Date: Tue, 21 Apr 2015 13:03:59 +0200 (CEST)
From: Jiri Kosina <jkosina@suse.cz>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
cc: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
        Andy Lutomirski <luto@amacapital.net>,
        Richard Weinberger <richard@nod.at>,
        David Herrmann <dh.herrmann@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Al Viro <viro@zeniv.linux.org.uk>, Borislav Petkov <bp@alien8.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Tom Gundersen <teg@jklm.no>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Daniel Mack <daniel@zonque.org>, Djalal Harouni <tixxdz@opendz.org>
Subject: Re: [GIT PULL] kdbus for 4.1-rc1
In-Reply-To: <20150421105123.GB5579@kroah.com>
Message-ID: <alpine.LNX.2.00.1504211255110.3695@pobox.suse.cz>
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On Tue, 21 Apr 2015, Greg Kroah-Hartman wrote:

> > We do need something for the multicast messaging. Whether that's
> > supporting AF_LOCAL, SOCK_RDP with multicast or something else (POSIX
> > message queue extensions ?). There's no real IP layer reliable ordered
> > multicast delivery system that is low latency and lightweight because
> > once it hits real networks it changes from a hard problem into a
> > seriously hard problem because of multicast implosions and the like.
> 
> This was attempted in the past with AF_DBUS, but the networking
> maintainers rightfully pointed out that the model there did not work.

BTW, I don't think this has been brought up in this discussion yet ... 
please correct me if I am wrong, my memory is very faint here (*), but 
wasn't the main objection to AF_BUS that defining what happens when one of 
the subscribed receivers disconnects is a policy matter, and as such 
belongs to userspace (which wasn't the case with the submitted AF_BUS 
implementation)?

Was that considered unfixable and AF_BUS consequently given up because of 
this?

I personally think that AF_BUS makes quite a lot of sense -- it builds on 
what we already have (AF_UNIX credential passing, memfd sealing, etc), it 
basically "just implements a missing socket semantics" (wrt. reliability 
and multicasting).

(*) and I really would like to avoid the digging out and reading thread 
    similar to this one, about AF_BUS, again

Thanks,

-- 
Jiri Kosina
SUSE Labs
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