2.6内核字符驱动示例程序（2）（转载）

kf701_dev->timer_char = 'A';
        init_timer( &kf701_dev->timer );
        kf701_dev->timer_interval = HZ * TIMER_INTERVAL;
        kf701_dev->timer.function = timer_function;
        kf701_dev->timer.expires = jiffies + kf701_dev->timer_interval;
        kf701_dev->timer.data = (unsigned long)kf701_dev;
        add_timer( &kf701_dev->timer );
        printk(KERN_DEBUG "%s:init timer OK\n",DEVICE);

        return SUCCESS;
}

static void __exit chardev_exit(void)
{
        dev_t devno = MKDEV( major, minor );
        // 以相反的顺序清除
        del_timer_sync( &kf701_dev->timer );
        printk(KERN_DEBUG "%s:del timer OK\n",DEVICE);
        kfree( kf701_dev->buf );
        cdev_del( &kf701_dev->cdev );
        kfree( kf701_dev );
        printk(KERN_DEBUG "%s:kfree OK\n",DEVICE);
        unregister_chrdev_region( devno, 1 );
        printk(KERN_DEBUG "%s:unregister device OK\n",DEVICE);
}

int chardev_open(struct inode *inode, struct file *file)
{
        struct my_dev *dev = container_of(inode->i_cdev, struct my_dev, cdev);
        file->private_data = dev;
        printk(KERN_DEBUG "%s:open OK\n",DEVICE);
        return SUCCESS;
}

int chardev_release(struct inode *inode, struct file *file)
{
        printk(KERN_DEBUG "%s:release OK\n",DEVICE);
        return SUCCESS;
}

ssize_t chardev_read(struct file *file, char __user *buf, size_t count,loff_t *offset)
{
        struct my_dev *dev = file->private_data;
        ssize_t retval = 0;

        if( down_interruptible(&dev->sem) )
                return -ERESTARTSYS;
        // 增加了对NONBLOCK的支持
        while( 0 == dev->index )
        {
                up(&dev->sem);
                if( file->f_flags & O_NONBLOCK )
                        return -EAGAIN;
                // 在这里准备睡眠,等待条件为真
                if( wait_event_interruptible(dev->rq, (0 != dev->index)) )
                        return -ERESTARTSYS; // 返回非0表示被信号中断
                if( down_interruptible(&dev->sem) )
                        return -ERESTARTSYS; // 先取得锁再检查条件
        }

        if( *offset >= dev->index )
                goto out;
        if( (*offset+count) > dev->index )
                count = dev->index - *offset;
        if( copy_to_user(buf, dev->buf + *offset, count) )
        {
                retval = -EFAULT;
                goto out;
        }
        *offset += count;
        retval = count;

out:
        up(&dev->sem);
        return retval;
}

// omit offset argument for write

ssize_t chardev_write(struct file *file, const char __user *buf, size_t count, loff_t *offset)
{
        struct my_dev *dev = file->private_data;
        ssize_t retval = -ENOMEM;
        if( down_interruptible(&dev->sem) )
                return -ERESTARTSYS;
        if( count > dev->size )
                count = dev->size - 1;
        if( copy_from_user(dev->buf, buf, count) )
        {
                retval = -EFAULT;
                goto out;
        }
        dev->index = count;
        retval = count;

out:
        up(&dev->sem);
        // 唤醒阻塞在 read 和 select 上的进程
        if( retval > 0 )
                wake_up_interruptible(&dev->rq);
        return retval;
}