guix/gnu/services.scm

;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2016 Chris Marusich <cmmarusich@gmail.com>
;;;
;;; 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 (gnu services)
  #:use-module (guix gexp)
  #:use-module (guix monads)
  #:use-module (guix store)
  #:use-module (guix records)
  #:use-module (guix profiles)
  #:use-module (guix discovery)
  #:use-module (guix sets)
  #:use-module (guix ui)
  #:use-module ((guix utils) #:select (source-properties->location))
  #:use-module (guix modules)
  #:use-module (gnu packages base)
  #:use-module (gnu packages bash)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-9)
  #:use-module (srfi srfi-9 gnu)
  #:use-module (srfi srfi-26)
  #:use-module (srfi srfi-34)
  #:use-module (srfi srfi-35)
  #:use-module (ice-9 vlist)
  #:use-module (ice-9 match)
  #:export (service-extension
            service-extension?
            service-extension-target
            service-extension-compute

            service-type
            service-type?
            service-type-name
            service-type-extensions
            service-type-compose
            service-type-extend
            service-type-default-value
            service-type-description
            service-type-location

            %service-type-path
            fold-service-types
            lookup-service-types

            service
            service?
            service-kind
            service-value
            service-parameters                    ;deprecated

            simple-service
            modify-services
            service-back-edges
            fold-services

            service-error?
            missing-value-service-error?
            missing-value-service-error-type
            missing-value-service-error-location
            missing-target-service-error?
            missing-target-service-error-service
            missing-target-service-error-target-type
            ambiguous-target-service-error?
            ambiguous-target-service-error-service
            ambiguous-target-service-error-target-type

            system-service-type
            boot-service-type
            cleanup-service-type
            activation-service-type
            activation-service->script
            %linux-bare-metal-service
            special-files-service-type
            extra-special-file
            etc-service-type
            etc-directory
            setuid-program-service-type
            profile-service-type
            firmware-service-type
            gc-root-service-type

            %boot-service
            %activation-service
            etc-service))

;;; Comment:
;;;
;;; This module defines a broad notion of "service types" and "services."
;;;
;;; A service type describe how its instances extend instances of other
;;; service types.  For instance, some services extend the instance of
;;; ACCOUNT-SERVICE-TYPE by providing it with accounts and groups to create;
;;; others extend SHEPHERD-ROOT-SERVICE-TYPE by passing it instances of
;;; <shepherd-service>.
;;;
;;; When applicable, the service type defines how it can itself be extended,
;;; by providing one procedure to compose extensions, and one procedure to
;;; extend itself.
;;;
;;; A notable service type is SYSTEM-SERVICE-TYPE, which has a single
;;; instance, which is the root of the service DAG.  Its value is the
;;; derivation that produces the 'system' directory as returned by
;;; 'operating-system-derivation'.
;;;
;;; The 'fold-services' procedure can be passed a list of procedures, which it
;;; "folds" by propagating extensions down the graph; it returns the root
;;; service after the applying all its extensions.
;;;
;;; Code:

(define-record-type <service-extension>
  (service-extension target compute)
  service-extension?
  (target  service-extension-target)              ;<service-type>
  (compute service-extension-compute))            ;params -> params

(define &no-default-value
  ;; Value used to denote service types that have no associated default value.
  '(no default value))

(define-record-type* <service-type> service-type make-service-type
  service-type?
  (name       service-type-name)                  ;symbol (for debugging)

  ;; Things extended by services of this type.
  (extensions service-type-extensions)            ;list of <service-extensions>

  ;; Given a list of extensions, "compose" them.
  (compose    service-type-compose                ;list of Any -> Any
              (default #f))

  ;; Extend the services' own parameters with the extension composition.
  (extend     service-type-extend                 ;list of Any -> parameters
              (default #f))

  ;; Optional default value for instances of this type.
  (default-value service-type-default-value       ;Any
                 (default &no-default-value))

  ;; Meta-data.
  (description  service-type-description          ;string
                (default #f))
  (location     service-type-location             ;<location>
                (default (and=> (current-source-location)
                                source-properties->location))
                (innate)))

(define (write-service-type type port)
  (format port "#<service-type ~a ~a>"
          (service-type-name type)
          (number->string (object-address type) 16)))

(set-record-type-printer! <service-type> write-service-type)

(define %distro-root-directory
  ;; Absolute file name of the module hierarchy.
  (dirname (search-path %load-path "guix.scm")))

(define %service-type-path
  ;; Search path for service types.
  (make-parameter `((,%distro-root-directory . "gnu/services")
                    (,%distro-root-directory . "gnu/system"))))

(define (all-service-modules)
  "Return the default set of service modules."
  (cons (resolve-interface '(gnu services))
        (all-modules (%service-type-path))))

