[PATCH v2 0/2] Avoid abort on QMP attempt to add an object with duplicate id

[PATCH v2 0/2] Avoid abort on QMP attempt to add an object with duplicate id

[Eric Auger]

Attempting to add an object through QMP with an id that is
already used leads to a qemu abort. This is a regression since
d2623129a7de ("qom: Drop parameter @errp of object_property_add()
& friends").

The first patch fixes the issue and the second patch adds a test
to check the error is gracefully returned to the QMP client.

Best Regards

Eric

This series can be found at:
https://github.com/eauger/qemu/tree/qom-graceful-v2

History:
- v1 -> v2:
  - use the try terminology.
  - turn object_property_try_add() into a non-static function
  - add the test


Eric Auger (2):
  qom: Introduce object_property_try_add_child()
  tests/qmp-cmd-test: Add qmp/object-add-duplicate-id

 include/qom/object.h       | 24 ++++++++++++++++++++++--
 qom/object.c               | 22 +++++++++++++++++-----
 qom/object_interfaces.c    |  7 +++++--
 tests/qtest/qmp-cmd-test.c | 18 ++++++++++++++++++
 4 files changed, 62 insertions(+), 9 deletions(-)

-- 
2.20.1

[PATCH v2 1/2] qom: Introduce object_property_try_add_child()

[Eric Auger]

object_property_add() does not allow object_property_try_add()
to gracefully fail as &error_abort is passed as an error handle.

However such failure can easily be triggered from the QMP shell when,
for instance, one attempts to create an object with an id that already
exists. This is achived from the following call path:

user_creatable_add_type -> object_property_add_child ->
object_property_add

For instance, call twice:
object-add qom-type=memory-backend-ram id=mem1 props.size=1073741824
and QEMU aborts.

This behavior is undesired as a user/management application mistake
in reusing a property ID shouldn't result in loss of the VM and live
data within.

This patch introduces a new function, object_property_try_add_child()
which takes an error handle and turn object_property_try_add() into
a non-static one.

Now the call path becomes:

user_creatable_add_type -> object_property_try_add_child ->
object_property_try_add

and the error is returned gracefully to the QMP client.

(QEMU) object-add qom-type=memory-backend-ram id=mem2  props.size=4294967296
{"return": {}}
(QEMU) object-add qom-type=memory-backend-ram id=mem2  props.size=4294967296
{"error": {"class": "GenericError", "desc": "attempt to add duplicate property
'mem2' to object (type 'container')"}}

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Fixes: d2623129a7de ("qom: Drop parameter @errp of object_property_add() & friends")
---
 include/qom/object.h    | 24 ++++++++++++++++++++++--
 qom/object.c            | 22 +++++++++++++++++-----
 qom/object_interfaces.c |  7 +++++--
 3 files changed, 44 insertions(+), 9 deletions(-)

diff --git a/include/qom/object.h b/include/qom/object.h
index 94a61ccc3f..91cf058d86 100644
--- a/include/qom/object.h
+++ b/include/qom/object.h
@@ -1039,7 +1039,7 @@ Object *object_ref(Object *obj);
 void object_unref(Object *obj);
 
 /**
- * object_property_add:
+ * object_property_try_add:
  * @obj: the object to add a property to
  * @name: the name of the property.  This can contain any character except for
  *  a forward slash.  In general, you should use hyphens '-' instead of
@@ -1056,10 +1056,22 @@ void object_unref(Object *obj);
  *   meant to allow a property to free its opaque upon object
  *   destruction.  This may be NULL.
  * @opaque: an opaque pointer to pass to the callbacks for the property
+ * @errp: error handle
  *
  * Returns: The #ObjectProperty; this can be used to set the @resolve
  * callback for child and link properties.
  */
+ObjectProperty *object_property_try_add(Object *obj, const char *name,
+                                        const char *type,
+                                        ObjectPropertyAccessor *get,
+                                        ObjectPropertyAccessor *set,
+                                        ObjectPropertyRelease *release,
+                                        void *opaque, Error **errp);
+
+/**
+ * object_property_add: same as object_property_try_add with
+ * errp hardcoded to &error_abort
+ */
 ObjectProperty *object_property_add(Object *obj, const char *name,
                                     const char *type,
                                     ObjectPropertyAccessor *get,
@@ -1495,10 +1507,11 @@ Object *object_resolve_path_type(const char *path, const char *typename,
 Object *object_resolve_path_component(Object *parent, const char *part);
 
