qemu-ga-win: Fail loudly on bare 'set-time'

The command is not implemented correctly yet. The documentation allows
to not pass any value to set, in which case the time is re-read from
RTC. However, reading CMOS on Windows is not trivial to implement. So
instead of pretending we've set the correct time, fail explicitly.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

qga/commands-win32.c

@@ -625,31 +625,31 @@ void qmp_guest_set_time(bool has_time, int64_t time_ns, Error **errp)
     FILETIME tf;
     LONGLONG time;
 
-    if (has_time) {
-        /* Okay, user passed a time to set. Validate it. */
-        if (time_ns < 0 || time_ns / 100 > INT64_MAX - W32_FT_OFFSET) {
-            error_setg(errp, "Time %" PRId64 "is invalid", time_ns);
-            return;
-        }
+    if (!has_time) {
+        /* Unfortunately, Windows libraries don't provide an easy way to access
+         * RTC yet:
+         *
+         * https://msdn.microsoft.com/en-us/library/aa908981.aspx
+         */
+        error_setg(errp, "Time argument is required on this platform");
+        return;
+    }
+
+    /* Validate time passed by user. */
+    if (time_ns < 0 || time_ns / 100 > INT64_MAX - W32_FT_OFFSET) {
+        error_setg(errp, "Time %" PRId64 "is invalid", time_ns);
+        return;
+    }
 
-        time = time_ns / 100 + W32_FT_OFFSET;
+    time = time_ns / 100 + W32_FT_OFFSET;
 
-        tf.dwLowDateTime = (DWORD) time;
-        tf.dwHighDateTime = (DWORD) (time >> 32);
+    tf.dwLowDateTime = (DWORD) time;
+    tf.dwHighDateTime = (DWORD) (time >> 32);
 
-        if (!FileTimeToSystemTime(&tf, &ts)) {
-            error_setg(errp, "Failed to convert system time %d",
-                       (int)GetLastError());
-            return;
-        }
-    } else {
-        /* Otherwise read the time from RTC which contains the correct value.
-         * Hopefully. */
-        GetSystemTime(&ts);
-        if (ts.wYear < 1601 || ts.wYear > 30827) {
-            error_setg(errp, "Failed to get time");
-            return;
-        }
+    if (!FileTimeToSystemTime(&tf, &ts)) {
+        error_setg(errp, "Failed to convert system time %d",
+                   (int)GetLastError());
+        return;
     }
 
     acquire_privilege(SE_SYSTEMTIME_NAME, &local_err);

qga/qapi-schema.json

@@ -121,7 +121,10 @@
 # given value, then sets the Hardware Clock (RTC) to the
 # current System Time. This will make it easier for a guest
 # to resynchronize without waiting for NTP. If no @time is
-# specified, then the time to set is read from RTC.
+# specified, then the time to set is read from RTC. However,
+# this may not be supported on all platforms (i.e. Windows).
+# If that's the case users are advised to always pass a
+# value.
 #
 # @time: #optional time of nanoseconds, relative to the Epoch
 #        of 1970-01-01 in UTC.