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