[RFC][PATCH][v2] Define/use siginfo_from_ancestor_ns()

[Sukadev Bhattiprolu]

| 
| > +static inline int siginfo_from_ancestor_ns(siginfo_t *info)
| > +{
| > +	return SI_FROMUSER(info) && (info->si_pid == 0);
| > +}
| 
| Yes, this is problem... I doubt we can rely on !si_pid here.
| More on this later.

BTW, rather than clearing SIG_FROM_USER in send_signal(), can we
keep it till we dequeue the signal ? Yes, collect_signal() would
need to consider this flag. But when we dequeue, we can note that
it was from user and use that in the siginfo_from_ancestor() ?

Sukadev