Attaching file descriptors to processes with CLONE_FD

Agreed! Hell, I had to pile a variant of the old waitfd() API into the oracle enterprise kernel for the sake of *one program* that wanted to do ptrace() waits while also waiting on a message-passing fd from elsewhere. No point sending it upstream -- it was already rejected on the grounds that you can always just waitpid() from another thread. Not if the waitpid() is waiting for ptrace() results you can't.