frambuffer有个小问题

exynos_ion_dev = ion_device_create(&exynos_ion_ioctl);里面调用
static long exynos_ion_ioctl(struct ion_client *client, unsigned int cmd,
                                unsigned long arg)
{
        int ret = 0;
    //ToDo: Add custom ioctl here.
    
        return ret;
}
这是个什么接口？干什么用的呢？