Driver duplicate?

[greg@kroah.com (Greg KH)]

On Mon, Mar 07, 2016 at 03:00:50PM -0500, Kenneth Adam Miller wrote:
> I have a driver that manages three sets of identical data structures that
> differ only in address values. Currently, I pray that the device file to which
> I have callbacks mapped for the driver gets called sequentially, because there
> are pairs of mmap's that need to be made. I know that this isn't the most ideal
> way to do it, so I'm searching for a better way rather than to swap out the
> values on each method call.?
> 
> There are several things I am aware of but for each one I have questions:
> 1) there are kernel module parameters
> If I use kernel module parameters, I need to be able to insert the kernel
> module three times in order to have each one have a distinct set of global
> memory and mapped callbacks to distinct files. Can that be done? Second, I will
> need to compile the driver statically later. How can I pass those parameters
> that would otherwise be on the command line in statically?

Never use kernel module parameters for a driver, nor for any other
kernel module you create.  They are global and don't work for
device-specific issues.

> 2) I can compile the driver in three times with a compile time flag. This is
> the simplest and easiest, but it requires some buildroot and makefile foo that
> I think is a dirty hack.

It's also never accepted, don't do that.

> 3) I could have the init function create three separate files, since it is on
> init that I discover what my values are. But then I have to also associate
> identical functions that reference global variables in the kernel object.
> Duplicating the code would be worse that compiling the same code three times
> with a kernel parameter, even though that would help me solve my distinct
> globals problem. So how could I parameterisze a char device with data specific
> to the instance?

open() gives you the hook to do so, please just do that.  There's a
whole kernel tree full of examples of how to do this, take a look at
existing code please.

thanks,

greg k-h