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>

2 files changed, 62 insertions, 23 deletions

diff --git a/gnu/system.scm b/gnu/system.scm
index d67f9a615b..df60fda53b 100644
--- a/gnu/system.scm
+++ b/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
-              (default #f))
+  (hosts-file %operating-system-hosts-file         ; deprecated
+              (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)
-  "Return the default /etc/hosts file."
-  (plain-file "hosts" (local-host-aliases host-name)))
+(define (local-host-entries host-name)
+  "Return <host> records for @var{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
diff --git a/gnu/tests/ganeti.scm b/gnu/tests/ganeti.scm
index f647e9554c..b5624b7598 100644
--- a/gnu/tests/ganeti.scm
+++ b/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"))