Symbols exported to modules

• From a kernel module, only a limited number of kernel functions can be called

• Functions and variables have to be explicitly exported by the kernel to be visible from a kernel module

• Two macros are used in the kernel to export functions and variables:

• EXPORT_SYMBOL(symbolname), which exports a function or variable to all modules
• EXPORT_SYMBOL_GPL(symbolname), which exports a function or variable only to GPL modules

• A normal driver should not need any non-exported function.