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>

block/crypto.c

@@ -196,7 +196,6 @@ block_crypto_open_opts_init(QCryptoBlockFormat format,
     OptsVisitor *ov;
     QCryptoBlockOpenOptions *ret = NULL;
     Error *local_err = NULL;
-    Error *end_err = NULL;
 
     ret = g_new0(QCryptoBlockOpenOptions, 1);
     ret->format = format;
@@ -219,9 +218,11 @@ block_crypto_open_opts_init(QCryptoBlockFormat format,
         error_setg(&local_err, "Unsupported block format %d", format);
         break;
     }
+    if (!local_err) {
+        visit_check_struct(opts_get_visitor(ov), &local_err);
+    }
 
-    visit_end_struct(opts_get_visitor(ov), &end_err);
-    error_propagate(&local_err, end_err);
+    visit_end_struct(opts_get_visitor(ov));
 
  out:
     if (local_err) {
@@ -242,7 +243,6 @@ block_crypto_create_opts_init(QCryptoBlockFormat format,
     OptsVisitor *ov;
     QCryptoBlockCreateOptions *ret = NULL;
     Error *local_err = NULL;
-    Error *end_err = NULL;
 
     ret = g_new0(QCryptoBlockCreateOptions, 1);
     ret->format = format;
@@ -265,9 +265,11 @@ block_crypto_create_opts_init(QCryptoBlockFormat format,
         error_setg(&local_err, "Unsupported block format %d", format);
         break;
     }
+    if (!local_err) {
+        visit_check_struct(opts_get_visitor(ov), &local_err);
+    }
 
-    visit_end_struct(opts_get_visitor(ov), &end_err);
-    error_propagate(&local_err, end_err);
+    visit_end_struct(opts_get_visitor(ov));
 
  out:
     if (local_err) {

docs/qapi-code-gen.txt

@@ -899,10 +899,12 @@ Example:
             goto out_obj;
         }
         visit_type_UserDefOne_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:
         error_propagate(errp, err);
     }
@@ -1007,7 +1009,10 @@ Example:
             goto out;
         }
         visit_type_UserDefOneList(v, "arg1", &arg1, &err);
-        visit_end_struct(v, err ? NULL : &err);
+        if (!err) {
+            visit_check_struct(v, &err);
+        }
+        visit_end_struct(v);
         if (err) {
             goto out;
         }
@@ -1026,7 +1031,7 @@ Example:
         v = qapi_dealloc_get_visitor(qdv);
         visit_start_struct(v, NULL, NULL, 0, NULL);
         visit_type_UserDefOneList(v, "arg1", &arg1, NULL);
-        visit_end_struct(v, NULL);
+        visit_end_struct(v);
         qapi_dealloc_visitor_cleanup(qdv);
     }
 

hw/ppc/spapr_drc.c

@@ -297,7 +297,8 @@ static void prop_get_fdt(Object *obj, Visitor *v, const char *name,
         case FDT_END_NODE:
             /* shouldn't ever see an FDT_END_NODE before FDT_BEGIN_NODE */
             g_assert(fdt_depth > 0);
-            visit_end_struct(v, &err);
+            visit_check_struct(v, &err);
+            visit_end_struct(v);
             if (err) {
                 error_propagate(errp, err);
                 return;

hw/virtio/virtio-balloon.c

@@ -138,17 +138,18 @@ static void balloon_stats_get_all(Object *obj, Visitor *v, const char *name,
     for (i = 0; i < VIRTIO_BALLOON_S_NR; i++) {
         visit_type_uint64(v, balloon_stat_names[i], &s->stats[i], &err);
         if (err) {
-            break;
+            goto out_nested;
         }
     }
-    error_propagate(errp, err);
-    err = NULL;
-    visit_end_struct(v, &err);
+    visit_check_struct(v, &err);
+out_nested:
+    visit_end_struct(v);
 
+    if (!err) {
+        visit_check_struct(v, &err);
+    }
 out_end:
-    error_propagate(errp, err);
-    err = NULL;
-    visit_end_struct(v, &err);
+    visit_end_struct(v);
 out:
     error_propagate(errp, err);
 }

include/qapi/visitor-impl.h

@@ -43,8 +43,11 @@ struct Visitor
     void (*start_struct)(Visitor *v, const char *name, void **obj,
                          size_t size, Error **errp);
 
+    /* Optional; intended for input visitors */
+    void (*check_struct)(Visitor *v, Error **errp);
+
     /* Must be set to visit structs */
-    void (*end_struct)(Visitor *v, Error **errp);
+    void (*end_struct)(Visitor *v);
 
     /* Must be set */
     void (*start_list)(Visitor *v, const char *name, Error **errp);

include/qapi/visitor.h

@@ -192,10 +192,11 @@
  *  }
  * outlist:
  *  visit_end_list(v);
+ *  if (!err) {
+ *      visit_check_struct(v, &err);
+ *  }
  * outobj:
- *  error_propagate(errp, err);
- *  err = NULL;
- *  visit_end_struct(v, &err);
+ *  visit_end_struct(v);
  * out:
  *  error_propagate(errp, err);
  *  ...clean up v...
@@ -249,17 +250,27 @@ void visit_start_struct(Visitor *v, const char *name, void **obj,
                         size_t size, Error **errp);
 
