guix-devel/guix/scripts/offload.scm

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;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2014, 2015, 2016 Ludovic Courtès <ludo@gnu.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; 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 (ssh popen)
#:use-module (ssh dist)
#:use-module (ssh dist node)
#:use-module (ssh version)
#:use-module (guix config)
#:use-module (guix records)
#:use-module (guix store)
#:use-module (guix derivations)
#:use-module ((guix serialization)
#:select (nar-error? nar-error-file))
#:use-module (guix nar)
#:use-module (guix utils)
#:use-module ((guix build syscalls) #:select (fcntl-flock))
#:use-module ((guix build utils) #:select (which mkdir-p))
#:use-module (guix ui)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-11)
#:use-module (srfi srfi-26)
#:use-module (srfi srfi-34)
#:use-module (srfi srfi-35)
#:use-module (ice-9 popen)
#:use-module (ice-9 rdelim)
#:use-module (ice-9 match)
#:use-module (ice-9 regex)
#:use-module (ice-9 format)
#:use-module (ice-9 binary-ports)
#:export (build-machine
build-requirements
guix-offload))
;;; Commentary:
;;;
;;; Attempt to offload builds to the machines listed in
;;; /etc/guix/machines.scm, transferring missing dependencies over SSH, and
;;; retrieving the build output(s) over SSH upon success.
;;;
;;; This command should not be used directly; instead, it is called on-demand
;;; by the daemon, unless it was started with '--no-build-hook' or a client
;;; inhibited build hooks.
;;;
;;; Code:
(define-record-type* <build-machine>
build-machine make-build-machine
build-machine?
(name build-machine-name) ; string
(port build-machine-port ; number
(default 22))
(system build-machine-system) ; string
(user build-machine-user) ; string
(private-key build-machine-private-key ; file name
(default (user-openssh-private-key)))
(host-key build-machine-host-key) ; string
(compression build-machine-compression ; string
(default "zlib@openssh.com,zlib"))
(compression-level build-machine-compression-level ;integer
(default 3))
(daemon-socket build-machine-daemon-socket ; string
(default "/var/guix/daemon-socket/socket"))
(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 '())))
(define-record-type* <build-requirements>
build-requirements make-build-requirements
build-requirements?
(system build-requirements-system) ; string
(features build-requirements-features ; list of strings
(default '())))
(define %machine-file
;; File that lists machines available as build slaves.
(string-append %config-directory "/machines.scm"))
(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 <> "/.ssh/id_rsa")))
(define %user-module
;; Module in which the machine description file is loaded.
(let ((module (make-fresh-user-module)))
(module-use! module (resolve-interface '(guix scripts offload)))
module))
(define* (build-machines #:optional (file %machine-file))
"Read the list of build machines from FILE and return it."
(catch #t
(lambda ()
;; Avoid ABI incompatibility with the <build-machine> record.
(set! %fresh-auto-compile #t)
(save-module-excursion
(lambda ()
(set-current-module %user-module)
(primitive-load file))))
(lambda args
(match args
(('system-error . rest)
(let ((err (system-error-errno args)))
;; Silently ignore missing file since this is a common case.
(if (= ENOENT err)
'()
(leave (_ "failed to open machine file '~a': ~a~%")
file (strerror err)))))
(('syntax-error proc message properties form . rest)
(let ((loc (source-properties->location properties)))
(leave (_ "~a: ~a~%")
(location->string loc) message)))
(x
(leave (_ "failed to load machine file '~a': ~s~%")
file args))))))
(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
(build-machine-compression machine)
#:compression-level
(build-machine-compression-level machine))))
(match (connect! session)
('ok
;; 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)
(x
;; Connection failed or timeout expired.
(leave (_ "failed to connect to '~a': ~a~%")
(build-machine-name machine) (get-error session))))))
(define* (connect-to-remote-daemon session
#:optional
(socket-name "/var/guix/daemon-socket/socket"))
"Connect to the remote build daemon listening on SOCKET-NAME over SESSION,
an SSH session. Return a <nix-server> object."
(define redirect
;; Code run in SESSION to redirect the remote process' stdin/stdout to the
;; daemon's socket, à la socat. The SSH protocol supports forwarding to
;; Unix-domain sockets but libssh doesn't have an API for that, hence this
;; hack.
