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To: Lars Eggert <larse@ISI.EDU>
Cc: net@FreeBSD.ORG, brian@Awfulhak.org
Subject: Re: Changing UDP select() behavior
In-Reply-To: Message from Lars Eggert <larse@ISI.EDU>
of "Tue, 13 Mar 2001 16:43:26 PST." <3AAEBEAE.F823CB8E@isi.edu>
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Date: Wed, 14 Mar 2001 01:06:01 +0000
From: Brian Somers <brian@Awfulhak.org>
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> Hi,
>
> I'm wondering if anyone has ever considered modifying the UDP behavior with
> regard to selecting:
>
> Currently, writing to a UDP socket either enqueues packets in the interface
> queue (returning success), or drops them on the floor (returning ENOBUFS)
> if the queue is full. Selecting-to-write on a UDP socket always succeeds,
> never blocks.
>
> I'm considering changing this, so that a select-to-write on a UDP socket
> will block until queue space becomes available. (I don't think this would
> violate UDP semantics, but is a big enough change to warrant a new sockopt
> to enable it.)
>
> Has this been considered/implemented in any OS? Does anyone see any serious
> problems with it? Feedback greatly appreciated!
This'd be nice if it could be made to work. I guess the problem is
that you don't actually know if a write() will succeed 'till you try
it (and try to allocate an mbuf).
Having said this, it would be nice if it was possible to pre-allocate
(a small number of) mbufs for a pipe() or socketpair(), giving a
reliable SOCK_DGRAM file-descriptor based ipc mechanism.
> Lars
> --
> Lars Eggert <larse@isi.edu> Information Sciences Institute
> http://www.isi.edu/larse/ University of Southern California
--
Brian <brian@Awfulhak.org> <brian@[uk.]FreeBSD.org>
<http://www.Awfulhak.org> <brian@[uk.]OpenBSD.org>
Don't _EVER_ lose your sense of humour !
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