[bug#54986] [PATCH v2 3/3 WIP] services: mpd: Support socket activation.

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

Am Samstag, dem 23.04.2022 um 19:35 +0200 schrieb Maxime Devos:
> Liliana Marie Prikler schreef op za 23-04-2022 om 16:39 [+0200]:
> > +@item @code{shepherd-endpoints} (default: @code{'()})
> > +The endpoints shepherd shall bind and spawn MPD from.  If this
> > field is
> > +not empty (checked via @code{null?}), a systemd-style service is
> > used
> > +rather than a forkexec-service.
> 
> systemd-style / forkexec-service looks like an implementation detail
> to me, not something useful to the user.
> 
> >  This delays the start of MPD until the
> > +first client connects.
> 
> Likewise.
Even if this was just an implementation detail, I shall point to
Hyrum's law.

> >   As a side effect @code{port} and @code{address}
> > +may be ignored.
> 
> Could these three fields be unified, keeping 'port' and 'address'
> only for some backwards compatibility?  E.g.:
> 
>   (mpd-configuration
>     (endpoints (list (shepherd-endpoint [a AF_INET6 address])
>                      (shepherd-endpoint [a AF_UNIX address]))))
Not AFAIK.  MPD is less strict than Guile when it comes to addresses,
so converting from address+port to socket addresses is nontrivial. 
That being said, I'm not sure if they are even ignored.  MPD only warns
about pid_file, so they might also be used.

Cheers