bug#36754: SSH connections to hydra-slave{1, 2, 3} fail during builds (was: New linux-libre failed to build on armhf on Berlin)

[Mark H Weaver]

I wrote earlier:
> I now believe that these failures are related to the newly added armhf
> build slaves, and that they have nothing to do with the recent changes
> to our linux-libre packages.

I should mention that the armhf build slaves are on a private network,
and I use my public-facing internet server to forward TCP connections to
them, using the following entries in /etc/inetd.conf:

--8<---------------cut here---------------start------------->8---
# TCP-level forwards for SSH connections to build machines for the GNU
# Guix build farm:
7275    stream  tcp     nowait  nobody  /bin/nc /bin/nc -w 10 172.19.189.11 7275
7276    stream  tcp     nowait  nobody  /bin/nc /bin/nc -w 10 172.19.189.12 7276
7274    stream  tcp     nowait  nobody  /bin/nc /bin/nc -w 10 172.19.189.13 7274
--8<---------------cut here---------------end--------------->8---

It's possible that this arrangement is somehow part of the problem.
However, note that nothing has changed here in several years, and it
worked fine on hydra.gnu.org.  The build slaves were running a *very*
old version of Guix though.  It seems likely that the new Guile-SSH code
doesn't cope well with this setup.

       Mark