This layer consists of a set of functions that take care of most of the POSIX filesystem details for you — they provide a POSIX personality. If you're writing a device resource manager, you'll want to use this layer so that you don't have to worry too much about the details involved in presenting a POSIX filesystem to the world.
This layer consists of default handlers that the resource manager library uses if you don't provide a handler. For example, if you don't provide an io_open handler, iofunc_open_default() is called.
The iofunc layer also contains helper functions that the default handlers call. If you override the default handlers with your own, you can still call these helper functions. For example, if you provide your own io_read handler, you can call iofunc_read_verify() at the start of it to make sure that the client has access to the resource.
The names of the functions and structures for this layer have the form iofunc_*. The header file is <sys/iofunc.h>. For more information, see the QNX Neutrino C Library Reference.