Description of problem: Grub2's TFTP implementation does not send another ACK upon receiving the last data packet a second time. This results in the TFTP transfer breaking down in the face of packet loss and ending in a timeout error. This looks like so server -> data 1 -> grub grub -> ack 1 -> server server -> data 2 -> grub grub -> ack 2 -> server . . . server -> data k -> grub grub -> ack k -> (lost in the network) server -> data k -> grub server -> data k -> grub server -> data k -> grub server -> data k -> grub . . . until Grub reports a timeout error waiting for data k+1. Version-Release number of selected component (if applicable): 1:2.00-23.fc19 How reproducible: Always (if you have a busy network or a way of dropping some packets) Steps to Reproduce: 1. Load a large initramfs via tftp on a busy network that drops some packets Actual results: Times out due to the server not going onto the next block because grub does not re-transmitting the ACK that was lost for the previous block it has already received. Expected results: Grub should re-transmit the dropped ACK so the server will send the next packet. Additional info: The relevant part of RFC 1350 is (Section 2 -- Overview) "If a packet gets lost in the network, the intended recipient will timeout and may retransmit his last packet (which may be data or an acknowledgment), thus causing the sender of the lost packet to retransmit that lost packet. ... Notice that both machines involved in a transfer are considered senders and receivers. One sends data and receives acknowledgments, the other sends acknowledgments and receives data." http://www.ietf.org/rfc/rfc1350.txt
Created attachment 813514 [details] Patch to add re-transmission of ACKs
I've attached a patch against the F19 srpm to implement ACK re-transmission. I've also submitted it upstream for (hopefully) eventually inclussion https://savannah.gnu.org/bugs/?40293
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