编辑代码

#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/slab.h>
#include <linux/uaccess.h>

#define GLOBALMEM_SIZE 0x1000
#define MEM_CLEAR 0X1
#define GLOBALMEM_MAJOR 230
#define DEVICE_NUM 10

static int globalmem_major = GLOBALMEM_MAJOR;
module_param(globalmem_major, int, S_IRUGO);

struct globalmem_dev{
    struct cdev cdev;
    unsigned char mem[GLOBALMEM_SIZE];
};

struct globalmem_dev * globalmem_devp;

static int globalmem_open(struct inode *inode, struct file *filp)
{
    struct globalmem_dev *dev = container_of(inode->i_cdev,
                struct globalmem_dev, cdev);
    filp->private_data = dev;
    return 0;
}

static int globalmem_release(struct inode *inode, struct file *filp)
{
    return 0;
}

static long globalmem_ioctl(struct file *filp, unsigned int cmd,
                unsigned long arg)
{
    struct globalmem_dev *dev = filp->private_data;

    switch (cmd){
    case MEM_CLEAR :
        memset(dev->mem, 0, GLOBALMEM_SIZE);
        printk(KERN_INFO "globalmem is set to zero\n");
        break;

    default:
        return -EINVAL;
    }
    return 0;
}

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;

    if(p >= GLOBALMEM_SIZE)
        return 0;
    if(count > GLOBALMEM_SIZE - p)
        count = GLOBALMEM_SIZE - p;

    if(copy_to_user(buf, dev->mem + p, count)) {
        ret = -EFAULT;
    }else {
        *ppos += count;
        ret = count;

        printk(KERN_INFO "read %u byte(s) from %lu \n", count, p);
    }

    return ret;

}

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;
    struct globalmem_dev *dev = filp->private_data;

     if(p >= GLOBALMEM_SIZE)
        return 0;
    if(count > GLOBALMEM_SIZE - p)
        count = GLOBALMEM_SIZE - p;

    if(copy_from_user(dev->mem + p, buf, count)) {
        ret = -EFAULT;
    }else {
        *ppos += count;
        ret = count;

        printk(KERN_INFO "write %u byte(s) from %lu \n", count, p);
    }

    return ret;    

}

static loff_t globalmem_llseek(struct file *filp, loff_t offset, int orig)
{
    loff_t ret = 0;
    switch (orig){
    case 0: /*from the beginning of the file*/
        if (offset < 0 ){
            ret = EINVAL;
            break;
        }
        if ((unsigned int )offset > GLOBALMEM_SIZE){
            ret = EINVAL;
            break;
        }
        filp->f_pos = (unsigned int)offset;
        ret = filp->f_pos;
        break;
    case 1: /*from the current position*/
        if ((filp->f_pos + offset) > GLOBALMEM_SIZE){
            ret = EINVAL;
            break;
        }
        if ((filp->f_pos + offset) < 0){
            ret = EINVAL;
            break;
        }
        filp->f_pos += (unsigned int)offset;
        ret = filp->f_pos;
        break;
    default:
        ret = -EINVAL;
        break;
    }
    return ret;
}







static const struct file_operations globalmem_fops = {
    .owner  = THIS_MODULE,
    .llseek = globalmem_llseek,
    .read = globalmem_read,
    .write = globalmem_write,
    .unlocked_ioctl = globalmem_ioctl,
    .open = globalmem_open,
    .release = globalmem_release,
};

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;
    err = cdev_add(&dev->cdev, devno, 1);
    if(err)
        printk(KERN_NOTICE "Error %d adding globalmem%d ", err, index);
}

static int __init globalmem_init(void)
{
    int ret;
    int i = 0;
    dev_t devno = MKDEV(globalmem_major, 0);
    
    if(globalmem_major)
        ret = register_chrdev_region(devno, DEVICE_NUM, "globalmem");
    else{
        ret = alloc_chrdev_region(&devno, 0, DEVICE_NUM, "globalmem");
        globalmem_major = MAJOR(devno);
    }
    if(ret < 0)
        return ret;

    globalmem_devp = kzalloc(sizeof(struct globalmem_dev) * DEVICE_NUM, GFP_KERNEL);
    if(!globalmem_devp){
        ret = -ENOMEM;
        goto fail_malloc;
    }

    for(i = 0; i < DEVICE_NUM; i++)
        globalmem_setup_cdev(globalmem_devp + i, i);
    return 0;

    fail_malloc:
    unregister_chrdev_region(devno, DEVICE_NUM);
    return ret;
}


static void __exit globalmem_exit(void)
{
    int i = 0;
    for ( i = 0; i < DEVICE_NUM; i++)
        cdev_del(&(globalmem_devp + i)->cdev);
    kfree(globalmem_devp);
    unregister_chrdev_region(MKDEV(globalmem_major, 0), DEVICE_NUM);
}

module_init(globalmem_init);
module_exit(globalmem_exit);

MODULE_AUTHOR("Barry Song <baohua@kernel.org>");
MODULE_LICENSE("GPL v2");