bug#59196: Update on bug#59196: `guix pull` fails on A20-OLinuXino-LIME2-eMMC

[Tanguy LE CARROUR]

Hi Guix,

After few… years (😵!?) I gave another try to Guix on A20-OLinuXino-LIME2.
Here is how it went…

I installed the latest Armbian (`25.2.0-trunk.72 bookworm`) on a new SD.
I updated the package list and then… `guix pull`!
83860 new commits and 7 hours later it successfully finished! 🎉
This is already better than last time!

Than, I tried to build the installation image:

```
$ guix system image --system=armhf-linux -e '((@ (gnu system install) 
os-with-u-boot) (@ (gnu system install) installation-os) "A20-OLinuXino-Lime2")'
Mise à jour du canal « guix » depuis le dépôt Git « 
https://git.savannah.gnu.org/git/guix.git »...
substitute: mise à jour des substituts depuis « https://ci.guix.gnu.org »... 
100.0 %
substitute: mise à jour des substituts depuis « https://bordeaux.guix.gnu.org 
»... 100.0 %
substitute: mise à jour des substituts depuis « https://ci.guix.gnu.org »... 
100.0 %
substitute: mise à jour des substituts depuis « https://bordeaux.guix.gnu.org 
»... 100.0 %
substitute: mise à jour des substituts depuis « https://ci.guix.gnu.org »... 
100.0 %
substitute: mise à jour des substituts depuis « https://bordeaux.guix.gnu.org 
»... 100.0 %
construction de /gnu/store/0nibhnjnvicz8j9vpnmd3cmff395nfww-config.scm.drv...
construction de /gnu/store/7whyplznhnkmsjwfqm85bdw44yz6v133-git.scm.drv...
construction de /gnu/store/q45178ins451323zfmhajswzmh0k47b7-hash.scm.drv...
construction de /gnu/store/ac3siz1a847aslxfbnw6hfhbdkxz79vr-module-import.drv...
construction de /gnu/store/zqs7axm2gc68fr6pnlr18k7zdmii5hxz-module-import.drv...
construction de 
/gnu/store/7shg17mgalpbrfdpbw80jy3cjafmr2b1-module-import-compiled.drv...
construction de 
/gnu/store/m1r2036l5r3dms4lsgyqqk8v71zyfzrq-module-import-compiled.drv...
construction de 
/gnu/store/xnfzrk0cxg405d463j7xl5y767xf3xaw-compute-guix-derivation.drv...
Computing Guix derivation for 'armhf-linux'... /
susubstitute: mise à jour des substituts depuis « https://ci.guix.gnu.org »...  
 0.0 %Backtrace:
substitute: In ice-9/boot-9.scm:
substitute:   1752:10 17 (with-exception-handler _ _ #:unwind? _ # _)
substitute: In unknown file:
substitute:           16 (apply-smob/0 #<thunk b6745290>)
substitute: In ice-9/boot-9.scm:
substitute:     724:2 15 (call-with-prompt _ _ #<procedure 
default-prompt-handle…>)
substitute: In ice-9/eval.scm:
substitute:     619:8 14 (_ #(#(#<directory (guile-user) b673a6e0>)))
substitute: In guix/ui.scm:
substitute:    2275:7 13 (run-guix . _)
substitute:   2238:10 12 (run-guix-command _ . _)
substitute: In ice-9/boot-9.scm:
substitute:   1752:10 11 (with-exception-handler _ _ #:unwind? _ # _)
substitute:   1752:10 10 (with-exception-handler _ _ #:unwind? _ # _)
substitute: In guix/scripts/substitute.scm:
substitute:    842:18  9 (_)
substitute:    348:26  8 (process-query #<output: file 4> _ #:cache-urls _ 
#:acl _)
substitute: In guix/substitutes.scm:
substitute:    365:27  7 (lookup-narinfos/diverse _ _ #<procedure b678d380 at 
g…> …)
substitute:    322:31  6 (lookup-narinfos _ _ #:open-connection _ # _)
substitute:    245:26  5 (fetch-narinfos _ _ #:open-connection _ # _)
substitute: In ice-9/boot-9.scm:
substitute:   1685:16  4 (raise-exception _ #:continuable? _)
substitute:   1685:16  3 (raise-exception _ #:continuable? _)
substitute:   1780:13  2 (_ #<&compound-exception components: (#<&error> 
#<&orig…>)
substitute:   1685:16  1 (raise-exception _ #:continuable? _)
substitute:   1685:16  0 (raise-exception _ #:continuable? _)
substitute: 
substitute: ice-9/boot-9.scm:1685:16: In procedure raise-exception:
substitute: In procedure write_wait_fd: unimplemented
guix system: erreur : `/usr/bin/guix substitute' died unexpectedly
```

😞

Plan B was to try to install Guix on the same drive following Julien’s blog 
post [1],
but I have no idea what a proper OLinuXino-Lime2 system config file
should look like!? For instance, what should the `bootloader` section be?! 🤔

[1]: https://guix.gnu.org/blog/2019/guix-on-an-arm-board/

Any help, idea or advice would be welcome!

Best regards,

-- 
Tanguy