`(begin
(use-modules (ice-9 match) (rnrs io ports))
(let ((sock (socket AF_UNIX SOCK_STREAM 0))
(stdin (current-input-port))
(stdout (current-output-port)))
(setvbuf stdin _IONBF)
(setvbuf stdout _IONBF)
(connect sock AF_UNIX ,socket-name)
(let loop ()
(match (select (list stdin sock) '() (list stdin stdout sock))
((reads writes ())
(when (memq stdin reads)
(match (get-bytevector-some stdin)
((? eof-object?)
(primitive-exit 0))
(bv
(put-bytevector sock bv))))
(when (memq sock reads)
(match (get-bytevector-some sock)
((? eof-object?)
(primitive-exit 0))
(bv
(put-bytevector stdout bv))))
(loop))
(_
(primitive-exit 1)))))))
(let ((channel
(open-remote-pipe* session OPEN_BOTH
;; Sort-of shell-quote REDIRECT.
"guile" "-c"
(object->string
(object->string redirect)))))
(open-connection #:port channel)))
;;;
;;; Synchronization.
;;;
(define (lock-file file)
"Wait and acquire an exclusive lock on FILE. Return an open port."
(mkdir-p (dirname file))
(let ((port (open-file file "w0")))
(fcntl-flock port 'write-lock)
port))
(define (unlock-file lock)
"Unlock LOCK."
(fcntl-flock lock 'unlock)
(close-port lock)
#t)
(define-syntax-rule (with-file-lock file exp ...)
"Wait to acquire a lock on FILE and evaluate EXP in that context."
(let ((port (lock-file file)))
(dynamic-wind
(lambda ()
#t)
(lambda ()
exp ...)
(lambda ()
(unlock-file port)))))
(define-syntax-rule (with-machine-lock machine hint exp ...)
"Wait to acquire MACHINE's exclusive lock for HINT, and evaluate EXP in that
context."
(with-file-lock (machine-lock-file machine hint)
exp ...))
(define (machine-slot-file machine slot)
"Return the file name of MACHINE's file for SLOT."
;; For each machine we have a bunch of files representing each build slot.
;; When choosing a build machine, we attempt to get an exclusive lock on one
;; of these; if we fail, that means all the build slots are already taken.
;; Inspired by Nix's build-remote.pl.
(string-append (string-append %state-directory "/offload/"
(build-machine-name machine)
"/" (number->string slot))))
(define (acquire-build-slot machine)
"Attempt to acquire a build slot on MACHINE. Return the port representing
the slot, or #f if none is available.
This mechanism allows us to set a hard limit on the number of simultaneous
connections allowed to MACHINE."
(mkdir-p (dirname (machine-slot-file machine 0)))
(with-machine-lock machine 'slots
(any (lambda (slot)
(let ((port (open-file (machine-slot-file machine slot)
"w0")))
(catch 'flock-error
(lambda ()
(fcntl-flock port 'write-lock #:wait? #f)
;; Got it!
(format (current-error-port)
"process ~a acquired build slot '~a'~%"
(getpid) (port-filename port))
port)
(lambda args
;; PORT is already locked by another process.
(close-port port)
#f))))
(iota (build-machine-parallel-builds machine)))))
(define (release-build-slot slot)
"Release SLOT, a build slot as returned as by 'acquire-build-slot'."
(close-port slot))
;;;
;;; Offloading.
;;;
(define (build-log-port)
"Return the default port where build logs should be sent. The default is
file descriptor 4, which is open by the daemon before running the offload
hook."
(let ((port (fdopen 4 "w0")))
;; Make sure file descriptor 4 isn't closed when PORT is GC'd.
(set-port-revealed! port 1)
port))
(define* (transfer-and-offload drv machine
#:key
(inputs '())
(outputs '())
(max-silent-time 3600)
build-timeout
print-build-trace?)
"Offload DRV to MACHINE. Prior to the actual offloading, transfer all of
INPUTS to MACHINE; if building DRV succeeds, retrieve all of OUTPUTS from
MACHINE."
(define session
(open-ssh-session machine))
(define store
(connect-to-remote-daemon session
(build-machine-daemon-socket machine)))
(set-build-options store
#:print-build-trace print-build-trace?
#:max-silent-time max-silent-time
#:timeout build-timeout)
;; Protect DRV from garbage collection.
