offload: Make the compression methods configurable.

* guix/scripts/offload.scm (<build-machine>)[compression]
[compression-level]: New fields.
(open-ssh-session): Honor them.
* doc/guix.texi (Daemon Offload Setup): Document them.

1 files changed, 7 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 5c94a56c01..738b7fb10c 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -921,6 +921,13 @@ Port number of SSH server on the machine.
 The SSH private key file to use when connecting to the machine, in
 OpenSSH format.
 
+@item @code{compression} (default: @code{"zlib@@openssh.com,zlib"})
+@itemx @code{compression-level} (default: @code{3})
+The SSH-level compression methods and compression level requested.
+
+Note that offloading relies on SSH compression to reduce bandwidth usage
+when transferring files to and from build machines.
+
 @item @code{daemon-socket} (default: @code{"/var/guix/daemon-socket/socket"})
 File name of the Unix-domain socket @command{guix-daemon} is listening
 to on that machine.