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02/07: offload: Use Guile-SSH instead of GNU lsh.
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From: |
Ludovic Courtès |
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Subject: |
02/07: offload: Use Guile-SSH instead of GNU lsh. |
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Date: |
Fri, 25 Nov 2016 22:45:43 +0000 (UTC) |
civodul pushed a commit to branch master
in repository guix.
commit 21531add3205e400707c8fbfd841845f9a71863a
Author: Ludovic Courtès <address@hidden>
Date: Sun Mar 2 22:39:48 2014 +0100
offload: Use Guile-SSH instead of GNU lsh.
* guix/scripts/offload.scm (<build-machine>)[ssh-options]: Remove.
[host-key, host-key-type]: New fields.
(%lsh-command, %lshg-command, user-lsh-private-key): Remove.
(user-openssh-private-key, private-key-from-file*): New procedures.
(host-key->type+key, open-ssh-session): New procedures.
(remote-pipe): Remove 'mode' parameter. Rewrite in terms of
'open-ssh-session' etc. Update users.
(send-files)[missing-files]: Rewrite using the bidirectional channel
port.
Remove call to 'call-with-compressed-output-port'.
(retrieve-files): Remove call to 'call-with-decompressed-port'.
(machine-load): Remove exit status logic.
* doc/guix.texi (Requirements): Mention Guile-SSH.
(Daemon Offload Setup): Document 'host-key' and 'private-key'. Show the
default value on each @item line.
* m4/guix.m4 (GUIX_CHECK_GUILE_SSH): New macro.
* config-daemon.ac: Use 'GUIX_CHECK_GUILE_SSH'. Set
'HAVE_DAEMON_OFFLOAD_HOOK' as a function of that.
---
config-daemon.ac | 18 ++-
doc/guix.texi | 69 ++++++++----
guix/scripts/offload.scm | 279 ++++++++++++++++++++++------------------------
m4/guix.m4 | 18 +++
4 files changed, 213 insertions(+), 171 deletions(-)
diff --git a/config-daemon.ac b/config-daemon.ac
index 8a3e6d8..056c939 100644
--- a/config-daemon.ac
+++ b/config-daemon.ac
@@ -128,12 +128,20 @@ if test "x$guix_build_daemon" = "xyes"; then
dnl 'restore-file-set', which requires unbuffered custom binary input
dnl ports from Guile >= 2.0.10.)
GUIX_CHECK_UNBUFFERED_CBIP
- guix_build_daemon_offload="$ac_cv_guix_cbips_support_setvbuf"
- if test "x$guix_build_daemon_offload" = "xyes"; then
- AC_DEFINE([HAVE_DAEMON_OFFLOAD_HOOK], [1],
- [Define if the daemon's 'offload' build hook is being built.])
- fi
+ dnl Check for Guile-SSH, which is required by 'guix offload'.
+ GUIX_CHECK_GUILE_SSH
+
+ case "x$ac_cv_guix_cbips_support_setvbuf$guix_cv_have_recent_guile_ssh" in
+ xyesyes)
+ guix_build_daemon_offload="yes"
+ AC_DEFINE([HAVE_DAEMON_OFFLOAD_HOOK], [1],
+ [Define if the daemon's 'offload' build hook is being built (requires
Guile-SSH).])
+ ;;
+ *)
+ guix_build_daemon_offload="no"
+ ;;
+ esac
dnl Temporary directory used to store the daemon's data.
GUIX_TEST_ROOT_DIRECTORY
diff --git a/doc/guix.texi b/doc/guix.texi
index ebb138e..f1cb007 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -567,6 +567,12 @@ guix import}). It is of
interest primarily for developers and not for casual users.
@item
address@hidden Note: We need at least 0.10.2 for 'channel-send-eof'.
+Support for build offloading (@pxref{Daemon Offload Setup}) depends on
address@hidden://github.com/artyom-poptsov/guile-ssh, Guile-SSH},
+version 0.10.2 or later.
+
address@hidden
When @url{http://zlib.net, zlib} is available, @command{guix publish}
can compress build byproducts (@pxref{Invoking guix publish}).
