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Re: On the naming of System and Home services modules.

From: Xinglu Chen
Subject: Re: On the naming of System and Home services modules.
Date: Wed, 15 Sep 2021 15:06:58 +0200

On Wed, Sep 15 2021, Andrew Tropin wrote:

> This topic was raised a few times during development of Guix Home
> project and also during the review of wip-guix-home branch.  I made a
> separate thread to do an exhaustive discussion of it.
> * Services and Confusion
> It's an optional section, you can skip it, but I still find it somehow
> related to the topic.
> I want to re-raise the issue related to system services concept.  When
> I started using Guix I found system services to be confusing,
> originally I thought it's a way to declare services managed by init
> system, but later I realised that only some of system services becomes
> Shepherd services and many of them doesn't.  It's not a unique problem
> I see this issue appear again and again in different Guix chats and
> communities.
> - System services :: just building blocks, nodes of DAG representing
> a system, which after folding, results in a complete operating system
> or other artifact.
> - Shepherd services :: long-living processes/daemons managed by init
> system or user-space Shepherd. It's what people used to refer as services.
> It will be very hard and costly to rename system services to something
> less confusing, but at least let's try to keep those concepts as
> distinct as possible.  Probably originally system and Shepherd
> services were closely related, but not now, so let's express it very
> clearly in docs/chats/mailing lists.
> Another player on this field is "home services", which is a similar to
> system services, but used for describing a separate DAG, which after
> folding, results in home environment (artifact containing user's
> program configurations and profile with packages declared by user).
> * Putting Home Services to ~(gnu services ...)~
> In the thread Ludovic suggested:
>> Regarding module names: what about putting everything in the (gnu
>> home …) name space.  For services, I wonder if we could simply use
>> (gnu services home), for the essential services, and other (gnu
>> services …) module, but that assumes some code can be shared between
>> System and Home.  Thoughts?
> ** Shortcomings
> While it's a nice idea, I see some shortcomings here:
> *** Code Reuse
> Mcron, Shepherd and a few other fundamental pieces are reused between
> Guix Home and Guix System, but it's easily done by exporting a few
> symbols from related modules.
> Records even for the same services have slightly different fields and
> because of macro nature can't be reused between Home and System
> services. In more details I mentioned this problem here:

Some services might be useful to have in both Guix System and Guix Home;
for instance, Guix System currently has a service for configuring
Syncthing, and I think it makes sense to also have one for Guix Home,
this would mean that people not using Guix System (me :-)) could also
have Guix manage Syncthing.  With the current approach, we would have to
copy and paste quite a bit of code, and if the Syncthing service for
Guix System changes, then the one for Guix Home might have to change as

I have thought about a ‘define-configuration’ macro that would generate
one configuration record for Guix system and optionally, one for Guix
Home.  For example

  (define-configuration syncthing-configuration

would work as it currently does, and

  (define-configuration syncthing-configuration
    (home-service? #t))

would generate a <syncthing-configuration> record and a
<home-syncthing-configuration> record.

There is the problem of <syncthing-configuration> and
<home-syncthing-configuration> not having the same fields.  To solve
this, Each clause could have an ‘home-service?’ field, and the code
would look like

  (define-configuration syncthing-configuration
     (package syncthing)
     "Syncthing package to use.")
     (list-of-strings ’())
     "Command line arguments to pass to the Syncthing package.")
     (integer 0)
     "Sum of logging flags.")
     (maybe-string 'disabled)
     "The user as which the Syncthing service is to be run."
     (home-service? #f))  ; not for Guix Home
     (string "users")
     "The group as which the Syncthing service is to be run."
     (home-service? #f))  ; likewise ^^
     (maybe-string 'disabled)
     "Common configuration and data directory.")
    (home-service? #t))

This would mean that <syncthing-configuration> would have all the
fields, but <home-syncthing-configuration> would have all but the ‘user’
and ‘group’ fields.

We could also have a ‘define-home-configuration’ macro that would create
a <home-NAME-configuration> record and optionally, a
<NAME-configuration> record.  Then ‘home-service?’ would be
‘system-service?’ instead.

