Clever Geek Handbook

The need to use MACROS, for example module_init and module_exit, when writing loadable kernel modules

What are the MACRO, such as module_init

, and module_exit

when writing loadable kernel modules? Also, why are we using MACRO such as __init

or __exit

. Even though we can do this job without using them.

  • Without MACROS

    /*
Without using MACROS
Author: Sricharan Chiruvolu
Date: 14 Dec 2014
*/
#include <linux/module.h>
#include <linux/kernel.h>
int init_module(void){
    printk(KERN_ALERT "This is our first program.");
    return 0;
}
void cleanup_module(void){
    printk(KERN_ALERT "End of our first program.");
}

  • With MACROs

    /* 
Edited first.c; Added macros module_init and module_exit
Author: Sricharan Chiruvolu
Date: 14 Dec 2014
*/
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>

static int __init first_init(void)
{
    printk(KERN_ALERT "This is our first program.");
    return 0;
}

static void __exit first_exit(void)
{
    printk(KERN_ALERT "End of our first program.");
}

module_init(first_init);
module_exit(first_exit);

What is the difference?

+3


source to share


1 answer


module_{init,exit}()

adds the required template to initialize / clean the module and runs the I / O code when the module file is loaded / unloaded into or from kernel space.

__init

tells the kernel that this function is executed once and is never returned mainly for embedded drivers, but rather module_init()

to initialize the module when it is in insmod.

Refer to Rubini and Corbet

"



The __init attribute causes the initialization function to be discarded, and its memory is fixed after initialization is full. However, it only works for built-in drivers; it has no effect on modules. __exit instead leads to the omission of the noted when the driver is not built as a module; again, in modules, this has no effect.

Using __init (and __initdata for items) can reduce the amount of memory used by the kernel. There is no harm in marking a module's initialization function with __init, although there is currently no benefit. Initialization section management has not yet been implemented for modules, but this is a possible improvement for the future.

"



+5


source






More articles:


All Articles