[lwip-devel] bug report: TCP and ARP queueing probably clashes

[Leon Woestenberg]

Hello all,

thanks to Bo-Er reporting on the lwip-users mailing list, I suspect the 
Ethernet ARP queueing
code clashes with the TCP queueing code, and as such this is a bug in 
the current HEAD code.

Summary:

lwIP used a 'zero-copy' strategy on outgoing packets, however, it was 
changed to 'copy-on-demand'
strategy to cope with packet obufs referencing volatile application memory.

This strategy *probably* clashes with the TCP queueing code, if both 
queues adapt the packet
pbuf chain.

Temporary solution:

For applications where TCP connections are involved, please disable 
ETHARP_QUEUEING.

For applications that do not use TCP, enabling ETHARP_QUEUEING should 
work 100% stable.

I will file a bug report, and in the meantime try to get a full 
understanding of the TCP protocol
implementation for unACKed/unsent queueing to see if, and how to solve 
this properly.

One solution would be to queue UDP traffic only in ARP, however the current
internal API will not allow this in a clean way.

Regards,

Leon Woestenberg.