* gnu/system.scm (etc-directory): Change default value of #:profile.
Change contents of SHELLS. Use /run/current-system/profile/{s,}bin in
BASHRC.
(operating-system-boot-script)[%modules]: Add (guix build
linux-initrd). Add call to 'activate-current-system' in gexp.
(operating-system-initrd-file, operating-system-grub.cfg): New
procedures.
(operating-system-derivation): Don't build grub.cfg here and remove it
from the file union.
* gnu/system/vm.scm (qemu-image): Remove #:populate.
(operating-system-build-gid, operating-system-default-contents):
Remove.
(system-qemu-image): Remove call to
'operating-system-default-contents'. Use 'operating-system-grub.cfg'
to get grub.cfg. Add GRUB.CFG to #:inputs.
(system-qemu-image/shared-store): Likewise, but don't add GRUB.CFG to
#:inputs.
(system-qemu-image/shared-store-script): Pass --system kernel option.
* guix/build/activation.scm (%booted-system, %current-system): New
variables.
(boot-time-system, activate-current-system): New procedures.
* guix/build/install.scm (evaluate-populate-directive): Add case
for ('directory name uid gid mode).
(directives, populate-root-file-system): New procedures.
* guix/build/vm.scm (initialize-hard-disk): Replace calls to
'evaluate-populate-directive' by a call to
'populate-root-file-system'.
* gnu/services/dmd.scm (dmd-configuration-file): Use
/run/current-system/profile/bin.
* gnu/services/xorg.scm (slim-service): Likewise.
* gnu/system/vm.scm (qemu-image): Rename #:inputs-to-copy to #:inputs,
and #:initialize-store? to #:register-closures?. Add #:copy-inputs?.
Adjust build gexp accordingly.
(system-qemu-image): Remove #:initialize-store? argument and add
#:copy-inputs?.
(system-qemu-image/shared-store): Add #:inputs, #:register-closures?,
and #:copy-inputs? arguments.
* guix/build/vm.scm (register-closure): New procedure.
(MS_BIND): New variable.
(initialize-hard-disk): Rename #:initialize-store? to
#:register-closures?, #:closures-to-copy to #:closures, and add
#:copy-closures?.
Add 'target-directory' and 'target-store' variables.
Call 'populate-store' only when COPY-CLOSURES?.
Bind-mount the store to TARGET-STORE when REGISTER-CLOSURES? and not
COPY-CLOSURES?. Add call to 'register-closure'.
* guix/build/linux-initrd.scm (pidof): New procedure.
(mount-root-file-system)[mark-as-not-killable]: New procedure.
Use it for unionfs when VOLATILE-ROOT?.
* gnu/services/base.scm (%do-not-kill-file): New variable.
(user-processes-service)[stop]: Honor it.
* gnu/services/base.scm (file-system-service): New procedure.
(user-processes-service): Add 'requirements' parameter.
* gnu/services/dmd.scm (dmd-configuration-file): Use (guix build
linux-initrd).
* guix/build/linux-initrd.scm (guix): Export 'check-file-system'.
* gnu/system.scm (file-union): New procedure.
(essential-services): Use it. Add that to the returned list.
* guix/build/linux-initrd.scm (switch-root): Delete file from the old
root. Chdir to / after 'chroot' call. Re-open file descriptors 0, 1,
and 2.
(boot-system): Move 'loading' message after the 'switch-root' call.
* gnu/system.scm (operating-system-boot-script): Add loop that closes
file descriptor before calling 'execl'.
* guix/build/linux-initrd.scm (move-essential-file-systems,
switch-root): New procedures.
(MS_MOVE): New variable.
(boot-system): Remove 'mount-essential-file-systems' call for ROOT.
Use 'switch-root' instead of chdir + chroot.
* gnu/system.scm (operating-system-derivation)[boot-file-systems]: Keep "/".
* gnu/system/linux-initrd.scm (file-system->spec): Keep the 'check?'
flag.
(qemu-initrd)[helper-packages]: New variable. Pass it as #:to-copy.
<gexp>: Add 'set-path-environment-variable' call. Remove #:unionfs
argument for 'boot-system'.
* gnu/system/vm.scm (%linux-vm-file-systems): Add 'check?' field/
(virtualized-operating-system): Likewise for the "9p" file system.
