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, 23 insertions, 11 deletions

diff --git a/guix/ssh.scm b/guix/ssh.scm
index b8bea8028a..1ed8406633 100644
--- a/guix/ssh.scm
+++ b/guix/ssh.scm
@@ -27,8 +27,6 @@
   #:use-module (ssh channel)
   #:use-module (ssh popen)
   #:use-module (ssh session)
-  #:use-module (ssh dist)
-  #:use-module (ssh dist node)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-11)
   #:use-module (srfi srfi-26)
@@ -102,6 +100,20 @@ Throw an error on failure."
                                  "guix" "repl" "-t" "machine")))
     (port->inferior pipe)))
 
+(define (inferior-remote-eval exp session)
+  "Evaluate EXP in a new inferior running in SESSION, and close the inferior
+right away."
+  (let ((inferior (remote-inferior session)))
+    (dynamic-wind
+      (const #t)
+      (lambda ()
+        (inferior-eval exp inferior))
+      (lambda ()
+        ;; Close INFERIOR right away to prevent finalization from happening in
+        ;; another thread at the wrong time (see
+        ;; <https://bugs.gnu.org/26976>.)
+        (close-inferior inferior)))))
+
 (define* (remote-daemon-channel session
                                 #:optional
                                 (socket-name
@@ -277,15 +289,15 @@ Return the list of store items actually sent."
   ;; Compute the subset of FILES missing on SESSION and send them.
   (let* ((files   (if recursive? (requisites local files) files))
          (session (channel-get-session (nix-server-socket remote)))
-         (node    (make-node session))
-         (missing (node-eval node
-                             `(begin
-                                (use-modules (guix)
-                                             (srfi srfi-1) (srfi srfi-26))
-
-                                (with-store store
-                                  (remove (cut valid-path? store <>)
-                                          ',files)))))
+         (missing (inferior-remote-eval
+                   `(begin
+                      (use-modules (guix)
+                                   (srfi srfi-1) (srfi srfi-26))
+
+                      (with-store store
+                        (remove (cut valid-path? store <>)
+                                ',files)))
+                   session))
          (count   (length missing))
          (sizes   (map (lambda (item)
                          (path-info-nar-size (query-path-info local item)))