Re: Bugs with execline/s6 documentation and skalibs functions using posix_spawn()

From: Casper Ti. Vector <>
Date: Wed, 28 Jun 2023 08:54:12 +0800

On Tue, Jun 27, 2023 at 09:27:17PM +0000, Laurent Bercot wrote:
> Testing the behaviour may be challenging, however, because I suspect
> the CentOS 7 implementation of posix_spawn() is just racy, and they
> simply documented that they don't care.

Actually I copied the fragment of posix_spawn(3) from a Devuan Chimaera
machine, so the problem may be not specific to CentOS 7. I did not test
CentOS 6 or other distro (version)s, for example; but on Rocky Linux 8,
which I unfortunately also need to support at work, the behaviour is
as expected. Attached is a simple test.

From the posix_spawn(3), which had the similar statement across the
three different versions above, there is also a statement two paragraphs
later: "The posix_spawn() and posix_spawnp() functions fail only in the
case where the underlying fork(2), vfork(2) or clone(2) call fails".
So if the manpage is followed to the word, the CentOS 7 behaviour is
expected; if posix_spawn(3p) is followed instead, any exec() error must
also be caught and result in returning 0, which we really expect.

If we assume posix_spawn(3) and posix_spawn(3p) were the only possible
behaviours (which is frankly not that reliable, judging from how
neither manpage noted the violation of conformance), then the two
behaviours could be distinguished with the attached test.

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Received on Wed Jun 28 2023 - 02:54:12 CEST

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