Linux Kernel Architecture

Chapter7:Modules

__attribute_used__ \

__attribute__((section(".modinfo"),unused)) = __stringify(tag) "=" info

In addition to this general macro that generatestag = infoentries, there are a range of macros that create

entries with pre-defined meanings. These are discussed below.

Module License

The module license is set usingMODULE_LICENSE:

<module.h>

#define MODULE_LICENSE(_license) MODULE_INFO(license, _license)

The technical implementation is not particularly stunning. More interesting is the question as to which

license types are classified as GPL-compatible by the kernel.

❑ GPLandGPLv2stand for the second version of the GNU Public License; in the first definition, any

later version of the license (that may not yet exist) may also be used.

❑ GPL and additional rightsmust be used if further clauses, which must be compatible with the

free software definition software, have been added to the GPL.

❑ Dual BSD/GPL,Dual MIT/GPL,orDual MPL/GPLare used for modules whose sources are available

under a dual license (GPL combined with the Berkeley, MIT, or Mozilla license).

❑ Proprietary modules (or modules whose license is not compatible with GPL) must use

Proprietary.

❑ unspecifiedis used if no explicit license is specified.

Author and Description

Each module should contain brief information about the author (with e-mail address, if possible) and a

description of the purpose of the module:

<module.h>

#define MODULE_AUTHOR(_author) MODULE_INFO(author, _author)

#define MODULE_DESCRIPTION(_description) MODULE_INFO(description, _description)

Alternative Name

MODULE_ALIAS(alias)is used to give a module alternative names (alias) by which it can be addressed

in userspace. This mechanism enables a distinctionto be made between, for example, alternative drivers,

when only one of the drivers can be used although externally they all implement the same functionality.

It is also essential for constructing systematic names. This enables, for instance, assigning one or more

alias names to a module. These aliases specify the identification numbers of all PCI devices that are

supported by the module. When such a device is found in the system, the kernel can (with the help of the

userspace) automatically insert the corresponding module.

Elementary Version Control

Some indispensable version control information is always stored in the.modinfosection, regardless of

whether the version control feature is enabled or disabled. This allows a distinction to be made between