(add-temp-root store (derivation-file-name drv))
(send-files (cons (derivation-file-name drv) inputs)
store)
(format (current-error-port) "offloading '~a' to '~a'...~%"
(derivation-file-name drv) (build-machine-name machine))
(format (current-error-port) "@ build-remote ~a ~a~%"
(derivation-file-name drv) (build-machine-name machine))
(guard (c ((nix-protocol-error? c)
(format (current-error-port)
(_ "derivation '~a' offloaded to '~a' failed: ~a~%")
(derivation-file-name drv)
(build-machine-name machine)
(nix-protocol-error-message c))
;; Use exit code 100 for a permanent build failure. The daemon
;; interprets other non-zero codes as transient build failures.
(primitive-exit 100)))
(parameterize ((current-build-output-port (build-log-port)))
(build-derivations store (list drv))))
(retrieve-files outputs store)
(format (current-error-port) "done with offloaded '~a'~%"
(derivation-file-name drv)))
(define (store-import-channel session)
"Return an output port to which archives to be exported to SESSION's store
can be written."
;; Using the 'import-paths' RPC on a remote store would be slow because it
;; makes a round trip every time 32 KiB have been transferred. This
;; procedure instead opens a separate channel to use the remote
;; 'import-paths' procedure, which consumes all the data in a single round
;; trip.
(define import
`(begin
(use-modules (guix))
(with-store store
(setvbuf (current-input-port) _IONBF)
(import-paths store (current-input-port)))))
(open-remote-output-pipe session
(string-join
`("guile" "-c"
,(object->string
(object->string import))))))
(define (store-export-channel session files)
"Return an input port from which an export of FILES from SESSION's store can
be read."
;; Same as above: this is more efficient than calling 'export-paths' on a
;; remote store.
(define export
`(begin
(use-modules (guix))
(with-store store
(setvbuf (current-output-port) _IONBF)
(export-paths store ',files (current-output-port)))))
(open-remote-input-pipe session
(string-join
`("guile" "-c"
,(object->string
(object->string export))))))
(define (send-files files remote)
"Send the subset of FILES that's missing to REMOTE, a remote store."
(with-store store
;; Compute the subset of FILES missing on SESSION and send them.
(let* ((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)))))
(count (length missing))
(port (store-import-channel session)))
(format #t (N_ "sending ~a store item to '~a'...~%"
"sending ~a store items to '~a'...~%" count)
count (session-get session 'host))
;; Send MISSING in topological order.
(export-paths store missing port)
;; Tell the remote process that we're done. (In theory the
;; end-of-archive mark of 'export-paths' would be enough, but in
;; practice it's not.)
(channel-send-eof port)
;; Wait for completion of the remote process.
(let ((result (zero? (channel-get-exit-status port))))
(close-port port)
result))))
(define (retrieve-files files remote)
"Retrieve FILES from SESSION's store, and import them."
(let* ((session (channel-get-session (nix-server-socket remote)))
(host (session-get session 'host))
(port (store-export-channel session files))
(count (length files)))
(format #t (N_ "retrieving ~a store item from '~a'...~%"
"retrieving ~a store items from '~a'...~%" count)
count host)
;; We cannot use the 'import-paths' RPC here because we already
;; hold the locks for FILES.
(let ((result (restore-file-set port
#:log-port (current-error-port)
#:lock? #f)))
(close-port port)
result)))
;;;
;;; Scheduling.
;;;
(define (machine-matches? machine requirements)
"Return #t if MACHINE matches REQUIREMENTS."
(and (string=? (build-requirements-system requirements)
(build-machine-system machine))
(lset<= string=?
(build-requirements-features requirements)
(build-machine-features machine))))
(define (machine-load machine)
"Return the load of MACHINE, divided by the number of parallel builds
allowed on MACHINE. Return +∞ if MACHINE is unreachable."
;; Note: This procedure is costly since it creates a new SSH session.
(match (false-if-exception (open-ssh-session machine))
((? session? session)
(let* ((pipe (open-remote-pipe* session OPEN_READ
"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
(match (string-tokenize line)
((one five fifteen . _)
(let* ((raw (string->number five))
(jobs (build-machine-parallel-builds machine))
(normalized (/ raw jobs)))
(format (current-error-port) "load on machine '~a' is ~s\
(normalized: ~s)~%"
(build-machine-name machine) raw normalized)
normalized))
(_
+inf.0))))) ;something's fishy about MACHINE, so avoid it
(_
+inf.0))) ;failed to connect to MACHINE, so avoid it
(define (machine-lock-file machine hint)
"Return the name of MACHINE's lock file for HINT."
