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

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