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SubjectRe: [PATCH 2/4] clone: add CLONE_PIDFD
On Mon, Apr 15, 2019 at 12:52:09PM +0200, Oleg Nesterov wrote:
> On 04/14, Christian Brauner wrote:
> >
> > @@ -2260,6 +2363,10 @@ long _do_fork(unsigned long clone_flags,
> > }
> >
> > put_pid(pid);
> > +
> > + if (clone_flags & CLONE_PIDFD)
> > + nr = pidfd;
> > +
>
> Well, this doesn't look nice ...
>
> CLONE_PARENT_SETTID doesn't look very usefule, so what if we add
>
> if ((clone_flags & (CLONE_PIDFD|CLONE_PARENT_SETTID)) ==
> (CLONE_PIDFD|CLONE_PARENT_SETTID))
> return ERR_PTR(-EINVAL);
>
> at the start of copy_process() ?
>
> Then it can do
>
> if (clone_flags & CLONE_PIDFD) {
> retval = pidfd_create(pid, &pidfdf);
> if (retval < 0)
> goto bad_fork_free_pid;
> retval = put_user(retval, parent_tidptr)
> if (retval < 0)
> goto bad_fork_free_pid;
> }

Uhhh Oleg, that is nifty. I have to say I like that a lot. This would
let us return the pid and the pidfd in one go and we can also start
pidfd numbering at 0.

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