Re: sysfs & udev & multi-BUS device driver

[Greg KH <greg@kroah.com>]

On Mon, Aug 07, 2006 at 10:51:10PM +0200, Klaus Hitschler wrote:
> Hi,
> 
> I'm maintaining a device driver for CAN-BUS interfaces since kernel version 
> 2.2.x (Controller Area Network - a BUS for automotive use) .  Since that time 
> I implemented all that nice kernel features which were coming and going. 
> (http://www.peak-system.com/linux)
> 
> The driver now comprises support for ISA/PCI/USB/PCMCIA/Parallelport devices. 
> All support is done inside the same driver (I know It would be better to 
> partion it :-))

Hm, you do realize that your USB driver isn't going to work in the near
future due to the closed license of your code?  That's not very nice :(

Any reasons you can't release all of it under the GPL?  It only looks to
be a very small amount of code, which should be pretty trivial to
reverse engineer (and it looks like you might have a bug in it...)

> Now I plan to add support for udev and sysfs. 

You can't use sysfs support in non-GPL code, so you're probably going to
have to figure out how to fix your USB driver code first.

> There's one feature I'd like to retain. The current users do know PCI devices 
> as /dev/pcan0 to /dev/pcan7, ISA devices as /dev/pcan8 to /dev/pcan15, ..., 
> USB devices as /dev/pcan32 to /dev/pcan39, and from /dev/pcan40 start PCMCIA 
> based devices.
> 
> With udev rules it should be easy to create device nodes with the same 
> numbering scheme. But how can I influence the 'kernel name' inside the driver 
> so I know that my internal  'minor' 32 matches to /dev/pcan32 ?

That's up to your code, it's the one that is going to generate the minor
numbers and the names that udev gets from the kernel.  Just make sure to
match them up properly.

> Can you link me to some infos that I can fill this mind gap between udev in 
> user space and device registration inside a driver.

Use the device_register() code (or class_device_register() on older
kernels).  It will create the proper sysfs stuff, and udev will pick up
on it automatically (as long as you provide the dev_t to those
functions.)

> Do you detect problems if I register the driver multilpe times for each BUS 
> ist is associated to?

I don't know, it depends on how your code interacts with this.  There is
no default ISA or PCI major number to mess with, and as long as you
don't use the USB major number, it's all up to you to create these
things.

good luck,

greg k-h

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