Hi David

On Mon, 2012-02-27 at 14:05 -0500, David Miller wrote:

From: Javier Martinez Canillas <redacted>
Date: Mon, 27 Feb 2012 15:00:06 +0100

quoted

Primary for performance reasons. D-bus is an IPC system for processes in
the same machine so traversing the whole TCP/IP stack seems a little
overkill to me.

You haven't actually tested what the cost of this actually is, so what
you're saying is mere speculation.  In many cases TCP/UDP over
loopback is actually faster than AF_UNIX.

you're right we haven't tested this, but because of the other points in
Javier's mail, which are the special semantics we need for this to fit
the D-Bus usage:

- total order is guaranteed: If sender A sends a message before B,

then

receiver C and D should both get message A first and then B.

- slow readers: dropping packets vs blocking the sender. Although
  datagrams are not reliable on IP, datagrams on Unix sockets are

never

  lost. So if one receiver has its buffer full the sender is blocked
instead of dropping packets. That way we guarantee a reliable
communication channel.

- multicast group acess control: controlling who can join the

multicast

group.

- multicast on loopback is not supported: which means we have to use a
NIC (i.e: eth0). 

Because of all of this, UDP/IP multicast wasn't even considered as an
option. We might be wrong in some/all of those, so could you please
comment on them to check if that's so?

thanks