The Linux USB Input Subsystem, Part I
In the previous section, we saw that the device drivers basically sat between the hardware and the input core, translating hardware events, usually interrupts, into input events. To make use of those input events, we use handlers, which provide a user-space interface.
The input subsystem includes most of the handlers you'll likely need: a keyboard handler to provide a console, a mouse handler for applications like the X Window System, a joystick handler for games and also a touchscreen handler. There is also a general-purpose handler called the event handler, which basically provides input events to user space. This means you almost never need to write a handler in the kernel, because you can do the same thing with the event handler and equivalent code in user space. This API discussion is covered in the second part of this article.
I'd like to thank Greg Kroah-Hartman and Vojtech Pavlik for their assistance with this article.
Brad Hards is the technical director for Sigma Bravo, a small professional services company in Canberra. In addition to Linux, his technical focus includes aircraft system integration and certification, GPS and electronic warfare. Comments on this article can be sent to firstname.lastname@example.org.
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