services: postgresql: Add log directory support.

* gnu/services/databases.scm (postgresql-configuration-log-directory): New
procedure.
(<postgresql-configuration>)[log-directory]: New field.
(postgresql-activation): Create the log directory.
(postgresql-shepherd-service): Honor it.
* gnu/tests/databases.scm (%postgresql-log-directory): New variable.
(log-file): New test case.
* doc/guix.texi (Database Services): Document it.

doc/guix.texi

@@ -19344,6 +19344,11 @@ The configuration file to use when running PostgreSQL@.  The default
 behaviour uses the postgresql-config-file record with the default values
 for the fields.
 
+@item @code{log-directory} (default: @code{"/var/log/postgresql"})
+The directory where @command{pg_ctl} output will be written in a file
+named @code{"pg_ctl.log"}.  This file can be useful to debug PostgreSQL
+configuration errors for instance.
+
 @item @code{data-directory} (default: @code{"/var/lib/postgresql/data"})
 Directory in which to store the data.
 

gnu/services/databases.scm

@@ -52,6 +52,7 @@
             postgresql-configuration-port
             postgresql-configuration-locale
             postgresql-configuration-file
+            postgresql-configuration-log-directory
             postgresql-configuration-data-directory
 
             postgresql-service
@@ -164,6 +165,8 @@ host	all	all	::1/128 	md5"))
                       (default "en_US.utf8"))
   (config-file        postgresql-configuration-file
                       (default (postgresql-config-file)))
+  (log-directory      postgresql-configuration-log-directory
+                      (default "/var/log/postgresql"))
   (data-directory     postgresql-configuration-data-directory
                       (default "/var/lib/postgresql/data"))
   (extension-packages postgresql-configuration-extension-packages
@@ -200,15 +203,18 @@ host	all	all	::1/128 	md5"))
 
 (define postgresql-activation
   (match-lambda
-    (($ <postgresql-configuration> postgresql port locale config-file data-directory
+    (($ <postgresql-configuration> postgresql port locale config-file
-        extension-packages)
+                                   log-directory data-directory
+                                   extension-packages)
      #~(begin
          (use-modules (guix build utils)
                       (ice-9 match))
 
          (let ((user (getpwnam "postgres"))
-               (initdb (string-append #$(final-postgresql postgresql extension-packages)
+               (initdb (string-append
-                                      "/bin/initdb"))
+                        #$(final-postgresql postgresql
+                                            extension-packages)
+                        "/bin/initdb"))
                (initdb-args
                 (append
                  (if #$locale
@@ -225,6 +231,11 @@ host	all	all	::1/128 	md5"))
                (mkdir-p socket-directory)
                (chown socket-directory (passwd:uid user) (passwd:gid user))))
 
+           ;; Create the log directory.
+           (when (string? #$log-directory)
+             (mkdir-p #$log-directory)
+             (chown #$log-directory (passwd:uid user) (passwd:gid user)))
+
            ;; Drop privileges and init state directory in a new
            ;; process.  Wait for it to finish before proceeding.
            (match (primitive-fork)
@@ -247,8 +258,9 @@ host	all	all	::1/128 	md5"))
 
 (define postgresql-shepherd-service
   (match-lambda
-    (($ <postgresql-configuration> postgresql port locale config-file data-directory
+    (($ <postgresql-configuration> postgresql port locale config-file
-        extension-packages)
+                                   log-directory data-directory
+                                   extension-packages)
      (let* ((pg_ctl-wrapper
              ;; Wrapper script that switches to the 'postgres' user before
              ;; launching daemon.
@@ -260,13 +272,21 @@ host	all	all	::1/128 	md5"))
                   (match (command-line)
                     ((_ mode)
                      (let ((user (getpwnam "postgres"))
-                           (pg_ctl #$(file-append (final-postgresql postgresql extension-packages)
+                           (pg_ctl #$(file-append
+                                      (final-postgresql postgresql
+                                                        extension-packages)
                                                   "/bin/pg_ctl"))
                            (options (format #f "--config-file=~a -p ~d"
                                             #$config-file #$port)))
                        (setgid (passwd:gid user))
                        (setuid (passwd:uid user))
-                       (execl pg_ctl pg_ctl "-D" #$data-directory "-o" options
+                       (execl pg_ctl pg_ctl "-D" #$data-directory
+                              #$@(if (string? log-directory)
+                                     (list "-l"
+                                           (string-append log-directory
+                                                          "/pg_ctl.log"))
+                                     '())
+                              "-o" options
                               mode)))))))
             (pid-file (in-vicinity data-directory "postmaster.pid"))
             (action (lambda args

gnu/tests/databases.scm

@@ -214,6 +214,9 @@
 ;;; The PostgreSQL service.
 ;;;
 
+(define %postgresql-log-directory
+  "/var/log/postgresql")
+
 (define %postgresql-os
   (simple-operating-system
    (service postgresql-service-type
@@ -262,6 +265,23 @@
                 (start-service 'postgres))
              marionette))
 
+          (test-assert "log-file"
+            (marionette-eval
+             '(begin
+                (use-modules (ice-9 ftw)
+                             (ice-9 match))
+                (current-output-port
+                 (open-file "/dev/console" "w0"))
+                (let ((server-log-file
+                       (string-append #$%postgresql-log-directory
+                                      "/pg_ctl.log")))
+                  (and (file-exists? server-log-file)
+                       (display
+                        (call-with-input-file server-log-file
+                          get-string-all)))
+                  #t))
+             marionette))
+
           (test-end)
           (exit (= (test-runner-fail-count (test-runner-current)) 0)))))