 /*
- * Complete an object visit started earlier.
+ * Prepare for completing an object visit.
  *
  * @errp obeys typical error usage, and reports failures such as
  * unparsed keys remaining in the input stream.
  *
+ * Should be called prior to visit_end_struct() if all other
+ * intermediate visit steps were successful, to allow the visitor one
+ * last chance to report errors.  May be skipped on a cleanup path,
+ * where there is no need to check for further errors.
+ */
+void visit_check_struct(Visitor *v, Error **errp);
+
+/*
+ * Complete an object visit started earlier.
+ *
  * Must be called after any successful use of visit_start_struct(),
  * even if intermediate processing was skipped due to errors, to allow
  * the backend to release any resources.  Destroying the visitor early
  * behaves as if this was implicitly called.
  */
-void visit_end_struct(Visitor *v, Error **errp);
+void visit_end_struct(Visitor *v);
 
 
 /*** Visiting lists ***/

qapi/opts-visitor.c

@@ -159,13 +159,13 @@ opts_start_struct(Visitor *v, const char *name, void **obj,
 
 
 static void
-opts_end_struct(Visitor *v, Error **errp)
+opts_check_struct(Visitor *v, Error **errp)
 {
     OptsVisitor *ov = to_ov(v);
     GHashTableIter iter;
     GQueue *any;
 
-    if (--ov->depth > 0) {
+    if (ov->depth > 0) {
         return;
     }
 
@@ -177,6 +177,18 @@ opts_end_struct(Visitor *v, Error **errp)
         first = g_queue_peek_head(any);
         error_setg(errp, QERR_INVALID_PARAMETER, first->name);
     }
+}
+
+
+static void
+opts_end_struct(Visitor *v)
+{
+    OptsVisitor *ov = to_ov(v);
+
+    if (--ov->depth > 0) {
+        return;
+    }
+
     g_hash_table_destroy(ov->unprocessed_opts);
     ov->unprocessed_opts = NULL;
     if (ov->fake_id_opt) {
@@ -516,6 +528,7 @@ opts_visitor_new(const QemuOpts *opts)
     ov->visitor.type = VISITOR_INPUT;
 
     ov->visitor.start_struct = &opts_start_struct;
+    ov->visitor.check_struct = &opts_check_struct;
     ov->visitor.end_struct   = &opts_end_struct;
 
     ov->visitor.start_list = &opts_start_list;

qapi/qapi-dealloc-visitor.c

@@ -67,7 +67,7 @@ static void qapi_dealloc_start_struct(Visitor *v, const char *name, void **obj,
     qapi_dealloc_push(qov, obj);
 }
 
-static void qapi_dealloc_end_struct(Visitor *v, Error **errp)
+static void qapi_dealloc_end_struct(Visitor *v)
 {
     QapiDeallocVisitor *qov = to_qov(v);
     void **obj = qapi_dealloc_pop(qov);

qapi/qapi-visit-core.c

@@ -36,9 +36,16 @@ void visit_start_struct(Visitor *v, const char *name, void **obj,
     error_propagate(errp, err);
 }
 
-void visit_end_struct(Visitor *v, Error **errp)
+void visit_check_struct(Visitor *v, Error **errp)
 {
-    v->end_struct(v, errp);
+    if (v->check_struct) {
+        v->check_struct(v, errp);
+    }
+}
+
+void visit_end_struct(Visitor *v)
+{
+    v->end_struct(v);
 }
 
 void visit_start_list(Visitor *v, const char *name, Error **errp)

qapi/qmp-input-visitor.c

@@ -125,9 +125,11 @@ static void qmp_input_push(QmpInputVisitor *qiv, QObject *obj, Error **errp)
 }
 
 
-static void qmp_input_pop(QmpInputVisitor *qiv, Error **errp)
+static void qmp_input_check_struct(Visitor *v, Error **errp)
 {
+    QmpInputVisitor *qiv = to_qiv(v);
     StackObject *tos = &qiv->stack[qiv->nb_stack - 1];
+
     assert(qiv->nb_stack > 0);
 
     if (qiv->strict) {
@@ -140,6 +142,20 @@ static void qmp_input_pop(QmpInputVisitor *qiv, Error **errp)
             if (g_hash_table_iter_next(&iter, (void **)&key, NULL)) {
                 error_setg(errp, QERR_QMP_EXTRA_MEMBER, key);
             }
+        }
+    }
+}
+
+static void qmp_input_pop(Visitor *v)
+{
+    QmpInputVisitor *qiv = to_qiv(v);
+    StackObject *tos = &qiv->stack[qiv->nb_stack - 1];
+
+    assert(qiv->nb_stack > 0);
+
+    if (qiv->strict) {
+        GHashTable * const top_ht = qiv->stack[qiv->nb_stack - 1].h;
+        if (top_ht) {
             g_hash_table_unref(top_ht);
         }
         tos->h = NULL;
@@ -175,12 +191,6 @@ static void qmp_input_start_struct(Visitor *v, const char *name, void **obj,
     }
 }
 
