Re: [PATCH v3] Add systemd socket launching support

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@IRO.UMontreal.CA>
> Cc: matthew@mattleach.net, emacs-devel@gnu.org
> Date: Thu, 31 Mar 2016 14:14:01 -0400
> 
> In other similar functionality I've seen over the years, an alternative
> was to pass the fd as an additional argument on the command line, but in
> any case whether it's received from the environment or the command line,
> the file-descriptor to use will just be an integer, and it's already
> exposed to Lisp.

It's an attack vector expecting to happen, so we should try to avoid
that.

> So, AFAICT we just need 3 elements:
> - a function to get the FD number from systemd (which we could write in
>   Elisp, but is much better implemented as a call to systemd's support
>   library).
> - a way to create a process-object from an existing file-descriptor number.
> - changes in server.el to connect the previous 2 elements together.
> 
> AFAICT, only the first part is systemd-specific, so I think it would
> make sense to try and avoid having systemd-specific details leak to the
> other parts.

I agree, and the last version of the patch already does that: it only
requires a boolean flag exposed to other APIs.