@end itemize
@@ -814,9 +820,11 @@ available on the system---making it much harder to view
them as
@cindex offloading
@cindex build hook
-When desired, the build daemon can @dfn{offload}
-derivation builds to other machines
-running Guix, using the @code{offload} @dfn{build hook}. When that
+When desired, the build daemon can @dfn{offload} derivation builds to
+other machines running Guix, using the @code{offload} @dfn{build
address@hidden feature is available only when
address@hidden://github.com/artyom-poptsov/guile-ssh, Guile-SSH} is
+present.}. When that
feature is enabled, a list of user-specified build machines is read from
@file{/etc/guix/machines.scm}; every time a build is requested, for
instance via @code{guix build}, the daemon attempts to offload it to one
@@ -832,16 +840,18 @@ The @file{/etc/guix/machines.scm} file typically looks
like this:
(list (build-machine
(name "eightysix.example.org")
(system "x86_64-linux")
+ (host-key "ssh-ed25519 address@hidden")
(user "bob")
- (speed 2.)) ; incredibly fast!
+ (speed 2.)) ;incredibly fast!
(build-machine
(name "meeps.example.org")
(system "mips64el-linux")
+ (host-key "ssh-rsa address@hidden")
(user "alice")
(private-key
(string-append (getenv "HOME")
- "/.lsh/identity-for-guix"))))
+ "/.ssh/identity-for-guix"))))
@end example
@noindent
@@ -875,31 +885,50 @@ The user account to use when connecting to the remote
machine over SSH.
Note that the SSH key pair must @emph{not} be passphrase-protected, to
allow non-interactive logins.
address@hidden host-key
+This must be the machine's SSH @dfn{public host key} in OpenSSH format.
+This is used to authenticate the machine when we connect to it. It is a
+long string that looks like this:
+
address@hidden
+ssh-ed25519 address@hidden hint@@example.org
address@hidden example
+
+If the machine is running the OpenSSH daemon, @command{sshd}, the host
+key can be found in a file such as
address@hidden/etc/ssh/ssh_host_ed25519_key.pub}.
+
+If the machine is running the SSH daemon of address@hidden,
address@hidden, the host key is in @file{/etc/lsh/host-key.pub} or a
+similar file. It can be converted to the OpenSSH format using
address@hidden (@pxref{Converting keys,,, lsh, LSH Manual}):
+
address@hidden
+$ lsh-export-key --openssh < /etc/lsh/host-key.pub
+ssh-rsa address@hidden
address@hidden example
+
@end table
A number of optional fields may be specified:
address@hidden @code
-
address@hidden port
-Port number of SSH server on the machine (default: 22).
address@hidden @asis
address@hidden private-key
-The SSH private key file to use when connecting to the machine.
address@hidden @code{port} (default: @code{22})
+Port number of SSH server on the machine.
-Currently offloading uses address@hidden as its SSH client
-(@pxref{Invoking lsh,,, GNU lsh Manual}). Thus, the key file here must
-be an lsh key file. This may change in the future, though.
address@hidden @code{private-key} (default: @file{~/.ssh/id_rsa})
+The SSH private key file to use when connecting to the machine, in
+OpenSSH format.
address@hidden parallel-builds
-The number of builds that may run in parallel on the machine (1 by
-default.)
address@hidden @code{parallel-builds} (default: @code{1})
+The number of builds that may run in parallel on the machine.
address@hidden speed
address@hidden @code{speed} (default: @code{1.0})
A ``relative speed factor''. The offload scheduler will tend to prefer
machines with a higher speed factor.
address@hidden features
address@hidden @code{features} (default: @code{'()})
A list of strings denoting specific features supported by the machine.
An example is @code{"kvm"} for machines that have the KVM Linux modules
and corresponding hardware support. Derivations can request features by
@@ -915,7 +944,7 @@ machines, since offloading works by invoking the @code{guix
archive} and
this is the case by running:
@example
-lsh build-machine guile -c "'(use-modules (guix config))'"
+ssh build-machine guile -c "'(use-modules (guix config))'"
@end example
There is one last thing to do once @file{machines.scm} is in place. As
diff --git a/guix/scripts/offload.scm b/guix/scripts/offload.scm
index 33d141e..327c99d 100644
--- a/guix/scripts/offload.scm
+++ b/guix/scripts/offload.scm
@@ -17,6 +17,10 @@
;;; along with GNU Guix. If not, see <http://www.gnu.org/licenses/>.
