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[Qemu-devel] [PATCH v8 20/26] qapi: Make output visitor return qnull() i
From: |
Markus Armbruster |
Subject: |
[Qemu-devel] [PATCH v8 20/26] qapi: Make output visitor return qnull() instead of NULL |
Date: |
Wed, 16 Sep 2015 13:06:23 +0200 |
Before commit 1d10b44, it crashed. Since then, it returns NULL, with
a FIXME comment. The FIXME is valid: code that assumes QObject *
can't be null exists. I'm not aware of a way to feed this problematic
return value to code that actually chokes on null in the current code,
but the next few commits will create one, failing "make check".
Commit 481b002 solved a very similar problem by introducing a special
null QObject. Using this special null QObject is clearly the right
way to resolve this FIXME, so do that, and update the test
accordingly.
However, the patch isn't quite right: it messes up the reference
counting. After about SIZE_MAX visits, the reference counter
overflows, failing the assertion in qnull_destroy_obj(). Because
that's many orders of magnitude more visits of nulls than we expect,
we take this patch despite its flaws, to get the QMP introspection
stuff in without further delay. We'll want to fix it for real before
the release.
Signed-off-by: Markus Armbruster <address@hidden>
Reviewed-by: Eric Blake <address@hidden>
Reviewed-by: Daniel P. Berrange <address@hidden>
---
qapi/qmp-output-visitor.c | 8 ++++++--
tests/test-qmp-output-visitor.c | 3 ++-
2 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/qapi/qmp-output-visitor.c b/qapi/qmp-output-visitor.c
index efc19d5..8dce087 100644
--- a/qapi/qmp-output-visitor.c
+++ b/qapi/qmp-output-visitor.c
@@ -66,9 +66,13 @@ static QObject *qmp_output_first(QmpOutputVisitor *qov)
{
QStackEntry *e = QTAILQ_LAST(&qov->stack, QStack);
- /* FIXME - find a better way to deal with NULL values */
+ /*
+ * FIXME Wrong, because qmp_output_get_qobject() will increment
+ * the refcnt *again*. We need to think through how visitors
+ * handle null.
+ */
if (!e) {
- return NULL;
+ return qnull();
}
return e->value;
diff --git a/tests/test-qmp-output-visitor.c b/tests/test-qmp-output-visitor.c
index 338ada0..a48ae72 100644
--- a/tests/test-qmp-output-visitor.c
+++ b/tests/test-qmp-output-visitor.c
@@ -485,7 +485,8 @@ static void test_visitor_out_empty(TestOutputVisitorData
*data,
QObject *arg;
arg = qmp_output_get_qobject(data->qov);
- g_assert(!arg);
+ g_assert(qobject_type(arg) == QTYPE_QNULL);
+ qobject_decref(arg);
}
static void init_native_list(UserDefNativeListUnion *cvalue)
--
2.4.3
- [Qemu-devel] [PATCH v8 06/26] qapi-types: Convert to QAPISchemaVisitor, fixing flat unions, (continued)
- [Qemu-devel] [PATCH v8 06/26] qapi-types: Convert to QAPISchemaVisitor, fixing flat unions, Markus Armbruster, 2015/09/16
- [Qemu-devel] [PATCH v8 14/26] qapi-visit: Rearrange code a bit, Markus Armbruster, 2015/09/16
- [Qemu-devel] [PATCH v8 07/26] qapi-visit: Convert to QAPISchemaVisitor, fixing bugs, Markus Armbruster, 2015/09/16
- [Qemu-devel] [PATCH v8 03/26] qapi: QAPISchema code generation helper methods, Markus Armbruster, 2015/09/16
- [Qemu-devel] [PATCH v8 20/26] qapi: Make output visitor return qnull() instead of NULL,
Markus Armbruster <=
- [Qemu-devel] [PATCH v8 17/26] qapi: De-duplicate parameter list generation, Markus Armbruster, 2015/09/16
- [Qemu-devel] [PATCH v8 18/26] qapi-commands: De-duplicate output marshaling functions, Markus Armbruster, 2015/09/16
- [Qemu-devel] [PATCH v8 22/26] qom: Don't use 'gen': false for qom-get, qom-set, object-add, Markus Armbruster, 2015/09/16
- [Qemu-devel] [PATCH v8 09/26] qapi: De-duplicate enum code generation, Markus Armbruster, 2015/09/16
- [Qemu-devel] [PATCH v8 05/26] tests/qapi-schema: Convert test harness to QAPISchemaVisitor, Markus Armbruster, 2015/09/16