Re: [lwip-users] udp (RFC!)

[Kieran Mansley]

On Mon, 17 Mar 2003, Leon Woestenberg wrote:
> Still, my preference would be to defer a copy to the lower levels (like your
> DMA
> system).

How would it tell the difference between a pbuf that came through the
sockets layer (and so needed to be copied) and one which came through the
raw API (and so doesn't)?

> Implementing copying at the high level will induce this everyone using lwIP,
> removing the current zero-copy feature for everyone.

It would be nice to have zero-copy transmits, but at the moment I think
it's a bug rather than a feature.  As far as I know there are no zero copy
transmit TCP stacks in existence that do so through the sockets layer,
simply because it's very hard.  Even if you do postpone copies until they
are necessary you'll end up copying most of them all anyway (in the case
of TCP that is, with UDP you might be able to get away with it a bit
more).

Kieran