 /**
- * object_property_add_child:
+ * object_property_try_add_child:
  * @obj: the object to add a property to
  * @name: the name of the property
  * @child: the child object
+ * @errp: error handle
  *
  * Child properties form the composition tree.  All objects need to be a child
  * of another object.  Objects can only be a child of one object.
@@ -1512,6 +1525,13 @@ Object *object_resolve_path_component(Object *parent, const char *part);
  *
  * Returns: The newly added property on success, or %NULL on failure.
  */
+ObjectProperty *object_property_try_add_child(Object *obj, const char *name,
+                                              Object *child, Error **errp);
+
+/**
+ * object_property_add_child: same as object_property_try_add_child with
+ * errp hardcoded to &error_abort
+ */
 ObjectProperty *object_property_add_child(Object *obj, const char *name,
                                           Object *child);
 
diff --git a/qom/object.c b/qom/object.c
index 6ece96bc2b..96e85cdaf7 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -1132,7 +1132,7 @@ void object_unref(Object *obj)
     }
 }
 
-static ObjectProperty *
+ObjectProperty *
 object_property_try_add(Object *obj, const char *name, const char *type,
                         ObjectPropertyAccessor *get,
                         ObjectPropertyAccessor *set,
@@ -1651,8 +1651,8 @@ static void object_finalize_child_property(Object *obj, const char *name,
 }
 
 ObjectProperty *
-object_property_add_child(Object *obj, const char *name,
-                          Object *child)
+object_property_try_add_child(Object *obj, const char *name,
+                              Object *child, Error **errp)
 {
     g_autofree char *type = NULL;
     ObjectProperty *op;
@@ -1661,14 +1661,26 @@ object_property_add_child(Object *obj, const char *name,
 
     type = g_strdup_printf("child<%s>", object_get_typename(child));
 
-    op = object_property_add(obj, name, type, object_get_child_property, NULL,
-                             object_finalize_child_property, child);
+    op = object_property_try_add(obj, name, type, object_get_child_property,
+                                 NULL, object_finalize_child_property,
+                                 child, errp);
+    if (!op) {
+        goto out;
+    }
     op->resolve = object_resolve_child_property;
+out:
     object_ref(child);
     child->parent = obj;
     return op;
 }
 
+ObjectProperty *
+object_property_add_child(Object *obj, const char *name,
+                          Object *child)
+{
+    return object_property_try_add_child(obj, name, child, &error_abort);
+}
+
 void object_property_allow_set_link(const Object *obj, const char *name,
                                     Object *val, Error **errp)
 {
diff --git a/qom/object_interfaces.c b/qom/object_interfaces.c
index 7e26f86fa6..1e05e41d2f 100644
--- a/qom/object_interfaces.c
+++ b/qom/object_interfaces.c
@@ -82,8 +82,11 @@ Object *user_creatable_add_type(const char *type, const char *id,
     }
 
     if (id != NULL) {
-        object_property_add_child(object_get_objects_root(),
-                                  id, obj);
+        object_property_try_add_child(object_get_objects_root(),
+                                      id, obj, &local_err);
+        if (local_err) {
+            goto out;
+        }
     }
 
     user_creatable_complete(USER_CREATABLE(obj), &local_err);
-- 
2.20.1

[PATCH v2 2/2] tests/qmp-cmd-test: Add qmp/object-add-duplicate-id

[Eric Auger]

