Using Modules

Modules provide a means for multiple drivers to share common functionality; for example, if a variety of types of device might be accessed on the same bus, a module might be created to provide a common interface to the bus.

Your driver can access these modules via the kernel functions get_module() and put_module(), which obtain and release references to a specified module. When you call get_module(), you obtain a structure that provides information about the module, plus pointers to the module’s functions. The module is defined in a header file provided by the module’s author, similar to this:

#define MY_MODULE_NAME "generic/mymodule/v1"

struct my_module_info {
   module_info module;
   int32 (*function1)();
   int32 (*function2)();
   void (*configure)(int32 parameter, int32 value);
};

When you want to access the module’s functions, you call get_module() to get a pointer to this structure from the kernel:

struct my_module_info*minfo = NULL;

/* get a pointer to the module */

get_module(MY_MODULE_NAME, (module_info**) &minfo);

Once you’ve done this, you can call the module’s functions through the structure:

minfo->configure(0, 10);

When you’re done with the module, you should call put_module() to release it. The kernel loads and unloads modules as needed, and properly calling put_module() lets the kernel do its job.

put_module(MY_MODULE_NAME);

If you want a better understanding of how modules work, see the “Writing Modules” section.