(define-module (guix scripts offload)
+ #:use-module (ssh key)
+ #:use-module (ssh auth)
+ #:use-module (ssh session)
+ #:use-module (ssh channel)
#:use-module (guix config)
#:use-module (guix records)
#:use-module (guix store)
@@ -65,14 +69,13 @@
(system build-machine-system) ; string
(user build-machine-user) ; string
(private-key build-machine-private-key ; file name
- (default (user-lsh-private-key)))
+ (default (user-openssh-private-key)))
+ (host-key build-machine-host-key) ; string
(parallel-builds build-machine-parallel-builds ; number
(default 1))
(speed build-machine-speed ; inexact real
(default 1.0))
(features build-machine-features ; list of strings
- (default '()))
- (ssh-options build-machine-ssh-options ; list of strings
(default '())))
(define-record-type* <build-requirements>
@@ -86,19 +89,11 @@
;; File that lists machines available as build slaves.
(string-append %config-directory "/machines.scm"))
-(define %lsh-command
- "lsh")
-
-(define %lshg-command
- ;; FIXME: 'lshg' fails to pass large amounts of data, see
- ;; <http://lists.lysator.liu.se/pipermail/lsh-bugs/2014q1/000639.html>.
- "lsh")
-
-(define (user-lsh-private-key)
- "Return the user's default lsh private key, or #f if it could not be
+(define (user-openssh-private-key)
+ "Return the user's default SSH private key, or #f if it could not be
determined."
(and=> (getenv "HOME")
- (cut string-append <> "/.lsh/identity")))
+ (cut string-append <> "/.ssh/id_rsa")))
(define %user-module
;; Module in which the machine description file is loaded.
@@ -134,60 +129,79 @@ determined."
(leave (_ "failed to load machine file '~a': ~s~%")
file args))))))
-;;; FIXME: The idea was to open the connection to MACHINE once for all, but
-;;; lshg is currently non-functional.
-;; (define (open-ssh-gateway machine)
-;; "Initiate an SSH connection gateway to MACHINE, and return the PID of the
-;; running lsh gateway upon success, or #f on failure."
-;; (catch 'system-error
-;; (lambda ()
-;; (let* ((port (open-pipe* OPEN_READ %lsh-command
-;; "-l" (build-machine-user machine)
-;; "-i" (build-machine-private-key machine)
-;; ;; XXX: With lsh 2.1, passing '--write-pid'
-;; ;; last causes the PID not to be printed.
-;; "--write-pid" "--gateway" "--background"
-;; (build-machine-name machine)))
-;; (line (read-line port))
-;; (status (close-pipe port)))
-;; (if (zero? status)
-;; (let ((pid (string->number line)))
-;; (if (integer? pid)
-;; pid
-;; (begin
-;; (warning (_ "'~a' did not write its PID on stdout: ~s~%")
-;; %lsh-command line)
-;; #f)))
-;; (begin
-;; (warning (_ "failed to initiate SSH connection to '~a':\
-;; '~a' exited with ~a~%")
-;; (build-machine-name machine)
-;; %lsh-command
-;; (status:exit-val status))
-;; #f))))
-;; (lambda args
-;; (leave (_ "failed to execute '~a': ~a~%")
-;; %lsh-command (strerror (system-error-errno args))))))
-
-(define-syntax with-error-to-port
- (syntax-rules ()
- ((_ port exp0 exp ...)
- (let ((new port)
- (old (current-error-port)))
- (dynamic-wind
- (lambda ()
- (set-current-error-port new))
- (lambda ()
- exp0 exp ...)
- (lambda ()
- (set-current-error-port old)))))))
-
-(define* (remote-pipe machine mode command
- #:key (error-port (current-error-port)) (quote? #t))
- "Run COMMAND (a string list) on MACHINE, assuming an lsh gateway has been
-set up. When QUOTE? is true, perform shell-quotation of all the elements of
-COMMAND. Return either a pipe opened with MODE, or #f if the lsh client could
-not be started."
+(define (host-key->type+key host-key)
+ "Destructure HOST-KEY, an OpenSSH host key string, and return two values:
+its key type as a symbol, and the actual base64-encoded string."
