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Message-ID: <64d6f20f-918b-4ad8-93fd-ff085f969215@gmail.com>
Date: Sat, 20 Sep 2025 14:46:31 -0400
From: Demi Marie Obenour <demiobenour@...il.com>
To: musl@...ts.openwall.com, Laurent Bercot <ska-dietlibc@...rnet.org>
Subject: Re: closefrom and close_range wrappers
On 9/20/25 14:36, Demi Marie Obenour wrote:
> On 9/20/25 12:33, Laurent Bercot wrote:
>>
>>> I think he was talking about a case where the wrapper's parent and child
>>> are trying to communicate some sort of event through FD closure, and the
>>> event is not necessarily the child's death. A use case might be a DHCP
>>> client signalling to a network manager that a lease was obtained,
>>> without using Freedesktop COM, I mean D-Bus. The DHCP client must
>>> continue to run to renew the lease when it ends. Although the common
>>> solution in the DHCP clients I am aware of is to background the program,
>>> which would also make the wrapper exit.
>>
>> If the event is not the child's death, then the child needs to know
>> the fd in order to close it. If it is a known fd, then the wrapper can
>> close it as well. If the number of the fd is transmitted through a
>> complex protocol that the wrapper cannot intercept, that's pretty bad
>> architecture and a pretty bad place to insert a wrapper, and at this
>> point close_range is just providing the pig with a vanity mirror to help
>> it put the lipstick on.
> The sad reality is that GLib decided [1] to not bother with setting
> O_CLOEXEC. GLib is incredibly widely used, so it isn't feasible
> for a library to be incompatible with it. In turn, this requires
> that library code that spawns a process use close_range() or
> an equivalent operation to do so.
>
> Also, the use of GSubprocess means that leaked file descriptors are
> not a reliable means of process supervision in 2025. Linux cgroups
> and illumos contracts *are*. The BSDs don't have any reliable method
> I know of beyond process groups
>
> [1]: https://mail.gnome.org/archives/gtk-devel-list/2015-March/msg00038.html
It's worth noting that none of these are needed if one can assume that
only code one controls is running. It's only needed if one has to deal
with arbitrary third-party code.
--
Sincerely,
Demi Marie Obenour (she/her/hers)
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