system: Deprecate hosts-file.

* gnu/system.scm (operating-system-hosts-file): Deprecate procedure.
(warn-hosts-file-field-deprecation): New procedure, helper for
deprecated variable.
(operating-system)[hosts-file]: Use helper to warn deprecated field.
(local-host-aliases): Mark as deprecated.
(local-host-entries): New procedure.
(operating-system-default-essential-services,
hurd-default-essential-services): Use hosts-service-type.  Use
'%operating-system-hosts-file' and 'local-host-entries'.
(default-/etc/hosts): Remove procedure.
(operating-system-etc-service): Remove hosts file.
* doc/guix.texi (operating-system Reference)
(Networking Services) (Virtualization Services): Rewrite documentation
entries to use hosts-service-type.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>

doc/guix.texi

@@ -16481,13 +16481,6 @@ supported hardware.
 @item @code{host-name}
 The host name.
 
-@item @code{hosts-file}
-@cindex hosts file
-A file-like object (@pxref{G-Expressions, file-like objects}) for use as
-@file{/etc/hosts} (@pxref{Host Names,,, libc, The GNU C Library
-Reference Manual}).  The default is a file with entries for
-@code{localhost} and @var{host-name}.
-
 @item @code{mapped-devices} (default: @code{'()})
 A list of mapped devices.  @xref{Mapped Devices}.
 
@@ -21012,22 +21005,33 @@ line contains a entry that maps a known server name of the Facebook
 on-line service---e.g., @code{www.facebook.com}---to the local
 host---@code{127.0.0.1} or its IPv6 equivalent, @code{::1}.
 
-This variable is typically used in the @code{hosts-file} field of an
+This variable is typically used as a @code{hosts-service-type}
-@code{operating-system} declaration (@pxref{operating-system Reference,
+service extension (@pxref{Service Reference, @code{hosts-service-type}}):
-@file{/etc/hosts}}):
 
 @lisp
-(use-modules (gnu) (guix))
+(use-modules (gnu) (gnu services) (guix) (srfi srfi-1) (ice-9 match))
+(use-service-modules networking)
 
 (operating-system
-  (host-name "mymachine")
+  ;; @dots{}
-  ;; ...
+
-  (hosts-file
+  (service
-    ;; Create a /etc/hosts file with aliases for "localhost"
+    (simple-service 'block-facebook-hosts hosts-service-type
-    ;; and "mymachine", as well as for Facebook servers.
+                    (let ((host-pairs
-    (plain-file "hosts"
+                            (filter-map
-                (string-append (local-host-aliases host-name)
+                              (lambda (x)
-                               %facebook-host-aliases))))
+                                (and (not (or (string-null? x)
+                                              (string-prefix? "#" x)))
+	                             (remove string-null?
+                                             (string-split
+                                               x
+                                               char-set:whitespace))))
+                              (string-split %facebook-host-aliases #\newline))))
+                      (map (match-lambda
+                             ((addr name)
+                              (host addr name)))
+                           host-pairs)))
+    ;; @dots{}
 @end lisp
 
 This mechanism can prevent programs running locally, such as Web
@@ -34555,7 +34559,7 @@ and to make maintenance and recovery tasks easy.  It consists of multiple
 services which are described later in this section.  In addition to the Ganeti
 service, you will need the OpenSSH service (@pxref{Networking Services,
 @code{openssh-service-type}}), and update the @file{/etc/hosts} file
-(@pxref{operating-system Reference, @code{hosts-file}}) with the cluster name
+(@pxref{Service Reference, @code{hosts-service-type}}) with the cluster name
 and address (or use a DNS server).
 
 All nodes participating in a Ganeti cluster should have the same Ganeti and
@@ -34569,14 +34573,6 @@ cluster node that supports multiple storage backends, and installs the
 (operating-system
   ;; @dots{}
   (host-name "node1")
-  (hosts-file (plain-file "hosts" (format #f "
-127.0.0.1       localhost
-::1             localhost
-
-192.168.1.200   ganeti.example.com
-192.168.1.201   node1.example.com node1
-192.168.1.202   node2.example.com node2
-")))
 
   ;; Install QEMU so we can use KVM-based instances, and LVM, DRBD and Ceph
   ;; in order to use the "plain", "drbd" and "rbd" storage backends.
@@ -34604,6 +34600,14 @@ cluster node that supports multiple storage backends, and installs the
                           (openssh-configuration
                            (permit-root-login 'prohibit-password)))
 
