On Tue, Oct 30, 2018 at 12:07 PM Mauricio Vasquez <mauricio.vasquez@xxxxxxxxx> wrote: > > > On 10/26/18 2:13 PM, Matthew Tejo wrote: > > Hey, > > I started trying out xdp programs recently and I was comparing what > > comes out of tcp dump and my test program. It seems like the first syn > > in the packet never appears in my logged out put, the rest of the > > packets do. > > > > I am using a vm and using the loopback interface and a virtual one > > created by docker, both will only start from the second outgoing > > packet. > > > > Tcpdump shows syn -> syn,ack -> ack. But the xdp program only starts > > from syn,ack then ack. Im logging using bpf_trace_printk and put the > > statement at the beginning of the section being loaded so something > > should at least print every time? > > > > Is there something Im over looking? > > > > Thanks and let me know if I can clarify anything. > > Matt > > > Hello Matthew, > > If you are using generic XDP [1] you are probably hitting a known issue > with TCP traffic [2]. > > AFAIK there is not a solution for that issue yet, Linux kernel v4.19 has > a native XDP driver for veth [3], this probably solves this issue > (please somebody correct me if I am wrong). > > I hope this helps, > > Mauricio. > > > [1] https://lwn.net/Articles/720072/ > > [2] https://www.spinics.net/lists/xdp-newbies/msg00440.html > > [3] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=948d4f214fde43743c57aae0c708bff44f6345f2 > Oh. That looks pretty similar to what I'm running into. I guess Im still out of luck for the loop back device. Thanks for the links Matt
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