This new test checks that attempting to create an object
with an existing ID gracefully fails.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
---
 tests/qtest/qmp-cmd-test.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/tests/qtest/qmp-cmd-test.c b/tests/qtest/qmp-cmd-test.c
index 9f5228cd99..9510051c35 100644
--- a/tests/qtest/qmp-cmd-test.c
+++ b/tests/qtest/qmp-cmd-test.c
@@ -213,6 +213,22 @@ static void test_object_add_without_props(void)
     qtest_quit(qts);
 }
 
+static void test_object_add_with_duplicate_id(void)
+{
+    QTestState *qts;
+    QDict *resp;
+
+    qts = qtest_init(common_args);
+    resp = qtest_qmp(qts, "{'execute': 'object-add', 'arguments':"
+                    " {'qom-type': 'memory-backend-ram', 'id': 'ram1', 'props': {'size': 4294967296 } } }");
+    g_assert_nonnull(resp);
+    g_assert(qdict_haskey(resp, "return"));
+    resp = qtest_qmp(qts, "{'execute': 'object-add', 'arguments':"
+                    " {'qom-type': 'memory-backend-ram', 'id': 'ram1', 'props': {'size': 4294967296 } } }");
+    qmp_assert_error_class(resp, "GenericError");
+    qtest_quit(qts);
+}
+
 int main(int argc, char *argv[])
 {
     QmpSchema schema;
@@ -225,6 +241,8 @@ int main(int argc, char *argv[])
 
     qtest_add_func("qmp/object-add-without-props",
                    test_object_add_without_props);
+    qtest_add_func("qmp/object-add-duplicate-id",
+                   test_object_add_with_duplicate_id);
     /* TODO: add coverage of generic object-add failure modes */
 
     ret = g_test_run();
-- 
2.20.1

Re: [PATCH v2 2/2] tests/qmp-cmd-test: Add qmp/object-add-duplicate-id

[Thomas Huth]

On 24/06/2020 14.43, Eric Auger wrote:
> This new test checks that attempting to create an object
> with an existing ID gracefully fails.
> 
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> ---
>   tests/qtest/qmp-cmd-test.c | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)

Acked-by: Thomas Huth <thuth@redhat.com>

Re: [PATCH v2 0/2] Avoid abort on QMP attempt to add an object with duplicate id

[no-reply]

Patchew URL: https://patchew.org/QEMU/20200624124301.7112-1-eric.auger@redhat.com/



Hi,

This series failed the docker-quick@centos7 build test. Please find the testing commands and
their output below. If you have Docker installed, you can probably reproduce it
locally.

=== TEST SCRIPT BEGIN ===
#!/bin/bash
make docker-image-centos7 V=1 NETWORK=1
time make docker-test-quick@centos7 SHOW_ENV=1 J=14 NETWORK=1
=== TEST SCRIPT END ===

