Managing and Developing Dynamically Loadable Kernel Modules

Developing Dynamically Loadable Kernel Modules

Chapter 12534

The _unload() function must clean up any resources that were

allocated to the module, and it must remove all references to the module.

Typical cleanup tasks include releasing private memory acquired by the

module, removing device interrupts, disabling interrupts from the

device, and canceling any outstanding timeout requests made by the

module.

The module’s _unload() function should return 0 on success and an

errno value on failure. In the event of failure, the function must leave

the module in a sane state, since the module will remain loaded after the

return.

The system will never attempt to unload a module that it thinks is busy.

However, the system cannot determine under all cases when the module

is in use. Currently, a module is considered to be busy when another

module that depends on it is also loaded. In addition, WSIO class drivers

and STREAMS drivers track the open() and close() calls; these

types of modules are busy whenever there is at least one open on the

device using the driver. Under most other circumstances, the module

must determine for itself whether it is appropriate for it to be unloaded.

When a module is still in use, its _unload() function can return a

nonzero value to cancel the unload.

The argument passed to the _unload() function by the DLKM

infrastructure is the same type-speciﬁc value that was passed to the

module’s _load() function. The use of this argument is described in

“Initializing and Terminating DLKM Modules” on page 538.

master File Deﬁnition

Each DLKM module has its own master ﬁle. The format of the master

ﬁle includes the following section keywords:

❏ $VERSION – indicates the version number for the ﬁle format. Version

is deﬁned as an integer. A single line containing the version is

entered. For PA systems, the only supported version is 1.

For Itanium-based systems, version 2 is a supported ﬁle format for

Boot Time Loaded modules. If $VERSION is 2 in the master and

system ﬁles the phases keyword in the master ﬁle and the

$LOADPHASE keyword in the system ﬁle would need to be speciﬁed.

❏ $LOADABLE – indicates that the module is dynamically loadable. If

this section keyword does not exist, the module can only be statically

conﬁgured into the kernel. Optionally, this section may contain either