qga: Add guest-get-timezone command

Adds a new command `guest-get-timezone` reporting the currently
configured timezone on the system. The information on what timezone is
currently is configured is useful in case of Windows VMs where the
offset of the hardware clock is required to have the same offset. This
can be used for management systems like `oVirt` to detect the timezone
difference and warn administrators of the misconfiguration.

Signed-off-by: Vinzenz Feenstra <vfeenstr@redhat.com>
Reviewed-by: Sameeh Jubran <sameeh@daynix.com>
Tested-by: Sameeh Jubran <sameeh@daynix.com>
* moved stub implementation to end of function for consistency
* document that timezone names are for informational use only.
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

qga/commands.c

@@ -510,3 +510,41 @@ GuestHostName *qmp_guest_get_host_name(Error **err)
     }
     return result;
 }
+
+GuestTimezone *qmp_guest_get_timezone(Error **errp)
+{
+#if GLIB_CHECK_VERSION(2, 28, 0)
+    GuestTimezone *info = NULL;
+    GTimeZone *tz = NULL;
+    gint64 now = 0;
+    gint32 intv = 0;
+    gchar const *name = NULL;
+
+    info = g_new0(GuestTimezone, 1);
+    tz = g_time_zone_new_local();
+    if (tz == NULL) {
+        error_setg(errp, QERR_QGA_COMMAND_FAILED,
+                   "Couldn't retrieve local timezone");
+        goto error;
+    }
+
+    now = g_get_real_time() / G_USEC_PER_SEC;
+    intv = g_time_zone_find_interval(tz, G_TIME_TYPE_UNIVERSAL, now);
+    info->offset = g_time_zone_get_offset(tz, intv);
+    name = g_time_zone_get_abbreviation(tz, intv);
+    if (name != NULL) {
+        info->has_zone = true;
+        info->zone = g_strdup(name);
+    }
+    g_time_zone_unref(tz);
+
+    return info;
+
+error:
+    g_free(info);
+    return NULL;
+#else
+    error_setg(errp, QERR_UNSUPPORTED);
+    return NULL;
+#endif
+}

qga/qapi-schema.json

@@ -1101,3 +1101,28 @@
 ##
 { 'command': 'guest-get-users',
   'returns': ['GuestUser'] }
+
+##
+# @GuestTimezone:
+#
+# @zone:    Timezone name. These values may differ depending on guest/OS and
+#           should only be used for informational purposes.
+# @offset:  Offset to UTC in seconds, negative numbers for time zones west of
+#           GMT, positive numbers for east
+#
+# Since: 2.10
+##
+{ 'struct': 'GuestTimezone',
+  'data':   { '*zone': 'str', 'offset': 'int' } }
+
+##
+# @guest-get-timezone:
+#
+# Retrieves the timezone information from the guest.
+#
+# Returns: A GuestTimezone dictionary.
+#
+# Since: 2.10
+##
+{ 'command': 'guest-get-timezone',
+  'returns': 'GuestTimezone' }