qom: use object_resolve_path_type for links

This allows to restrict partial matches to objects of the expected
type.  It will let people use bare names to reference drives
even though their name might be the same as a device's (e.g.
-drive id=hd0,if=none,... -device ...,drive=hd0,id=hd0).

As a useful byproduct, this fixes a problem with links of interface
type.  When a link property's type is an interface, the code expects
the implementation object (not the parent object) to be stored in the
variable.  The parent object does not contain the right vtable.

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

qerror.c

diff --git a/qerror.c b/qerror.c
index 3d179c8..8e6efaf 100644
--- a/qerror.c
+++ b/qerror.c
@@ -48,6 +48,10 @@
         .desc      = "Could not add client",
     },
     {
+        .error_fmt = QERR_AMBIGUOUS_PATH,
+        .desc      = "Path '%(path)' does not uniquely identify a %(object)"
+    },
+    {
         .error_fmt = QERR_BAD_BUS_FOR_DEVICE,
         .desc      = "Device '%(device)' can't go on a %(bad_bus_type) bus",
     },

qerror.h

diff --git a/qerror.h b/qerror.h
index 8c36ddb..e8718bf 100644
--- a/qerror.h
+++ b/qerror.h
@@ -54,6 +54,9 @@
 #define QERR_ADD_CLIENT_FAILED \
     "{ 'class': 'AddClientFailed', 'data': {} }"
 
+#define QERR_AMBIGUOUS_PATH \
+    "{ 'class': 'AmbiguousPath', 'data': { 'path': %s } }"
+
 #define QERR_BAD_BUS_FOR_DEVICE \
     "{ 'class': 'BadBusForDevice', 'data': { 'device': %s, 'bad_bus_type': %s } }"
 

qom/object.c

diff --git a/qom/object.c b/qom/object.c
index ea0efc6..2bd15b8 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -840,6 +840,7 @@
     bool ambiguous = false;
     const char *type;
     char *path;
+    gchar *target_type;
 
     type = object_property_get_type(obj, name, NULL);
 
@@ -847,28 +848,30 @@
 
     if (*child) {
         object_unref(*child);
+        *child = NULL;
     }
 
     if (strcmp(path, "") != 0) {
         Object *target;
 
-        target = object_resolve_path(path, &ambiguous);
-        if (target) {
-            /* Go from link<FOO> to FOO.  */
-            gchar *target_type = g_strndup(&type[5], strlen(type) - 6);
-            if (object_dynamic_cast(target, target_type)) {
-                object_ref(target);
-                *child = target;
-            } else {
-                error_set(errp, QERR_INVALID_PARAMETER_TYPE, name, type);
-            }
+        /* Go from link<FOO> to FOO.  */
+        target_type = g_strndup(&type[5], strlen(type) - 6);
+        target = object_resolve_path_type(path, target_type, &ambiguous);
 
-            g_free(target_type);
+        if (ambiguous) {
+            error_set(errp, QERR_AMBIGUOUS_PATH, path);
+        } else if (target) {
+            object_ref(target);
+            *child = target;
         } else {
-            error_set(errp, QERR_DEVICE_NOT_FOUND, path);
+            target = object_resolve_path(path, &ambiguous);
+            if (target || ambiguous) {
+                error_set(errp, QERR_INVALID_PARAMETER_TYPE, name, target_type);
+            } else {
+                error_set(errp, QERR_DEVICE_NOT_FOUND, path);
+            }
         }
-    } else {
-        *child = NULL;
+        g_free(target_type);
     }
 
     g_free(path);