services: mpd: Log to syslog by default.

Rationale: the tristate value was awkward to deal with, the default log file
name was odd (/var/log/mpd/log) and it required special attention to create
the 'mpd' parent directory as root and chowning it to the MPD user.  It also
didn't match the default behavior of MPD, which is to log to systemd or syslog
unless a log file is specified.

* gnu/services/audio.scm (mpd-log-file-sanitizer): New procedure.
(mpd-configuration) [log-file]: Remove default maybe value.  Add sanitizer.
(mpd-shepherd-service): Validate the log file parent directory exists and has
the right permissions.  Conditionally add syslogd to requirements.
(mympd-log-to-sanitizer): New procedure.
(mympd-configuration) [log-to]: Change type to maybe-string.  Update doc and
add sanitizer.
(mympd-shepherd-service) [requirement]: Fix to use syslogd.  Adjust
accordingly.
[start] Adjust accordingly.
(mympd-log-rotation): Check log-to via maybe-value-set?.
* doc/guix.texi (Audio Services): Update doc.

1 files changed, 8 insertions, 9 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 93aedee0ce..7df9a6b8a2 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -34288,10 +34288,10 @@ will depend on.
 @item @code{environment-variables} (default: @code{'("PULSE_CLIENTCONFIG=/etc/pulse/client.conf" "PULSE_CONFIG=/etc/pulse/daemon.conf")}) (type: list-of-strings)
 A list of strings specifying environment variables.
 
-@item @code{log-file} (default: @code{"/var/log/mpd/log"}) (type: maybe-string)
-The location of the log file.  Set to @code{syslog} to use the local
-syslog daemon or @code{%unset-value} to omit this directive from the
-configuration file.
+@item @code{log-file} (type: maybe-string)
+The location of the log file.  Unless specified, logs are sent to the
+local syslog daemon.  Alternatively, a log file name can be specified,
+for example @file{/var/log/mpd.log}.
 
 @item @code{log-level} (type: maybe-string)
 Supress any messages below this threshold.  The available values, in
@@ -34565,11 +34565,10 @@ HTTP port to listen on.
 How much detail to include in logs, possible values: @code{0} to
 @code{7}.
 
-@item @code{log-to} (default: @code{"/var/log/mympd/log"}) (type: string-or-symbol)
-Where to send logs.  By default, the service logs to
-@file{/var/log/mympd.log}.  The alternative is @code{'syslog}, which
-sends output to the running syslog service under the @samp{daemon}
-facility.
+@item @code{log-to} (type: maybe-string)
+Where to send logs.  Unless specified, the service logs to the local
+syslog service under the @samp{daemon} facility.  Alternatively, a log
+file name can be specified, for example @file{/var/log/mympd.log}.
 
 @item @code{lualibs} (default: @code{"all"}) (type: maybe-string)
 See