* guix/build/linux-initrd.scm (mount-root-file-system): Change #:unionfs
default. Call 'check-file-system' before mounting ROOT, when
VOLATILE-ROOT? is false.
(check-file-system): New procedure.
(mount-file-system): Honor 'check?' element in list; add
'check-file-system' call.
(boot-system): Remove #:root-fs-type and #:unionfs parameters.
[root-mount-point?, root-fs-type]: New variables.
Call 'mount-file-system' on all MOUNTS but "/".
* guix/ftp-client.scm (%ftp-login): Add #\return before #\newline.
Fixes access to some FTP servers, such as
ftp://invisible-island.net ("ProFTPD 1.3.4a Server").
* gnu/system.scm (<operating-system>)[initrd]: Default to
'qemu-initrd'.
(<file-system>): New record type.
(operating-system-root-file-system): New procedure.
(operating-system-derivation): Take the device name for GRUB from
'operating-system-root-file-system'. Pass the
'operating-system-initrd' procedure the list of boot file systems.
* gnu/system/linux-initrd.scm (file-system->spec): New procedure.
(qemu-initrd): Add 'file-systems' parameter, and remove #:mounts
parameter.
[file-system-type-predicate]: New procedure.
[linux-modules]: Use it.
Adjust #:mounts argument in 'boot-system' call.
(gnu-system-initrd): Remove.
* gnu/system/vm.scm (%linux-vm-file-systems): New variable.
(expression->derivation-in-linux-vm): Adjust call to 'qemu-initrd'.
(virtualized-operating-system): New procedure.
(system-qemu-image/shared-store-script)[initrd]: Remove. Use
'virtualized-operating-system'. Get the 'initrd' file from OS-DRV.
* guix/build/linux-initrd.scm (mount-qemu-smb-share, mount-qemu-9p):
Remove.
(MS_RDONLY, MS_BIND): New global variables.
(bind-mount): Remove local 'MS_BIND' definition.
(mount-root-file-system): New procedure, with code formerly in
'boot-system'.
(mount-file-system): New procedure.
(boot-system): Add #:root-fs-type parameter. Remove 'MS_RDONLY' local
variable. Use 'mount-root-file-system' and 'mount-file-system'.
* doc/guix.texi (Using the Configuration System): Add 'file-system'
declaration.
* guix/gexp.scm (gexp->derivation, gexp->script): Use 'default-guile'
instead of an explicit reference to 'guile-final'.
(default-guile): New procedure.
* guix/monads.scm (run-with-store)[default-guile]: New procedure.
Use it.
* gnu/system.scm (<operating-system>)[pam-services, setuid-programs]:
New fields.
(etc-directory)[bashrc]: Prepend /run/setuid-programs to $PATH.
(operating-system-etc-directory): Honor
'operating-system-pam-services'.
(%setuid-programs): New variable.
(operating-system-boot-script): Add (guix build utils) to the set of
imported modules. Call 'activate-setuid-programs' in boot script.
* gnu/system/linux.scm (base-pam-services): New procedure.
* guix/build/activation.scm (%setuid-directory): New variable.
(activate-setuid-programs): New procedure.
* build-aux/hydra/demo-os.scm: Add 'pam-services' field.
* guix/derivations.scm (derivation->string): New procedure.
(derivation-hash, derivation): Use it.
Memoization here yields a 5% improvement on "guix build -e '(@ (gnu
packages emacs) emacs)' -n --no-substitutes".
* guix/monads.scm: Unexport 'lower-inputs' and 'derivation-expression'.
(text-file*): Add comment about the switch to 'gexp->derivation'.
(lower-inputs): Add comment about its doom.
(derivation-expression): Likewise.
* guix/gexp.scm (lower-inputs*): Rename to...
(lower-inputs): ... this. Update callers.
* tests/monads.scm (derivation-expression): New procedure.
* doc/guix.texi (The Store Monad): Use 'gexp->derivation' instead of
'derivation-expression'. Remove documentation of
'derivation-expression'.
* guix/ui.scm (read/eval): Use THE-ROOT-MODULE so that macros are
properly expanded.
* tests/guix-build.sh: Use 'gexp->derivation' instead of
'derivation-expression'.monads: Hide 'derivation-expression' and 'lower-inputs'.
* guix/gexp.scm: New file.
* tests/gexp.scm: New file.
* Makefile.am (MODULES): Add guix/gexp.scm.