+ (define (type->symbol type)
+ (and (string-prefix? "ssh-" type)
+ (string->symbol (string-drop type 4))))
+
+ (match (string-tokenize host-key)
+ ((type key _)
+ (values (type->symbol type) key))
+ ((type key)
+ (values (type->symbol type) key))))
+
+(define (private-key-from-file* file)
+ "Like 'private-key-from-file', but raise an error that 'with-error-handling'
+can interpret meaningfully."
+ (catch 'guile-ssh-error
+ (lambda ()
+ (private-key-from-file file))
+ (lambda (key proc str . rest)
+ (raise (condition
+ (&message (message (format #f (_ "failed to load SSH \
+private key from '~a': ~a")
+ file str))))))))
+
+(define (open-ssh-session machine)
+ "Open an SSH session for MACHINE and return it. Throw an error on failure."
+ (let ((private (private-key-from-file* (build-machine-private-key machine)))
+ (public (public-key-from-file
+ (string-append (build-machine-private-key machine)
+ ".pub")))
+ (session (make-session #:user (build-machine-user machine)
+ #:host (build-machine-name machine)
+ #:port (build-machine-port machine)
+ #:timeout 5 ;seconds
+ ;; #:log-verbosity 'protocol
+ #:identity (build-machine-private-key machine)
+
+ ;; We need lightweight compression when
+ ;; exchanging full archives.
+ #:compression "zlib"
+ #:compression-level 3)))
+ (connect! session)
+
+ ;; Authenticate the server. XXX: Guile-SSH 0.10.1 doesn't know about
+ ;; ed25519 keys and 'get-key-type' returns #f in that case.
+ (let-values (((server) (get-server-public-key session))
+ ((type key) (host-key->type+key
+ (build-machine-host-key machine))))
+ (unless (and (or (not (get-key-type server))
+ (eq? (get-key-type server) type))
+ (string=? (public-key->string server) key))
+ ;; Key mismatch: something's wrong. XXX: It could be that the server
+ ;; provided its Ed25519 key when we where expecting its RSA key.
+ (leave (_ "server at '~a' returned host key '~a' of type '~a' \
+instead of '~a' of type '~a'~%")
+ (build-machine-name machine)
+ (public-key->string server) (get-key-type server)
+ key type)))
+
+ (let ((auth (userauth-public-key! session private)))
+ (unless (eq? 'success auth)
+ (disconnect! session)
+ (leave (_ "SSH public key authentication failed for '~a': ~a~%")
+ (build-machine-name machine) (get-error session))))
+
+ session))
+
+(define* (remote-pipe machine command
+ #:key (quote? #t))
+ "Run COMMAND (a list) on MACHINE, and return an open input/output port,
+which is also an SSH channel. When QUOTE? is true, perform shell-quotation of
+all the elements of COMMAND."
(define (shell-quote str)
;; Sort-of shell-quote STR so it can be passed as an argument to the
;; shell.
@@ -195,20 +209,15 @@ not be started."
(lambda ()
(write str))))
- ;; Let the child inherit ERROR-PORT.
- (with-error-to-port error-port
- (apply open-pipe* mode %lshg-command
- "-l" (build-machine-user machine)
- "-p" (number->string (build-machine-port machine))
-
- ;; XXX: Remove '-i' when %LSHG-COMMAND really is lshg.
- "-i" (build-machine-private-key machine)
-
- (append (build-machine-ssh-options machine)
- (list (build-machine-name machine))
- (if quote?
- (map shell-quote command)
- command)))))
+ ;; TODO: Use (ssh popen) instead.
+ (let* ((session (open-ssh-session machine))
+ (channel (make-channel session)))
+ (channel-open-session channel)
+ (channel-request-exec channel
+ (string-join (if quote?
+ (map shell-quote command)
+ command)))
+ channel))
;;;
@@ -335,10 +344,11 @@ hook."
(unless (= EEXIST (system-error-errno args))
(apply throw args)))))))
- (let ((pipe (remote-pipe machine OPEN_READ
+ (let ((pipe (remote-pipe machine
`("guile" "-c" ,(object->string script)))))
(read-string pipe)
- (let ((status (close-pipe pipe)))
+ (let ((status (channel-get-exit-status pipe)))
+ (close-port pipe)
(unless (zero? status)
;; Better be safe than sorry: if we ignore the error here, then FILE
;; may be GC'd just before we start using it.
@@ -367,10 +377,10 @@ hook."
