I think David Hermann had some review comments. --Andy On Oct 3, 2017, at 11:38 AM, <Mario.Limonciello@xxxxxxxx> <Mario.Limonciello@xxxxxxxx> wrote: >> -----Original Message----- >> From: Andy Lutomirski [mailto:luto@xxxxxxxxxx] >> Sent: Tuesday, October 3, 2017 11:48 AM >> To: Darren Hart <dvhart@xxxxxxxxxxxxx> >> Cc: Greg KH <greg@xxxxxxxxx>; Limonciello, Mario >> <Mario_Limonciello@xxxxxxxx>; Andy Shevchenko >> <andy.shevchenko@xxxxxxxxx>; LKML <linux-kernel@xxxxxxxxxxxxxxx>; >> Platform Driver <platform-driver-x86@xxxxxxxxxxxxxxx>; Andy Lutomirski >> <luto@xxxxxxxxxx>; quasisec@xxxxxxxxxx; Pali Rohár <pali.rohar@xxxxxxxxx> >> 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 <dvhart@xxxxxxxxxxxxx> 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?
