Managing and Developing Dynamically Loadable Kernel Modules

Developing Dynamically Loadable Kernel Modules

Chapter 12 543

if ( wsio_uninstall_driver(&

module_name

_wsio_info) ) {

/* Uninstall failed! Return to a loaded, functional

* state. */

printf(“

module_name

> wsio_uninstall_driver

failed!!\n”);

return (ENXIO);

}

/* Cancel pending timeouts, free allocated memory and

* resources, etc.

if (

module_name

_debug)

printf(“

module_name

> Unloaded\n”);

return (0);

}

NOTE The wsio_uninstall_driver() function call returns 0 on success.

However (and inconsistently), the wsio_install_driver() function

call returns 1 on success.

WSIO Interface Drivers

A WSIO interface driver requires an _attach() function for any

interface card it intends to claim. It will also require a _probe()

function if it intends to install device probes. When installing a WSIO

interface driver, the driver must register itself with WSIO and set up the

_attach() function and any device probes.

Because the timing of initialization differs between loadable and

statically linked modules, some of the steps that are handled

automatically during boot for static drivers must be explicitly performed

by the _load() function.

The primary difference in making a WSIO interface driver loadable

concerns the handling of the attach list. Historically, drivers have added

their _attach() functions to a global list, and the _attach() function

was responsible for calling the next driver's _attach() function in the

list. However, this method does not allow the driver to remove its

_attach() function from the list; thus, this approach cannot support

unloading.