  TEST    iotest-qcow2: 114
  TEST    iotest-qcow2: 117
**
ERROR:/tmp/qemu-test/src/tests/qtest/qmp-cmd-test.c:225:test_object_add_with_duplicate_id: assertion failed: (qdict_haskey(resp, "return"))
ERROR - Bail out! ERROR:/tmp/qemu-test/src/tests/qtest/qmp-cmd-test.c:225:test_object_add_with_duplicate_id: assertion failed: (qdict_haskey(resp, "return"))
make: *** [check-qtest-aarch64] Error 1
make: *** Waiting for unfinished jobs....
  TEST    iotest-qcow2: 120
  TEST    iotest-qcow2: 126
---
  TEST    check-qtest-x86_64: tests/qtest/qmp-test
  TEST    check-qtest-x86_64: tests/qtest/qmp-cmd-test
**
ERROR:/tmp/qemu-test/src/tests/qtest/qmp-cmd-test.c:225:test_object_add_with_duplicate_id: assertion failed: (qdict_haskey(resp, "return"))
ERROR - Bail out! ERROR:/tmp/qemu-test/src/tests/qtest/qmp-cmd-test.c:225:test_object_add_with_duplicate_id: assertion failed: (qdict_haskey(resp, "return"))
make: *** [check-qtest-x86_64] Error 1
  TEST    iotest-qcow2: 220
  TEST    iotest-qcow2: 226
  TEST    iotest-qcow2: 229
---
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['sudo', '-n', 'docker', 'run', '--label', 'com.qemu.instance.uuid=d6cb3d069c7a44ecbf5b02c17a39e884', '-u', '1003', '--security-opt', 'seccomp=unconfined', '--rm', '-e', 'TARGET_LIST=', '-e', 'EXTRA_CONFIGURE_OPTS=', '-e', 'V=', '-e', 'J=14', '-e', 'DEBUG=', '-e', 'SHOW_ENV=1', '-e', 'CCACHE_DIR=/var/tmp/ccache', '-v', '/home/patchew2/.cache/qemu-docker-ccache:/var/tmp/ccache:z', '-v', '/var/tmp/patchew-tester-tmp-litaiimt/src/docker-src.2020-06-24-09.18.47.9149:/var/tmp/qemu:z,ro', 'qemu:centos7', '/var/tmp/qemu/run', 'test-quick']' returned non-zero exit status 2.
filter=--filter=label=com.qemu.instance.uuid=d6cb3d069c7a44ecbf5b02c17a39e884
make[1]: *** [docker-run] Error 1
make[1]: Leaving directory `/var/tmp/patchew-tester-tmp-litaiimt/src'
make: *** [docker-run-test-quick@centos7] Error 2

real    16m25.200s
user    0m5.519s


The full log is available at
http://patchew.org/logs/20200624124301.7112-1-eric.auger@redhat.com/testing.docker-quick@centos7/?type=message.
---
Email generated automatically by Patchew [https://patchew.org/].
Please send your feedback to patchew-devel@redhat.com

Re: [PATCH v2 0/2] Avoid abort on QMP attempt to add an object with duplicate id

[Auger Eric]

