[lwip-devel] [bug #44805] sendmsg implementation to support scatter/gather IO

[Simon Goldschmidt]

Update of bug #44805 (project lwip):

                  Status:                    None => Invalid                

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Follow-up Comment #1:

I'm afraid the code won't work. The reason is that you removed memory copies
(using netbuf_ref, not copying the data into the netbuf).

You simply can't expect all data being sent when netconn_send() returns. This
is because you might have a DMA-capable netif that puts packets on a tx list
in 'linkoutput' and because the application thread might have a higher
priority than lwIP.

Summing it up, to implement zero-copy TX from sockets, you would have to let
the application thread wait for a transmit-confirmation from the netif driver
(e.g. the point where pbuf_free() is being called for the TX pbufs). If we had
that, we could use sendto() and modify it to send the data by reference
instead of copying it.

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