Hello_kernel of kernel programming

foreword

Through hello_kernel programming to achieve the following goals:

• Kernel programming framework understanding
• Module parameter call
• function call between modules
• Use of commands related to kernel modules

Environmental preparation

There are two ways to prepare the kernel source tree:

Method 1: Download the kernel source code from kernel.org and compile it manually
Method 2: Install the kernel source tree consistent with the system version through yum

yum install -y kernel-devel-`uname -r`

After installation, there will be a source directory of the corresponding version in the /usr/src/kernels path, and /lib/modules/ uname -r/build will point to the corresponding source directory.

Kernel programming example

There are three instances of kernel programming here:

• First look at the kernel module
• Module parameter passing

• function call between modules

  First look at the kernel module

kernel_hello.c

#include <linux/init.h>         // module_init module_exit 宏定义
#include <linux/module.h>       // MODULE_LICENSE MODULE_AUTHOR MODULE_DESCRIPTION MODULE_VERSION

/* 以下4个宏分别是许可证，作者，模块描述，模块版本 */
MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("calling love");
MODULE_DESCRIPTION("hello kernel programming");
MODULE_VERSION("1.0");

/* 模块入口函数 */
static int hello_init(void)
{
    printk(KERN_ALERT "hello_init() start\n"); // 内核日志输出,KERN_ALERT表示日志的级别,是个字符串

    return 0;
}

/* 模块退出函数 */
static void hello_exit(void)
{
    printk(KERN_ALERT "hello_exit() start\n");
}

/* 注册到内核 */
module_init(hello_init);
module_exit(hello_exit);

Makefile

KDIR := /lib/modules/$(shell uname -r)/build
PWD  := $(shell pwd)

obj-m := kernel_hello.o

all:
    $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules

clean:
    rm -f *.o *.ko .*.o.d *~ .*.cmd *.mod.c *.order *.ko.* *.symvers -r .tmp_versions

KDIR: Source tree path, can also be specified directly/usr/src/kernels/2.6.32-642.13.1.el6.x86_64