Re: [PATCH 2/4] clone.2: Describe the user namespace

There is one other bit that needs to be documented in clone, although
I am not certain where/how.

The sequences:

unshare(CLONE_NEWPID).
clone(CLONE_VM)

setns(fd, CLONE_NEWPID).
clone(CLONE_VM).

Now fail.

Basically the rule is all threads must be in the same pid namespace.

The joy of reviews with good comments that come much later than hoped.

Eric