On Thu, Apr 18, 2019 at 12:53:00AM +0100, Al Viro wrote: > Why would you want to duplicate large chunks of anything? > The above is not even compile-tested, but... I can put > together a patch if you wish. Or am I missing something > here? Actually, there's another broken part - pppox. And that one is nastier - you've just lost everything outside of protocol family ioctls on those sockets. Try e.g. SIOCGIFMTU in 32bit process on those. We really can't reuse native ->ioctl() there - proto family ->compat_ioctl() *must* return -ENOIOCTLCMD on everything it doesn't handle.