netdev - [RFC] [DCCP]: Deprecate SOCK_DCCP in favour of SOCK

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Date:	Tue, 13 May 2008 08:28:53 +0100
From:	Gerrit Renker <gerrit@....abdn.ac.uk>
To:	netdev@...r.kernel.org, dccp@...r.kernel.org
Cc:	Arnaldo <acme@...hat.com>
Subject: [RFC] [DCCP]: Deprecate SOCK_DCCP in favour of SOCK_DGRAM

There is an API and an address resolution problem involved in specifying a
separate/distinct socket type `SOCK_DCCP'.

The problem is that the default getaddrinfo(3) does not support the `alien'
SOCK_DCCP socket type (it returns `ai_socktype not supported'), thus requiring
various cheats/work-arounds in order to bring up a DCCP socket on a dual-stack
host.

In order to get an address at all,
 * a hint with an ai_socktype=SOCK_DGRAM or SOCK_STREAM needs to be supplied;
 * using ai_socktype=0 causes IPv4 addresses to be returned first, so that a
   server on a dual-stack host needs to be coaxed into v6 mode to accept
   incoming v6 connections.

The suggestion therefore is to not use a separate SOCK_DCCP socket type,
and to put DCCP up under SOCK_DGRAM (being in fact datagram-based), i.e.

	socket(sd, SOCK_DCCP, 0);	

is replaced by	

	socket(sd, SOCK_DGRAM, IPPROTO_DCCP);

Having also seen the work-arounds in programs that other people wrote,
I believe that the above change will make it in the long term easier for
people to write DCCP-enabled applications.

It also relieves the libc writers from having to support another socket type.

A quick look at SCTP shows that they also did not introduce new socket types,
relying on the existing SOCK_STREAM/SOCK_SEQPACKET ones.

It might be still early enough to resolve this, before it is widely used
and can then only be supported via work-arounds.

I can't see a disadvantage here and the only work required is to update that
datagram-based not automatically means connection-less.

Is there support for this change or are there reasons to keep SOCK_DCCP?
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