Maybe it’s too complicated and not worth it, but it’s just an idea I
have had.

> The intersection of home and system services should be very low, so
> there is not much benifit here as well.

Quite the opposite, I think it would be great if home and system
services could integrate more with each other.  In NixOS, the NixOS
modules and Home Manager modules feel like two very distinct things, and
it’s not really easy to share things between them.

A while ago, someone on IRC mentioned that it would be nice to have Mcron in
Guix System run Mcron jobs that were specified in Guix Home.  The
rationale is that Guix Home for a user will not activate---run user
Shepherd, thus running Mcron---until that user logs in.  This means that
Bob’s Mcron jobs will only run when Bob is logged in.  The Mcron jobs in
specified in Guix System will run regardless if the user that those jobs
belong to logs in.  But if Bob wants their Mcron jobs to run regardless
if he logs in, he needs root access to be able to add jobs to his Guix
System config and run ‘guix system reconfigure’.  This does mean that
the sysadmin has to add ‘mcron-service-type’ to the ‘services’ field of
the <operating-system> record, though.

> Utilitary functions like serialization helpers and so on can be
> declared in a shared module and reused between System and Home
> services.
> Recaping the section: All the necessarry code already reused, the
> future home/system services are not expected to share much code,
> different utilitary functions can be shared via (gnu services utils)
> or (gnu services configuration) modules.
> *** Confusion
> I already mentioned that I see a lot of confusion between System and
> Shepherd services and I expect some confusion between home and system
> services, it will be especially true if we place them in the same
> namespace.
> People will be trying to use home services inside operating systems,
> #+begin_src scheme
> (operating-system
>   (services
>    (list (service home-mcron-service-type ...))))
> #+end_src
> and configuration record for system services inside home services.
> #+begin_src scheme
> (home-environment
>  ... (service home-mcron-service-type
>               (mcron-configuration ...)))
> #+end_src

With the above proposal, the user would use ‘home-mcron-configuration’
for home service, so I don’t think this should be a problem.  And as
Maxime mentioned, we could have a ‘validate’ field which would give a
friendly error message if the wrong configuration record was given.

> ** Summary
> Let's keep System and Home services separate for the sake of clarity,
> reuse code via shared modules or just exports in (gnu services ...).
> * Putting Home Services to ~(gnu home services ...)~
> Another idea I saw is to move:
> ~(gnu home-services)~ -> ~(gnu home services)~
> ~(gnu home-services gnupg)~ -> ~(gnu home services gnupg)~
> ...
> Sounds reasonable, I'll just mention the ideas behind ~home-services~
> name.
> System services have following naming conventions for the public API:
> in ~(gnu services CATEGORY)~ there are ~APP-service-type~,
> ~APP-configuration~ and other related symbols.
> Not to be confused, I decided to prefix all service types and
> configurations with ~home-~, so the exported symbols looks like:
> ~home-APP-service-type~ and ~home-APP-configuration~.
> The same rule applies for module names: We do the same way as system
> services do, but with ~home-~ prefix: ~(gnu services CATEGORY)~ for
> system, ~(gnu home-services CATEGORY)~ for home.
> All namespaces containing ~system~ now becomes ~home~: ~(gnu system)~ and
> ~(gnu home)~ respectively.
> I find such approach to be consistent and doesn't see to much reasons
> to change it.
> However, ~(gnu home services ...)~ also looks cool, but it would be a
> little inconsistent with system services, which will have one level of
> nestiness less: ~(gnu services)~.
> IMO, ~(gnu home services ...)~ would be a good choice if we use ~(gnu
> system services)~ for system services.

Yeah, having both (gnu system service) and (gnu home service) could make
sense, but since we only have (gnu services), I don’t think it makes
much sense.

> * Conclusion
> I'm quite satisfied with current state of naming, but probably I miss
> some points and, also, maybe there are some other good or even better
> naming schemes.  In case there is a better naming approach, we can
> decide on using it, It would be not an easy change, but until
> wip-guix-home branch is not merged, it still easier to do this than do
> it later.

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