GNU bug report logs - #61095
possible misuse of posix_spawn API on non-linux OSes

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Message #41 received at 61095-done <at> debbugs.gnu.org (full text, mbox):

From: Ludovic Courtès <ludo <at> gnu.org>
To: Omar Polo <op <at> omarpolo.com>
Cc: Josselin Poiret <dev <at> jpoiret.xyz>, Andrew Whatson <whatson <at> tailcall.au>,
 61095-done <at> debbugs.gnu.org
Subject: Re: bug#61095: possible misuse of posix_spawn API on non-linux OSes
Date: Sun, 02 Apr 2023 15:44:01 +0200

Hi!

Omar Polo <op <at> omarpolo.com> skribis:

> On 2023/03/30 22:21:28 +0200, Josselin Poiret <dev <at> jpoiret.xyz> wrote:
>> Hi Ludo,
>> 
>> Ludovic Courtès <ludo <at> gnu.org> writes:
>> 
>> > Coming next is an updated patch series addressing this as proposed
>> > above.  Let me know what y’all think!
>> >
>> > I tested the ‘posix_spawn_file_actions_addclosefrom_np’ path by building in:
>> >
>> >   guix time-machine --branch=core-updates -- shell -CP -D -f guix.scm
>> 
>> I didn't test, but this LGTM!  Maybe someone on OpenBSD could test this
>> patchset?
>
>     % gmake check
>     <snip />
>     gmake[5]: Entering directory '/home/op/w/guile/test-suite/standalone'
>     PASS: test-system-cmds
>
> it seems to work on OpenBSD 7.3 :)

Awesome!  Pushed as 9cc85a4f52147fcdaa4c52a62bcc87bdb267d0a9.

> but note that our libc doesn't have posix_spawn_file_actions_addclosefrom_np,
> so this is using the "racy" code path.

Yeah, not great.  :-/  I hope that function will be adopted by other
libcs, especially since ‘closefrom’ is already available.

> Just for curiosity, as it's outside the scope of the bug, what's the
> reason posix_spawn was used instead of a more classic fork() +
> closefrom()?

There’s a long discussion at:

  https://issues.guix.gnu.org/52835

Essentially, ‘fork’ is unusable in multi-threaded context, in addition
to being inefficient.

Thanks,
Ludo’.

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