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    SubjectRe: [PATCH 0/10] af_unix: add multicast and filtering features to AF_UNIX
    Hi David

    On Mon, 2012-02-27 at 14:05 -0500, David Miller wrote:
    > From: Javier Martinez Canillas <>
    > Date: Mon, 27 Feb 2012 15:00:06 +0100
    > > 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,
    > 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
    > 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
    > 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?


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