字符设备模板１

源代码：

/****************************************************************************** 
*Name: memdev.c 
*Desc: 字符设备驱动程序的框架结构，该字符设备并不是一个真实的物理设备， 
* 而是使用内存来模拟一个字符设备 
*Parameter:  
*Return: 
*Author: derek 
*Date: 2013-6-4 
********************************************************************************/  
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/types.h>
#include <linux/spinlock.h>
#include <linux/blkdev.h>
#include <linux/module.h>  
#include <linux/fs.h>  
#include <linux/errno.h>  
#include <linux/mm.h>  
#include <linux/cdev.h>  
  
#define MEMDEV_MAJOR        260 /*预设的mem的主设备号*/  
#define MEMDEV_NR_DEVS      2 /*设备数*/  
#define MEMDEV_SIZE         4096  
#define CHAR_DEV_NAME       "memdev"
  
/*mem设备描述结构体*/  
struct mem_dev   
{   
  char *data;   
  unsigned long size;   
};  
  
static int mem_major = MEMDEV_MAJOR;  
  
module_param(mem_major, int, S_IRUGO);  
  
struct mem_dev *mem_devp; /*设备结构体指针*/  
  
struct cdev cdev;   
  
/*文件打开函数*/  
int mem_open(struct inode *inode, struct file *filp)  
{  
    struct mem_dev *dev;  
      
    /*获取次设备号*/  
    int num = MINOR(inode->i_rdev);  

    if (num >= MEMDEV_NR_DEVS)   
            return -ENODEV;  
    dev = &mem_devp[num];  
      
    /*将设备描述结构指针赋值给文件私有数据指针*/  
    filp->private_data = dev;  
      
    return 0;   
}  
  
/*文件释放函数*/  
int mem_release(struct inode *inode, struct file *filp)  
{  
    return 0;  
}  
  
/*读函数*/  
static ssize_t mem_read(struct file *filp, char __user *buf, size_t size, loff_t *ppos)  
{  
    unsigned long p = *ppos;  
    unsigned int count = size;  
    int ret = 0;  
    struct mem_dev *dev = filp->private_data; /*获得设备结构体指针*/  

    /*判断读位置是否有效*/  
    if (p >= MEMDEV_SIZE)  
        return 0;  
    if (count > MEMDEV_SIZE - p)  
        count = MEMDEV_SIZE - p;  

    /*读数据到用户空间*/  
    if (copy_to_user(buf, (void*)(dev->data + p), count))  
    {  
        ret = - EFAULT;  
    }  
    else  
    {  
        *ppos += count;  
        ret = count;  
        printk(KERN_INFO "read %d bytes(s) from %d
", count, p);  
    }  

    return ret;  
}  
  
/*写函数*/  
static ssize_t mem_write(struct file *filp, const char __user *buf, size_t size, loff_t *ppos)  
{  
    unsigned long p = *ppos;  
    unsigned int count = size;  
    int ret = 0;  
    struct mem_dev *dev = filp->private_data; /*获得设备结构体指针*/  

    /*分析和获取有效的写长度*/  
    if (p >= MEMDEV_SIZE)  
        return 0;  
    if (count > MEMDEV_SIZE - p)  
        count = MEMDEV_SIZE - p;  

    /*从用户空间写入数据*/  
    if (copy_from_user(dev->data + p, buf, count))  
        ret = - EFAULT;  
    else  
    {  
        *ppos += count;  
        ret = count;  
        printk(KERN_INFO "written %d bytes(s) from %d
", count, p);  
    }  

    return ret;  
}  
  
/* seek文件定位函数 */  
static loff_t mem_llseek(struct file *filp, loff_t offset, int whence)  
{   
    loff_t newpos;  
  
    switch(whence) {  
      case 0: /* SEEK_SET */  
        newpos = offset;  
        break;  
  
      case 1: /* SEEK_CUR */  
        newpos = filp->f_pos + offset;  
        break;  
  
      case 2: /* SEEK_END */  
        newpos = MEMDEV_SIZE -1 + offset;  
        break;  
  
      default: /* can't happen */  
        return -EINVAL;  
    }  
    if ((newpos<0) || (newpos>MEMDEV_SIZE))  
     return -EINVAL;  
       
    filp->f_pos = newpos;  
    return newpos;  
}  
  
/*文件操作结构体*/  
static const struct file_operations mem_fops =  
{  
    .owner = THIS_MODULE,  
    .llseek = mem_llseek,  
    .read = mem_read,  
    .write = mem_write,  
    .open = mem_open,  
    .release = mem_release,  
};  

struct class *pclass;  

