FreeBSD Device Drivers

Character Drivers

Character drivers are basically KLDs that create character devices. As mentioned previously, character devices provide either a character-stream-oriented I/O interface or, alternatively, an unstructured (raw) interface. These (character-device) interfaces establish the conventions for accessing a device, which include the set of procedures that can be called to do I/O operations (McKusick and Neville-Neil, 2005). In short, character drivers produce character devices, which provide device access. For example, the lpt(4) driver creates the /dev/lpt0 character device, which is used to access the parallel port printer. In FreeBSD 4.0 and later, most devices have a character-device interface.

In general, three components are common ...