Re: [PATCH 2/2] pasta: propagate exit code from child command

[Stefano Brivio <sbrivio@redhat.com>]

On Wed,  8 Feb 2023 16:54:41 +0100
Paul Holzinger <pholzing@redhat.com> wrote:

> Exits codes are very useful for scripts, when the pasta child execvp()
> call fails with ENOENT that parent should also exit with > 0. In short
> the parent should always exit with the code from the child to make it
> useful in scripts.
> 
> It is easy to test with: `pasta -- bash -c "exit 3"; echo $?`
> 
> Signed-off-by: Paul Holzinger <pholzing@redhat.com>
> ---
>  pasta.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/pasta.c b/pasta.c
> index 3f6477c..4b18d7e 100644
> --- a/pasta.c
> +++ b/pasta.c
> @@ -64,9 +64,14 @@ void pasta_child_handler(int signal)
>  
>  	if (pasta_child_pid &&
>  	    !waitid(P_PID, pasta_child_pid, &infop, WEXITED | WNOHANG)) {
> -		if (infop.si_pid == pasta_child_pid)
> -			exit(EXIT_SUCCESS);
> -			/* Nothing to do, detached PID namespace going away */
> +		if (infop.si_pid == pasta_child_pid) {
> +			if (infop.si_code == CLD_EXITED)
> +				exit(infop.si_status);
> +
> +			/* else killed by signal, si_status == SIGNUM in this case */

It took me a while to figure out that SIGNUM is not a constant I wasn't
aware of, just the signal number -- I guess you meant 'signum' from
sigaction() or suchlike?

Maybe you could go with:

			/* If killed by a signal, si_status is its number */

> +			exit(infop.si_status + 128);

This is a bit arbitrary -- returning n + 128 is what Bash, zsh, and a
few other shells do, and probably a reasonable convention given that
POSIX says we need to return a value greater than 128. Still I would
mention it:

			/* Arbitrary: return signal number + 128 */

or:

			/* If killed by a signal, si_status is the number.
			 * Follow common shell convention of returning it + 128.
			 */

> +		}
> +		/* Nothing to do, detached PID namespace going away */

This should be moved back into the conditional block (swapping the two
lines above, or moving this comment at the beginning of the block).

If si_pid is not the child, we need to do other stuff (that is, reap
clones).

>  	}
>  
>  	waitid(P_ALL, 0, NULL, WEXITED | WNOHANG);

-- 
Stefano