(false-if-exception (delete-file file)))
roots)))))
- (let ((pipe (remote-pipe machine OPEN_READ
+ (let ((pipe (remote-pipe machine
`("guile" "-c" ,(object->string script)))))
(read-string pipe)
- (close-pipe pipe)))
+ (close-port pipe)))
(define* (offload drv machine
#:key print-build-trace? (max-silent-time 3600)
@@ -384,7 +394,7 @@ there, and write the build log to LOG-PORT. Return the
exit status."
;; Normally DRV has already been protected from GC when it was transferred.
;; The '-r' flag below prevents the build result from being GC'd.
- (let ((pipe (remote-pipe machine OPEN_READ
+ (let ((pipe (remote-pipe machine
`("guix" "build"
"-r" ,%gc-root-file
,(format #f "--max-silent-time=~a"
@@ -397,14 +407,20 @@ there, and write the build log to LOG-PORT. Return the
exit status."
;; Since 'guix build' writes the build log to its
;; stderr, everything will go directly to LOG-PORT.
- #:error-port log-port)))
+ ;; #:error-port log-port ;; FIXME
+ )))
+ ;; Make standard error visible.
+ (channel-set-stream! pipe 'stderr)
+
(let loop ((line (read-line pipe)))
(unless (eof-object? line)
(display line log-port)
(newline log-port)
(loop (read-line pipe))))
- (close-pipe pipe)))
+ (let loop ((status (channel-get-exit-status pipe)))
+ (close-port pipe)
+ status)))
(define* (transfer-and-offload drv machine
#:key
@@ -438,7 +454,7 @@ MACHINE."
with exit code ~a~%"
(derivation-file-name drv)
(build-machine-name machine)
- (status:exit-val status))
+ status)
;; Use exit code 100 for a permanent build failure. The daemon
;; interprets other non-zero codes as transient build failures.
@@ -448,24 +464,14 @@ with exit code ~a~%"
"Send the subset of FILES that's missing to MACHINE's store. Return #t on
success, #f otherwise."
(define (missing-files files)
- ;; Return the subset of FILES not already on MACHINE.
- (let*-values (((files)
- (format #f "~{~a~%~}" files))
- ((missing pids)
- (filtered-port
- (append (list (which %lshg-command)
- "-l" (build-machine-user machine)
- "-p" (number->string
- (build-machine-port machine))
- "-i" (build-machine-private-key machine))
- (build-machine-ssh-options machine)
- (cons (build-machine-name machine)
- '("guix" "archive" "--missing")))
- (open-input-string files)))
- ((result)
- (read-string missing)))
- (for-each waitpid pids)
- (string-tokenize result)))
+ ;; Return the subset of FILES not already on MACHINE. Use 'head' as a
+ ;; hack to make sure the remote end stops reading when we're done.
+ (let* ((pipe (remote-pipe machine
+ `("guix" "archive" "--missing")
+ #:quote? #f)))
+ (format pipe "~{~a~%~}" files)
+ (channel-send-eof pipe)
+ (string-tokenize (read-string pipe))))
(with-store store
(guard (c ((nix-protocol-error? c)
@@ -476,40 +482,28 @@ success, #f otherwise."
;; Compute the subset of FILES missing on MACHINE, and send them in
;; topologically sorted order so that they can actually be imported.
- ;;
- ;; To reduce load on the machine that's offloading (since it's typically
- ;; already quite busy, see hydra.gnu.org), compress with gzip rather
- ;; than xz: For a compression ratio 2 times larger, it is 20 times
- ;; faster.
(let* ((files (missing-files (topologically-sorted store files)))
- (pipe (remote-pipe machine OPEN_WRITE
- '("gzip" "-dc" "|"
- "guix" "archive" "--import")
+ (pipe (remote-pipe machine
+ '("guix" "archive" "--import")
#:quote? #f)))
(format #t (_ "sending ~a store files to '~a'...~%")
(length files) (build-machine-name machine))
- (call-with-compressed-output-port 'gzip pipe
- (lambda (compressed)
- (catch 'system-error
- (lambda ()
- (export-paths store files compressed))
- (lambda args
- (warning (_ "failed while exporting files to '~a': ~a~%")
- (build-machine-name machine)
- (strerror (system-error-errno args))))))
- #:options '("--fast"))
-
- ;; Wait for the 'lsh' process to complete.
