lwip_ioctl adds offset?

Hi everybody,

I wrote a basic tftp server and before sendind the final ACK I store the received data to flash. Waiting for this ACK the client resends the last data package.

After the data was stored in flash, I use lwip_ioctl to check if there is pending data in the receive buffer (the resend data) and empty it with lwip_recvfrom() before sending the final ACK.

That works out pretty well, but most times there is an offset of 1956 added to the value returned by ioctl, sometimes (maybe 1 out of 100) it is a little bit less or more.

Has anyone an idea where this offset comes from?

Thanks for all information you can provide!

--wolf