From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752851AbdFRAZK (ORCPT ); Sat, 17 Jun 2017 20:25:10 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:36906 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751689AbdFRAZH (ORCPT ); Sat, 17 Jun 2017 20:25:07 -0400 Date: Sat, 17 Jun 2017 21:28:27 +0200 From: Greg Kroah-Hartman To: Dmitry Torokhov Cc: htejun@gmail.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] sysfs: add devm_sysfs_create_group() and friends Message-ID: <20170617192827.GF2974@kroah.com> References: <20151030114706.GA2243@localhost> <20151030144037.GC27072@kroah.com> <20151030151311.GA20183@dtor-pixel> <20151107002407.GD28499@kroah.com> <20151107072337.GA12209@dtor-ws> <20170607171208.GD13116@dtor-ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170607171208.GD13116@dtor-ws> User-Agent: Mutt/1.8.3 (2017-05-23) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 07, 2017 at 10:12:08AM -0700, Dmitry Torokhov wrote: > On Fri, Nov 06, 2015 at 11:23:37PM -0800, Dmitry Torokhov wrote: > > On Fri, Nov 06, 2015 at 04:24:07PM -0800, Greg Kroah-Hartman wrote: > > > On Fri, Oct 30, 2015 at 08:13:11AM -0700, Dmitry Torokhov wrote: > > > > On Fri, Oct 30, 2015 at 07:40:37AM -0700, Greg Kroah-Hartman wrote: > > > > > On Fri, Oct 30, 2015 at 04:47:06AM -0700, Dmitry Torokhov wrote: > > > > > > Many drivers create additional driver-specific device attributes when > > > > > > binding to the device and providing managed version of sysfs_create_group() > > > > > > will simplify unbinding and error handling in probe path for such drivers. > > > > > > > > > > But they really shouldn't, because if they do this, they have raced > > > > > userspace and tools don't know that the files are present. > > > > > > > > > > I don't want to encourage drivers to do this at all, so I don't want to > > > > > make it easier for them to do things incorrectly. > > > > > > > > The solution is not to forbid drivers from establishing attributes but > > > > rather notify userspace when device is fully bound to the driver. Then > > > > userspace that actually cares about these attributes will listen to > > > > proper events. > > > > > > > > We can either do KOBJ_BOUND/KOBJ_UNBOUND or reuse > > > > KOBJ_ONLINE/KOBJ_OFFLINE. I'd prefer the former (adding new events). > > > > > > bound/unbound makes a bit more sense, maybe that would work, haven't > > > thought that much about it. Given that no one in the "real world" seem > > > to notice the race condition, that means that people aren't really using > > > tools like libudev to read sysfs attributes, so maybe no one even cares > > > about the contents of them :) > > > > Could be, or they have workarounds for this scenario. > > So I have another concrete use-case for this feature: firmware updating. > > Several touch controllers may come up in either normal (application) or > boot mode, depending on whether firmware/configuration is corrupted or > not when they are powered on. In boot mode we do not create input > device instance (because we do not necessarily know the characteristics > of the input device in question). > > I would like to have firmware update scripts to be fired via udev. The > scripts would check the current firmware version and state of the device > and decide whether they need to update firmware or not. To do that they > need to have driver bound to the physical device (i2c or spi), and > therefore I can't rely on ADD events as those happen too early. Having > the BOUND/UNBOUND events will allow me to do this cleanly. Yeah, this is what convinced me we need this. The act of binding/unbinding a driver to a device is a state change for the device, and userspace should learn about it. > I will look into using this mechanism on chrome OS. If you resend the patches, I can work on adding support for it in libudev to see how that works out as well. thanks, greg k-h