Hi,

On 6/24/20 3:35 PM, no-reply@patchew.org wrote:
> Patchew URL: https://patchew.org/QEMU/20200624124301.7112-1-eric.auger@redhat.com/
> 
> 
> 
> Hi,
> 
> This series failed the docker-quick@centos7 build test. Please find the testing commands and
> their output below. If you have Docker installed, you can probably reproduce it
> locally.
> 
> === TEST SCRIPT BEGIN ===
> #!/bin/bash
> make docker-image-centos7 V=1 NETWORK=1
> time make docker-test-quick@centos7 SHOW_ENV=1 J=14 NETWORK=1
> === TEST SCRIPT END ===
> 
>   TEST    iotest-qcow2: 114
>   TEST    iotest-qcow2: 117
> **
> ERROR:/tmp/qemu-test/src/tests/qtest/qmp-cmd-test.c:225:test_object_add_with_duplicate_id: assertion failed: (qdict_haskey(resp, "return"))
> ERROR - Bail out! ERROR:/tmp/qemu-test/src/tests/qtest/qmp-cmd-test.c:225:test_object_add_with_duplicate_id: assertion failed: (qdict_haskey(resp, "return"))
> make: *** [check-qtest-aarch64] Error 1
> make: *** Waiting for unfinished jobs....
>   TEST    iotest-qcow2: 120
>   TEST    iotest-qcow2: 126
> ---
>   TEST    check-qtest-x86_64: tests/qtest/qmp-test
>   TEST    check-qtest-x86_64: tests/qtest/qmp-cmd-test
> **
> ERROR:/tmp/qemu-test/src/tests/qtest/qmp-cmd-test.c:225:test_object_add_with_duplicate_id: assertion failed: (qdict_haskey(resp, "return"))
> ERROR - Bail out! ERROR:/tmp/qemu-test/src/tests/qtest/qmp-cmd-test.c:225:test_object_add_with_duplicate_id: assertion failed: (qdict_haskey(resp, "return"))
> make: *** [check-qtest-x86_64] Error 1
>   TEST    iotest-qcow2: 220
>   TEST    iotest-qcow2: 226
>   TEST    iotest-qcow2: 229
> ---
>     raise CalledProcessError(retcode, cmd)
> subprocess.CalledProcessError: Command '['sudo', '-n', 'docker', 'run', '--label', 'com.qemu.instance.uuid=d6cb3d069c7a44ecbf5b02c17a39e884', '-u', '1003', '--security-opt', 'seccomp=unconfined', '--rm', '-e', 'TARGET_LIST=', '-e', 'EXTRA_CONFIGURE_OPTS=', '-e', 'V=', '-e', 'J=14', '-e', 'DEBUG=', '-e', 'SHOW_ENV=1', '-e', 'CCACHE_DIR=/var/tmp/ccache', '-v', '/home/patchew2/.cache/qemu-docker-ccache:/var/tmp/ccache:z', '-v', '/var/tmp/patchew-tester-tmp-litaiimt/src/docker-src.2020-06-24-09.18.47.9149:/var/tmp/qemu:z,ro', 'qemu:centos7', '/var/tmp/qemu/run', 'test-quick']' returned non-zero exit status 2.
> filter=--filter=label=com.qemu.instance.uuid=d6cb3d069c7a44ecbf5b02c17a39e884
> make[1]: *** [docker-run] Error 1
> make[1]: Leaving directory `/var/tmp/patchew-tester-tmp-litaiimt/src'
> make: *** [docker-run-test-quick@centos7] Error 2
> 
> real    16m25.200s
> user    0m5.519s
> 
> 
> The full log is available at
> http://patchew.org/logs/20200624124301.7112-1-eric.auger@redhat.com/testing.docker-quick@centos7/?type=message.
> ---
> Email generated automatically by Patchew [https://patchew.org/].
> Please send your feedback to patchew-devel@redhat.com
> 
Hum, time make docker-test-quick@centos7 SHOW_ENV=1 J=14 NETWORK=1

passes for me, run on top of 2/2.

I don't get what's wrong here?

Eric

Re: [PATCH v2 1/2] qom: Introduce object_property_try_add_child()

[Paolo Bonzini]

On 24/06/20 14:43, Eric Auger wrote:
> +    op = object_property_try_add(obj, name, type, object_get_child_property,
> +                                 NULL, object_finalize_child_property,
> +                                 child, errp);
> +    if (!op) {
> +        goto out;
> +    }
>      op->resolve = object_resolve_child_property;
> +out:
>      object_ref(child);
>      child->parent = obj;
>      return op;

I think if there's an error you need to return NULL without ref-ing
child, shouldn't you?

You can then add another test that object_property_add_child succeeds
after object_property_try_add_child fails.

Paolo

Re: [PATCH v2 1/2] qom: Introduce object_property_try_add_child()

[Auger Eric]

Hi Paolo,

On 6/24/20 4:12 PM, Paolo Bonzini wrote:
> On 24/06/20 14:43, Eric Auger wrote:
>> +    op = object_property_try_add(obj, name, type, object_get_child_property,
>> +                                 NULL, object_finalize_child_property,
>> +                                 child, errp);
>> +    if (!op) {
>> +        goto out;
>> +    }
>>      op->resolve = object_resolve_child_property;
>> +out:
>>      object_ref(child);
>>      child->parent = obj;
>>      return op;
> 
> I think if there's an error you need to return NULL without ref-ing
> child, shouldn't you?
hum yes you're fully right, the out label is badly placed.
> 
> You can then add another test that object_property_add_child succeeds
> after object_property_try_add_child fails.
OK

