globals: Allow global properties to be optional

Making some global properties optional will let us simplify
compat code when a given property works on most (but not all)
subclasses of a given type.

Device types will be able to opt out from optional compat
properties by simply not registering those properties.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
index 9614f76ae6..0a84c42756 100644
--- a/include/hw/qdev-core.h
+++ b/include/hw/qdev-core.h
@@ -250,6 +250,8 @@ struct PropertyInfo {
 /**
  * GlobalProperty:
  * @used: Set to true if property was used when initializing a device.
+ * @optional: If set to true, GlobalProperty will be skipped without errors
+ *            if the property doesn't exist.
  *
  * An error is fatal for non-hotplugged devices, when the global is applied.
  */
@@ -258,6 +260,7 @@ typedef struct GlobalProperty {
     const char *property;
     const char *value;
     bool used;
+    bool optional;
 } GlobalProperty;
 
 static inline void