/*设备驱动模块加载函数*/  
static int memdev_init(void)  
{  
    int result;  
    int i;  

    dev_t devno = MKDEV(mem_major, 0);  

    if (mem_major)  { /* 静态申请设备号*/  
        result = register_chrdev_region(devno, 2, CHAR_DEV_NAME);  
    } else {/* 动态分配设备号 */  
        result = alloc_chrdev_region(&devno, 0, 2, CHAR_DEV_NAME);  
        mem_major = MAJOR(devno);  
    }   

    if (result < 0)  
        return result;  

    /*初始化cdev结构*/  
    cdev_init(&cdev, &mem_fops);  
    cdev.owner = THIS_MODULE;  
    cdev.ops = &mem_fops;  

    /* 注册字符设备 */  
    cdev_add(&cdev, MKDEV(mem_major, 0), MEMDEV_NR_DEVS);  

    /* 为设备描述结构分配内存*/  
    mem_devp = kmalloc(MEMDEV_NR_DEVS * sizeof(struct mem_dev), GFP_KERNEL);  
    if (!mem_devp) /*申请失败*/  
    {  
        result = - ENOMEM;  
        goto fail_malloc;  
    }  
    memset(mem_devp, 0, sizeof(struct mem_dev));  

    /*为设备分配内存*/  
    for (i=0; i < MEMDEV_NR_DEVS; i++)   
    {  
        mem_devp[i].size = MEMDEV_SIZE;  
        mem_devp[i].data = kmalloc(MEMDEV_SIZE, GFP_KERNEL);  
        memset(mem_devp[i].data, 0, MEMDEV_SIZE);  
    }  

    pclass = class_create(THIS_MODULE, CHAR_DEV_NAME);  
    if (IS_ERR(pclass))  
    {  
        printk("class_create failed!/n");  
        kfree(mem_devp);
        goto fail_malloc;  
    }  

    device_create(pclass, NULL, devno, NULL, CHAR_DEV_NAME);  
    return 0;  

fail_malloc:   
    unregister_chrdev_region(devno, 1);  
    return result;  
}  
  
/*模块卸载函数*/  
static void memdev_exit(void)  
{  
    device_destroy(pclass, MKDEV(mem_major, 0));  
    class_destroy(pclass);
    cdev_del(&cdev); /*注销设备*/  
    kfree(mem_devp); /*释放设备结构体内存*/  
    unregister_chrdev_region(MKDEV(mem_major, 0), 2); /*释放设备号*/  
}  
  
MODULE_AUTHOR("derek yi");  
MODULE_LICENSE("GPL");  
  
module_init(memdev_init);  
module_exit(memdev_exit);  

ｍａｋｅｆｉｌｅ：

ifneq ($(KERNELRELEASE),)

obj-m:=memdev.o

else

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

default:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules

clean:
    rm -rf *.o *.mod.c *.mod.o *.ko

endif

测试代码：

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <linux/fcntl.h>

int main()
{
    int fd;
    char buf[]="this is a example for character devices driver by derek!";
    char buf_read[4096]; //memdev设备的内容读入到该buf中

    if((fd = open("/dev/memdev",O_RDWR))==-1) //打开memdev设备
        printf("open memdev WRONG！
");
    else
        printf("open memdev SUCCESS!
");

    printf("write: %s
", buf); 

    write(fd, buf, sizeof(buf)); //把buf中的内容写入memdev设备 
    lseek(fd, 0, SEEK_SET); //把文件指针重新定位到文件开始的位置 
    read(fd, buf_read, sizeof(buf)); //把memdev设备中的内容读入到buf_read中

    printf("read: %s
",buf_read);
    close(fd);

    return 0;
}