qdev: add a maximum device allowed field for the bus.

Add a max_dev field to BusClass to specify the maximum amount of devices allowed
on the bus (has no effect if max_dev=0)
Signed-off-by: NKONRAD Frederic <fred.konrad@greensocs.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/qdev-core.h

@@ -145,6 +145,8 @@ struct BusClass {
      */
     char *(*get_fw_dev_path)(DeviceState *dev);
     int (*reset)(BusState *bus);
+    /* maximum devices allowed on the bus, 0: no limit. */
+    int max_dev;
 };
 
 typedef struct BusChild {

hw/qdev-monitor.c

@@ -283,6 +283,7 @@ static DeviceState *qbus_find_dev(BusState *bus, char *elem)
 static BusState *qbus_find_recursive(BusState *bus, const char *name,
                                      const char *bus_typename)
 {
+    BusClass *bus_class = BUS_GET_CLASS(bus);
     BusChild *kid;
     BusState *child, *ret;
     int match = 1;
@@ -293,6 +294,17 @@ static BusState *qbus_find_recursive(BusState *bus, const char *name,
     if (bus_typename && !object_dynamic_cast(OBJECT(bus), bus_typename)) {
         match = 0;
     }
+    if ((bus_class->max_dev != 0) && (bus_class->max_dev <= bus->max_index)) {
+        if (name != NULL) {
+            /* bus was explicitly specified: return an error. */
+            qerror_report(ERROR_CLASS_GENERIC_ERROR, "Bus '%s' is full",
+                          bus->name);
+            return NULL;
+        } else {
+            /* bus was not specified: try to find another one. */
+            match = 0;
+        }
+    }
     if (match) {
         return bus;
     }