字符设备驱动示例

mem_cdev.c

/* http://blog.chinaunix.net/uid-28732854-id-3858242.html */

    /*******************************memdev.h********************************/
    #ifndef _MEMDEV_H_
    #define _MEMDEV_H_

    #ifndef MEMDEV_MAJOR
    #define MEMDEV_MAJOR 251 /*预设的mem的主设备号*/
    #endif

    #ifndef MEMDEV_NR_DEVS
    #define MEMDEV_NR_DEVS 2 /*设备数*/
    #endif

    #ifndef MEMDEV_SIZE
    #define MEMDEV_SIZE 4096
    #endif

    /*mem设备描述结构体*/
    struct mem_dev
    {
      char *data;
      unsigned long size;
    };

    #endif /* _MEMDEV_H_ */

    /*********************memdev.c******************************/
    #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 <linux/slab.h>
    #include <asm/io.h>
    #include <asm/system.h>
    #include <asm/uaccess.h>
    #include "memdev.h"

    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 %ld\n", 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 %ld\n", 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,
    };

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

        if (result < 0)
            return result;

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

        /* 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);
        }
        return 0;

    fail_malloc:
        unregister_chrdev_region(devno, 1);

        return result;
    }

    /*模块卸载函数*/
    static void memdev_exit(void)
    {
        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("www.enjoylinux.cn");
    MODULE_LICENSE("GPL");

    module_init(memdev_init);
    module_exit(memdev_exit);

    /******************app_mem.c************************/

    #include <stdio.h>
    #include <string.h>

    int main()
    {
    FILE *fp0 = NULL;
    char Buf[4096];
    /*初始化Buf*/
    strcpy(Buf, "Mem is char dev!");
    printf("BUF: %s\n",Buf);
    /*打开设备文件*/
    fp0 = fopen("/dev/memdev0","r+");
    if (fp0 == NULL) {
    printf("Open Memdev0 Error!\n");
    return -1;
    }
    /*写入设备*/
    fwrite(Buf, sizeof(Buf), 1, fp0);
    /*重新定位文件位置（思考没有该指令，会有何后果)*/
    fseek(fp0, 0, SEEK_SET);
    /*清除Buf*/
    strcpy(Buf, "Buf is NULL!");
    printf("BUF: %s\n",Buf);
    /*读出设备*/
    fread(Buf, sizeof(Buf), 1, fp0);
    /*检测结果*/
    printf("BUF: %s\n",Buf);
    return 0;
    }