To make this chapter more interesting and hands-on, we shall begin evolving a miscellaneous class character "driver" called a simple encrypt decrypt – or sed for short – driver (not to be confused with the well-known sed(1) utility). No, you won't get a grand prize for guessing that it provides some kind of – very simplistic – text encryption/decryption support.
The point here is that we shall imagine that in the specification for this driver, one clause demands that the work (practically speaking, the encryption/decryption functionality) is carried out within a given time interval – in effect, within a given deadline. In order to check this, we shall design our driver so that it has a kernel timer that will expire in the given time interval; the driver will check that the functionality does indeed complete within this time constraint...
