Starting the kdbus discussions

[Simon McVittie]

On 03/01/14 23:18, Lennart Poettering wrote:
> On Fri, 03.01.14 13:18, Simon McVittie (simon.mcvittie at collabora.co.uk) wrote:
>>> As you can see: the first 16 bytes are 100% identical between dbus1 and
>>> gvariant messages. Only beyond that the gvariant marshalling results in
>>> different serialization.
>>
>> This seems perverse: if the header is compatible but the content isn't,
>> then the message is not compatible, and as a result, there's no value in
>> the header being compatible.
> 
> Well, the header already has a field for indinicating the "protocol
> version", which we make use of here.

Ah - identical semantics, different contents. Sure, that's fine, but:

> dbus1 messages have protocol
> version 1, gvariant messages have protocol version 2.

Please do not deploy "protocol version 2" anywhere until the D-Bus
Specification describes it: this field (and anything else numeric,
really) is not extensible except via D-Bus Specification updates. While
kdbus is still being designed, a quick one-line patch that says
"reserved for a GVariant-based serialization" (a lot like the current
reservation of "m" for maybe types) would be enough.

    S