Understanding linux joydev driver

I am trying to understand the joydev driver (http://lxr.linux.no/linux+v2.6.36/drivers/input/joydev.c)

Where can I found informaion about that dirver?

Why there is joydev_client struct? why his field isn't embedded inside joydev struct?

Th开发者_开发问答anks Dan

The joydev_client struct is used in apps to receive the joystick events (hence "client"). "joydev" by itself is used by the driver internally. You wouldn't want to expose the internal state of the hardware to all users, so there's two seperate structs - "user friendly" data in the client struct, private data in the main struct.