Ludovic Courtès writes:

Hello!

> Jan Nieuwenhuizen <janneke@gnu.org> skribis:
>
>>> Having an RC argument passed directly by the bootloader seems like a
>>> good way to proceed for me. This is somehow remotely similar to what we
>>> are doing with the "initrd" on Linux (pointing to some piece of code
>>> that needs to be loaded before starting the init process).
>>>
>>> You would also need to store this RC argument in the <boot-parameters>
>>> record, by adding a new field or stuffing it in the "initrd"
>>> field. Then, we wouldn't need an extra service I guess.
>>
>> Hmm...I don't understand...probably I'm missing something.
>>
>> I was thinking to just extend boot-parameters with
>> --rc-file=%hurd-rc-script, and then add %hurd-rc-script to the SYSTEM
>> service...How would I get the RC script into SYSTEM without a service?
>
> Normally, if you have the system (as returned by ‘guix system build’),
> that’s enough to derive any other kind of thing you might want.
>
> So for example, you could have a “startup” (or “rc”) entry in the
> ‘system’ directory by extending ‘system-service-type’.  And since the
> system is known from the boot command line, bingo.
>
> The guideline IMO should be to remain as close as possible to Guix
> System on GNU/Linux.  It’s OK to depart a bit from upstream Hurd though
> because those bits are not actually used (Debian does its own thing).

Okay, that makes sense. Using --system=SYSTEM => SYSTEM/rc now.

>>> If we are going that way, the procedures in (gnu build hurd-boot) could
>>> be passed the "hurd" package to install, and we could maybe get rig of
>>> the "/hurd" symlink?
>>
>> Hehe, that would be nice...but IME /hurd isn't easy to get rid of.
>
> Some of the /hurd names are embedded in libc, via the Hurd’s paths.h.
> Some names are compared by string (!); for instance, symlink.c in libc
> has:
>
>   /* A symlink is a file whose translator is "/hurd/symlink\0target\0".  */
>
>   memcpy (buf, _HURD_SYMLINK, sizeof (_HURD_SYMLINK));
>   memcpy (&buf[sizeof (_HURD_SYMLINK)], from, len);
>
> That makes it next to impossible to remove /hurd.
>
> I think it should be treated like /bin/sh and /run/current-system: set
> up at activation time.

Ah right...I think this is exactly what I found (and forgot).  The file
system embeds the full file-name...that's unfortunate.

>> +(define %hurd-rc-script
>> +  ;; The RC script to be started upon boot.
>> +  (program-file "rc"
>> +                (with-imported-modules '((guix build utils)
>> +                                         (gnu build hurd-boot)
>> +                                         (guix build syscalls))
>
> Probably use ‘source-module-closure’ to be on the safe side.

Nice!

>> +(define (hurd-rc-entry mrc)
>> +  "Return, as a monadic value, an entry for the RC script in the system
>> +directory."
>> +  (mlet %store-monad ((rc mrc))
>> +    (return `(("rc" ,rc)))))
>> +
>> +(define hurd-startup-service-type
>> +  ;; The service that creates the initial RC startup file.
>> +  (service-type (name 'startup)
>> +                (extensions
>> +                 (list (service-extension system-service-type hurd-rc-entry)))
>> +                (compose identity)
>> +                (extend (const (lower-object %hurd-rc-script)))
>> +                (description
>> +                 "Produce the operating system's RC script, which is executed
>> +by RUNSYSTEM.")))
>
> Is this service really meant to be extensible?  If not, we could just do:

(no)

>   (service-type (name 'startup)
>                 (extensions
>                  (list (service-extension system-service-type hurd-rc-entry)))
>                 (default-value %hurd-rc-script))
>
> where:
>
>   (define (hurd-rc-entry rc)
>     (mlet %store-monad ((rc (lower-object rc)))
>       (return `(("rc" ,rc)))))

Thanks, done!

>> +  (append
>> +   (if (hurd-target?)
>> +       (list #~(string-append "--rc-file=" #$%hurd-rc-script))
>> +       '())
>> +   (list (string-append "--root="
>> +                        ;; Note: Always use the DCE format because that's what
>> +                        ;; (gnu build linux-boot) expects for the '--root'
>> +                        ;; kernel command-line option.
>> +                        (file-system-device->string root-device
>> +                                                    #:uuid-type 'dce))
>> +         #~(string-append "--system=" #$system)
>> +         #~(string-append "--load=" #$system "/boot"))))
>
> So my suggestion is to avoid --rc-file since you know that SYSTEM/rc
> exists.

Done!

> Ludo’, who jumps in the middle of the discussion.  :-)

Very helpful indeed :-) -- attaching new version (and much tempted to
push to wip-hurd-vm now).

Any more wishes or ideas, things to be done before merging?  Not all
patches were reviewed in their current form, I think.

Janneke