services: Add 'file-database' service.

* gnu/services/admin.scm (%default-file-database-update-schedule)
(%default-file-database-excluded-directories): New variables.
(<file-database-configuration>): New record type.
(file-database-mcron-jobs): New procedure.
(file-database-service-type): New variable.
* doc/guix.texi (File Search Services): New node.

doc/guix.texi

@@ -388,6 +388,7 @@ Services
 * Printing Services::           Local and remote printer support.
 * Desktop Services::            D-Bus and desktop services.
 * Sound Services::              ALSA and Pulseaudio services.
+* File Search Services::        Tools to search for files.
 * Database Services::           SQL databases, key-value stores, etc.
 * Mail Services::               IMAP, POP3, SMTP, and all that.
 * Messaging Services::          Messaging services.
@@ -18428,6 +18429,7 @@ declaration.
 * Printing Services::           Local and remote printer support.
 * Desktop Services::            D-Bus and desktop services.
 * Sound Services::              ALSA and Pulseaudio services.
+* File Search Services::        Tools to search for files.
 * Database Services::           SQL databases, key-value stores, etc.
 * Mail Services::               IMAP, POP3, SMTP, and all that.
 * Messaging Services::          Messaging services.
@@ -24938,6 +24940,66 @@ details.
 
 @end defvar
 
+@node File Search Services
+@subsection File Search Services
+
+@cindex file search
+@cindex searching for a file
+The services in this section populate @dfn{file databases} that let you
+search for files on your machine.  These services are provided by the
+@code{(gnu services admin)} module.
+
+The first one, @code{file-database-service-type}, periodically runs the
+venerable @command{updatedb} command (@pxref{Invoking updatedb,,, find,
+GNU Findutils}).  That command populates a database of file names that
+you can then search with the @command{locate} command (@pxref{Invoing
+locate,,, find, GNU Findutils}), as in this example:
+
+@example
+locate important-notes.txt
+@end example
+
+You can enable this service with its default settings by adding this
+snippet to your operating system services:
+
+@lisp
+(service file-database-service-type)
+@end lisp
+
+This updates the database once a week, excluding files from
+@file{/gnu/store}---these are more usefully handled by @command{guix
+locate} (@pxref{Invoking guix locate}).  You can of course provide a
+custom configuration, as described below.
+
+@defvar file-database-service-type
+This is the type of the file database service, which runs
+@command{updatedb} periodically.  Its associated value must be a
+@code{file-database-configuration} record, as described below.
+@end defvar
+
+@deftp {Data Type} file-database-configuration
+Record type for the @code{file-database-service-type} configuration,
+with the following fields:
+
+@table @asis
+@item @code{package} (default: @code{findutils})
+The GNU@tie{}Findutils package from which the @command{updatedb} command
+is taken.
+
+@item @code{schedule} (default: @code{%default-file-database-update-schedule})
+String or G-exp denoting an mcron schedule for the periodic
+@command{updatedb} job (@pxref{Guile Syntax,,, mcron, GNU@tie{}mcron}).
+
+@item @code{excluded-directories} (default @code{%default-file-database-excluded-directories})
+List of directories to ignore when building the file database.  By
+default, this includes @file{/tmp} and @file{/gnu/store}, which should
+instead be indexed by @command{guix locate} (@pxref{Invoking guix
+locate}).  This list is passed to the @option{--prunepaths} option of
+@command{updatedb} (@pxref{Invoking updatedb,,, find,
+GNU@tie{}Findutils}).
+@end table
+@end deftp
+
 @node Database Services
 @subsection Database Services
 

gnu/services/admin.scm

@@ -21,16 +21,21 @@
 
 (define-module (gnu services admin)
   #:use-module (gnu packages admin)
+  #:use-module ((gnu packages base)
+                #:select (canonical-package findutils))
   #:use-module (gnu packages certs)
   #:use-module (gnu packages package-management)
   #:use-module (gnu services)
+  #:use-module (gnu services configuration)
   #:use-module (gnu services mcron)
   #:use-module (gnu services shepherd)
+  #:use-module ((guix store) #:select (%store-prefix))
   #:use-module (guix gexp)
   #:use-module (guix modules)
   #:use-module (guix packages)
   #:use-module (guix records)
   #:use-module (srfi srfi-1)
+  #:use-module (ice-9 match)
   #:use-module (ice-9 vlist)
   #:export (%default-rotations
             %rotated-files
@@ -55,6 +60,15 @@
             log-cleanup-configuration-expiry
             log-cleanup-configuration-schedule
 
+            file-database-service-type
+            file-database-configuration
+            file-database-configuration?
+            file-database-configuration-package
+            file-database-configuration-schedule
+            file-database-configuration-excluded-directories
+            %default-file-database-update-schedule
+            %default-file-database-excluded-directories
+
             unattended-upgrade-service-type
             unattended-upgrade-configuration
             unattended-upgrade-configuration?
@@ -255,6 +269,75 @@ Old log files are removed or compressed according to the configuration.")
    (description
     "Periodically delete old log files.")))
 
+
+;;;
+;;; File databases.
+;;;
+
+(define %default-file-database-update-schedule
+  ;; Default mcron schedule for the periodic 'updatedb' job: once every
+  ;; Sunday.
+  "10 23 * * 0")
+
+(define %default-file-database-excluded-directories
+  ;; Directories excluded from the 'locate' database.
+  (list (%store-prefix)
+        "/tmp" "/var/tmp" "/var/cache" ".*/\\.cache"
+        "/run/udev"))
+
+(define (string-or-gexp? obj)
+  (or (string? obj) (gexp? obj)))
+
+(define string-list?
+  (match-lambda
+    (((? string?) ...) #t)
+    (_ #f)))
+
+(define-configuration/no-serialization file-database-configuration
+  (package
+    (file-like (let-system (system target)
+                 ;; Unless we're cross-compiling, avoid pulling a second copy
+                 ;; of findutils.
+                 (if target
+                     findutils
+                     (canonical-package findutils))))
+    "The GNU@tie{}Findutils package from which the @command{updatedb} command
+is taken.")
+  (schedule
+   (string-or-gexp %default-file-database-update-schedule)
+   "String or G-exp denoting an mcron schedule for the periodic
+@command{updatedb} job (@pxref{Guile Syntax,,, mcron, GNU@tie{}mcron}).")
+  (excluded-directories
+   (string-list %default-file-database-excluded-directories)
+   "List of directories to ignore when building the file database.  By
+default, this includes @file{/tmp} and @file{/gnu/store}, which should instead
+be indexed by @command{guix locate} (@pxref{Invoking guix locate}).  This list
+is passed to the @option{--prunepaths} option of
+@command{updatedb} (@pxref{Invoking updatedb,,, find, GNU@tie{}Findutils})."))
+
+(define (file-database-mcron-jobs configuration)
+  (match-record configuration <file-database-configuration>
+    (package schedule excluded-directories)
+    (let ((updatedb (program-file
+                     "updatedb"
+                     #~(execl #$(file-append package "/bin/updatedb")
+                              "updatedb"
+                              #$(string-append "--prunepaths="
+                                               (string-join
+                                                excluded-directories))))))
+      (list #~(job #$schedule #$updatedb)))))
+
+(define file-database-service-type
+  (service-type
+   (name 'file-database)
+   (extensions (list (service-extension mcron-service-type
+                                        file-database-mcron-jobs)))
+   (description
+    "Periodically update the file database used by the @command{locate} command,
+which lets you search for files by name.  The database is created by running
+the @command{updatedb} command.")
+   (default-value (file-database-configuration))))
+
 
 ;;;
 ;;; Unattended upgrade.