[RFC PATCH] pidfd: implement PIDFD_THREAD flag for pidfd_open()

[Oleg Nesterov]

On 01/27, Oleg Nesterov wrote:
>
> I'll (hopefully) send v2 on top of
>
> 	pidfd: cleanup the usage of __pidfd_prepare's flags
> 	pidfd: don't do_notify_pidfd() if !thread_group_empty()
>
> on Monday

Sorry, I don't have time to finish v2 today, I need to update the comments
and write the changelog.

But the patch itself is ready, I am sending it for review.

Tycho, Christian, any comments?

Oleg.