[libvirt] [PATCH] Revert "dbus: correctly build reply message"

[Daniel P. Berrangé]

On Mon, Sep 09, 2019 at 03:47:21PM +0400, Marc-André Lureau wrote:
> Hi
> 
> On Fri, Sep 6, 2019 at 7:37 PM Michal Privoznik <mprivozn at redhat.com> wrote:
> >
> > This reverts commit 39dded7bb61444bb608fadd3f82f6fe93d08fd0e.
> >
> > This commit broke virpolkittest on Ubuntu 18 which has an old
> > dbus (v1.12.2). Any other distro with the recent one works
> > (v1.12.16) which hints its a bug in dbus somewhere. Revert the
> > commit to stop tickling it.
> >
> > Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> 
> This patch is no longer necessary for dbus-vmstate in this series. I
> found this "bug" when implementing an alternative solution. So
> reverting it is fine by me.
> 
> However, it may be revealing a transient bug in
> virDBusMessageIterDecode() rather than libdbus. It would be worth to
> have VIR_DEBUG() output from the failing test.

It is not really a bug - rather its due to the short cut taken by
the test suite.

virpolkittest is mocking the dbus_connection_send_with_reply_and_block
method.

This method accepts a DBusMessage input (the MethodCall) and has to
create  DBusMessage as output (the MethodReply)

The DBusMessage input has no serial number set, since this is the job
of the real dbus_connection_send_with_reply_and_block() method impl.

The dbus_message_new_method_return() impl expects the original message
to have a valid serial number though.

Thus when we create the DBusMessage output, we hit an assertion failure
when calling dbus_message_new_method_return().

This is in fact why the code intentionally uses

  dbus_message_new(DBUS_MESSAGE_TYPE_METHOD_RETURN)

in the first place.

What's strange though is why it ever succeeds on any distro. The
assertion we're seeing should *always* hit us on every distro.


Regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|