[bug#61803] [PATCH 0/3] [shepherd] improve race-free spawn+wait

[Ulf Herrman <striness@tilde.club>]

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Ludovic Courtès <ludo@gnu.org> writes:

>> From 177592ee9d4b7fc6dcc80e545e8ad615a1d6786c Mon Sep 17 00:00:00 2001
>> From: ulfvonbelow <striness@tilde.club>
>> Date: Sat, 25 Feb 2023 00:56:57 -0600
>> Subject: [PATCH 3/3] service: add spawn-shell-command replacement for
>>  `system'.
>>
>> We already have a replacement for `system*' that avoids racing, but not for
>> `system'.
>>
>> * configure.ac (SHELL): new substitution variable.
>> * modules/shepherd/system.scm.in (%shell-filename): new variable.
>> * modules/shepherd/service.scm
>>   (spawn-shell-command, real-system): new procedures.
>> * modules/shepherd.scm (main): replace `system' with `spawn-shell-command'.
> Out of curiosity, do you have a need for ‘system’?

I don't.

> I’m inclined to recommend against its use, in which case this patch is
> unnecessary.

I tend to agree, but make-system-constructor and make-system-destructor
both use it and are documented in the manual, so we should either make
them work properly or remove them.

>> +(define %shell-filename "@SHELL@")
>
> This is the configure-time shell so it will be wrong when
> cross-compiling.
>
> I’d just do:
>
>   (define %shell (or (getenv "SHELL") "/bin/sh"))
>

The rationale behind not taking that straightforward approach was to
closely emulate the normal behavior of 'system' on guix, where the shell
path used is a hardcoded store path, though since guix's libc is likely
the only one where this is anything other than /bin/sh, I suppose it
does make a lot more sense to patch it in the guix package definition
(or accept the minor behavioral difference) than to try to automagically
figure it out at configure-time, which also has the problems you
mentioned.

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