Re: [PATCH v6 2/5] userfaultfd: add /dev/userfaultfd for fine grained access control

[Greg KH]

On Wed, Aug 17, 2022 at 02:47:25PM -0700, Axel Rasmussen wrote:
> +static int userfaultfd_dev_open(struct inode *inode, struct file *file)
> +{
> +	return 0;

If your open does nothing, no need to list it here at all, right?

> +}
> +
> +static long userfaultfd_dev_ioctl(struct file *file, unsigned int cmd, unsigned long flags)
> +{
> +	if (cmd != USERFAULTFD_IOC_NEW)
> +		return -EINVAL;
> +
> +	return new_userfaultfd(flags);
> +}
> +
> +static const struct file_operations userfaultfd_dev_fops = {
> +	.open = userfaultfd_dev_open,
> +	.unlocked_ioctl = userfaultfd_dev_ioctl,
> +	.compat_ioctl = userfaultfd_dev_ioctl,

Why do you need to set compat_ioctl?  Shouldn't it just default to the
existing one?

And why is this a device node at all?  Shouldn't the syscall handle all
of this (to be honest, I didn't read anything but the misc code, sorry.)

thanks,

greg k-h