I think I found the problem. It is necessary to run the statistics display application in the same network namespace where the user level filter and the eBPF kernel code are running; I think even in the same 'ip netns exec' instance. On Wed, 30 Nov 2022 at 13:58, Chris Ward <tjcw01@xxxxxxxxx> wrote: > > I have a test case similar to code in xdp-project/xdp-tutorial/ which > maintains a statistic map in a per-cpu array, and user-space code > which displays the statistics periodically. > > When I run this, the user space code always displays zeros. I have > instrumented my eBPF kernel code with bpf_trace_printk and it appears > to be putting the correct values into the map. The user code is > iterating over all possible CPUs, but is always finding zeros in the > per-cpu array slots. > > Can anybody tell me what is going wrong ? > > My test case is here > https://github.com/tjcw/bpf-examples/tree/tjcw-integration-1.2-ebpftrace/AF_XDP-filter > ; af_xdp_kern.c is the eBPF code, af_xdp_user.c is the userspace code > which drives the eBPF code, and filter-xdp_stats.c is the code which > should display the statistics. It all builds with 'make' in that > directory, and there is a run script which I use with > tjcw@r28b29-n10:~/workspace/bpf-examples/AF_XDP-filter/netperf-namespace$ > sudo FILTER=af_xdp_kern ./run.sh > to run the user code and eBPF code with data being transferred between > 2 network namespaces on the machine. > While it is running, > tjcw@r28b29-n10:~/workspace/bpf-examples/AF_XDP-filter$ sudo > ./filter-xdp_stats > should display statistics, but in fact displays zeros. > > My test case is coded to the '1.0' BPF interface, where the code in > xdp-tutorial is coded to the pre-release BPF interface. > > Thanks for all the help you can give ! > > Chris Ward, IBM