(string-append %state-directory "/offload/"
(build-machine-name machine)
"." (symbol->string hint) ".lock"))
(define (machine-choice-lock-file)
"Return the name of the file used as a lock when choosing a build machine."
(string-append %state-directory "/offload/machine-choice.lock"))
(define %slots
;; List of acquired build slots (open ports).
'())
(define (choose-build-machine machines)
"Return the best machine among MACHINES, or #f."
;; Proceed like this:
;; 1. Acquire the global machine-choice lock.
;; 2. For all MACHINES, attempt to acquire a build slot, and filter out
;; those machines for which we failed.
;; 3. Choose the best machine among those that are left.
;; 4. Release the previously-acquired build slots of the other machines.
;; 5. Release the global machine-choice lock.
(with-file-lock (machine-choice-lock-file)
(define machines+slots+loads
(filter-map (lambda (machine)
;; Call 'machine-load' from here to make sure it is called
;; only once per machine (it is expensive).
(let ((slot (acquire-build-slot machine)))
(and slot
(list machine slot (machine-load machine)))))
machines))
(define (undecorate pred)
(lambda (a b)
(match a
((machine1 slot1 load1)
(match b
((machine2 slot2 load2)
(pred machine1 load1 machine2 load2)))))))
(define (machine-less-loaded-or-faster? m1 l1 m2 l2)
;; Return #t if M1 is either less loaded or faster than M2, with L1
;; being the load of M1 and L2 the load of M2. (This relation defines a
;; total order on machines.)
(> (/ (build-machine-speed m1) (+ 1 l1))
(/ (build-machine-speed m2) (+ 1 l2))))
(let loop ((machines+slots+loads
(sort machines+slots+loads
(undecorate machine-less-loaded-or-faster?))))
(match machines+slots+loads
(((best slot load) others ...)
;; Return the best machine unless it's already overloaded.
(if (< load 2.)
(match others
(((machines slots loads) ...)
;; Release slots from the uninteresting machines.
(for-each release-build-slot slots)
;; Prevent SLOT from being GC'd.
(set! %slots (cons slot %slots))
best))
(begin
;; BEST is overloaded, so try the next one.
(release-build-slot slot)
(loop others))))
(() #f)))))
(define* (process-request wants-local? system drv features
#:key
print-build-trace? (max-silent-time 3600)
build-timeout)
"Process a request to build DRV."
(let* ((local? (and wants-local? (string=? system (%current-system))))
(reqs (build-requirements
(system system)
(features features)))
(candidates (filter (cut machine-matches? <> reqs)
(build-machines))))
(match candidates
(()
;; We'll never be able to match REQS.
(display "# decline\n"))
((_ ...)
(let ((machine (choose-build-machine candidates)))
(if machine
(begin
;; Offload DRV to MACHINE.
(display "# accept\n")
(let ((inputs (string-tokenize (read-line)))
(outputs (string-tokenize (read-line))))
(transfer-and-offload drv machine
#:inputs inputs
#:outputs outputs
#:max-silent-time max-silent-time
#:build-timeout build-timeout
#:print-build-trace? print-build-trace?)))
;; Not now, all the machines are busy.
(display "# postpone\n")))))))
;;;
;;; Installation tests.
;;;
(define (assert-node-repl node name)
"Bail out if NODE is not running Guile."
(match (node-guile-version node)
(#f
(leave (_ "Guile could not be started on '~a'~%")
name))
((? string? version)
;; Note: The version string already contains the word "Guile".
(info (_ "'~a' is running ~a~%")
name (node-guile-version node)))))
(define (assert-node-has-guix node name)
"Bail out if NODE lacks the (guix) module, or if its daemon is not running."
(match (node-eval node
'(begin
(use-modules (guix))
(with-store store
(add-text-to-store store "test"
"Hello, build machine!"))))
((? string? str)
(info (_ "Guix is usable on '~a' (test returned ~s)~%")
name str))
(x
(leave (_ "failed to use Guix module on '~a' (test returned ~s)~%")
name x))))
(define %random-state
(delay
(seed->random-state (logxor (getpid) (car (gettimeofday))))))
(define (nonce)
(string-append (gethostname) "-"
(number->string (random 1000000 (force %random-state)))))
(define (assert-node-can-import node name daemon-socket)
"Bail out if NODE refuses to import our archives."
