poll方法事例

#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <linux/cdev.h>
#include <asm/uaccess.h>
#include <linux/kernel.h>
#include <linux/poll.h>
#include <linux/wait.h>
#include <linux/slab.h>
#include <linux/string.h>

#define DEVICE_NAME "chardev"

static int chardev_open(struct inode *inodp, struct file *filp);
static ssize_t chardev_read(struct file *filp, char __user *buff, size_t count, loff_t *f_pos);
static ssize_t chardev_write(struct file *filp, const char __user *buff, size_t count, loff_t *f_pos);
static unsigned int chardev_poll(struct file *filp, struct poll_table_struct *p);
static int chardev_release(struct inode *inodp, struct file *filp);

static struct file_operations chardev_fops = {
        .open = chardev_open,
        .read = chardev_read,
        .write = chardev_write,
        .poll = chardev_poll,
        .release = chardev_release,
};

struct chardev {
        char data[8192];
        dev_t devno;
        struct cdev cdev;
        struct semaphore sem;
        wait_queue_head_t rqueue;
};

static struct chardev *dev = NULL;

static int chardev_open(struct inode *inodp, struct file *filp)
{
        struct chardev *device = NULL;

        device = container_of(inodp->i_cdev, struct chardev, cdev);
        filp->private_data = device;

        return 0;
}

static ssize_t chardev_read(struct file *filp, char __user *buff, size_t count, loff_t *f_pos)
{
        if (wait_event_interruptible(dev->rqueue, strlen(dev->data) != 0))
                        goto err;

        if (down_interruptible(&dev->sem))
                goto err;

        copy_to_user(buff, dev->data, strlen(dev->data));
        memset(dev->data, '\0', sizeof(dev->data));

        up(&dev->sem);
        return count;
err:
        return -ERESTARTSYS;
}

static ssize_t chardev_write(struct file *filp, const char __user *buff, size_t count, loff_t *f_pos)
{
        if (down_interruptible(&dev->sem))
                goto err;

        copy_from_user(dev->data, buff, count);

        up(&dev->sem);
        wake_up_interruptible(&dev->rqueue);
        return count;
err:
        return -ERESTARTSYS;
}

static unsigned int chardev_poll(struct file *filp, struct poll_table_struct *p)
{
        unsigned int mask = 0;

        if (down_interruptible(&dev->sem))
                goto err;

        poll_wait(filp, &dev->rqueue, p);

        mask |= POLLIN | POLLRDNORM;

        up(&dev->sem);

        return mask;
err:
        return -ERESTARTSYS;
}

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

static int __init chardev_init(void)
{
        int ret = -1;

        dev = kmalloc(sizeof(struct chardev), GFP_KERNEL);
        if (!dev)
                goto out;

        memset(dev, '\0', sizeof(struct chardev));
        init_MUTEX(&dev->sem);
        init_waitqueue_head(&dev->rqueue);
        ret = alloc_chrdev_region(&dev->devno, 0, 1, DEVICE_NAME);
        if (ret < 0)
                goto err;

        cdev_init(&dev->cdev, &chardev_fops);
        dev->cdev.owner = THIS_MODULE;
        dev->cdev.ops = &chardev_fops;
        ret = cdev_add(&dev->cdev, dev->devno, 1);
        if (!ret)
                goto out;
        unregister_chrdev_region(dev->devno, 1);
err:
        kfree(dev);
out:
        return ret;
}

static void __exit chardev_exit(void)
{
        cdev_del(&dev->cdev);
        unregister_chrdev_region(dev->devno, 1);
        kfree(dev);
}

MODULE_LICENSE("GPL");

module_init(chardev_init);
module_exit(chardev_exit);