(SCM_TESTS): Add tests/gexp.scm.
* doc/guix.texi (Derivations): Add #:inputs in 'derivation' example.
Mark 'build-expression->derivation' as deprecated, refer to
"G-Expressions". Remove paragraph about code strata.
(G-Expressions): New node.
definitions accordingly.
* guix/build/cmake-build-system.scm (configure): Add flags.
* gnu/packages/maths.scm (lapack): Drop special code.
* gnu/packages/ssh.scm (libssh): Drop special code.
* gnu/packages/slim.scm (slim): Drop special code and enable shared library.
Co-authored-by: Eric Bavier <bavier@member.fsf.org>
* guix/pk-crypto.scm (string->canonical-sexp, sign, generate-key): Pass
the procedure name as the first argument to 'throw'.
(gcrypt-error-printer): New procedure.
<top level>: Add call to 'set-exception-printer!'.
* guix/nar.scm (restore-one-item): Add 'proc' parameter to 'catch'
handler for 'gcry-error.
* guix/scripts/archive.scm (%options, generate-key-pair, authorize-key):
Likewise.
* guix/scripts/substitute-binary.scm (narinfo-signature->canonical-sexp):
Likewise.
Fixes <http://bugs.gnu.org/17312>.
* guix/scripts/authenticate.scm (guix-authenticate): Add calls to
'set-port-encoding!' and 'set-port-conversion-strategy!'. Wrap body
in 'with-fluids' form that sets '%default-port-encoding' and
'%default-port-conversion-strategy'.
* tests/guix-authenticate.sh: Add test.
* tests/pk-crypto.scm ("hash corrupt due to restrictive locale
encoding"): Add reference to bug.
* guix/pk-crypto.scm (string->canonical-sexp): Pass "ISO-8859-1" as the
2nd argument to 'string->pointer'.
* tests/pk-crypto.scm ("version"): New test.
("hash corrupt due to restrictive locale encoding"): New test.
* guix/build/linux-initrd.scm (make-essential-device-nodes): Make
/dev/fuse.
(boot-system): Add #:unionfs parameter. Invoke UNIONFS instead of
copying files over when VOLATILE-ROOT? is true.
* gnu/system/linux-initrd.scm (expression->initrd): Add #:inputs
parameter.
[files-to-copy]: New procedure.
[builder]: Add 'to-copy' parameter; honor it.
(qemu-initrd)[linux-modules]: Add 'fuse.ko' when VOLATILE-ROOT?.
Pass UNIONFS-FUSE/STATIC as #:inputs; change builder to pass #:unionfs
to 'boot-system'.
Fixes situations where the remote 'guix build' is invoked before the
.drv has been completely copied, as reported at
<https://lists.gnu.org/archive/html/guix-devel/2014-04/msg00174.html>.
In some cases 'send-files' would return before the other end is done
importing the files, and so the subsequent 'guix build' invocation would
just miss the .drv file it refers to.
* guix/utils.scm (call-with-decompressed-port): Don't close PORT.
(call-with-compressed-output-port): Likewise.
* tests/utils.scm ("compressed-output-port + decompressed-port"): Adjust
accordingly.
* guix/scripts/offload.scm (send-files): Add explicit (close-pipe pipe)
call.
(retrieve-files): Likewise.
Prevents garbage collection of the temporary store directory while
restoring a file set, as it could previously happen:
<https://lists.gnu.org/archive/html/guix-devel/2014-04/msg00167.html>.
* guix/nar.scm (temporary-store-directory): Rename to...
(temporary-store-file): ... this. Use 'add-permanent-root' instead of
'add-indirect-root'.
(with-temporary-store-file): New macro.
(restore-one-item): New procedure, with code formerly in
'restore-file-set'. Use 'with-temporary-store-file'.
(restore-file-set): Use it.
* guix/scripts/offload.scm (remove-gc-root): Rename to...
(remove-gc-roots): ... this.
[builder]: Use 'scandir' and remove all the files starting with
%GC-ROOT-FILE.
(transfer-and-offload): Adjust to renaming; remove
'false-if-exception' wraps.
Partially fixes <http://bugs.gnu.org/17212>.
* guix/utils.scm (errno): Move definition of 'bv' outside of the
procedure. Use 'bytevector-s32-native-ref' or
'bytevector-s64-native-ref' instead of 'bytevector-sint-ref'.
