Character and Block Driver Entry Points

Drivers for character and block devices export a cb_ops(9S) structure, which defines the driver entry points for block device access and character device access. Both types of drivers are required to support open(9E) and close(9E). Block drivers are required to support strategy(9E), while character drivers can choose to implement whatever mix of read(9E), write(9E), ioctl(9E), mmap(9E), or devmap(9E) entry points as appropriate for the type of device. Character drivers can also support a polling interface through chpoll(9E), as well as asynchronous I/O through aread(9E) and awrite(9E).

For information on character driver entry points, see Chapter 10, Drivers for Character Devices. For information on block driver entry points, see Chapter 11, Drivers for Block Devices.