From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753869AbZJEQ2b (ORCPT ); Mon, 5 Oct 2009 12:28:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753160AbZJEQ2b (ORCPT ); Mon, 5 Oct 2009 12:28:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46133 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751692AbZJEQ2a (ORCPT ); Mon, 5 Oct 2009 12:28:30 -0400 Message-ID: <4ACA1CBC.8020402@redhat.com> Date: Mon, 05 Oct 2009 12:20:12 -0400 From: john cooper User-Agent: Thunderbird 2.0.0.9 (X11/20071115) MIME-Version: 1.0 To: Christian Borntraeger , Rusty Russell CC: linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, john.cooper@redhat.com Subject: Re: [PATCH 1/4] virtio_blk: deprecate the 1024-byte ID field. References: <200909300248.09630.rusty@rustcorp.com.au> <200909300941.24736.borntraeger@de.ibm.com> In-Reply-To: <200909300941.24736.borntraeger@de.ibm.com> Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christian Borntraeger wrote: > Am Dienstag 29 September 2009 19:18:09 schrieb Rusty Russell: >> PCI, lguest and s390 can all only support 256-byte configuration >> space. So, this giant field broke just about everyone. >> Unfortunately, removing it is not so simple: we don't want to break >> old userspace, but we're going to want to re-use that part of the >> struct. >> >> So, modern users can #define VIRTIO_BLK_IDENTIFY_DEPRECATED to indicate >> that they know it's no longer in the config struct, and can use any >> new features (all new features which add a configuration field will >> conflict with this deprecated one). > > > Since s390 never used the giant id field, it would be ok for us just delete it > (without the #define). IIRC kvm-userspace also never used that. Since qemu > upstream seems to use that field your way seems to be the only compatible... It seems simply retiring use of the VIRTIO_BLK_F_IDENTIFY binary value should be sufficient. The patch which implemented the cooperating logic in qemu was dropped due to the config space issue. So the case of a virtio_blk driver successfully negotiating the feature and trying to access the now depreciated structure area should effectively be a non-issue. The bit value can be reclaimed for reuse in the future when concern over any suspected usage falls into the noise. -john -- john.cooper@redhat.com