Problem reported by John Darrington <john@darrington.wattle.id.au>.
* guix/nar.scm (write-file): Filter out "." and ".." from the result of
'scandir'. Previously we did this by passing a suitable predicate.
* build-aux/hydra/demo-os.scm: New file.
* Makefile.am (EXTRA_DIST): Add it.
* build-aux/hydra/gnu-system.scm (qemu-jobs): New procedure.
(hydra-jobs): Use it.
* guix/scripts/system.scm (read-operating-system): Export.
Fixes the creation of single-package profiles, reported by Ludovic Courtès.
* guix/build/union.scm (union-build): Add new internal procedure
'union-of-directories' that always creates a directory, containing the code
previously used only to merge multiple directories. Call it from the
multiple-directory case in 'union' and from the top-level 'union-build'.
* guix/pki.scm (write-acl): New procedure.
(ensure-acl): Use it. Fixes a regression introduced in 39831f1,
whereby 'ensure-acl' would yield a wrong-type-arg error.
* guix/scripts/archive.scm (authorize-key): Use 'write-acl'.
Before that, there was a small time window during which the GC could
wipe the .drv (before 'guix build' has been called), or the build
result (before 'retrieve-files' has started.)
* guix/scripts/offload.scm (remote-pipe): Add #:quote? parameter and
honor it.
(%gc-root-file): New variable.
(register-gc-root, remove-gc-root): New procedures.
(offload): Adjust comment. Run 'guix build' with '-r %GC-ROOT-FILE'.
(transfer-and-offload): Call 'register-gc-root' before
sending (derivation-file-name DRV). Call 'remove-gc-root' after the
call to 'offload' or 'retrieve-files'.
(send-files): Call 'remote-pipe' with #:quote? #f.
(retrieve-files): Likewise.
* guix/build/union.scm: Rewrite; only 'file=?' remains unchanged. Remove
'tree-union' and 'delete-duplicate-leaves' exports. Merge inputs in a
breadth-first fashion. Follow symlinks for purposes of making decisions
about the merge.
* tests/union.scm: Remove tests of 'tree-union' and 'delete-duplicate-leaves'.
* guix/scripts/package.scm (search-path-environment-variables)[manifest-entry->package]:
Use 'find-best-packages-by-name' instead of 'find-packages-by-name'.
On a profile with 140 packages, this reduces execution time of this
procedure from 5.8 seconds to 2.9 seconds (50% improvement.)
* guix/scripts/package.scm (maybe-register-gc-root): New procedure.
* tests/guix-package.sh (profile): Grep the output of "guix gc
--list-live" in a couple of places.
* guix/pki.scm (acl-entry-sexp, acl-sexp): Remove.
(public-keys->acl, current-acl): Return a native sexp.
(acl->public-keys, authorized-key?): Expect ACL to be a native sexp.
* guix/scripts/archive.scm (authorize-key): Convert ACL to
canonical-sexp when writing it.
* guix/scripts/substitute-binary.scm (guix-substitute-binary) <--query>:
Cache the result of (current-acl); pass it to 'valid-narinfo?' calls.
This saves 12% wall-clock time for "guix build emacs -n".
* guix/nar.scm (restore-file-set)[assert-valid-signature]: Rewrite in
terms of 'signature-case'.
* guix/scripts/substitute-binary.scm (narinfo-signature->canonical-sexp):
Call 'leave' instead of 'raise' when SIGNATURE is invalid.
(&nar-signature-error, &nar-invalid-hash-error): Remove.
(assert-valid-signature): Add 'narinfo' parameter; remove 'port'.
Rewrite in terms of 'signature-case' and 'leave'. Mention NARINFO's
URI in error messages. Adjust caller.
(narinfo-sha256): New procedure.
(assert-valid-narinfo): Use it.
(valid-narinfo?): Rewrite using 'narinfo-sha256' and
'signature-case'.
* tests/substitute-binary.scm (assert-valid-signature,
test-error-condition): Remove.
("corrupt signature data", "unauthorized public key", "invalid
signature"): Remove.
* guix/scripts/substitute-binary.scm (narinfo-signature->canonical-sexp):
Catch 'gcry-error' around 'string->canonical-sexp' call, and re-raise
as a SRFI-35 &message and &nar-signature-error.
