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成于坚持，败于止步

globalmem程序源码

#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/slab.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 /*4KB*/
#define MEM_CLEAR 0x1  /*clear globale memory*/
#define GLOBALMEM_MAJOR 199 /**/

static globalmem_major = GLOBALMEM_MAJOR;

struct globalmem_dev
{
    struct cdev cdev;
    unsigned char mem[GLOBALMEM_SIZE];
    struct semaphore sem;
};
struct globalmem_dev *globalmem_devp;

int globalmem_open(struct inode* inode, struct file * filp)
{
    filp->private_data = globalmem_devp;
    return 0;
}

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

//static int globalmem_ioctl(struct inode * inodep, struct file * filp, unsigned int cmd, unsigned long arg)
static int globalmem_ioctl(struct file * filp, unsigned int cmd, unsigned long arg)
{
    struct globalmem_dev * dev = filp->private_data;
    
    switch(cmd)
    {
        case MEM_CLEAR:
            if(down_interruptible(&dev->sem))
            {
                return -ERESTARTSYS;
            }
            memset(dev->mem, 0, GLOBALMEM_SIZE);
            up(&dev->sem);
            printk(KERN_INFO "globalmem is set to 0\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 count ? -ENXIO:0;
    }
    
    if(count > GLOBALMEM_SIZE - p)
    {
        count = GLOBALMEM_SIZE - p;
    }

    if(down_interruptible(&dev->sem))
    {
        return -ERESTARTSYS;
    }

    if(copy_to_user(buf, (void*)(dev->mem + p), count))
    {
        ret = -EFAULT;
    }
    else
    {
        *ppos += count;
        ret = count;
        printk(KERN_EMERG "read %d byte(s) from %d\n", count, p);
    }

    up(&dev->sem);

    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 (count ? -ENXIO : 0);
    }
    if(count > GLOBALMEM_SIZE - p)
    {
        count = GLOBALMEM_SIZE - p;
    }

    if(down_interruptible(&dev->sem))
    {
        return -ERESTARTSYS;
    }

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

        printk(KERN_EMERG "written %d byte(s) from %d\n", count, p);
    }


    up(&dev->sem);

    return ret;
}

static loff_t globalmem_llseek(struct file * filp, loff_t offset, int orig)
{
    loff_t ret = 0;

    switch(orig)
    {
        case 0:
            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:
            if((filp->f_pos + offset) > GLOBALMEM_SIZE)
            {
                ret = -EINVAL;
                break;
            }
            if((filp->f_pos + offset) < 0)
            {
                ret = -EINVAL;
                break;
            }
            filp->f_pos += offset;
            ret = filp->f_pos;
            break;
    }

    return ret;
}

static const struct file_operations globalmem_fops = 
{
    .owner = THIS_MODULE,
    .llseek = globalmem_llseek,
    .read = globalmem_read,
    .write = globalmem_write,
    .compat_ioctl = globalmem_ioctl,
    .open = globalmem_open,
    .write = globalmem_write,
};
static void globalmem_setup_cdev(struct globalmem_dev *dev, int index)
{
    int err;
    int devno = MKDEV(globalmem_major, 0);

    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_EMERG "Error %d adding globalmem %d\n", err, index);
    }
}

int globalmem_init(void)
{
    int result;
    dev_t devno = MKDEV(globalmem_major, 0);

    if(globalmem_major)
    {
        result = register_chrdev_region(devno, 1, "globalmem");
    }
    else
    {
        result = alloc_chrdev_region(&devno, 0, 1, "globalmem");
        globalmem_major = MAJOR(devno);
    }

    if(result < 0)
    {
        return result;
    }

    globalmem_devp = kmalloc(sizeof(struct globalmem_dev), GFP_KERNEL);
    if(!globalmem_devp)
    {
        result = -ENOMEM;
        goto fail_malloc;
    }
    memset(globalmem_devp, 0, sizeof(struct globalmem_dev));

    globalmem_setup_cdev(globalmem_devp, 0);
    //init_MUTEX(&globalmem_devp->sem);
    mutex_init(&globalmem_devp->sem);
    return 0;

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


void globalmem_exit(void)
{
    cdev_del(&globalmem_devp->cdev);
    kfree(globalmem_devp);
    unregister_chrdev_region(MKDEV(globalmem_major, 0), 1);
}

MODULE_AUTHOR("hmy");
MODULE_LICENSE("Dual BSD/GPL");

module_param(globalmem_major, int, S_IRUGO);

module_init(globalmem_init);
module_exit(globalmem_exit); 

我的专栏地址：http://blog.csdn.net/column/details/linux-driver-note.html

待续。。。。