From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1ND1PV-0002YL-SQ for qemu-devel@nongnu.org; Tue, 24 Nov 2009 14:50:49 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1ND1PQ-0002Qy-PQ for qemu-devel@nongnu.org; Tue, 24 Nov 2009 14:50:49 -0500 Received: from [199.232.76.173] (port=49614 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1ND1PQ-0002Qe-8m for qemu-devel@nongnu.org; Tue, 24 Nov 2009 14:50:44 -0500 Received: from e35.co.us.ibm.com ([32.97.110.153]:43961) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1ND1PP-0000OI-Ri for qemu-devel@nongnu.org; Tue, 24 Nov 2009 14:50:44 -0500 Received: from d03relay01.boulder.ibm.com (d03relay01.boulder.ibm.com [9.17.195.226]) by e35.co.us.ibm.com (8.14.3/8.13.1) with ESMTP id nAOJcWvL025565 for ; Tue, 24 Nov 2009 12:38:32 -0700 Received: from d03av04.boulder.ibm.com (d03av04.boulder.ibm.com [9.17.195.170]) by d03relay01.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id nAOJoUGU125444 for ; Tue, 24 Nov 2009 12:50:32 -0700 Received: from d03av04.boulder.ibm.com (loopback [127.0.0.1]) by d03av04.boulder.ibm.com (8.14.3/8.13.1/NCO v10.0 AVout) with ESMTP id nAODh7Yd030102 for ; Tue, 24 Nov 2009 06:43:07 -0700 Message-ID: <4B0C3901.5010100@linux.vnet.ibm.com> Date: Tue, 24 Nov 2009 13:50:25 -0600 From: Anthony Liguori MIME-Version: 1.0 References: <20091124194502.GA4250@redhat.com> In-Reply-To: <20091124194502.GA4250@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] Re: [PATCH] qemu/virtio-net: remove wrong s/g layout assumptions List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Shirley Ma , Rusty Russell , qemu-devel@nongnu.org Michael S. Tsirkin wrote: > virtio net currently assumes that the first s/g element it gets is > always virtio net header. This is wrong. > There should be no assumption on sg boundaries. For example, the guest > should be able to put the virtio_net_hdr in the front of the skbuf data > if there is room. Get rid of this assumption, properly consume space > from iovec, always. > Practically speaking, we ought to advertise a feature bit to let a kernel know that we are no longer broken. Otherwise, there are a ton of old userspaces that will break with new guests. -- Regards, Anthony Liguori