastructure List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefano Stabellini Cc: Anthony Perard , "qemu-devel@nongnu.org" , Wei Liu On 06/30/2011 12:21 PM, Stefano Stabellini wrote: > On Thu, 30 Jun 2011, Wei Liu wrote: >> On Thu, Jun 30, 2011 at 4:31 PM, Alexander Graf wrote: >>> On 29.06.2011, at 15:59, Wei Liu wrote: >>> >>>> Hi, QEMU folks >>>> >>>> I know that I might have a bad title for this post, but I just don't >>>> have better idea for the title. >>>> >>>> I'm developing virtio support for Xen pv guest, hoping to reuse the >>>> virtio infrastructure in qemu, i.e. I'm planning to use qemu as >>>> "virtio backend" for Xen pv. And qemu can be run as pv backend if >>>> proper "machine" option is given. >>>> >>>> Maybe you've known that Xen pv guest utilizes Xenbus/Xenstore to >>>> configure its paravirt devices. So I'm to configure virtio devices >>>> with Xenbus/Xenstore as well. But in nowdays XenDevice in qemu does >>>> not include a DeviceState. To my understanding, it is not connected to >>>> qemu's internal buses or whatever (correct me if I'm wrong, I'm >>>> relatively new to qemu). >>> I'm not a huge fan of adding multiple different transports for virtio if we don't have to. IIRC Xen PV guests can do PCI device assignment, right? That means there is a PCI bus for them which we could reuse to run virtio-pci on. >>> >>> By then, you'd get all the virtio code for free and don't have to worry about maintaining yet another transport (which _is_ cumbersome) >>> >> Good point, I will check this. >> >> I thought that Xen pv pci assignment is only used for pci passthrough. >> But I will check the possibility to assign pv backend to guest. >> >> Stefano, how would you say about this? > > Yes, the PCI bus is an empty PCI bus created by xen-pcifront and it is > only used for PCI passthrough. It couldn't be used as is for virtio-pci. What's keeping us from doing so? Doesn't MMIO emulation work with Xen PV? Alex