Linux---字符设备驱动程序设计

编写一个虚拟字符设备驱动程序char.c,

1. 以内核模块的形式插入内核，编译方法与内核编译方法一致。
2. 创建设备节点，然后通过编写一个测试程序，
3. 功能：首先向设备中写入数据，再从设备中读出数据，并把数据显示在屏幕上。

4. 要求：设备名为：demo,主设务号为250，次设备号为0。

1、首先，要确保环境已经安装好了

开始写

写三个文件 

char.c 

Makefile    ps：M必须大写

test.c   用于测试

vi char.c
vi Makefile
vi test.c

这三个文件的具体代码我放在文末

写好了之后执行make命令

make

然后加载驱动程序

sudo insmod char.ko
lsmod //查看是否加载成功

必须使用管理员权限

在dev目录下创建设备文件

sudo mknod /dev/mychar c 250 0
//要使用管理员权限  
//1. 命令中的数字要和驱动程序定义的major,minor保持一致。
//2. Mychar文件名与测试程序 中的名字一致

编译运行测试程序

gcc test.c -o test
sudo ./test

 

char.c代码

#include    
#include
#include
#include
#include
#include
#include
#include

MODULE_LICENSE("GPL v2");   
MODULE_AUTHOR("Bob Geng");
MODULE_DESCRIPTION("a simple driver");

#define N    128

int major  = 250;
int minor  = 0;
struct cdev mycdev;    //字符型结构体

char buf[N] ={"hello world !!"};
int char_open (struct inode * myinode, struct file *fp)
{
    printk("char is opened\n");
    return 0;	
}
int char_release (struct inode *myinode, struct file *fp)
{
    printk("char is closeed\n");
    return 0;
}


static ssize_t char_read (struct file *filep, char __user *user_buf, size_t count, loff_t * off)
{  // 1. ssize_t :ssize_t是signed size_t；size_t: unsigned int
//2. Off:当前文件的偏移量
    ssize_t ret =0;
    long num =0;
    printk("char_read is called\n");
    printk("count is %d\n",count);
    num = copy_to_user(user_buf,buf,count);
    if(num < 0 )
    {
        printk("copy_to_user is failed\n");
        return ret;
    }
    return ret;
}

ssize_t char_write (struct file *filep, const char __user *from, size_t count, loff_t *off)
{
    ssize_t ret =0; 
    long num =0;
    printk("char_write is called \n");
    printk("count is %d\n",count);
 //   if(count > N )  return -ENOMEM;
    if(count > N )   count = N ;
    num = copy_from_user(buf,from,count);
    if(num < 0 )
    {
        printk("copy_to_user is failed\n");
        return ret;
    }
    printk("from  user is  %s\n",buf);
    return ret; 
}
struct file_operations fops={
    .owner = THIS_MODULE,
    .open  = char_open,
    .release = char_release,   
    .read  = char_read, 
    .write  = char_write, 
};
static int __init char_init(void)
{
    int ret;
    dev_t devno = MKDEV(major,minor);
    ret = register_chrdev_region(devno,1,"char");  //静态申请设备号
    if(ret < 0 )
    {
        printk("fail to get devno\n");
        return ret;
    }
    mycdev.owner = THIS_MODULE;
    cdev_init(&mycdev,&fops);
    ret = cdev_add(&mycdev,devno,1);
    if(ret < 0 )
    {
        printk("cdev_add fail to system\n");
        return ret;
    }
    printk("init_module\n");
    return 0;
}

static void __exit char_exit(void)
{

    dev_t devno = MKDEV(major,minor);
    cdev_del(&mycdev);
    unregister_chrdev_region(devno, 1);
    printk("cleanup_module\n");
}

module_init(char_init);
module_exit(char_exit);

Makefile代码

ifeq ($(KERNELRELEASE),)
KERNELDIR ?= /lib/modules/$(shell uname -r)/build  
#KERNELDIR ?= /home/linux/workdir/source-pack/linux-3.2-net/ （交叉编译）
M=$(PWD) modules
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 Module* modules*
.PHONY: modules modules_install clean
else
obj-m :=char.o
endif

test.c代码

#include
#include
#include
#include 
#include 
#include 
#include 
#include 
#include 

#define   N   128
char buf[N] ; 
int main()
{
    int fd;
    if (  (fd = open("/dev/mychar",O_RDWR)) <  0)
    {
        perror("open");
        exit(-1);
    }

    if(read(fd,buf,N ) < 0 )
    {
        perror("read");
        exit(-1);
    }
    printf("read from mychar is %s\n",buf);
   // memset(buf,0,sizeof(buf));
    //strcpy(buf,"goddbye\0");
 printf("please input second buf:\n");
 scanf("%s",buf);
    if(write(fd,buf,N+1) < 0)
    {
        perror("write");
        exit(-1);
    }

    if(read(fd,buf,N ) < 0 )
    {
        perror("read");
        exit(-1);
    }
 printf("second read from mychar is %s\n",buf);
 getchar();
    printf("mychar is opened\n");
    close(fd);
}