Managing and Developing Dynamically Loadable Kernel Modules

Managing Dynamically Loadable Kernel Modules

Chapter 12 501

modules to be conﬁgured into the kernel while the system is running

❏ Conserving system resources by permitting the unloading of

infrequently used modules when not in use

❏ Providing administrators with the ability to demand load and unload

modules

❏ Providing the kernel with the ability to automatically load modules

DLKM Loading Concepts

When a module is dynamically loaded, its object ﬁle is read from disk

and loaded into newly allocated kernel memory. Once in memory, the

module’s symbols are relocated and any external references are resolved.

Special code in the module is then executed to perform any required

module-speciﬁc setup. Then the code speciﬁc to the module’s type, if any,

is executed, making the newly loaded module accessible to the rest of the

kernel.

A module can be loaded in the following ways:

❏ Demand Load

A demand load is a user level request for a speciﬁc module to be

loaded. The load is accomplished through the kmadmin command.