(let ((session (node-session node)))
(with-store store
(let* ((item (add-text-to-store store "export-test" (nonce)))
(remote (connect-to-remote-daemon session daemon-socket)))
(send-files (list item) remote)
(if (valid-path? remote item)
(info (_ "'~a' successfully imported '~a'~%")
name item)
(leave (_ "'~a' was not properly imported on '~a'~%")
item name))))))
(define (assert-node-can-export node name daemon-socket)
"Bail out if we cannot import signed archives from NODE."
(let* ((session (node-session node))
(remote (connect-to-remote-daemon session daemon-socket))
(item (add-text-to-store remote "import-test" (nonce)))
(port (store-export-channel session (list item))))
(with-store store
(if (and (import-paths store port)
(valid-path? store item))
(info (_ "successfully imported '~a' from '~a'~%")
item name)
(leave (_ "failed to import '~a' from '~a'~%")
item name)))))
(define (check-machine-availability machine-file)
"Check that each machine in MACHINE-FILE is usable as a build machine."
(let ((machines (build-machines machine-file)))
(info (_ "testing ~a build machines defined in '~a'...~%")
(length machines) machine-file)
(let* ((names (map build-machine-name machines))
(sockets (map build-machine-daemon-socket machines))
(sessions (map open-ssh-session machines))
(nodes (map make-node sessions)))
(for-each assert-node-repl nodes names)
(for-each assert-node-has-guix nodes names)
(for-each assert-node-can-import nodes names sockets)
(for-each assert-node-can-export nodes names sockets))))
;;;
;;; Entry point.
;;;
(define (guix-offload . args)
(define request-line-rx
;; The request format. See 'tryBuildHook' method in build.cc.
(make-regexp "([01]) ([a-z0-9_-]+) (/[[:graph:]]+.drv) ([[:graph:]]*)"))
(define not-coma
(char-set-complement (char-set #\,)))
;; Make sure $HOME really corresponds to the current user. This is
;; necessary since lsh uses that to determine the location of the yarrow
;; seed file, and fails if it's owned by someone else.
(and=> (passwd:dir (getpw (getuid)))
(cut setenv "HOME" <>))
;; We rely on protocol-level compression from libssh to optimize large data
;; transfers. Warn if it's missing.
(unless (zlib-support?)
(warning (_ "Guile-SSH lacks zlib support"))
(warning (_ "data transfers will *not* be compressed!")))
(match args
((system max-silent-time print-build-trace? build-timeout)
(let ((max-silent-time (string->number max-silent-time))
(build-timeout (string->number build-timeout))
(print-build-trace? (string=? print-build-trace? "1")))
(parameterize ((%current-system system))
(let loop ((line (read-line)))
(unless (eof-object? line)
(cond ((regexp-exec request-line-rx line)
=>
(lambda (match)
(with-error-handling
(process-request (equal? (match:substring match 1) "1")
(match:substring match 2) ; system
(call-with-input-file
(match:substring match 3)
read-derivation)
(string-tokenize
(match:substring match 4) not-coma)
#:print-build-trace? print-build-trace?
#:max-silent-time max-silent-time
#:build-timeout build-timeout))))
(else
(leave (_ "invalid request line: ~s~%") line)))
(loop (read-line)))))))
(("test" rest ...)
(with-error-handling
(let ((file (match rest
((file) file)
(() %machine-file)
(_ (leave (_ "wrong number of arguments~%"))))))
(check-machine-availability (or file %machine-file)))))
(("--version")
(show-version-and-exit "guix offload"))
(("--help")
(format #t (_ "Usage: guix offload SYSTEM PRINT-BUILD-TRACE
Process build offload requests written on the standard input, possibly
offloading builds to the machines listed in '~a'.~%")
%machine-file)
(display (_ "
This tool is meant to be used internally by 'guix-daemon'.\n"))
(show-bug-report-information))
(x
(leave (_ "invalid arguments: ~{~s ~}~%") x))))
;;; Local Variables:
;;; eval: (put 'with-machine-lock 'scheme-indent-function 2)
;;; eval: (put 'with-file-lock 'scheme-indent-function 1)
;;; eval: (put 'with-error-to-port 'scheme-indent-function 1)
;;; End:
;;; offload.scm ends here