Re: [lwip-devel] (no subject)

[Leon Woestenberg]

Hello Luke,

address@hidden wrote:
> On Thu, 18 Mar 2004, Leon Woestenberg wrote:
>
> > Does copy-on-queue work correctly for non-ROM REF pbufs?
>
> Are you referring to pbuf_take()? The only place this seems to used is in
> etharp.c - I currently just assert if pbuf_take() is called, though I have
> never seen it happen yet. It should be very easy to implement this
> function though.
lwIP operates in zero-copy mode by default (i.e. it tries to do zero 
memory/buffer copies when the user application is providing data to
sent).

In some cases where the data cannot be put on the link, it can be queued
inside lwIP (copy-on-queue). Currently only etharp.c does this, but the 
link layer driver itself can also queue for outgoing packets (work in 
progress for some drivers).

If it does not happen in your case, that either means you are not using
referenced application data, or your ARP cache always has the 
destination address cached.

Main point is, you cannot count on this.

> This leads me to wonder about the implementation of ping - what if the
> ping payload is not a RAM pbuf? My guess is at the moment it gets modified
> in place, which might not be such a good idea. Should ping be calling
> pbuf_take() as well?
Good point, will look into this when I'm less busy.

Leon.