> -----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?
