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# 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.

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