Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754291Ab0LOSIi (ORCPT ); Wed, 15 Dec 2010 13:08:38 -0500 Received: from mtagate6.uk.ibm.com ([194.196.100.166]:52993 "EHLO mtagate6.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751226Ab0LOSIf convert rfc822-to-8bit (ORCPT ); Wed, 15 Dec 2010 13:08:35 -0500 Date: Wed, 15 Dec 2010 19:08:44 +0100 From: Cornelia Huck To: Kay Sievers Cc: Greg KH , Sebastian Ott , linux-kernel@vger.kernel.org Subject: Re: [RFC] bind/unbind uevent Message-ID: <20101215190844.2b757eea@gondolin> In-Reply-To: References: <20101207183305.GA21802@suse.de> <20101208160255.GB10313@suse.de> <20101213193617.GA18262@suse.de> <20101214192952.GA9106@suse.de> <20101215142113.7d416d78@gondolin> <20101215162316.GA31141@suse.de> <20101215183508.2f0b608b@gondolin> Organization: IBM Deutschland Research & Development GmbH Vorsitzender des Aufsichtsrats: Martin Jetter =?ISO-8859-15?Q?Gesch=E4ftsf=FChrung:?= Dirk Wittkopp Sitz der Gesellschaft: =?ISO-8859-15?Q?B=F6blingen?= Registergericht: Amtsgericht Stuttgart, HRB 243294 X-Mailer: Claws Mail 3.7.6 (GTK+ 2.20.1; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3250 Lines: 79 On Wed, 15 Dec 2010 18:51:48 +0100, Kay Sievers wrote: > 2010/12/15 Cornelia Huck : > > On Wed, 15 Dec 2010 08:23:16 -0800, Greg KH wrote: > >> On Wed, Dec 15, 2010 at 02:21:13PM +0100, Cornelia Huck wrote: > > >> How about I turn it around for you, please show me how the driver core > >> does _not_ support this today? ?If you can prove that this isn't working > >> properly, then great, I'll gladly accept patches to resolve it. > > > > Looking at device_add(): > > ... > > > This will not be a problem if a device driver registers a child device > > (since it can specify the attributes there). > > Which is the proper way to do it. No driver should ever mangle a > device which it does not own. It's like adding properties of a block > device directly to a usb_interface device. That just can not work > correctly for many reasons, inside and outside of the kernel. That's fine for new device drivers. > > > I think the basic problem is that the KOBJ_ADD uevent notifies > > userspace that "a device is there", while the device will only be > > really useable by userspace once a driver has bound to it. > > This device represents a device on a bus, and can usually do its own > things. A driver can bind to it, but should not mangle it. > > > A module > > load triggered by KOBJ_ADD is fine, but trying to actually use the > > device after KOBJ_ADD is racy. This will not matter in the usual case, > > since either the matching/probing is fast enough or userspace will wait > > for something like a block device anyway, but we've seen problems on > > s390. A KOBJ_BIND/UNBIND would make a proper distinction between > > "device is there" and "device is usable". > > We don't rally want any such events. We expect a new child device > being created from the driver, instead of re-using the existing bus > device. Do we want to force a device driver to create a child device just to notify userspace of the bind? > > > (Besides, what happens on unbind/bind? Shouldn't userspace know that a > > device is now bound to a different driver?) > > It does that by watching the child devices the driver creates and destroys. > > We already have enough events to handle on today's boxes, we really > don't want to add new ones, which are only needed to work around such > use cases, which ideally just should be fixed. > > If you can not change the current drivers to create child devices, the > driver can probably just send change events for the already existing > devices it mangles from the driver. Since introducing child devices would change the userspace interface, a change event on BUS_NOTIFY_BOUND_DRIVER would probably be the most reasonable for our busses. > > We don't want to encourage any such use model in general, and such > hacks should be bus/driver specific (and only for legacy reasons), and > they do not belong into the driver core. At the end of the day, we just want a working system :) Cornelia -- 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/