Re: wait4(2) do not fail with WNOHANG if there is no child

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Sun, 6 Nov 2016 12:30:04 +0100
    From:        Nicolas Joly <njoly%pasteur.fr@localhost>
    Message-ID:  <20161106113004.GA7631%issan.sis.pasteur.fr@localhost>

  | Don't we need to report an error because of the "shall" wording in the
  | ERRORS section.
  | 
  | [...]
  | The waitid() function shall fail if:
  | 
  | [ECHILD]
  |     The calling process has no existing unwaited-for child processes.
  | [...]

And also, or course, if the parent has a (single) child process (unwaited),
say child_pid, but we do

	waitid(P_PID, child_pid + 100, ..., WNOHANG, ...)

then that clause doesn't apply (whereas the text in the ECHILD case for
waitpid() would) as the process does have an existing unwaited for child
process - just not the one that the waitid() is asking about.

The WNOHANG there is actually probably irrelevant.

kre