Driver duplicate?

[Greg KH]

On Mon, Mar 07, 2016 at 03:21:44PM -0500, Kenneth Adam Miller wrote:
> 
> 
> On Mon, Mar 7, 2016 at 3:17 PM, Greg KH <greg at kroah.com> wrote:
> 
>     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.
> 
> 
> After I had the idea in the second email, I think that using the kernel api to
> distinguish which char device a callback maps to in order to utilize the
> corresponding data is the best way.
> 
> If I could do something along the lines of retrieving the file name, as in a
> char *,

There is no such "thing" in the kernel (think of symlinks, or different
names for the same major:minor pair).

> from the file * that is passed in with the callback, or distinguish any
> one of these:
> 
> static dev_t LSKSMM_dev;
> static struct cdev LSKSMM_cdev;
> static struct class *LSKSMM_class;
> static struct device *LSKSMM_device;

Those are all different things, none of them get passed into open().

I don't think you have thought this through very far, where is your
source code to take a look at it?

> which are also created on module init, it would really make things convenient
> and easy. I'm currently digging around in the kernel headers, but I think
> probably somebody somewhere knows what I'm looking for. Some unique field that
> I can retain on init that I can get back in my mmap/ioctl call to recognize
> what data to use.

Again, it's all provided directly to you in your open() call, what's
wrong with that?

thanks,

greg k-h