+                 (simple-service 'ganeti-hosts-entries hosts-service-type
+                                 (list
+                                   (host "192.168.1.200" "ganeti.example.com")
+                                   (host "192.168.1.201" "node1.example.com"
+                                         '("node1"))
+                                   (host "192.168.1.202" "node2.example.com"
+                                         '("node2"))))
+
                  (service ganeti-service-type
                           (ganeti-configuration
                            ;; This list specifies allowed file system paths

gnu/system.scm

@@ -14,6 +14,7 @@
 ;;; Copyright © 2020, 2022 Efraim Flashner <efraim@flashner.co.il>
 ;;; Copyright © 2021 Maxime Devos <maximedevos@telenet.be>
 ;;; Copyright © 2021 raid5atemyhomework <raid5atemyhomework@protonmail.com>
+;;; Copyright © 2023 Bruno Victal <mirai@makinata.eu>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -97,7 +98,7 @@
             operating-system-user-services
             operating-system-packages
             operating-system-host-name
-            operating-system-hosts-file
+            operating-system-hosts-file ;deprecated
             operating-system-hurd
             operating-system-kernel
             operating-system-kernel-file
@@ -169,7 +170,8 @@
             read-boot-parameters-file
             boot-parameters->menu-entry
 
-            local-host-aliases
+            local-host-aliases                    ;deprecated
+            local-host-entries
             %root-account
             %setuid-programs
             %sudoers-specification
@@ -208,6 +210,15 @@ VERSION is the target version of the boot-parameters record."
                          #$system "/boot")))
 
 ;; System-wide configuration.
+
+(define-with-syntax-properties (warn-hosts-file-field-deprecation
+                                (value properties))
+  (when value
+    (warning (source-properties->location properties)
+             (G_ "the 'hosts-file' field is deprecated, please use \
+'hosts-service-type' instead~%")))
+  value)
+
 ;; TODO: Add per-field docstrings/stexi.
 (define-record-type* <operating-system> operating-system
   make-operating-system
@@ -239,8 +250,9 @@ VERSION is the target version of the boot-parameters record."
             (default %base-firmware))
 
   (host-name operating-system-host-name)          ; string
-  (hosts-file operating-system-hosts-file         ; file-like | #f
+  (hosts-file %operating-system-hosts-file         ; deprecated
-              (default #f))
+              (default #f)
+              (sanitize warn-hosts-file-field-deprecation))
 
   (mapped-devices operating-system-mapped-devices ; list of <mapped-device>
                   (default '()))
@@ -296,6 +308,10 @@ VERSION is the target version of the boot-parameters record."
                             source-properties->location))
             (innate)))
 
+(define-deprecated (operating-system-hosts-file os)
+  hosts-service-type
+  (%operating-system-hosts-file os))
+
 (define* (operating-system-kernel-arguments
           os root-device #:key (version %boot-parameters-version))
   "Return all the kernel arguments, including the ones not specified directly
@@ -733,7 +749,8 @@ bookkeeping."
          (non-boot-fs  (non-boot-file-system-service os))
          (swaps        (swap-services os))
          (procs        (service user-processes-service-type))
-         (host-name    (host-name-service (operating-system-host-name os)))
+         (host-name    (operating-system-host-name os))
+         (hosts-file   (%operating-system-hosts-file os))
          (entries      (operating-system-directory-base-entries os)))
     (cons* (service system-service-type entries)
            (service linux-builder-service-type
@@ -755,12 +772,19 @@ bookkeeping."
                                     (operating-system-groups os))
                             (operating-system-skeletons os))
            (operating-system-etc-service os)
+           ;; XXX: hosts-file is deprecated
+           (if hosts-file
+               (simple-service 'deprecated-hosts-file etc-service-type
+                               (list `("hosts" ,hosts-file)))
+               (service hosts-service-type
+                        (local-host-entries host-name)))
            (service fstab-service-type
                     (filter file-system-needed-for-boot?
                             (operating-system-file-systems os)))
            (session-environment-service
             (operating-system-environment-variables os))
-           host-name procs root-fs
+           (host-name-service host-name)
+           procs root-fs
            (service setuid-program-service-type
                     (operating-system-setuid-programs os))
            (service profile-service-type
@@ -774,7 +798,9 @@ bookkeeping."
                                   (operating-system-firmware os)))))))
 
