The scullpipe driver is a special form of scull that implements a pipe-like device.
Within a driver, a process blocked in a read call is awakened when data arrives,usu-
ally the hardware issues an interrupt to signal such an event, and the driver awakens
waiting processes as part of handling the interrupt. The scullpipe driver works differ-
ently, so that it can be run without requiring any particular hardware or an interrupt
handler. We chose to use another process to generate the data and wake the reading
process .similarly, reading processes are used to wake writer processes that are wait-
ing for buffer space to become available.