Thanks

Eric
> 
> Paolo
> 

Re: [PATCH v2 1/2] qom: Introduce object_property_try_add_child()

[Auger Eric]

Hi Paolo,

On 6/24/20 4:17 PM, Auger Eric wrote:
> Hi Paolo,
> 
> On 6/24/20 4:12 PM, Paolo Bonzini wrote:
>> On 24/06/20 14:43, Eric Auger wrote:
>>> +    op = object_property_try_add(obj, name, type, object_get_child_property,
>>> +                                 NULL, object_finalize_child_property,
>>> +                                 child, errp);
>>> +    if (!op) {
>>> +        goto out;
>>> +    }
>>>      op->resolve = object_resolve_child_property;
>>> +out:
>>>      object_ref(child);
>>>      child->parent = obj;
>>>      return op;
>>
>> I think if there's an error you need to return NULL without ref-ing
>> child, shouldn't you?
> hum yes you're fully right, the out label is badly placed.
Looks the unref is done in user_creatable_add_type() in case of error.
Isn't it the corresponding one? Anyway I think it is better to avoid
getting the ref here as you suggest (and also free type) and don't unref
in user_creatable_add_type.

Thanks

Eric
>>
>> You can then add another test that object_property_add_child succeeds
>> after object_property_try_add_child fails.
> OK
> 
> Thanks
> 
> Eric
>>
>> Paolo
>>

Re: [PATCH v2 2/2] tests/qmp-cmd-test: Add qmp/object-add-duplicate-id

[Auger Eric]

Hi Thomas,

On 6/24/20 2:43 PM, Eric Auger wrote:
> This new test checks that attempting to create an object
> with an existing ID gracefully fails.
> 
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> ---
>  tests/qtest/qmp-cmd-test.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/tests/qtest/qmp-cmd-test.c b/tests/qtest/qmp-cmd-test.c
> index 9f5228cd99..9510051c35 100644
> --- a/tests/qtest/qmp-cmd-test.c
> +++ b/tests/qtest/qmp-cmd-test.c
> @@ -213,6 +213,22 @@ static void test_object_add_without_props(void)
>      qtest_quit(qts);
>  }
>  
> +static void test_object_add_with_duplicate_id(void)
> +{
> +    QTestState *qts;
> +    QDict *resp;
> +
> +    qts = qtest_init(common_args);
> +    resp = qtest_qmp(qts, "{'execute': 'object-add', 'arguments':"
> +                    " {'qom-type': 'memory-backend-ram', 'id': 'ram1', 'props': {'size': 4294967296 } } }");
> +    g_assert_nonnull(resp);
> +    g_assert(qdict_haskey(resp, "return"));
> +    resp = qtest_qmp(qts, "{'execute': 'object-add', 'arguments':"
> +                    " {'qom-type': 'memory-backend-ram', 'id': 'ram1', 'props': {'size': 4294967296 } } }");
in v3 I will add here:
    g_assert_nonnull(resp);

Thanks
Eric
> +    qmp_assert_error_class(resp, "GenericError");
> +    qtest_quit(qts);
> +}
> +
>  int main(int argc, char *argv[])
>  {
>      QmpSchema schema;
> @@ -225,6 +241,8 @@ int main(int argc, char *argv[])
>  
>      qtest_add_func("qmp/object-add-without-props",
>                     test_object_add_without_props);
> +    qtest_add_func("qmp/object-add-duplicate-id",
> +                   test_object_add_with_duplicate_id);
>      /* TODO: add coverage of generic object-add failure modes */
>  
>      ret = g_test_run();
> 

Re: [PATCH v2 1/2] qom: Introduce object_property_try_add_child()

[Paolo Bonzini]

