list_head和container_of用法

#include <linux/module.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <asm/uaccess.h>

#define DEVICE_NAME "sky"
#define DATAALIGN (sizeof(unsigned long) - 1)

struct char_device
{
        struct cdev cdev;
        dev_t devno;
};

struct data_list
{
        struct list_head list;
        unsigned int dlen;
        char data[0];
};

static struct char_device dev;
static struct list_head head = LIST_HEAD_INIT(head);

static ssize_t char_read(struct file *filp, char __user *buf, size_t count, loff_t *pos)
{
        struct data_list *node;
        struct list_head *list;

        for (list = head.next; list != &head; list = list->next)
        {
                node = container_of(list, struct data_list, list);
                if (copy_to_user(buf, node->data, node->dlen))
                {
                        goto copy_err;
                }
                else
                {
                        return node->dlen;
                }
        }

        return count;
copy_err:
        return -EFAULT;
}

static ssize_t char_write(struct file *filp, const char __user *buf, size_t count, loff_t *pos)
{
        struct data_list *new;
        size_t size;

        size = (sizeof(struct data_list) + count + DATAALIGN) & ~DATAALIGN;
        new = kmalloc(size, GFP_KERNEL);
        if (!new)
        {
                goto kmalloc_err;
        }

        memset(new, '\0', size);
        if (copy_from_user(new->data, buf, count))
        {
                goto copy_err;
        }
        else
        {
                new->dlen = count;
                list_add(&new->list, &head);
        }

        return count;
copy_err:
        kfree(new);
kmalloc_err:
        return -EFAULT;
}

static struct file_operations fops =
{
        .read = char_read,
        .write = char_write,
};

static int __init sky_init(void)
{
        if (alloc_chrdev_region(&dev.devno, 0, 1, DEVICE_NAME) < 0)
        {
                goto alloc_err;
        }

        cdev_init(&dev.cdev, &fops);
        dev.cdev.owner = THIS_MODULE;
        dev.cdev.ops = &fops;
        if (cdev_add(&dev.cdev, dev.devno, 1) < 0)
        {
                goto add_err;
        }

        return 0;
add_err:
        unregister_chrdev_region(dev.devno, 1);
alloc_err:
        return -1;
}

static void __exit sky_exit(void)
{
        struct list_head *list;
        struct data_list *node;

        while ((list = head.next) != &head)
        {
                list_del(list);
                node = container_of(list, struct data_list, list);
                if (node)
                {
                        kfree(node);
                }
        }

        cdev_del(&dev.cdev);
        unregister_chrdev_region(dev.devno, 1);
}

MODULE_LICENSE("GPL");

module_init(sky_init);
module_exit(sky_exit);