(리눅스 시스템 프로그래밍) LKM + C 예제코드

  $ sudo apt-get update
  $ apt-cache search linux-headers-$(uname -r)
  linux-headers-4.15.0-041500-generic - Linux kernel headers for version 4.15.0 on 64 bit x86 SMP
  $ sudo apt-get install (헤더명)
  $ cd /usr/src/(헤더명)
  $ ls

  **jinhyeok@CRA230**:**~**$   apt-cache search linux-headers-$(uname -r)
  linux-headers-4.15.0-041500-generic - Linux kernel headers for version 4.15.0 on 64 bit x86 SMP

 /**
 * @file    hello.c
 * @author  Jinhyeok Jeong
 * @date    24 March 2019
 * @version 0.1
 * @brief  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.
 * @see http://www.derekmolloy.ie/ for a full description and follow-up descriptions.
*/

#include <linux/init.h>             // Macros used to mark up functions e.g., __init __exit
#include <linux/module.h>           // Core header for loading LKMs into the kernel
#include <linux/kernel.h>           // Contains types, macros, functions for the kernel

MODULE_LICENSE("GPL");              ///< The license type -- this affects runtime behavior
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_VERSION("0.1");              ///< The version of the module

static char *name = "world";        ///< An example LKM argument -- default value is "world"
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

/** @brief 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.
 *  @return returns 0 if successful
 */
static int __init helloBBB_init(void){
   printk(KERN_INFO "EBB: Hello %s from the BBB LKM!\n", name);
   return 0;
}

/** @brief 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.
 */
static void __exit helloBBB_exit(void){
   printk(KERN_INFO "EBB: Goodbye %s from the BBB LKM!\n", name);
}

/** @brief 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_init(helloBBB_init);
module_exit(helloBBB_exit);

jinhyeok@CRA230:~/Linux_Kernel_Programming$ make
make -C /lib/modules/4.15.0-041500-generic/build M=/home/jinhyeok/Linux_Kernel_Programming modules
make[1]: 디렉터리 '/usr/src/linux-headers-4.15.0-041500-generic' 들어감
  CC [M]  /home/jinhyeok/Linux_Kernel_Programming/hello.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC      /home/jinhyeok/Linux_Kernel_Programming/hello.mod.o
  LD [M]  /home/jinhyeok/Linux_Kernel_Programming/hello.ko
make[1]: 디렉터리 '/usr/src/linux-headers-4.15.0-041500-generic' 나감
jinhyeok@CRA230:~/Linux_Kernel_Programming$ ls
Makefile        hello.c   hello.mod.c  hello.o
Module.symvers  hello.ko  hello.mod.o  modules.order

//로드하기
sudo insmode hello.ko

//언로드하기
sudo rmmod hello.ko

jinhyeok@CRA230:/var/log$ cd /var/log
jinhyeok@CRA230:/var/log$ sudo tail -f kern.log
Mar 24 17:08:08 CRA230 kernel: [141413.098009] EBB: Hello world from the BBB LKM!
Mar 24 17:13:07 CRA230 kernel: [141711.746656] EBB: Goodbye world from the BBB LKM!

jinhyeok@CRA230:~/Linux_Kernel_Programming$ sudo insmod hello.ko name=jinhyeok
jinhyeok@CRA230:~/Linux_Kernel_Programming$ sudo rmmod hello.ko

jinhyeok@CRA230:/proc$ cd /proc
jinhyeok@CRA230:/proc$ cat modules|grep hello
hello 16384 0 - Live 0x          (null) (OE)

jinhyeok@CRA230:~$ cd /sys/module/hello/parameters/
jinhyeok@CRA230:/sys/module/hello/parameters$ cat name
jinhyeok