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Re: [lwip-devel] sequential API dual-stack listen and the (unreferenced)

From: James G. Smith
Subject: Re: [lwip-devel] sequential API dual-stack listen and the (unreferenced) tcp_listen_dual macro
Date: Wed, 27 Jun 2012 09:22:17 +0100
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On 06/26/2012 09:01 PM, address@hidden wrote:
> I don't know about that. I deliberately didn't add this to the
> sequential APIs, since I did not find a standard way to do so on sockets
> (I hadn't considered the netconn API, I must confess). If there is a way
> to do so on any other (BSD-like) socket implementation, I'd strongly
> suggest to follow that instead of inventing our own thing.

On 06/26/2012 04:39 PM, James G. Smith wrote:
> that mimics the operation of the Linux/BSD IPV6_V6ONLY control

That is why I mentioned the IPV6_V6ONLY flag. FreeBSD defaults to 0 (so
dual by default when listening on an AF_INET6 socket), though some older
Linux kernels seem to default to on, hence requiring an explicit:


to disable the V6ONLY feature (and enable dual) on the socket.

So for the "per-socket" approach I would just update lwip_setsockopt (et
al) to implement compatible support (making porting *BSD code
transparent) and use a NETCONN_FLAG_ to control the actual listener
function called for the socket.

Whether it is enabled or disabled by default can be a cost-free (build
time) "opt.h" configuration option; since even if people disagree over
the default on or off state; at least it can be overridden easily with

I will generate and submit a patch sometime over the next couple of days
that can at least be another step in the discussion :-)

-- Jamie

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