netdev - Re: [PATCH 7/9] AF_UNIX: Documentation on multicast Unix Sockets

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Message-Id: <201011222107.41548.remi@remlab.net>
Date:	Mon, 22 Nov 2010 21:07:40 +0200
From:	"Rémi Denis-Courmont" <remi@...lab.net>
To:	Alban Crequy <alban.crequy@...labora.co.uk>, netdev@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/9] AF_UNIX: Documentation on multicast Unix Sockets

Le lundi 22 novembre 2010 20:36:20 Alban Crequy, vous avez écrit :
> +Multicast Unix sockets
> +======================
> +
> +Multicast group memberships are stored in struct unix_mcast nodes. An Unix
> +socket can join several multicast groups. Struct unix_mcast nodes are
> doubly +linked:
> +- In (struct unix_sock)->mcast_subscriptions
> +- In (struct unix_sock)->mcast_members

I may be stupid, but I found this whole documentation very confusing, and so 
the API it tries to describe. Traditionally:
- Senders may or not may be part of the group and are not kept track of.
- Receivers join to the group then receive message sent to it.
- Loopback defines whether a sender receives its own echo if it sends to a
group that it has joined.
- If connected to a multicast group, messages from the socket are routed to 
the group (in absence of a contradictoy socket address). This has no effect on 
membership to the multicast group under any circumstance.

You cannot 'listen' or 'accept' on a multicast group.

So I am not entirely clear what semantics your patchset is following. But it 
does not seem like "multicast" to me and therefore seems not very well 
documented :-(

-- 
Rémi Denis-Courmont
http://www.remlab.net/
http://fi.linkedin.com/in/remidenis
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