qapi: Split visit_end_struct() into pieces

As mentioned in previous patches, we want to call visit_end_struct()
functions unconditionally, so that visitors can release resources
tied up since the matching visit_start_struct() without also having
to worry about error priority if more than one error occurs.

Even though error_propagate() can be safely used to ignore a second
error during cleanup caused by a first error, it is simpler if the
cleanup cannot set an error.  So, split out the error checking
portion (basically, input visitors checking for unvisited keys) into
a new function visit_check_struct(), which can be safely skipped if
any earlier errors are encountered, and leave the cleanup portion
(which never fails, but must be called unconditionally if
visit_start_struct() succeeded) in visit_end_struct().

Generated code in qapi-visit.c has diffs resembling:

|@@ -59,10 +59,12 @@ void visit_type_ACPIOSTInfo(Visitor *v,
|         goto out_obj;
|     }
|     visit_type_ACPIOSTInfo_members(v, obj, &err);
|-    error_propagate(errp, err);
|-    err = NULL;
|+    if (err) {
|+        goto out_obj;
|+    }
|+    visit_check_struct(v, &err);
| out_obj:
|-    visit_end_struct(v, &err);
|+    visit_end_struct(v);
| out:

and in qapi-event.c:

@@ -47,7 +47,10 @@ void qapi_event_send_acpi_device_ost(ACP
|         goto out;
|     }
|     visit_type_q_obj_ACPI_DEVICE_OST_arg_members(v, &param, &err);
|-    visit_end_struct(v, err ? NULL : &err);
|+    if (!err) {
|+        visit_check_struct(v, &err);
|+    }
|+    visit_end_struct(v);
|     if (err) {
|         goto out;

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1461879932-9020-20-git-send-email-eblake@redhat.com>
[Conflict with a doc fixup resolved]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

2 files changed, 12 insertions, 16 deletions

diff --git a/qom/object.c b/qom/object.c
index 8e6e68d..3bc8a00 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -2036,10 +2036,9 @@ static void property_get_tm(Object *obj, Visitor *v, const char *name,
     if (err) {
         goto out_end;
     }
+    visit_check_struct(v, &err);
 out_end:
-    error_propagate(errp, err);
-    err = NULL;
-    visit_end_struct(v, errp);
+    visit_end_struct(v);
 out:
     error_propagate(errp, err);
 
diff --git a/qom/object_interfaces.c b/qom/object_interfaces.c
index cad5542..51e62e2 100644
--- a/qom/object_interfaces.c
+++ b/qom/object_interfaces.c
@@ -42,7 +42,7 @@ Object *user_creatable_add(const QDict *qdict,
     char *type = NULL;
     char *id = NULL;
     Object *obj = NULL;
-    Error *local_err = NULL, *end_err = NULL;
+    Error *local_err = NULL;
     QDict *pdict;
 
     pdict = qdict_clone_shallow(qdict);
@@ -63,21 +63,15 @@ Object *user_creatable_add(const QDict *qdict,
     if (local_err) {
         goto out_visit;
     }
-
-    obj = user_creatable_add_type(type, id, pdict, v, &local_err);
+    visit_check_struct(v, &local_err);
     if (local_err) {
         goto out_visit;
     }
 
- out_visit:
-    visit_end_struct(v, &end_err);
-    if (end_err) {
-        error_propagate(&local_err, end_err);
-        if (obj) {
-            user_creatable_del(id, NULL);
-        }
-        goto out;
-    }
+    obj = user_creatable_add_type(type, id, pdict, v, &local_err);
+
+out_visit:
+    visit_end_struct(v);
 
 out:
     QDECREF(pdict);
@@ -130,7 +124,10 @@ Object *user_creatable_add_type(const char *type, const char *id,
             break;
         }
     }
-    visit_end_struct(v, local_err ? NULL : &local_err);
+    if (!local_err) {
+        visit_check_struct(v, &local_err);
+    }
+    visit_end_struct(v);
     if (local_err) {
         goto out;
     }