Module guidelines

Module developers should follow these guidelines:

• Message types that are not understood by the modules should be passed to the next module.

• The module that acts on an M_IOCTL(D7str) message type should send an M_IOCACK(D7str) or M_IOCNAK(D7str) message in response to the ioctl. If the module does not understand the ioctl, it should pass the M_IOCTL message to the next module.

• Modules should be designed in such a way that they do not pertain to any particular driver but can be used by all drivers.

• In general, modules should not require the data in an M_DATA(D7str) message to follow a particular format, such as a specific alignment. This makes it easier to arbitrarily push modules on top of each other in a sensible fashion. Not following this rule may limit module reusability.

• Filter modules pushed between a service user and a service provider may not alter the contents of the M_PROTO(D7str) or M_PCPROTO(D7str) block in messages. The contents of the data blocks may be manipulated, but the message boundaries must be preserved.

• A multithreaded module is responsible for protecting module-specific data against multiprocessor race conditions.