offload: Use (guix inferior) instead of (ssh dist node).

Using inferiors and thus 'guix repl' simplifies setup on build
machines (no need to worry about GUILE_LOAD_PATH etc.)

Furthermore, the 'guix repl -t machine' protocol running in a remote
pipe addresses several issues with the current implementation of nodes
and RREPLs in Guile-SSH: fewer round trips, doesn't leave a 'guile
--listen' process behind it, stateless (since a new process is started
each time), more efficient (the SSH channel can be reused), more
reliable (no 'pgrep', 'pkill', and shellology; see
<https://github.com/artyom-poptsov/guile-ssh/issues/11> as an example.)

* guix/ssh.scm (inferior-remote-eval): New procedure.
(send-files): Use it instead of 'make-node' and 'node-eval'.
* guix/scripts/offload.scm (node-guile-version): New procedure.
(node-free-disk-space, transfer-and-offload, node-load)
(choose-build-machine, assert-node-has-guix): Use 'remote-inferior'
instead of 'make-node' and 'inferior-eval' instead of 'node-eval'.
(assert-node-can-import, assert-node-can-export): Likewise, and add
'session' parameter.
(check-machine-availability): Likewise, and add calls to
'close-inferior' and 'disconnect!'.
(check-machine-status): Likewise.
* doc/guix.texi (Daemon Offload Setup): Remove bit related to 'guile' in
$PATH and $GUILE_LOAD_PATH; mention 'guix' alone.

1 files changed, 3 insertions, 5 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index f86a2885a7..c182995b2b 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -1051,13 +1051,11 @@ name, and they will be scheduled on matching build machines.
 @end table
 @end deftp
 
-The @code{guile} command must be in the search path on the build
-machines.  In addition, the Guix modules must be in
-@code{$GUILE_LOAD_PATH} on the build machine---you can check whether
-this is the case by running:
+The @command{guix} command must be in the search path on the build
+machines.  You can check whether this is the case by running:
 
 @example
-ssh build-machine guile -c "'(use-modules (guix config))'"
+ssh build-machine guix repl --version
 @end example
 
 There is one last thing to do once @file{machines.scm} is in place.  As