(narinfo-maker): Handle when SIGNATURE is #f or an invalid canonical
sexp.
(&nar-signature-error, &nar-invalid-hash-error): New variables.
(assert-valid-signature): Use them. Expect 'signature' to be a
canonical sexp.
(read-narinfo): Remove authentication and authorization checks.
(%signature-line-rx): New variable.
(assert-valid-narinfo, valid-narinfo?): New procedures.
(guix-substitute-binary): Wrap body in 'with-error-handling'.
[valid?]: New procedure.
<--query>: Show only store items of narinfos that match
'valid-narinfo?'.
<--substitute>: Call 'assert-valid-narinfo'.
* tests/substitute-binary.scm (test-error*): Use 'test-equal'.
(%keypair): Remove.
(%public-key, %private-key): Load from signing-key.{pub,sec}.
(signature-body): Add #:public-key parameter.
(call-with-narinfo): New procedure.
(with-narinfo): New macro.
("corrupt signature data", "unauthorized public key", "invalid
signature"): Make the first argument to 'assert-valid-signature' a
canonical sexp.
("invalid hash", "valid read-narinfo", "valid write-narinfo"):
Remove.
("query narinfo with invalid hash", "query narinfo signed with
authorized key", "query narinfo signed with unauthorized key",
"substitute, invalid hash", "substitute, unauthorized key"): New
tests.
* guix/scripts/substitute-binary.scm (<narinfo>)[uri-base]: New field.
(narinfo-maker): Pass CACHE-URL as the 'uri-base' value.
(string->narinfo): Add 'cache-uri' parameter.
(lookup-narinfo)[cache-entry]: Switch to version 1. Add 'cache-uri'
field. Adjust body accordingly.
(remove-expired-cached-narinfos): Switch to version 1 by default.
* guix/scripts/substitute-binary.scm (<narinfo>): Add the 'signature'
and 'contents' fields.
(narinfo-signature->canonical-sexp): New function.
(narinfo-maker): Add the 'signature' argument and use it.
(assert-valid-signature): New function.
(read-narinfo): Support the Signature field.
(write-narinfo): Use 'narinfo-contents'.
(%allow-unauthenticated-substitutes?): New variable.
* guix/base64.scm, tests/base64.scm, tests/substitute-binary.scm: New files.
* Makefile.am (SCM_TESTS): Add tests/base64.scm and
tests/substitute-binary.scm.
(MODULES): Add guix/base64.scm.
* test-env.in: Set 'GUIX_ALLOW_UNAUTHENTICATED_SUBSTITUTES'.
* guix/scripts/offload.scm (transfer-and-offload): Use 'upload' lock
instead of 'bandwidth' around 'send-files' calls, and 'download' lock
around 'retrieve-files' call.
* guix/scripts/offload.scm (remote-pipe): Remove '-z' lsh command line
argument. This makes transfers almost an order of magnitude slower.
OpenSSH's ssh(1) man page notes: "Compression is desirable on modem lines
and other slow connections, but will only slow down things on fast
networks." See also
<http://www.spikelab.org/blog/transfer-largedata-scp-tarssh-tarnc-compared.html>.
* guix/build/download.scm (http-fetch)[post-2.0.7?]: Use
'string->number' and numeric comparison. This fixes version
comparison with "2.0.10" and subsequent 2.0 releases.
* guix/utils.scm (call-with-decompressed-port,
call-with-compressed-output-port): New procedures.
* tests/utils.scm ("compressed-output-port + decompressed-port"):
Rewrite to use them.
* guix/scripts/authenticate.scm (guix-authenticate): Add clauses
for ("rsautl" "-sign" "-inkey" key) and ("rsautl" "-verify" "-inkey" _
"-pubin").
* tests/guix-authenticate.sh (hash): Add test using -sign and -verify in
a pipeline.
* guix/scripts/authenticate.scm (read-canonical-sexp): Change to expect
a port instead of a file name.
(read-hash-data): Likewise.
(sign-with-key, validate-signature): New procedures.
(guix-authenticate): Rewrite in terms of these two procedures.
* guix/utils.scm (decompressed-port, compressed-port): New procedures.
* guix/scripts/substitute-binary.scm (decompressed-port): Remove.
(guix-substitute-binary): Pass a symbol or #f as the first argument to
'decompress-port'.
