Automatic default message handling

If there are functions that the resource manager doesn't want to handle for some reason (e.g., a digital-to-analog converter doesn't support a function such as lseek(), or the software doesn't require it), the shared library will conveniently supply default actions.

There are two levels of default actions:

• The first level simply returns ENOSYS to the client application, informing it that that particular function is not supported.
• The second level (i.e., the iofunc_*() shared library) allows a resource manager to automatically handle various functions.

For more details on default actions, see the section on Second-level default message handling in this chapter.