Re: [PATCH v3 3/4] kselftest/arm64: Add tests for SVE vector configuration

[Dave Martin <Dave.Martin@arm.com>]

On Mon, Aug 02, 2021 at 12:33:30PM +0100, Mark Brown wrote:
> On Mon, Aug 02, 2021 at 11:25:29AM +0100, Dave Martin wrote:
> 
> > That's a reasonable position, but thinking about it a bit more, there's
> > not really any loop at all here.
> > 
> > There definitely is an unwaited-for child and we don't pass WHONANG to
> > wait(), so it will either return the child pid, or fail.
> > 
> > Without WUNTRACED or similar, the child must terminate to wake up the
> > wait().
> 
> > So is this just a matter of
> 
> > 	pid = wait(&ret);
> > 	if (pid == -1) {
> > 		/* barf */
> > 	}
> > 	assert(pid == child);
> > 
> > 	if (!WIFEXITED(ret)) {
> > 		/* barf */
> > 	}
> > 
> > 	if (WEXITSTATUS(ret) != 0) {
> > 		/* barf */
> > 	}
> > 
> > 	/* parse child's stdout etc. */
> 
> That really doesn't seem like a good idea - it's just asking for
> fragility if a signal gets delivered to the parent process or something.
> Even if almost all the time there will only be one trip through the loop
> we should still have the loop there for those few cases where it
> triggers.

This concern only applies when the program actually registers signal
handlers.

wait() can't return for any other reason, and it mustn't, precisely
because historically software would have made this assumption.  This is
one reason why wait3() etc. are separate functions.

That aside though, can't we use popen(3)?

I tend to forget about popen because it is "boring" to use it, but it
looks like it fits this case quite well.  Then it would be libc's
problem how to fork and wait safely.

[...]

Cheers
---Dave

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