* tests/utils.scm ("compressed-port, decompressed-port, non-file"): New
test.
* guix/utils.scm (filtered-port): Make sure the 'execl' child process
always exits, and does (primitive-_exit 1) upon execution failure.
Use 'primitive-_exit' in the 'dump-port' child process.
* tests/utils.scm ("filtered-port, does not exist"): New test.
* guix/pk-crypto.scm (gcrypt-version): New procedure.
* guix/scripts/archive.scm (%key-generation-parameters): New variable.
(%options) <generate-key>: Use it.
* tests/pk-crypto.scm ("sign + verify, Ed25519"): Skip if using gcrypt < 1.6.0.
* guix/scripts/offload.scm (with-error-to-port): New macro.
(remote-pipe): Add #:error-port parameter. Use 'with-error-to-port'
around 'open-pipe*' call.
(build-log-port): New procedure.
(offload): Change #:log-port to default to (build-log-port). Call
'remote-pipe' with #:error-port LOG-PORT.
* guix/scripts/substitute-binary.scm (fetch): Add #:quiet-404?
parameter. Upon &http-get-error, re-raise C if the QUIET-404? is
true and the code is 404.
(fetch-narinfo): Pass #:quiet-404? #t.
* guix/pk-crypto.scm (bytevector->hash-data): Add #:key-type parameter.
Use the 'pkcs1' flag when KEY-TYPE is 'rsa', and 'rfc6979' when
KEY-TYPE is 'ecc' or 'dsa'.
(key-type): New procedure.
* guix/scripts/authenticate.scm (read-hash-data): Add 'key-type'
parameter. Pass it to 'bytevector->hash-data'. Adjust caller
accordingly.
* tests/pk-crypto.scm (%ecc-key-pair): New variable.
("key-type"): New test.
("sign + verify"): Pass #:key-type to 'bytevector->hash-data'.
("sign + verify, Ed25519"): New test.
* gnu/packages/gcc.scm (gcc-4.7): Change /nix/store in comment.
* gnu/system/vm.scm (operating-system-default-contents):
Use (%store-prefix) instead of "/nix/store".
* guix/derivations.scm (derivation-path->output-path,
derivation-path->output-paths): Change to /gnu/store in docstring.
* gnu/packages/ld-wrapper.scm (%store-directory): Change the default to
/gnu/store.
* guix/build/utils.scm (%store-directory): New procedure.
(remove-store-references): Use it for the default value of 'store'.
* guix/packages.scm (patch-and-repack)[builder]: Change default store to
/gnu/store.
* guix/scripts/offload.scm (offload): Remove default value for
'build-timeout'. Pass '--timeout' to the remote 'guix build'
process.
(transfer-and-offload, process-request): Remove default value for
'build-timeout'.
* guix/scripts/offload.scm (transfer-and-offload): New procedure, with
core formerly in 'process-request'.
(choose-build-machine): Remove 'requirements' parameter.
(process-request): Reply 'decline' when none of MACHINES matches the
requirements, and 'postpone' when MACHINES are busy.
* guix/scripts/offload.scm (machine-choice-lock-file,
machine-slot-file, acquire-build-slot, release-build-slot): New
procedures.
(choose-build-machine): Operate with (machine-choice-lock-file)
taken. Acquire a build slot for each of MACHINES. Release those not
used.
* guix/scripts/offload.scm (lock-machine, unlock-machine): Remove.
(lock-file, unlock-file): New procedures.
(with-file-lock): New macro.
(with-machine-lock): Rewrite in terms of 'with-file-lock'.
* guix/scripts/offload.scm (machine-lock-file, lock-machine,
unlock-machine): New procedures.
(with-machine-lock): New macro.
(process-request): Wrap 'send-files' and 'retrieve-files' calls in
'with-machine-lock'.
* guix/http-client.scm (&http-get-error): New condition type.
(http-fetch): Raise it instead of using 'error'.
* guix/scripts/substitute-binary.scm (fetch) <http>: Wrap body into
'guard' form; gracefully handle 'http-get-error?' conditions.
* guix/scripts/offload.scm (machine-load, machine-less-loaded?,
machine-less-loaded-or-faster?): New procedures.
(choose-build-machine): Use 'machine-less-loaded-or-faster?' when
sorting. Return the head of MACHINES unless it's loaded is >= 2.
Ludovic Courtès