From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1LzZCJ-0004Iw-Gz for qemu-devel@nongnu.org; Thu, 30 Apr 2009 12:33:19 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1LzZCE-0004Hl-TS for qemu-devel@nongnu.org; Thu, 30 Apr 2009 12:33:19 -0400 Received: from [199.232.76.173] (port=58077 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1LzZCE-0004Hb-NR for qemu-devel@nongnu.org; Thu, 30 Apr 2009 12:33:14 -0400 Received: from e39.co.us.ibm.com ([32.97.110.160]:45323) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1LzZCE-0007mv-3F for qemu-devel@nongnu.org; Thu, 30 Apr 2009 12:33:14 -0400 Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com [9.17.195.227]) by e39.co.us.ibm.com (8.13.1/8.13.1) with ESMTP id n3UGThg0008401 for ; Thu, 30 Apr 2009 10:29:43 -0600 Received: from d03av02.boulder.ibm.com (d03av02.boulder.ibm.com [9.17.195.168]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v9.2) with ESMTP id n3UGWvHU092634 for ; Thu, 30 Apr 2009 10:33:05 -0600 Received: from d03av02.boulder.ibm.com (loopback [127.0.0.1]) by d03av02.boulder.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id n3UGWsaR010400 for ; Thu, 30 Apr 2009 10:32:54 -0600 Message-ID: <49F9D2B3.60707@us.ibm.com> Date: Thu, 30 Apr 2009 11:32:51 -0500 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: [PATCH 9/9] Introduce VLANClientState::cleanup() References: <1239812969-8320-2-git-send-email-markmc@redhat.com> <200904291137.57852.paul@codesourcery.com> <49F9AB7C.7020803@redhat.com> <200904301702.32282.paul@codesourcery.com> In-Reply-To: <200904301702.32282.paul@codesourcery.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paul Brook Cc: Mark McLoughlin , Marcelo Tosatti , qemu-devel@nongnu.org, Markus Armbruster , Avi Kivity Paul Brook wrote: >> Sure, you can short-ciruit the case where you have a pair of devices, >> but then you need to revoke posted receive descriptors. >> > > Isn't the same true with a point-point API? When you add a third device to the > vlan you're going to have to break the tap-guest link, and insert a proxy in > the middle. > The difference is that if you assume vlan, then you have to handle renegotiation of features which is not actually possible. With virtio-net, once you enable guest GSO, you cannot disable it. You would have to implement GSO emulation within QEMU if you wanted to disable it on the tap device. If you don't assume vlan, then you can choose the least amount of features when in a vlan. Then you never have to deal with this problem. And yes, that means that if you wanted to support the existing syntax, you would need a flag like: -net tap,i-will-never-add-more-devices-to-this-vlan=on -net nic,model=virtio Although we should just add a new syntax. Honestly, vlans have to be the least useful feature in QEMU. Why in the world would anyone ever put more than one nic on a vlan? I understand why the bus architecture is appealing from a symmetry perspective but it's not at all useful from a user perspective. > Paul > -- Regards, Anthony Liguori