machine: Provide a function to check the dynamic sysbus allowlist

Provide a new function dynamic_sysbus_dev_allowed() which checks the
per-machine list of permitted dynamic sysbus devices and returns a
boolean result indicating whether the device is allowed.  We can use
this in the implementation of validate_sysbus_device(), but we will
also need it so that machine hotplug callbacks can validate devices
rather than assuming that any sysbus device might be hotpluggable
into the platform bus.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Message-id: 20210325153310.9131-3-peter.maydell@linaro.org

hw/core/machine.c

@@ -529,20 +529,31 @@ void machine_class_allow_dynamic_sysbus_dev(MachineClass *mc, const char *type)
     QAPI_LIST_PREPEND(mc->allowed_dynamic_sysbus_devices, g_strdup(type));
 }
 
-static void validate_sysbus_device(SysBusDevice *sbdev, void *opaque)
+bool device_is_dynamic_sysbus(MachineClass *mc, DeviceState *dev)
 {
-    MachineState *machine = opaque;
-    MachineClass *mc = MACHINE_GET_CLASS(machine);
     bool allowed = false;
     strList *wl;
+    Object *obj = OBJECT(dev);
+
+    if (!object_dynamic_cast(obj, TYPE_SYS_BUS_DEVICE)) {
+        return false;
+    }
 
     for (wl = mc->allowed_dynamic_sysbus_devices;
          !allowed && wl;
          wl = wl->next) {
-        allowed |= !!object_dynamic_cast(OBJECT(sbdev), wl->value);
+        allowed |= !!object_dynamic_cast(obj, wl->value);
     }
 
-    if (!allowed) {
+    return allowed;
+}
+
+static void validate_sysbus_device(SysBusDevice *sbdev, void *opaque)
+{
+    MachineState *machine = opaque;
+    MachineClass *mc = MACHINE_GET_CLASS(machine);
+
+    if (!device_is_dynamic_sysbus(mc, DEVICE(sbdev))) {
         error_report("Option '-device %s' cannot be handled by this machine",
                      object_class_get_name(object_get_class(OBJECT(sbdev))));
         exit(1);

include/hw/boards.h

@@ -52,6 +52,30 @@ void machine_set_cpu_numa_node(MachineState *machine,
  */
 void machine_class_allow_dynamic_sysbus_dev(MachineClass *mc, const char *type);
 
+/**
+ * device_is_dynamic_sysbus: test whether device is a dynamic sysbus device
+ * @mc: Machine class
+ * @dev: device to check
+ *
+ * Returns: true if @dev is a sysbus device on the machine's list
+ * of dynamically pluggable sysbus devices; otherwise false.
+ *
+ * This function checks whether @dev is a valid dynamic sysbus device,
+ * by first confirming that it is a sysbus device and then checking it
+ * against the list of permitted dynamic sysbus devices which has been
+ * set up by the machine using machine_class_allow_dynamic_sysbus_dev().
+ *
+ * It is valid to call this with something that is not a subclass of
+ * TYPE_SYS_BUS_DEVICE; the function will return false in this case.
+ * This allows hotplug callback functions to be written as:
+ *     if (device_is_dynamic_sysbus(mc, dev)) {
+ *         handle dynamic sysbus case;
+ *     } else if (some other kind of hotplug) {
+ *         handle that;
+ *     }
+ */
+bool device_is_dynamic_sysbus(MachineClass *mc, DeviceState *dev);
+
 /*
  * Checks that backend isn't used, preps it for exclusive usage and
  * returns migratable MemoryRegion provided by backend.