Re: [PATCH v3 1/3] pidfd: allow pidfd_open() on non-thread-group leaders

[Oleg Nesterov]

On 01/25, Oleg Nesterov wrote:
>
> On 01/25, Tycho Andersen wrote:
> >
> > One of the things I don't like about PIDFD_THREAD is that it's hard to
> > tell whether an arbitrary thread is a leader or not. Right now we do
> > it by parsing /proc/pid/status, which shows all the stuff from
> > do_task_stat() that we don't care about but which is quite expensive
> > to compute. (Maybe there's a better way?)
> >
> > With PIDFD_THREAD we could could do it twice, once with the flag, get
> > EINVAL, and then do it again. But ideally we wouldn't have to.
>
> Too late for me, most probably I misunderstood.
>
> If you want the PIDFD_THREAD behaviour, you can always use this flag
> without any check...
>
> Could you spell?

Just in case, we can even add PIDFD_AUTO (modulo naming) which acts as
PIDFD_THREAD if the target task is not a leader or 0 (current behaviour)
otherwise. Trivial.

Oleg.