On Thu, Aug 18, 2022 at 08:26:38AM +0200, Greg KH wrote:

On Wed, Aug 17, 2022 at 02:47:25PM -0700, Axel Rasmussen wrote:

quoted

+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?

quoted

+}
+
+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.)

Ah, read the documentation now.  Seems you want to make it easier for
people to get permissions on a system.  Doesn't seem wise, but hey, it's
not my feature...

thanks,

greg k-h