From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:46248) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QcIEV-0001at-K2 for qemu-devel@nongnu.org; Thu, 30 Jun 2011 10:28:44 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QcIES-0001Fv-M2 for qemu-devel@nongnu.org; Thu, 30 Jun 2011 10:28:43 -0400 Received: from cantor2.suse.de ([195.135.220.15]:50311 helo=mx2.suse.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QcIER-0001FW-EN for qemu-devel@nongnu.org; Thu, 30 Jun 2011 10:28:40 -0400 Message-ID: <4E0C8815.8010100@suse.de> Date: Thu, 30 Jun 2011 16:28:37 +0200 From: Alexander Graf MIME-Version: 1.0 References: <4E0C5A1E.3030806@suse.de> 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" , Jan Beulich , Wei Liu On 06/30/2011 04:11 PM, Stefano Stabellini wrote: > On Thu, 30 Jun 2011, Alexander Graf wrote: >> 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? > No, it does not. > The only realistic way that I can see to make virtio work with PV guests > is to write "virtio-xenstore". Hrm. What's technically keeping you from doing MMIO with PV guests? Alex