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Re: [lwip-users] tcp_write with zero-copy

From: Christiaan Simons
Subject: Re: [lwip-users] tcp_write with zero-copy
Date: Mon, 31 Oct 2005 12:51:53 +0100

> i'm using the raw-interface with lwip 1.1.0 and want to avoid the
> buffer-copy at tcp_write.

The doc/rawapi.txt says the copy argument should be 0 in this case.
My guess is you cannot avoid copying because TCP must queue/dequeue
output data for flow control purposes.

> Is there a regular path to deliver the data by giving a
> PBUF_TRANSPORT instead of a raw data buffer to
> tcp_write (or another tcp_output function) just like in sending udp-data,
> or do i have to patch the sources to do this ?

I won't recommend bypassing the transport layer, as far as I understand
PBUF_TRANSPORT is reserved for internal usage.

> (e.h. use a special value of the copy-flag to just assume the buffer
> being a pbuf)

That might be a usefull feature, many applications do have a notion of
Please note creating your own lwip branch can be quite cumbersome,
to keep up with future fixes / changes. Maybe Kieran can comment on this.


Christiaan Simons

Hardware / Software Engineer
Axon Digital Design

+31 (0)13 511 66 66
+31 (0)13 511 41 51


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