- (zero? (close-pipe pipe))))))
+
+ (export-paths store files pipe)
+ (channel-send-eof pipe)
+
+ ;; Wait for the remote process to complete.
+ (let ((status (channel-get-exit-status pipe)))
+ (close pipe)
+ status)))))
(define (retrieve-files files machine)
"Retrieve FILES from MACHINE's store, and import them."
(define host
(build-machine-name machine))
- (let ((pipe (remote-pipe machine OPEN_READ
- `("guix" "archive" "--export" ,@files
- "|" "xz" "-c")
+ (let ((pipe (remote-pipe machine
+ `("guix" "archive" "--export" ,@files)
#:quote? #f)))
(and pipe
(with-store store
@@ -522,14 +516,11 @@ success, #f otherwise."
;; We cannot use the 'import-paths' RPC here because we already
;; hold the locks for FILES.
- (call-with-decompressed-port 'xz pipe
- (lambda (decompressed)
- (restore-file-set decompressed
- #:log-port (current-error-port)
- #:lock? #f)))
+ (restore-file-set pipe
+ #:log-port (current-error-port)
+ #:lock? #f)
- ;; Wait for the 'lsh' process to complete.
- (zero? (close-pipe pipe)))))))
+ (close-port pipe))))))
;;;
@@ -547,13 +538,9 @@ success, #f otherwise."
(define (machine-load machine)
"Return the load of MACHINE, divided by the number of parallel builds
allowed on MACHINE."
- (let* ((pipe (remote-pipe machine OPEN_READ `("cat" "/proc/loadavg")))
- (line (read-line pipe))
- (status (close-pipe pipe)))
- (unless (eqv? 0 (status:exit-val status))
- (warning (_ "failed to obtain load of '~a': SSH client exited with ~a~%")
- (build-machine-name machine)
- (status:exit-val status)))
+ (let* ((pipe (remote-pipe machine '("cat" "/proc/loadavg")))
+ (line (read-line pipe)))
+ (close-port pipe)
(if (eof-object? line)
+inf.0 ;MACHINE does not respond, so assume it is infinitely loaded
diff --git a/m4/guix.m4 b/m4/guix.m4
index 6d8ec2e..6630598 100644
--- a/m4/guix.m4
+++ b/m4/guix.m4
@@ -171,6 +171,24 @@ AC_DEFUN([GUIX_CHECK_UNBUFFERED_CBIP], [
fi])
])
+dnl GUIX_CHECK_GUILE_SSH
+dnl
+dnl Check whether a recent-enough Guile-SSH is available.
+AC_DEFUN([GUIX_CHECK_GUILE_SSH], [
+ dnl Check whether 'channel-send-eof' (introduced in 0.10.2) is present.
+ AC_CACHE_CHECK([whether Guile-SSH is available and recent enough],
+ [guix_cv_have_recent_guile_ssh],
+ [GUILE_CHECK([retval],
+ [(and (@ (ssh channel) channel-send-eof)
+ (@ (ssh popen) open-remote-pipe)
+ (@ (ssh dist node) node-eval))])
+ if test "$retval" = 0; then
+ guix_cv_have_recent_guile_ssh="yes"
+ else
+ guix_cv_have_recent_guile_ssh="no"
+ fi])
+])
+
dnl GUIX_TEST_ROOT_DIRECTORY
AC_DEFUN([GUIX_TEST_ROOT_DIRECTORY], [
AC_CACHE_CHECK([for unit test root directory],
- branch master updated (7276b56 -> bc1ad4e), Ludovic Courtès, 2016/11/25
- 04/07: store: 'open-connection' can taken an open port., Ludovic Courtès, 2016/11/25
- 05/07: offload: Remove 'with-nar-error-handling' macro., Ludovic Courtès, 2016/11/25
- 07/07: offload: Drop 'remote-pipe'., Ludovic Courtès, 2016/11/25
- 01/07: gnu: guile-ssh: Update to 0.10.2., Ludovic Courtès, 2016/11/25
- 03/07: offload: Reuse SSH session during 'transfer-and-offload'., Ludovic Courtès, 2016/11/25
- 02/07: offload: Use Guile-SSH instead of GNU lsh.,
Ludovic Courtès <=
- 06/07: offload: Rewrite to make direct RPCs to the remote daemon., Ludovic Courtès, 2016/11/25