hello.c File Reference

An introductory "Hello World!" loadable kernel module (LKM) that can display a message in the /var/log/kern.log file when the module is loaded and removed. The module can accept an argument when it is loaded – the name, which appears in the kernel log files. More...

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>

Include dependency graph for hello.c:

Functions
	MODULE_LICENSE ("GPL")
	The license type – this affects runtime behavior. More...
	MODULE_AUTHOR ("Derek Molloy")
	The author – visible when you use modinfo. More...
	MODULE_DESCRIPTION ("A simple Linux driver for the BBB.")
	The description – see modinfo. More...
	MODULE_VERSION ("0.1")
	The version of the module. More...
	module_param (name, charp, S_IRUGO)
	Param desc. charp = char ptr, S_IRUGO can be read/not changed. More...
	MODULE_PARM_DESC (name,"The name to display in /var/log/kern.log")
	parameter description More...
static int __init	helloBBB_init (void)
	The LKM initialization function The static keyword restricts the visibility of the function to within this C file. The __init macro means that for a built-in driver (not a LKM) the function is only used at initialization time and that it can be discarded and its memory freed up after that point. More...
static void __exit	helloBBB_exit (void)
	The LKM cleanup function Similar to the initialization function, it is static. The __exit macro notifies that if this code is used for a built-in driver (not a LKM) that this function is not required. More...
	module_init (helloBBB_init)
	A module must use the module_init() module_exit() macros from linux/init.h, which identify the initialization function at insertion time and the cleanup function (as listed above) More...
	module_exit (helloBBB_exit)

Variables
static char *	name = "world"
	An example LKM argument – default value is "world". More...

Detailed Description

An introductory "Hello World!" loadable kernel module (LKM) that can display a message in the /var/log/kern.log file when the module is loaded and removed. The module can accept an argument when it is loaded – the name, which appears in the kernel log files.

Author

Derek Molloy

Date

4 April 2015

Version

0.1

See also

http://www.derekmolloy.ie/ for a full description and follow-up descriptions.

Function Documentation

static void __exit helloBBB_exit ( void  )

static

The LKM cleanup function Similar to the initialization function, it is static. The __exit macro notifies that if this code is used for a built-in driver (not a LKM) that this function is not required.

                                      {
   printk(KERN_INFO "EBB: Goodbye %s from the BBB LKM!\n", name);
}

static int __init helloBBB_init ( void  )

static

The LKM initialization function The static keyword restricts the visibility of the function to within this C file. The __init macro means that for a built-in driver (not a LKM) the function is only used at initialization time and that it can be discarded and its memory freed up after that point.

Returns

returns 0 if successful

                                     {
   printk(KERN_INFO "EBB: Hello %s from the BBB LKM!\n", name);
   return 0;
}

MODULE_AUTHOR

(

"Derek Molloy"

)

The author – visible when you use modinfo.

MODULE_DESCRIPTION

(

"A simple Linux driver for the BBB."

)

The description – see modinfo.

module_exit

(

helloBBB_exit

)

module_init

(

helloBBB_init

)

A module must use the module_init() module_exit() macros from linux/init.h, which identify the initialization function at insertion time and the cleanup function (as listed above)

MODULE_LICENSE

(

"GPL"

)

The license type – this affects runtime behavior.

module_param	(	name	,
		charp	,
		S_IRUGO
	)

Param desc. charp = char ptr, S_IRUGO can be read/not changed.

MODULE_PARM_DESC	(	name	,
		"The name to display in /var/log/kern.log"
	)

parameter description

MODULE_VERSION

(

"0.1"

)

The version of the module.

Variable Documentation

char* name = "world"

static

An example LKM argument – default value is "world".