Re: standards/51024 (NetBSD misses the mandatory waitid() syscall)

[Joerg Schilling <Joerg.Schilling%fokus.fraunhofer.de@localhost>]

Christos Zoulas <christos%zoulas.com@localhost> wrote:

> On Apr 4, 10:08am, christos%zoulas.com@localhost (Christos Zoulas) wrote:
> -- Subject: Re: standards/51024 (NetBSD misses the mandatory waitid() syscall
>
> | Do you have the reference where it says it needs to preserve all 32 bits
> | of exit code? I have not found one.
>
> The reason I am asking all this is because although FreeBSD has made the
> change to pass all 32 bits in this particular instance, they have overloaded
> the meaning of si_status, so that now the user code needs to understand
> what context we are in to interpret it properly. I.e.
>
> - it could be a full 32 bit exit code
> - it could be a signal number
> - it could be a composite 'wait status' (as it is always now with NetBSD,
>   except in the waitid case...).

Does the last apply to the signal handler for SIGCHLD only?
It is wrong in any case. Only the first two cases are correct.

> kern_exit.c:                    siginfo->si_status = WTERMSIG(p->p_xsig);
> kern_exit.c:                    siginfo->si_status = WTERMSIG(p->p_xsig);
> kern_exit.c:                    siginfo->si_status = p->p_xexit;
> kern_exit.c:                            siginfo->si_status = p->p_xsig;
> kern_exit.c:                            siginfo->si_status = p->p_xsig;
> kern_exit.c:                            siginfo->si_status = SIGCONT;
> kern_sig.c:             p->p_ksi->ksi_status = status;

Thank you for this hint, it seems that I would need to check FreeBSD. 
Fortunately I have access to an installation with a recent version.

si_status holds the exit() parameter in case of a normal exit (CLD_EXITED).

It holds the signal number in case the child has been terminated as a result of 
a signal: CLD_DUMPED, CLD_KILLED, CLD_TRAPPED, CLD_STOPPED. 

In case of CLD_CONTINUED, the status is 0.

So in general: si_status either contains the exit code or a signal number.

See the waitid() emulation in sh/jobs.c. The exit code of course cannot be 
retrieved from the historical wait() status value as this only holds the low 8 
bits. What you can see from the emulation code in sh/jobs.c is what is expected 
to be under what condition in si_code.

If you ever implement more than 255 signals, WTERMSIG() will not work as well.

Jörg

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