From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751184AbdJCSiF (ORCPT ); Tue, 3 Oct 2017 14:38:05 -0400 Received: from esa2.dell-outbound.iphmx.com ([68.232.149.220]:43662 "EHLO esa2.dell-outbound.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750812AbdJCSiE (ORCPT ); Tue, 3 Oct 2017 14:38:04 -0400 From: X-LoopCount0: from 10.166.132.152 X-IronPort-AV: E=Sophos;i="5.42,474,1500958800"; d="scan'208";a="155418023" X-DLP: DLP_GlobalPCIDSS To: , CC: , , , , , Subject: RE: [PATCH v3 4/8] platform/x86: wmi: create character devices when requested by drivers Thread-Topic: [PATCH v3 4/8] platform/x86: wmi: create character devices when requested by drivers Thread-Index: AQHTPClCs8ArSW0bhE6Px1JsMwinOaLSjwqAgAAbOYD//8q2UA== Date: Tue, 3 Oct 2017 18:38:00 +0000 Message-ID: References: <17fcf9748e83ede2751a00d8248cb32cbdc610d6.1506571188.git.mario.limonciello@dell.com> <20171003092323.GA13295@kroah.com> <20171003151039.GA14523@fury> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.143.18.86] Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by nfs id v93IcBho011865 > -----Original Message----- > From: Andy Lutomirski [mailto:luto@kernel.org] > Sent: Tuesday, October 3, 2017 11:48 AM > To: Darren Hart > Cc: Greg KH ; Limonciello, Mario > ; Andy Shevchenko > ; LKML ; > Platform Driver ; Andy Lutomirski > ; quasisec@google.com; Pali Rohár > Subject: Re: [PATCH v3 4/8] platform/x86: wmi: create character devices when > requested by drivers > > On Tue, Oct 3, 2017 at 8:10 AM, Darren Hart wrote: > > On Tue, Oct 03, 2017 at 11:23:23AM +0200, Greg KH wrote: > >> On Wed, Sep 27, 2017 at 11:02:16PM -0500, Mario Limonciello wrote: > >> > For WMI operations that are only Set or Query read or write sysfs > >> > attributes created by WMI vendor drivers make sense. > >> > > >> > For other WMI operations that are run on Method, there needs to be a > >> > way to guarantee to userspace that the results from the method call > >> > belong to the data request to the method call. Sysfs attributes don't > >> > work well in this scenario because two userspace processes may be > >> > competing at reading/writing an attribute and step on each other's > >> > data. > >> > > >> > When a WMI vendor driver declares a set of functions in a > >> > file_operations object the WMI bus driver will create a character > >> > device that maps to those file operations. > >> > > >> > That character device will correspond to this path: > >> > /dev/wmi/$driver > >> > > >> > This policy is selected as one driver may map and use multiple > >> > GUIDs and it would be better to only expose a single character > >> > device. > >> > > >> > The WMI vendor drivers will be responsible for managing access to > >> > this character device and proper locking on it. > >> > > >> > When a WMI vendor driver is unloaded the WMI bus driver will clean > >> > up the character device. > >> > >> Ok, thanks to Darren, I've gone and dug these up while my boxes were > >> building stable kernels... > >> > >> Why are you not just using the misc device interface here? Why do you > >> need a whole new major and minor range? Why not just register misc > >> devices dynamically as-needed? Should be much simpler and easier to > >> maintain and reduce your code size a lot. > > > > Thank you Greg, this simplifies things quite a bit. > > > > Mario, the misc device interface will remove a lot of the boiler plate > > setup and eliminate the need to allocate a new major number. > > > > In my mind, the problem with misc is that you may end up forever stuck > with a misc device, and they're distinct (visibly to userspace) from > all other character devices. > > If you really want to be fancy, you could try to dust off a non-awful > character device API, a la: > > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=u2f&i > d=d3ab93173d51cebf00dd2263fd0ce9f8cd6258f7 That's two years old. What's the history of it? Did you try to get it merged?