Memory Mapped Devices

For certain devices, such as frame buffers, application programs having direct access to device memory is more efficient than byte-stream I/O. Applications can map device memory into their address spaces using the mmap(2) system call. To support memory mapping, device drivers implement segmap(9E) and devmap(9E) entry points. For information on devmap(9E), see Chapter 12, Mapping Device and Kernel Memory. For information on segmap(9E), see Chapter 10, Drivers for Character Devices.

Drivers that define the devmap(9E) entry point usually do not define read(9E) and write(9E) entry points, as application programs perform I/O directly to the devices after calling mmap(2).