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

[Simon Goldschmidt]

Follow-up Comment #17, task #6735 (project lwip):

So if implementing PBUF_RAM_NOCOPY (and using it in TCP and all other
stack-internal uses of PBUF_RAM), this would still leave us with the fact that
the present zero-copy sending for UDP sockets would not work any more! At
least for most hardware (as DMA MACs are rather widely used).

I'd like to know how other stacks (that are advertising zero-copy) solve
this... Although this seems a problem only for the sockets layer, a netconn
app can use the new pbuf type.

One thing: I would *always* let the allocator deallocate the pbuf (e.g.
alloc; send; free) and let the lower layers (network driver?) ref the pbuf and
free it later, instead of the way described here earlier. Like Jared, I have
the feeling this could otherwise lead to many 'bugs' reported on lwip-users
and I also think the code should be the same for all pbuf types.

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