[bug#54986] [PATCH] gnu: mpd: Add support for socket activation.

[Liliana Marie Prikler <liliana.prikler@gmail.com>]

Am Freitag, dem 13.05.2022 um 17:55 +0200 schrieb Ludovic Courtès:
> Hi Liliana,
> 
> What’s the status of this patch series?  Would be nice to have it in!
The patch for MPD itself is good to go as far as I'm aware, the patch
for the service type is work in progress.

This question
> Ludovic Courtès <ludo@gnu.org> skribis:
> > The way I see it, service configuration should be oblivious to
> > whether it’s started as “forkexec”, systemd, or inetd.
has me in a bit of a bind in multiple ways.  For one, I don't see a
direct translation from MPD's configuration scheme to shepherd's.  For
another, the distinct semantics between forkexec and lazy loading cause
observable differences as in “What the fuck, I only ran mpc status, why
is the music now playing?” – this can be avoided if the user knows that
shepherd will be lazy-loading mpd and that it might as a result to
starting start playing on the first received command.

Moreover, I think the patch I added to make endpoint records
configurable from Guix could also serve to solve other bugs, e.g. SSH
only listening on IPv4 addresses, which would require us to be able to
specify whether to listen on IPv4, IPv6 or both through Guix.  Long
term, I think we should only keep the distinction between forkexec and
inetd/systemd for those services where it makes an observable
difference, like mpd.  For SSH, apart from bugs and perhaps people
using old shepherd, I don't think there'd be any reason to keep
forkexec beyond a certain point (in a future as distant as you would
want it to be).

Maxime also raised hygiene concerns that would be comparatively easy to
solve.

TL;DR: v2 [1/3] is good, [2/3 WIP] and [3/3 WIP] should be kept back
for now.

Cheers