Re: [PATCH 2/5] pidfd: add pidfd_wait()

[Christian Brauner]

On Thu, Jul 25, 2019 at 12:16:27PM +0200, Oleg Nesterov wrote:
> On 07/24, Christian Brauner wrote:
> >
> > +SYSCALL_DEFINE6(pidfd_wait, int, pidfd, int __user *, stat_addr,
> > +		siginfo_t __user *, info, struct rusage __user *, ru,
> > +		unsigned int, states, unsigned int, flags)
> > +{
> 
> Oh, I too think that P_PIDFD makes more sense.

I have already updated the patch to introduce P_PIDFD.

> 
> and could you explain in the changelog why? I am not arguing and if
> nothing else this is consistent with other pidfd features, but if you
> are parent/debugger you can't hit the problem with pid-reuse, unless
> you races with your sub-threads.

One of the things is that later on this will allow us to make it
possible to retrieve the exit status via waitid(P_PIDFD) for non-parent
processes if handed a _suitable_ pidfd that has this feature set. Maybe
even - if safe - make it possible to wait on a process as a non-parent.
And some tools just really want to do away with pids completely.

Christian