本文演示了Linux加载内核模块（驱动）的过程，文中实验环境为CentOS 5.9 64bit。
1，准备工作
安装基础软件包
yum install kernel-devel.x86_64 gcc.x86_64 gcc-c++.x86_64
然后会在/usr/src/kernels/下面安装好内核源码包，最好把目录的名字改一下，以便能够与/lib/modules/$(uname -r)/目录相响应，避免/lib/modules/$(uname -r)/目录中有一些软链接找不到内核源码包位置
mv /usr/src/kernels/2.6.* /usr/src/kernels/$(uname -r)-x86_64
2，加入内核模块（驱动）
进入字符设备驱动目录
[root@localhost ~]# cd /usr/src/kernels/$(uname -r)-x86_64/drivers/char
[root@localhost char]# mkdir mycdev #建立驱动目录
[root@localhost char]# cd mycdev/
[root@localhost char]# cat /proc/devices #找一个未使用的字符设备主设备号，比如199，记好
[root@localhost mycdev]# vim mycdev.c #建立内核态设备驱动程序，内容见下方
[root@localhost mycdev]# vim Makefile #建立Makefile文件，内容见下方
mycdev.c(字符设备驱动程序)内容
#include <linux/init.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <asm/uaccess.h>
#include <linux/cdev.h>
MODULE_AUTHOR("Edsionte Wu");
MODULE_LICENSE("GPL");
#define MYCDEV_MAJOR 199 /*the predefined mycdev's major devno*/
#define MYCDEV_SIZE 100
static int mycdev_open(struct inode *inode, struct file *fp)
{
return 0;
}
static int mycdev_release(struct inode *inode, struct file *fp)
{
return 0;
}
static ssize_t mycdev_read(struct file *fp, char __user *buf, size_t size, loff_t *pos)
{
unsigned long p = *pos;
unsigned int count = size;
//int i;
char kernel_buf[MYCDEV_SIZE] = "This is mycdev!";
if(p >= MYCDEV_SIZE)
return -1;
if(count > MYCDEV_SIZE)
count = MYCDEV_SIZE - p;
if (copy_to_user(buf, kernel_buf, count) != 0) {
printk("read error!\n");
return -1;
}
/*
for (i = 0; i < count; i++) {
__put_user(i, buf);//write 'i' from kernel space to user space's buf;
buf++;
}
*/
printk("edsionte's reader: %d bytes was read...\n", count);
return count;
}
static ssize_t mycdev_write(struct file *fp, const char __user *buf, size_t size, loff_t *pos)
{
return size;
}
/*filling the mycdev's file operation interface in the struct file_operations*/
static const struct file_operations mycdev_fops =
{
.owner = THIS_MODULE,
.read = mycdev_read,
.write = mycdev_write,
.open = mycdev_open,
.release = mycdev_release,
};
/*module loading function*/
static int __init mycdev_init(void)
{
int ret;
printk("mycdev module is staring..\n");
ret=register_chrdev(MYCDEV_MAJOR,"edsionte_cdev",&mycdev_fops);
if(ret<0)
{
printk("register failed..\n");
return 0;
}
else
{
printk("register success..\n");
}
return 0;
}
/*module unloading function*/
static void __exit mycdev_exit(void)
{
printk("mycdev module is leaving..\n");
unregister_chrdev(MYCDEV_MAJOR,"edsionte_cdev");
}
module_init(mycdev_init);
module_exit(mycdev_exit);
Makefile内容
obj-m:=mycdev.o
PWD:=$(shell pwd)
CUR_PATH:=$(shell uname -r)
KERNEL_PATH:=/lib/modules/$(CUR_PATH)/build
all:
make -C $(KERNEL_PATH) M=$(PWD) modules
clean:
make -C $(KERNEL_PATH) M=$(PWD) clean
提示一下，在kbuild中，用M=dir用来指定生成的内核模块的存放位置
[root@localhost mycdev]# make #将源代码编译成内核模块
[root@localhost mycdev]# insmod mycdev.ko #插入模块，此时可以在dmesg中看到模块注册信息
[root@localhost mycdev]# mknod /dev/mycdev c 199 0 #创建设备文件结点
[root@localhost mycdev]# chmod 777 /dev/mycdev #修改设备文件权限
3，进入用户态测试
[root@localhost ~]# cd /root
[root@localhost ~]# vim aaa.c #建立用户态驱动文件，内容如下
aaa.c(用户态测试程序)内容
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
int main()
{
int testdev;
int i, ret;
char buf[15];
testdev = open("/dev/mycdev", O_RDWR);
if (-1 == testdev) {
printf("cannot open file.\n");
exit(1);
}
if (ret = read(testdev, buf, 15) < 15) {
printf("read error!\n");
exit(1);
}
printf("%s\n", buf);
close(testdev);
return 0;
}
[root@localhost ~]# gcc aaa.c -o aaa #生成二进制可执行文件
[root@localhost ~]# ./aaa
This is mycdev!
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