On 24/06/20 18:02, Auger Eric wrote:
> Hi Paolo,
> 
> On 6/24/20 4:17 PM, Auger Eric wrote:
>> Hi Paolo,
>>
>> On 6/24/20 4:12 PM, Paolo Bonzini wrote:
>>> On 24/06/20 14:43, Eric Auger wrote:
>>>> +    op = object_property_try_add(obj, name, type, object_get_child_property,
>>>> +                                 NULL, object_finalize_child_property,
>>>> +                                 child, errp);
>>>> +    if (!op) {
>>>> +        goto out;
>>>> +    }
>>>>      op->resolve = object_resolve_child_property;
>>>> +out:
>>>>      object_ref(child);
>>>>      child->parent = obj;
>>>>      return op;
>>>
>>> I think if there's an error you need to return NULL without ref-ing
>>> child, shouldn't you?
>> hum yes you're fully right, the out label is badly placed.
> Looks the unref is done in user_creatable_add_type() in case of error.

There are two references involved:

- a reference returned from object_new.  user_creatable_add_type()
passes it back to the caller.  The object_unref() you found is done
before returning NULL, because in that case nothing is being passed to
the caller

- a reference stored in child->parent.  In case of error that reference
is dropped with object_property_del before returning NULL.
object_property_try_add_child must not store anything in child->parent
in case of error, and therefore it need not add that reference either.

I hope this is clearer.

Thanks,

Paolo

> Isn't it the corresponding one? Anyway I think it is better to avoid
> getting the ref here as you suggest (and also free type) and don't unref
> in user_creatable_add_type.
> 
> Thanks
> 
> Eric
>>>
>>> You can then add another test that object_property_add_child succeeds
>>> after object_property_try_add_child fails.
>> OK
>>
>> Thanks
>>
>> Eric
>>>
>>> Paolo
>>>
> 

Re: [PATCH v2 1/2] qom: Introduce object_property_try_add_child()

[Auger Eric]

Hi Paolo,

On 6/24/20 6:16 PM, Paolo Bonzini wrote:
> On 24/06/20 18:02, Auger Eric wrote:
>> Hi Paolo,
>>
>> On 6/24/20 4:17 PM, Auger Eric wrote:
>>> Hi Paolo,
>>>
>>> On 6/24/20 4:12 PM, Paolo Bonzini wrote:
>>>> On 24/06/20 14:43, Eric Auger wrote:
>>>>> +    op = object_property_try_add(obj, name, type, object_get_child_property,
>>>>> +                                 NULL, object_finalize_child_property,
>>>>> +                                 child, errp);
>>>>> +    if (!op) {
>>>>> +        goto out;
>>>>> +    }
>>>>>      op->resolve = object_resolve_child_property;
>>>>> +out:
>>>>>      object_ref(child);
>>>>>      child->parent = obj;
>>>>>      return op;
>>>>
>>>> I think if there's an error you need to return NULL without ref-ing
>>>> child, shouldn't you?
>>> hum yes you're fully right, the out label is badly placed.
>> Looks the unref is done in user_creatable_add_type() in case of error.
> 
> There are two references involved:
> 
> - a reference returned from object_new.  user_creatable_add_type()
> passes it back to the caller.  The object_unref() you found is done
> before returning NULL, because in that case nothing is being passed to
> the caller
> 
> - a reference stored in child->parent.  In case of error that reference
> is dropped with object_property_del before returning NULL.

> object_property_try_add_child must not store anything in child->parent
> in case of error, and therefore it need not add that reference either.
> 
> I hope this is clearer.

Yes it helps. Thank you for the clarifications.

Eric
> 
> Thanks,
> 
> Paolo
> 
>> Isn't it the corresponding one? Anyway I think it is better to avoid
>> getting the ref here as you suggest (and also free type) and don't unref
>> in user_creatable_add_type.
>>
>> Thanks
>>
>> Eric
>>>>
>>>> You can then add another test that object_property_add_child succeeds
>>>> after object_property_try_add_child fails.
>>> OK
>>>
>>> Thanks
>>>
>>> Eric
>>>>
>>>> Paolo
>>>>
>>
> 
>