Re: [PATCH 4/5] pidfd: add CLONE_WAIT_PID

From: Oleg Nesterov
Date: Thu Jul 25 2019 - 14:05:43 EST

On 07/25, Christian Brauner wrote:
> On Thu, Jul 25, 2019 at 12:35:44PM +0200, Oleg Nesterov wrote:
> >
> > I have to admit this feature looks a bit exotic to me...
> It might look like it from the kernels perspective but from the feedback
> on this when presenting on this userspace has real usecases for this.


but then perhaps we can make PF_WAIT_PID more flexible.

Say, we can add the new WXXX wait option and change eligible_child()

if ((p->flags & PF_WAIT_PID) && (wo->options & WXXX))
return 0;

this way the parent can tell waitid() whether the PF_WAIT_PID tasks should
be filtered or not.

And if we do this we can even add PR_SET_WAIT_PID/PR_CLR_WAIT_PID instead
of the new CLONE_ flag.