[systemd-devel] dbus-1/kdbus - question about 'queued owners'

[Simon McVittie]

On 10/04/15 15:20, Lukasz Skalski wrote:
> Currently I'm working on some testsuite (let's call it dbus1-spec-test)
> for dbus-1 specification.

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Quoting full text below for the dbus list; I'll respond as a reply to this.

> My idea is to test dbus-1 specification
> coverage on systems with dbus-daemon and on systems without dbus-daemon
> (but with latest systemd, bus-proxyd and kdbus) which will allow us (and
> all userspace apps) to smoothly switch to kdbus. First results of tests
> are really good:
> 
> Run Summary:    Type  Total    Ran Passed Failed Inactive
>               suites     11     11    n/a      0        0
>                tests     34     34     33      1        0
>              asserts    286    286    285      1      n/a
> 
> My testsuite have found only one inconsistency between dbus-1 and
> kdbus-enabled system. Problematic testcase (this one tests rather some
> dbus-daemon/bus-proxyd behaviors than specification) is as follow:
> 
> test_request_name_6 (void)
> {
>   GDBusConnection *connection_a;
>   GDBusConnection *connection_b;
> 
>   BusRequestNameFlagsReply request_reply;
>   BusReleaseNameFlagsReply release_reply;
> 
>   /* connect and set up two D-Bus client connections */
>   connection_a = connect_to_bus();
>   connection_b = connect_to_bus();
> 
>   /* 'connection_a' - synchronously acquire name on the bus */
>   request_reply = request_name (connection_a, "org.my.busname",
>                                 DBUS_NAME_FLAG_REPLACE_EXISTING |
>                                 DBUS_NAME_FLAG_DO_NOT_QUEUE);
> 
>   /* 'connection_a' should be primary owner */
>   CU_ASSERT (request_reply == DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER);
> 
>   /* 'connection_b' tries to own the same well-known name */
>   request_reply = request_name (connection_b, "org.my.busname",
>                                 DBUS_NAME_FLAG_REPLACE_EXISTING);
> 
>   /* 'connection_b' should be appended to the queue */
>   CU_ASSERT (request_reply == DBUS_REQUEST_NAME_REPLY_IN_QUEUE);
> 
>   /* once again 'connection_b' tries to own the same name */
>   request_reply = request_name (connection_b, "org.my.busname",
>                                 DBUS_NAME_FLAG_REPLACE_EXISTING);
> 
>   /* and once again we should get the same return code */
>   CU_ASSERT (request_reply == DBUS_REQUEST_NAME_REPLY_IN_QUEUE);
> 
>   /* 'connection_a' releases name */
>   release_reply = release_name (connection_a, "org.my.busname");
>   CU_ASSERT (release_reply == DBUS_RELEASE_NAME_REPLY_RELEASED);
> 
>   /* 'connection_b' (now primary owner) also release name
>   release_reply = release_name (connection_b, "org.my.busname");
>   CU_ASSERT (release_reply == DBUS_RELEASE_NAME_REPLY_RELEASED);
> 
>   /* 'connection_b' tries to release once again the same name */
>   release_reply = release_name (connection_b, "org.my.busname");
> 
>   /* This assert is source of failure - what we should get
>      here: REPLY_RELEASED or NON_EXISTENT ? */
>   CU_ASSERT (release_reply == DBUS_RELEASE_NAME_REPLY_NON_EXISTENT);
> 
>   g_object_unref (connection_a);
>   g_object_unref (connection_b);
> }
> 
> I think that code comments explain scenario of this test quite well. In
> this testcase I create two D-Bus client connections. Both connections
> request the same well-known name on bus. 'connection_a' becomes primary
> owner of the name. Because name replacement is not possible,
> 'connection_b' is appended to the queue. Next, 'connection_b' once again
> tries to own the same name and once again we have 'IN_QUEUE' as a return
> code. After this, 'connection_a' releases previously owned name. Now
> primary owner of "org.my.busname" name is 'connection_b'. First
> 'ReleaseName' returns RELEASED as it was expected. Inconsistency between
> dbus-daemon and kdbus has place when 'connection_b' once again tries to
> release "org.my.busname" name. After last 'ReleaseName' dbus-daemon
> returns NON_EXISTENT. In case of kdbus/bus-proxyd, we have RELEASED
> return code (if we add next/third 'ReleaseName' call for 'connection_b'
> it will return NON_EXISTENT) - it causes problems with last assert().
> 
> The main source of above problem is difference how dbus-daemon and kdbus
> handles placing the same connection in queue two times for the same
> well-know name.
> 
> Which solution, kdbus or dbus-daemon, do it correctly?

-- 
Simon McVittie
Collabora Ltd. <http://www.collabora.com/>