Add a new function object_resolve_and_typecheck(), whose purpose is
to look up the object at a given QOM path, confirm that it is the
expected type, and return it.  This is similar to the existing
object_resolve_path_type(), but it insists on a non-ambiguous path.

We were already using this functionality internally to object.c as
part of the object_resolve_link() function, so this patch implements
the new function by pulling the link-property specific parts out of
the more generic resolve-and-typecheck part.

The motivation for this function is that we want to allow devices to
provide an array of link properties; for that we will need to be able
to provide the expected type of the linked object in a different way
to the single-item link properties.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 include/qom/object.h | 17 +++++++++++++++++
 qom/object.c         | 41 +++++++++++++++++++++++------------------
 2 files changed, 40 insertions(+), 18 deletions(-)

diff --git a/include/qom/object.h b/include/qom/object.h
index 26df6137b9..797688f25e 100644
--- a/include/qom/object.h
+++ b/include/qom/object.h
@@ -1750,6 +1750,23 @@ ObjectProperty *object_class_property_add_link(ObjectClass *oc,
                                             Object *val, Error **errp),
                               ObjectPropertyLinkFlags flags);
 
+/**
+ * object_resolve_and_typecheck:
+ * @path: path to look up
+ * @name: name of property we are resolving for (used only in error messages)
+ * @target_type: QOM type we expect @path to resolve to
+ * @errp: error
+ *
+ * Look up the object at @path and return it. If it does not have the
+ * correct type @target_type, return NULL and set @errp.
+ *
+ * This is similar to object_resolve_path_type(), but it insists on a
+ * non-ambiguous path and it produces error messages that are
+ * specialised to the use case of setting a link property on an object.
+ */
+Object *object_resolve_and_typecheck(const char *path, const char *name,
+                                     const char *target_type, Error **errp);
+
 /**
  * object_property_add_str:
  * @obj: the object to add a property to
diff --git a/qom/object.c b/qom/object.c
index ff8ede8a32..046b15c7f4 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -1895,26 +1895,12 @@ static void object_get_link_property(Object *obj, Visitor *v,
     }
 }
 
-/*
- * object_resolve_link:
- *
- * Lookup an object and ensure its type matches the link property type.  This
- * is similar to object_resolve_path() except type verification against the
- * link property is performed.
- *
- * Returns: The matched object or NULL on path lookup failures.
- */
-static Object *object_resolve_link(Object *obj, const char *name,
-                                   const char *path, Error **errp)
+Object *object_resolve_and_typecheck(const char *path, const char *name,
+                                     const char *target_type, Error **errp)
 {
-    const char *type;
-    char *target_type;
     bool ambiguous = false;
     Object *target;
 
-    /* Go from link<FOO> to FOO.  */
-    type = object_property_get_type(obj, name, NULL);
-    target_type = g_strndup(&type[5], strlen(type) - 6);
     target = object_resolve_path_type(path, target_type, &ambiguous);
 
     if (ambiguous) {
@@ -1931,11 +1917,30 @@ static Object *object_resolve_link(Object *obj, const char *name,
         }
         target = NULL;
     }
-    g_free(target_type);
-
     return target;
 }
 
+/*
+ * object_resolve_link:
+ *
+ * Lookup an object and ensure its type matches the link property type.  This
+ * is similar to object_resolve_path() except type verification against the
+ * link property is performed.
+ *
+ * Returns: The matched object or NULL on path lookup failures.
+ */
+static Object *object_resolve_link(Object *obj, const char *name,
+                                   const char *path, Error **errp)
+{
+    const char *type;
+    g_autofree char *target_type = NULL;
+
+    /* Go from link<FOO> to FOO.  */
+    type = object_property_get_type(obj, name, NULL);
+    target_type = g_strndup(&type[5], strlen(type) - 6);
+    return object_resolve_and_typecheck(path, name, target_type, errp);
+}
+
 static void object_set_link_property(Object *obj, Visitor *v,
                                      const char *name, void *opaque,
                                      Error **errp)
-- 
2.43.0