Understanding Loadable Device Drivers

As of HP-UX Release 11.0, a new feature known as Dynamically Loadable Kernel Module (DLKM) provides the means to add a device driver to a running UNIX system without rebooting the system or rebuilding the kernel. This feature also makes it possible to dynamically remove a device driver from the UNIX system when the driver is no longer needed, thereby freeing system resources for other use.

The DLKM feature not only provides the infrastructure to load drivers into a running kernel, but it also allows a driver to be statically linked into the kernel—the way all drivers were included in the kernel prior to HP-UX 11.0. Simply setting a flag in one of the driver's configuration files determines whether a driver is to be configured as dynamically loadable or statically linked.

For HP-UX 11.0, the system must be in a run-time state before dynamic module loading is available. Thus, drivers required during system boot must be configured as statically linked.

DLKM Module Types

The DLKM feature currently supports the following types of drivers: WSIO class drivers, WSIO interface drivers, and STREAMS drivers. It also supports STREAMS modules and miscellaneous modules. An example of a miscellaneous module is a module containing support functions not required in the statically configured kernel but shared among multiple loadable modules.

New Module Packaging

As of HP-UX 11.0, each driver may have its own master and system files, whereas prior to HP-UX 11.0, the driver shared master files and had access to a single system file—the HP-UX system file (/stand/system by default). (The HP-UX system file is still supported in HP-UX 11.0.) This new way of packaging drivers together with the new way of writing driver source code is what makes the DLKM feature possible.




	NOTE: See the master(4) manpage for descriptions of the two kinds of `master` files, and the config(1M) manpage for a description of the HP-UX system file.

Advantages of DLKM Drivers

DLKM drivers/modules provide many advantages relative to static drivers/modules, including:

making it easier for administrators to install device drivers from other vendors
improving system availability by allowing device drivers and other modules to be configured into the kernel while the system is running
conserving system resources by unloading 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

Auto loading occurs when the kernel detects a particular loadable module is required to accomplish some task, but the module is not currently loaded. The kernel automatically loads the module.




	NOTE: Auto unloading is not supported in HP-UX 11.0.

Understanding Loadable Device Drivers

Technical documentation

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DLKM Module Types

New Module Packaging

Advantages of DLKM Drivers