Subject: Re: Linux 2.6.35/TIPC 2.0 ABI breaking changes

From: Leandro Lucarella <[email-masked]>
Date: Wed, 20 Oct 2010 14:20:18 -0300

Neil Horman, el 19 de octubre a las 16:18 me escribiste:
> 	Heres what I have so far.  Dave as a heads up please don't apply this
> yet.  I'd like to go over it a bit more and be sure of the implications here
> before I post it for inclusion officially.  I wanted Leandro to have a copy
> though so he could confirm functionality for us.  Leandro, This patch lets me
> pass the tipc test code for TIPC 1.6 that you posted earlier this morning.  If
> you could confirm that it works for you that would be grand.  While your doing
> that, I want to read over the spec for TIPC and make sure that I'm not breaking
> anything new with this patch.

I tried the patch (swapping the values of TIPC_SUB_SERVICE and
TIPC_SUB_PORTS) based on 2.6.35.4 and it didn't worked. dmesg sais:
NOT Swapping endianess in subscr_subscribe
NOT Swapping endianess in subscr_subscribe
TIPC: Subscription rejected, illegal request

I tried with a binary compiled with an older tipc.h header, I didn't
tried to recompile it using the new tipc.h (on purpose as the thing that
should be fixed is backwards compatibility).

I've read the TIPC 2.0 specification[1] a little more, and as I see, the
subscription messages are not supposed to go through the wire[2].

	8.  Topology Service

	TIPC provides a message-based mechanism for an application to
	learn about the port names that are visible to its node. This is
	achieved by communicating with a Topology Service that has
	knowledge of the contents of the node's name table.

So, if the idea is to comply with TIPC 2.0, the topology service should
accept the new TIPC_SUB_SERVICE and TIPC_SUB_PORTS values (0 and
1 in NBO respectively), and all the fields in the subscr struct should
be filled in NBO too.

However, if the idea is to keep backwards compatibility too, HBO should
be accepted as well as the old TIPC_SUB_SERVICE and TIPC_SUB_PORTS
values (2 and 1 in HBO respectively).

The real problem is, we can't figure out the endianess of the subscr
struct because 0x0 is a valid filter in TIPC 2.0.

The only solution I see is to change the TIPC 2.0 specification (which
is a "work-in-progress") to make the topology service use the port name
{2,2}, leaving {1,1} for backwards compatibility. Then add the constants
TIPC_SUB_SERVICE2 (0) and TIPC_TOP_SRV2 (2), or similar, to use the TIPC
2.0 interface and leave TIPC_SUB_SERVICE and TIPC_TOP_SRV for the TIPC
1.x interface.

Another option is to change the TIPC 2.0 specification to use the old
format (use HBO in subscriptions and keep TIPC_SUB_SERVICE as a separate
flag with value 2) and forget about all this. After all, I can't see
what advantages gives having to change the BO for internal messages
between the applications and the stack.

[1] http://tipc.sourceforge.net/doc/draft-spec-tipc-06.html
[2] http://tipc.sourceforge.net/doc/draft-spec-tipc-06.html#anchor92

-- 
Leandro Lucarella (AKA luca)                     http://llucax.com.ar/
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