Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755407AbaJWM2U (ORCPT ); Thu, 23 Oct 2014 08:28:20 -0400 Received: from e06smtp15.uk.ibm.com ([195.75.94.111]:59055 "EHLO e06smtp15.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755168AbaJWM2Q (ORCPT ); Thu, 23 Oct 2014 08:28:16 -0400 Date: Thu, 23 Oct 2014 14:28:08 +0200 From: Cornelia Huck To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH RFC v3 09/16] virtio: set FEATURES_OK Message-ID: <20141023142808.377551d8.cornelia.huck@de.ibm.com> In-Reply-To: <1414003404-505-10-git-send-email-mst@redhat.com> References: <1414003404-505-1-git-send-email-mst@redhat.com> <1414003404-505-10-git-send-email-mst@redhat.com> Organization: IBM Deutschland Research & Development GmbH Vorsitzende des Aufsichtsrats: Martina Koederitz =?UTF-8?B?R2VzY2jDpGZ0c2bDvGhydW5nOg==?= Dirk Wittkopp Sitz der Gesellschaft: =?UTF-8?B?QsO2Ymxpbmdlbg==?= Registergericht: Amtsgericht Stuttgart, HRB 243294 X-Mailer: Claws Mail 3.8.0 (GTK+ 2.24.10; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14102312-0021-0000-0000-000001836EF0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 22 Oct 2014 21:44:44 +0300 "Michael S. Tsirkin" wrote: > set FEATURES_OK as per virtio 1.0 spec > > Signed-off-by: Michael S. Tsirkin > --- > include/uapi/linux/virtio_config.h | 2 ++ > drivers/virtio/virtio.c | 29 ++++++++++++++++++++++------- > 2 files changed, 24 insertions(+), 7 deletions(-) > > dev->config->finalize_features(dev); > > + if (virtio_has_feature(dev, VIRTIO_F_VERSION_1)) { > + add_status(dev, VIRTIO_CONFIG_S_FEATURES_OK); > + status = dev->config->get_status(dev); > + if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) { > + printk(KERN_ERR "virtio: device refuses features: %x\n", > + status); > + err = -ENODEV; > + goto err; > + } > + } > + Ugh, I just realize that virtio-ccw has a problem with that mechanism :( Up to now, the driver only propagated status to the device: For virtio-ccw, this was easily implemented via a ccw that transmitted "status" to the device. However, the "read back status" part now actually requires that the driver can get "status" from the device, or has a comparable way to find out that the device won't accept the status it tried to write. I can think of two solutions: (1) Introduce a new ccw that actually reads the device status. (2) Make the WRITE_STATUS ccw fail (with a unit check) if the driver sets FEATURES_OK after it tried to set features the device won't accept. (1) is probably more generic, while (2) is more straightforward to implement. Good thing we actually try to finally implement this, I did not notice this problem during the review :( -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/