From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932928Ab1KCDwK (ORCPT ); Wed, 2 Nov 2011 23:52:10 -0400 Received: from ozlabs.org ([203.10.76.45]:43725 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754422Ab1KCDwH (ORCPT ); Wed, 2 Nov 2011 23:52:07 -0400 From: Rusty Russell To: Sasha Levin , "Michael S. Tsirkin" Cc: linux-kernel , kvm , virtualization , Anthony Liguori Subject: Re: virtio-pci new configuration proposal In-Reply-To: <1320259767.22582.2.camel@lappy> References: <1320259767.22582.2.camel@lappy> User-Agent: Notmuch/0.6.1-1 (http://notmuchmail.org) Emacs/23.3.1 (i686-pc-linux-gnu) Date: Thu, 03 Nov 2011 12:28:46 +1030 Message-ID: <8762j2t19l.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 02 Nov 2011 20:49:27 +0200, Sasha Levin wrote: > This is a proposal for a new layout of the virtio-pci config space. > > We will separate the current configuration into two: A virtio-pci common > configuration and a device specific configuration. This allows more flexibility > with adding features and makes usage easier, specifically in cases like the > ones in virtio-net where device specific configurations depend on device > specific features. Thanks for this Sasha. Several general comments: 1) How to we distinguish the two layouts? In theory, we need to do this forever. In practice we can deprecate the old layout in several years' time. 2) I don't think we want to turn the device-specific config into a linked list. We haven't needed variable-length config (yet!), and it's (slightly) more complex. That's also the part of the spec which is shared with non-PCI virtio implementations. 3) If we're changing the queue layout, it's a chance to fix a longstanding bug: let the guest notify the host of preferred queue size and alignment. Cheers, Rusty.