Driver duplicate?

[Kenneth Adam Miller]

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 *, 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;

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.


>
> thanks,
>
> greg k-h
>
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