linux设备驱动入门---globalmem字符设备驱动

/* globalmem字符设备驱动 
 * 作者：liwei.cai
 * 日期：2012-08-03
 * globalmem.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 <asm/io.h>
#include <asm/system.h>
#include <asm/uaccess.h>

#define GLOBALMEM_SIZE 0x1000 /* 全局内存大小：4KB */
#define MEM_CLEAR 0x01 /* 清零全局内存 */
#define GLOBALMEM_MAJOR 250 /* 预设的globalmem 的主设备号 */

static int globalmem_major = GLOBALMEM_MAJOR;

/* globalmem设备结构体 */
struct globalmem_dev
{
    struct cdev cdev; /* cdev结构体 */
    unsigned char mem[GLOBALMEM_SIZE]; /* 全局变量 */
};

//struct globalmem_dev dev; /* 设备结构体实例 */
struct globalmem_dev *globalmem_devp; /* 设备结构体指针 */

/* 文件打开函数 */
int globalmem_open(struct inode *inode, struct file *filp)
{
    /* 将设备结构体指针赋值给文件私有数据指针  */
    filp->private_data = globalmem_devp;
    return 0;
}

/* 文件释放函数 */
int globalmem_release(struct inode *inode, struct file *filp)
{
    return 0;
}

/* globalmem 设备驱动的读函数 */
static ssize_t globalmem_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 globalmem_dev *dev = filp->private_data;//获得设备结构体指针

    /* 分析和获取有效的读长度 */
    if(p >= GLOBALMEM_SIZE) //要读的偏移位置越界
    {
        return count ? -ENXIO : 0;
    }
    if (count > GLOBALMEM_SIZE - p) //要读的字节太大
    {
        count = GLOBALMEM_SIZE - p;
    }

        /* 内核控件-->用户空间 */
    if (copy_to_user(buf, (void*)(dev->mem + p), count))
    {
        ret = -EFAULT;
    }
    else
    {
        *ppos += count;
        ret = count;

        printk(KERN_INFO "read %d bytes(s) from %ld \n", count, p);
    }

    return ret;
}

/* globalmem 设备驱动的写函数 */
static ssize_t globalmem_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;
<span style="white-space: pre; ">    </span>struct globalmem_dev *dev = filp->private_data;//获取设备结构体指针

    /* 分析和获取有效的写长度 */
    if (p >= GLOBALMEM_SIZE) // 要写的偏移位置越界
    {
        return count ? -ENXIO : 0;
    }
    if (count > GLOBALMEM_SIZE - p) // 要写的字节数太多
    {
        count = GLOBALMEM_SIZE - p;
    }

    /* 用户空间 --> 内核空间 */
    if (copy_from_user(dev->mem + 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()函数对文件定位的起始位置可以是文件开头（SEEK_SET, 0）、
 * 当前位置（SEEK_CUR，1）和文件尾（SEEK_END，2）
 */
static loff_t globalmem_llseek(struct file *filp,
        loff_t offset, int orig)
{
    loff_t ret;
    switch(orig)
    {
        case 0: //从文件开头开始偏移
            if (offset < 0)
            {
                ret = -EINVAL;
                break;
            }
            if ((unsigned int)offset > GLOBALMEM_SIZE)// 偏移越界
            {
                ret = -EINVAL;
                break;
            }
            filp->f_pos = (unsigned int)offset;
            ret = filp->f_pos;
            break;
        case 1: //从当前位置开始偏移
            if((filp->f_pos + offset) > GLOBALMEM_SIZE) //偏移越界
            {
                ret = -EINVAL;
                break;
            }
            if ((filp->f_pos + offset) < 0)
            {
                ret = -EINVAL;
                break;
            }
            filp->f_pos += offset;
            ret = filp->f_pos;
            break;
        default:
            ret = -EINVAL;
    }
    return ret;
}

/* ioctl(）函数接受MEM_CLEAR命令,这个命令会将全局内存的有效数据长度清零
 * 对于设备不支持的命令，返回-EINCVAL
 */
static int globalmem_ioctl(struct inode *inodep, struct file *filp, 
        unsigned int cmd, unsigned long arg)
{
    struct globalmem_dev *dev = filp->private_data; /* 获得设备结构体指针 */
    switch(cmd)
    {
        case MEM_CLEAR://清除全局内存
            memset(dev->mem, 0, GLOBALMEM_SIZE);
            printk(KERN_INFO "globalmem is set to zero\n");
            break;

        default:
            return -EINVAL;
    }
    return 0;
}

/* 与globalmem的cdev关联的file_operations结构体 */
static const struct file_operations globalmem_fops =
{
    .owner = THIS_MODULE,
    .llseek = globalmem_llseek,
    .read = globalmem_read,
    .write = globalmem_write,
    .ioctl = globalmem_ioctl,
    .open =globalmem_open,
    .release = globalmem_release,
};

/* 初始化并添加cdev结构体 */
static void globalmem_setup_cdev(struct globalmem_dev *dev, int index)
{
    int err, devno = MKDEV(globalmem_major, index);

    cdev_init(&dev->cdev, &globalmem_fops);
    dev->cdev.owner = THIS_MODULE;
    dev->cdev.ops = &globalmem_fops;
    err = cdev_add(&dev->cdev, devno, 1);
    if(err)
    {
        printk(KERN_NOTICE "ERROR %d adding LED%d", err, index);
    }
}

/* globalmem设备驱动模块加载函数 */
int globalmem_init(void)
{
    int result;
    dev_t devno = MKDEV(globalmem_major, 0);

    /* 申请字符设备驱动区域 */
    if (globalmem_major)
    {
        result = register_chrdev_region(devno, 1, "globalmem");
    }
    else
    {
        /* 动态加载主设备号 */
        result = alloc_chrdev_region(&devno, 0, 1, "globalmem");
        globalmem_major = MAJOR(devno);
    }
    if (result < 0)
    {
        return result;
    }
    
    /* 动态申请设备结构体的内存 */
    globalmem_devp = kmalloc(sizeof(struct globalmem_dev), GFP_KERNEL);
    if (!globalmem_devp) //申请失败
    {
        result = -ENOMEM;
        goto fail_malloc;
    }
    memset(globalmem_devp, 0, sizeof(struct globalmem_dev));

    globalmem_setup_cdev(globalmem_devp, 0);
    return 0;

fail_malloc:unregister_chrdev_region(devno, 1);
            return result;
}

/* globalmem设备驱动卸载函数 */
void globalmem_exit(void)
{
    cdev_del(&globalmem_devp->cdev);  //注销cdev
//    cdev_del(&dev.cdev); /* 删除cdev结构 */
        kfree(globalmem_devp); //释放设备结构体内存

    unregister_chrdev_region(MKDEV(globalmem_major,0), 1); /*注销设备区域 */
}

MODULE_AUTHOR("Liwei.Cai");
MODULE_LICENSE("Dual BSD/GPL");

module_param(globalmem_major, int, S_IRUGO);

module_init(globalmem_init);
module_exit(globalmem_exit);