[lwip-devel] [task #6735] Provide new pbuf type: PBUF_RAM_NOCOPY

[Simon Goldschmidt]

Follow-up Comment #20, task #6735 (project lwip):

Jonathan,
Why can't PBUF_RAM_NOCOPY be freed by the allocating code as well, making the
driver reference the pbuf before enqueueing it for sending? I don't see any
indication for letting the stack (or driver) free the pbuf when looking at the
name (NOCOPY)... And it would certainly be more straightforward like the other
pbuf types that way...

> For us, this would make sense too.... copy as early as possible
> (if necessary) and make the stack itself 100% zero-copy.

But that would mean copying also for MACs that would support zero-copy
sending (like mine, currently!). I'd rather leave it with PBUF_REF and let the
driver copy everything but PBUF_RAM_NOCOPY. Which of course gives the problem
with chained pbufs containing e.g. PBUF_REF and PBUF_RAM_NOCOPY, but still,
some MACs *would* support zero-copy sending for UDP sockets.

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