字符驱动程序的例子：
《设备驱动开发详解(宋宝华)》P206-208，编写的second的驱动. 在被打开的时候初始化一个定时器并将其添加到内核定时器链表，每秒钟输出一个当前的jiffies,整个驱动，测试，Makefile的代码如下：
/***************************second.c驱动代码************************/
/*======================================================================
A "seond" device driver as an example of kernel timer
The initial developer of the original code is Baohua Song
<author@linuxdriver.cn>. All Rights Reserved.
======================================================================*/
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <asm/io.h>
#include <linux/slab.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <linux/timer.h> /*包括timer.h头文件*/
#include <asm/atomic.h>
#define SECOND_MAJOR 25 /*预设的second的主设备号*/
static int second_major = SECOND_MAJOR;
/*second设备结构体*/
struct second_dev
{
struct cdev cdev; /*cdev结构体*/
atomic_t counter;/* 一共经历了多少秒？*/
struct timer_list s_timer; /*设备要使用的定时器*/
};
struct second_dev *second_devp; /*设备结构体指针*/
/*定时器处理函数*/
static void second_timer_handle(unsigned long arg)
{
mod_timer(&second_devp->s_timer,jiffies + HZ);
atomic_inc(&second_devp->counter);
printk(KERN_NOTICE "current jiffies is %ld\n", jiffies);
}
/*文件打开函数*/
int second_open(struct inode *inode, struct file *filp)
{
/*初始化定时器*/
init_timer(&second_devp->s_timer);
second_devp->s_timer.function = &second_timer_handle;
second_devp->s_timer.expires = jiffies + HZ;
add_timer(&second_devp->s_timer); /*添加（注册）定时器*/
atomic_set(&second_devp->counter,0); //计数清0
return 0;
}
/*文件释放函数*/
int second_release(struct inode *inode, struct file *filp)
{
del_timer(&second_devp->s_timer);
return 0;
}
/*globalfifo读函数*/
static ssize_t second_read(struct file *filp, char __user *buf, size_t count,
loff_t *ppos)
{
int counter;
counter = atomic_read(&second_devp->counter);
if(put_user(counter, (int*)buf))
return - EFAULT;
else
return sizeof(unsigned int);
}
/*文件操作结构体*/
static const struct file_operations second_fops =
{
.owner = THIS_MODULE,
.open = second_open,
.release = second_release,
.read = second_read,
};
/*初始化并注册cdev*/
static void second_setup_cdev(struct second_dev *dev, int index)
{
int err, devno = MKDEV(second_major, index);
cdev_init(&dev->cdev, &second_fops);
dev->cdev.owner = THIS_MODULE;
dev->cdev.ops = &second_fops;
err = cdev_add(&dev->cdev, devno, 1);
if (err)
printk(KERN_NOTICE "Error %d adding LED%d", err, index);
}
/*设备驱动模块加载函数*/
int second_init(void)
{
int ret;
dev_t devno = MKDEV(second_major, 0);
/* 申请设备号*/
if (second_major)
ret = register_chrdev_region(devno, 1, "second");
else /* 动态申请设备号 */
{
ret = alloc_chrdev_region(&devno, 0, 1, "second");
second_major = MAJOR(devno);
}
if (ret < 0)
return ret;
/* 动态申请设备结构体的内存*/
second_devp = kmalloc(sizeof(struct second_dev), GFP_KERNEL);
if (!second_devp) /*申请失败*/
{
ret = - ENOMEM;
goto fail_malloc;
}
memset(second_devp, 0, sizeof(struct second_dev));
second_setup_cdev(second_devp, 0);
return 0;
fail_malloc: unregister_chrdev_region(devno, 1);
}
/*模块卸载函数*/
void second_exit(void)
{
cdev_del(&second_devp->cdev); /*注销cdev*/
kfree(second_devp); /*释放设备结构体内存*/
unregister_chrdev_region(MKDEV(second_major, 0), 1); /*释放设备号*/
}
MODULE_AUTHOR("Song Baohua");
MODULE_LICENSE("Dual BSD/GPL");
module_param(second_major, int, S_IRUGO);
module_init(second_init);
module_exit(second_exit);
/******************************second_test.c测试代码**************************************/
/*======================================================================
A test program to access /dev/second
This example is to help understand kernel timer
The initial developer of the original code is Baohua Song
<author@linuxdriver.cn>. All Rights Reserved.
======================================================================*/
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/time.h>
main()
{
int fd;
int counter = 0;
int old_counter = 0;
/*打开/dev/second设备文件*/
fd = open("/dev/second", O_RDONLY);
if (fd != - 1)
{
while (1)
{
read(fd,&counter, sizeof(unsigned int));//读目前经历的秒数
if(counter!=old_counter)
{
printf("seconds after open /dev/second :%d\n",counter);
old_counter = counter;
}
}
}
else
{
printf("Device open failure\n");
}
}
/*********************************************Makefile******************************************************/
ifeq ($(KERNELRELEASE),)
KERNELDIR ?= /usr/src/linux-headers-2.6.35-32-generic-pae/
PWD :=$(shell pwd)
modules:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
modules_install:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install
clean:
rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions
.PHONY: modules modules_install clean
else
obj-m:= second.o
endif
/*************************************************************************************************************/
驱动程序second.c的编译:
1.首先运行 make 生成 .ko文件
2.把驱动以模块的形式加载到内核中 ： sudo insmod second.ko
3.因为前边预设主设备号为25，且要打开的设备为/dev/second
所以加载号模块后，要建立字符设备：
mknod /dev/second c 25 0
4.编译测试程序运行结果：
