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

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Message-ID: <20080513170325.GB11499@gerrit.erg.abdn.ac.uk>
Date:	Tue, 13 May 2008 18:03:25 +0100
From:	Gerrit Renker <gerrit@....abdn.ac.uk>
To:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	David Stevens <dlstevens@...ibm.com>,
	David Miller <davem@...emloft.net>, dccp@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [RFC] [DCCP]: Deprecate SOCK_DCCP in favour of SOCK_DGRAM

| > the existing stuff alone, and then requiring programs that want to use
| > getaddrinfo to use it that way?
| 
| I wonder what is the problem with doing what I did when adding support
| for DCCP in ttcp, or for AF_LLC in ssh, ncftp, vsftpd, etc, i.e.
| getaddrinfo/getnameinfo wrappers that look if SOCK_DCCP or AF_LLC are
| being asked for and doing the right thing.
| 
Using work-arounds is brittle and frustrating when the API behaviour
suddenly changes. My experience of using such a wrapper was:

 * it passed UDP(-Lite), TCP through without changing the socket type;
 * when passed DCCP, it set the socket type to 0, to avoid `ai_socktype
   not supported' getaddrinfo error;
 * this used to work fine until about January, when something in the
   lookup machinery for dual-stack hosts changed:
   - before, AF_UNSPEC + ai_socktype=0 put IPv6 first into the result list,
   - now the the result order is reversed (IPv4 sockets are returned first)
 * so maybe "pretending to be UDP" (ai_socktype=SOCK_DGRAM) is a better
   workaround (at least it worked until this afternoon :)

| What would be the problem of SOCK_DCCP being handled in glibc in such a
| fashion?
That is probably the best and most robust solution one can think of.

Even the suggestion of changing to SOCK_DGRAM+IPPROTO_DCCP is just another
work-around and, as David and Remi confirmed, a bad one at that.

Gerrit
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