Hi, On Mon, Apr 12, 2021 at 11:30 AM Alexander Ahring Oder Aring <aahri...@redhat.com> wrote: > > Hi, > > On Fri, Apr 9, 2021 at 4:44 PM Guillaume Nault <gna...@redhat.com> wrote: > > > > On Mon, Apr 05, 2021 at 01:33:48PM -0400, Alexander Ahring Oder Aring wrote: > > > Hi, > > > > > > On Sat, Apr 3, 2021 at 11:34 AM Alexander Ahring Oder Aring > > > <aahri...@redhat.com> wrote: > > > > > > > ... > > > > > > > > > It seems to me that the only time DLM might need to retransmit data, > > > > > is > > > > > when recovering from a connection failure. So why can't we just resend > > > > > unacknowledged data at reconnection time? That'd probably simplify the > > > > > code a lot (no need to maintain a retransmission timeout on TX, no > > > > > need > > > > > to handle sequence numbers that are in the future on RX). > > > > > > > > > > > > > I can try to remove the timer, timeout and do the above approach to > > > > retransmit at reconnect. Then I test it again and I will report back > > > > to see if it works or why we have other problems. > > > > > > > > > > I have an implementation of this running and so far I don't see any > > > problems. > > > > > > > > Also, couldn't we set the DLM sequence numbers in > > > > > dlm_midcomms_commit_buffer_3_2() rather than using a callback function > > > > > in dlm_lowcomms_new_buffer()? > > > > > > > > ... > > > > > > > > Yes, I looked into TCP_REPAIR at first and I agree it can be used to > > > > solve this problem. However TCP_REPAIR can be used as a part of a more > > > > generic solution, there needs to be something "additional handling" > > > > done e.g. additional socket options to let the application layer save > > > > states before receiving errors. I am also concerned how it would work > > > > > > The code [0] is what I meant above. It will call > > > tcp_write_queue_purge(); before reporting the error over error > > > queue/callback. That need to be handled differently to allow dumping > > > the actual TCP state and restore at reconnect, at least that is what I > > > have in my mind. > > > > Thanks. That's not usable as is, indeed. > > Also, by retransmitting data from the previous send-queue, we risk > > resending messages that the peer already received (for example because > > the previous connection didn't receive the latest ACKs). I guess that > > receiving the same DLM messages twice is going to confuse the peer. > > So it looks like we'll need application level sequence numbers anyway. > > I agree, the new "retransmit all unacknowledged messages on reconnect" > method will filter at the receiving side the already received messages > because they have the sequence numbers, this case occurs a lot. > > However I think there is still the possibility to use TCP_REPAIR here, > we need to restore states about all 3 queues, rx, tx (write, > retransmit) and sequence numbers. Window size is an optional > additional thing. On the application layer we need to be sure that we > don't drop anything if error occurs and start to transmit them after > restoring the state again. Of course both endpoints need to support it > and have been correctly configured.
I am not sure if this ends in something like "ignore some error cases in TCP", at least TCP_RST is something which seems to be triggered sometimes because "smart hardware" in the network e.g. but cable out and in again (not sure about that one). I think restoring the state might be work, but transparent proxies (haproxy, etc.) could be confused? I am not sure here... - Alex