 (define (hurd-default-essential-services os)
-  (let ((entries (operating-system-directory-base-entries os)))
+  (let ((host-name    (operating-system-host-name os))
+        (hosts-file   (%operating-system-hosts-file os))
+        (entries      (operating-system-directory-base-entries os)))
     (list (service system-service-type entries)
           %boot-service
           %hurd-startup-service
@@ -794,6 +820,12 @@ bookkeeping."
                            (operating-system-file-systems os)))
           (pam-root-service (operating-system-pam-services os))
           (operating-system-etc-service os)
+          ;; XXX: hosts-file is deprecated
+          (if hosts-file
+              (simple-service 'deprecated-hosts-file etc-service-type
+                              (list `("hosts" ,hosts-file)))
+              (service hosts-service-type
+                       (local-host-entries host-name)))
           (service setuid-program-service-type
                    (operating-system-setuid-programs os))
           (service profile-service-type (operating-system-packages os)))))
@@ -912,14 +944,17 @@ of PROVENANCE-SERVICE-TYPE to its services."
   "
 This is the GNU system.  Welcome.\n")
 
-(define (local-host-aliases host-name)
+(define-deprecated (local-host-aliases host-name)
+  local-host-entries
   "Return aliases for HOST-NAME, to be used in /etc/hosts."
   (string-append "127.0.0.1 localhost " host-name "\n"
                  "::1       localhost " host-name "\n"))
 
-(define (default-/etc/hosts host-name)
+(define (local-host-entries host-name)
-  "Return the default /etc/hosts file."
+  "Return <host> records for @var{host-name}."
-  (plain-file "hosts" (local-host-aliases host-name)))
+  (map (lambda (address)
+         (host address "localhost" (list host-name)))
+       '("127.0.0.1" "::1")))
 
 (define (validated-sudoers-file file)
   "Return a copy of FILE, a sudoers file, after checking that it is
@@ -1068,8 +1103,6 @@ fi\n")))
        ,@(if nsswitch `(("nsswitch.conf" ,#~#$nsswitch)) '())
        ("profile" ,#~#$profile)
        ("bashrc" ,#~#$bashrc)
-       ("hosts" ,#~#$(or (operating-system-hosts-file os)
-                         (default-/etc/hosts (operating-system-host-name os))))
        ;; Write the operating-system-host-name to /etc/hostname to prevent
        ;; NetworkManager from changing the system's hostname when connecting
        ;; to certain networks.  Some discussion at

gnu/tests/ganeti.scm

@@ -1,6 +1,7 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2020, 2021 Marius Bakke <marius@gnu.org>
 ;;; Copyright © 2020 Brice Waegeneire <brice@waegenei.re>
+;;; Copyright © 2023 Bruno Victal <mirai@makinata.eu>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -22,6 +23,7 @@
   #:use-module (gnu tests)
   #:use-module (gnu system vm)
   #:use-module (gnu services)
+  #:use-module (gnu services base)
   #:use-module (gnu services ganeti)
   #:use-module (gnu services networking)
   #:use-module (gnu services ssh)
@@ -46,18 +48,15 @@
                         %base-file-systems))
     (firmware '())
 
-    ;; The hosts file must contain a nonlocal IP for host-name.
-    ;; In addition, the cluster name must resolve to an IP address that
-    ;; is not currently provisioned.
-    (hosts-file (plain-file "hosts" (format #f "
-127.0.0.1       localhost
-::1             localhost
-10.0.2.15       gnt1.example.com gnt1
-192.168.254.254 ganeti.example.com
-")))
-
     (packages (append (list ganeti-instance-debootstrap ganeti-instance-guix)
                       %base-packages))
+
+    ;; The hosts file must contain a nonlocal IP for host-name.
+    (essential-services
+     (modify-services (operating-system-default-essential-services this-operating-system)
+       (hosts-service-type config => (list
+                                      (host "127.0.0.1" "localhost")
+                                      (host "::1"       "localhost")))))
     (services
      (append (list (service static-networking-service-type
                             (list %qemu-static-networking))
@@ -65,6 +64,13 @@
                             (openssh-configuration
                              (permit-root-login 'prohibit-password)))
 
+                   ;; In addition, the cluster name must resolve to an IP address that
+                   ;; is not currently provisioned.
+                   (simple-service 'ganeti-host-entries hosts-service-type
+                                   (list
+                                    (host "10.0.2.15" "gnt1.example.com" '("gnt1"))
+                                    (host "192.168.254.254" "ganeti.example.com")))
+
                    (service ganeti-service-type
                             (ganeti-configuration
                              (file-storage-paths '("/srv/ganeti/file-storage"))