ssize_t cx18_v4l2_read(struct file *filp, char __user *buf, size_t count,
loff_t *pos);
ssize_t cx18_v4l2_write(struct file *filp, const char __user *buf, size_t count,
loff_t *pos);
ssize_t cx18_v4l2_read(struct file *filp, char __user *buf, size_t count,
loff_t *pos);
ssize_t cx18_v4l2_write(struct file *filp, const char __user *buf, size_t count,
loff_t *pos);