Re: 01/02: services: Allow modprobe to use "/etc/modprobe.d".

[Bengt Richter <bokr@bokr.com>]

Hi Brice, Ludo,

On +2020-04-06 07:54:47 +0000, Brice Waegeneire wrote:
> Hello Ludo',
> 
> On 2020-04-05 21:15, Ludovic Courtès wrote:
> > guix-commits@gnu.org skribis:
> > >                    #~(begin
> > >                        (setenv "LINUX_MODULE_DIRECTORY"
> > > "/run/booted-system/kernel/lib/modules")
> > > +                      ;; FIXME: Remove this crutch when the patch
> > > #40422,
> > > +                      ;; updating to kmod 27 is merged.
> > > +                      (setenv "MODPROBE_OPTIONS"
> > > +                              "-C /etc/modprobe.d")
> > 
> > [...]
> > 
> > > +  (services (cons* (service kernel-module-loader-service-type
> > > +                            '("ddcci" "ddcci_backlight"))
> > > +                   (simple-service 'ddcci-config etc-service-type
> > > +                                   (list `("modprobe.d/ddcci.conf"
> > > +                                           ,ddcci-config)))
> > > +                   %base-services))
> > 
> > Looking at this, I was wondering if it would be possible to not use
> > /etc/modprobe.d and instead have a way to tell the modprobe wrapper to
> > pass “-C /gnu/store/…-modprobe.d”, which would contain the right thing.
> > 
> > Thoughts?
> 
> What's the issue with using /etc/modrpobe.d?
>

I would think the fundamental issue is pure vs impure dependencies:
i.e., /gnu/... vs /var/guix vs /elsewhere/...

IIUC, the consequence of using /etc/... or ~/... or other non-/gnu/...
is that if you want to run something in a container with chrooted root,
you have to cow-fake /etc and all the rest of non-/gnu/... environment,
so your executable is not as generally usable as possible if
nuisance adjustments were not necessary.

People who might want to use it anyway have to think about a bunch
of stuff not relevant to what they actually want to do -- they
will wind up debugging functionally-irrelevant implementation stuff.

Maybe I misunderstand, but are you and Ludo on the same page
re the fundamental concept of guix and how it plays in various contexts?
(allowing for "practicality beats purity"[1] when absolutely necessary ;-)

> As noted in the comments I thought setting MODPROBE_OPTIONS was kinda of a
> hack; #40422[0] was there to fix it. But if you think it's appropriate to
> use this environment variable it can be done in a future
> “kernel-module-configuration-service-type” we discussed with Danny[1].
> Instead of extending “etc-service-type” we would use
> “activation-service-type”, as “%modprobe-wrapper” is currently put
> in place by a simple activation service.
> 
> [0]: https://issues.guix.info/issue/40422
> [1]: https://issues.guix.info/issue/40274#29
> 
> - Brice
> 
[1] python -c 'import this'

-- 
Regards,
Bengt Richter