(define* (fold-service-types proc seed
                             #:optional
                             (modules (all-service-modules)))
  "For each service type exported by one of MODULES, call (PROC RESULT).  SEED
is used as the initial value of RESULT."
  (fold-module-public-variables (lambda (object result)
                                  (if (service-type? object)
                                      (proc object result)
                                      result))
                                seed
                                modules))

(define lookup-service-types
  (let ((table
         (delay (fold-service-types (lambda (type result)
                                      (vhash-consq (service-type-name type)
                                                   type result))
                                    vlist-null))))
    (lambda (name)
      "Return the list of services with the given NAME (a symbol)."
      (vhash-foldq* cons '() name (force table)))))

;; Services of a given type.
(define-record-type <service>
  (make-service type value)
  service?
  (type       service-kind)
  (value      service-value))

(define-syntax service
  (syntax-rules ()
    "Return a service instance of TYPE.  The service value is VALUE or, if
omitted, TYPE's default value."
    ((_ type value)
     (make-service type value))
    ((_ type)
     (%service-with-default-value (current-source-location)
                                  type))))

(define (%service-with-default-value location type)
  "Return a instance of service type TYPE with its default value, if any.  If
TYPE does not have a default value, an error is raised."
  ;; TODO: Currently this is a run-time error but with a little bit macrology
  ;; we could turn it into an expansion-time error.
  (let ((default (service-type-default-value type)))
    (if (eq? default &no-default-value)
        (let ((location (source-properties->location location)))
          (raise
           (condition
            (&missing-value-service-error (type type) (location location))
            (&message
             (message (format #f (G_ "~a: no value specified \
for service of type '~a'")
                              (location->string location)
                              (service-type-name type)))))))
        (service type default))))

(define-condition-type &service-error &error
  service-error?)

(define-condition-type &missing-value-service-error &service-error
  missing-value-service-error?
  (type     missing-value-service-error-type)
  (location missing-value-service-error-location))



;;;
;;; Helpers.
;;;

(define service-parameters
  ;; Deprecated alias.
  service-value)

(define (simple-service name target value)
  "Return a service that extends TARGET with VALUE.  This works by creating a
singleton service type NAME, of which the returned service is an instance."
  (let* ((extension (service-extension target identity))
         (type      (service-type (name name)
                                  (extensions (list extension)))))
    (service type value)))

(define-syntax %modify-service
  (syntax-rules (=>)
    ((_ service)
     service)
    ((_ svc (kind param => exp ...) clauses ...)
     (if (eq? (service-kind svc) kind)
         (let ((param (service-value svc)))
           (service (service-kind svc)
                    (begin exp ...)))
         (%modify-service svc clauses ...)))))

(define-syntax modify-services
  (syntax-rules ()
    "Modify the services listed in SERVICES according to CLAUSES and return
the resulting list of services.  Each clause must have the form:

  (TYPE VARIABLE => BODY)

where TYPE is a service type, such as 'guix-service-type', and VARIABLE is an
identifier that is bound within BODY to the value of the service of that
TYPE.  Consider this example:

  (modify-services %base-services
    (guix-service-type config =>
                       (guix-configuration
                        (inherit config)
                        (use-substitutes? #f)
                        (extra-options '(\"--gc-keep-derivations\"))))
    (mingetty-service-type config =>
                           (mingetty-configuration
                            (inherit config)
                            (motd (plain-file \"motd\" \"Hi there!\")))))

It changes the configuration of the GUIX-SERVICE-TYPE instance, and that of
all the MINGETTY-SERVICE-TYPE instances.

This is a shorthand for (map (lambda (svc) ...) %base-services)."
    ((_ services clauses ...)
     (map (lambda (service)
            (%modify-service service clauses ...))
          services))))


;;;
;;; Core services.
;;;

(define (system-derivation mentries mextensions)
  "Return as a monadic value the derivation of the 'system' directory
containing the given entries."
  (mlet %store-monad ((entries    mentries)
                      (extensions (sequence %store-monad mextensions)))
    (lower-object
     (file-union "system"
                 (append entries (concatenate extensions))))))

(define system-service-type
  ;; This is the ultimate service type, the root of the service DAG.  The
  ;; service of this type is extended by monadic name/item pairs.  These items
  ;; end up in the "system directory" as returned by
  ;; 'operating-system-derivation'.
  (service-type (name 'system)
                (extensions '())
                (compose identity)
                (extend system-derivation)))

(define (compute-boot-script _ mexps)
  (mlet %store-monad ((gexps (sequence %store-monad mexps)))
    (gexp->file "boot"
                ;; Clean up and activate the system, then spawn shepherd.
                #~(begin #$@gexps))))

(define (boot-script-entry mboot)
  "Return, as a monadic value, an entry for the boot script in the system
directory."
  (mlet %store-monad ((boot mboot))
    (return `(("boot" ,boot)))))