-static void qmp_input_end_struct(Visitor *v, Error **errp)
-{
-    QmpInputVisitor *qiv = to_qiv(v);
-
-    qmp_input_pop(qiv, errp);
-}
 
 static void qmp_input_start_list(Visitor *v, const char *name, Error **errp)
 {
@@ -218,12 +228,6 @@ static GenericList *qmp_input_next_list(Visitor *v, GenericList **list,
     return entry;
 }
 
-static void qmp_input_end_list(Visitor *v)
-{
-    QmpInputVisitor *qiv = to_qiv(v);
-
-    qmp_input_pop(qiv, &error_abort);
-}
 
 static void qmp_input_start_alternate(Visitor *v, const char *name,
                                       GenericAlternate **obj, size_t size,
@@ -383,10 +387,11 @@ QmpInputVisitor *qmp_input_visitor_new(QObject *obj, bool strict)
 
     v->visitor.type = VISITOR_INPUT;
     v->visitor.start_struct = qmp_input_start_struct;
-    v->visitor.end_struct = qmp_input_end_struct;
+    v->visitor.check_struct = qmp_input_check_struct;
+    v->visitor.end_struct = qmp_input_pop;
     v->visitor.start_list = qmp_input_start_list;
     v->visitor.next_list = qmp_input_next_list;
-    v->visitor.end_list = qmp_input_end_list;
+    v->visitor.end_list = qmp_input_pop;
     v->visitor.start_alternate = qmp_input_start_alternate;
     v->visitor.type_int64 = qmp_input_type_int64;
     v->visitor.type_uint64 = qmp_input_type_uint64;

qapi/qmp-output-visitor.c

@@ -111,7 +111,7 @@ static void qmp_output_start_struct(Visitor *v, const char *name, void **obj,
     qmp_output_push(qov, dict);
 }
 
-static void qmp_output_end_struct(Visitor *v, Error **errp)
+static void qmp_output_end_struct(Visitor *v)
 {
     QmpOutputVisitor *qov = to_qov(v);
     QObject *value = qmp_output_pop(qov);

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);
 

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;
     }

scripts/qapi-commands.py

@@ -126,7 +126,10 @@ def gen_marshal(name, arg_type, ret_type):
         goto out;
     }
     visit_type_%(c_name)s_members(v, &arg, &err);
-    visit_end_struct(v, err ? NULL : &err);
+    if (!err) {
+        visit_check_struct(v, &err);
+    }
+    visit_end_struct(v);
     if (err) {
         goto out;
     }
@@ -157,7 +160,7 @@ def gen_marshal(name, arg_type, ret_type):
     v = qapi_dealloc_get_visitor(qdv);
     visit_start_struct(v, NULL, NULL, 0, NULL);
     visit_type_%(c_name)s_members(v, &arg, NULL);
-    visit_end_struct(v, NULL);
+    visit_end_struct(v);
     qapi_dealloc_visitor_cleanup(qdv);
 ''',
                      c_name=arg_type.c_name())

scripts/qapi-event.py

@@ -98,7 +98,10 @@ def gen_event_send(name, arg_type):
         goto out;
     }
     visit_type_%(c_name)s_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;
     }

scripts/qapi-visit.py

@@ -186,9 +186,10 @@ def gen_visit_alternate(name, variants):
             break;
         }
         visit_type_%(c_type)s_members(v, &(*obj)->u.%(c_name)s, &err);
-        error_propagate(errp, err);
-        err = NULL;
-        visit_end_struct(v, &err);
+        if (!err) {
+            visit_check_struct(v, &err);
+        }
+        visit_end_struct(v);
 ''',
                          c_type=var.type.c_name(),
                          c_name=c_name(var.name))
@@ -236,10 +237,12 @@ def gen_visit_object(name, base, members, variants):
         goto out_obj;
     }
     visit_type_%(c_name)s_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:
     error_propagate(errp, err);
 }

tests/test-qmp-input-visitor.c

@@ -303,7 +303,8 @@ static void test_visitor_in_null(TestInputVisitorData *data,
     error_free_or_abort(&err);
     visit_type_null(v, "b", &err);
     error_free_or_abort(&err);
-    visit_end_struct(v, &error_abort);
+    visit_check_struct(v, &error_abort);
+    visit_end_struct(v);
 }
 
 static void test_visitor_in_union_flat(TestInputVisitorData *data,

tests/test-qmp-output-visitor.c

@@ -498,7 +498,8 @@ static void test_visitor_out_null(TestOutputVisitorData *data,
 
     visit_start_struct(data->ov, NULL, NULL, 0, &error_abort);
     visit_type_null(data->ov, "a", &error_abort);
-    visit_end_struct(data->ov, &error_abort);
+    visit_check_struct(data->ov, &error_abort);
+    visit_end_struct(data->ov);
     arg = qmp_output_get_qobject(data->qov);
     g_assert(qobject_type(arg) == QTYPE_QDICT);
     qdict = qobject_to_qdict(arg);