On Mon, Aug 23, 2021 at 04:35:51PM IST, Yaniv Agman wrote: > Using the recently added libbpf tc API worked fine for us in v0.4.0. > After updating libbpf and syncing with master branch, we get the > following error: > > libbpf: Kernel error message: Exclusivity flag on, cannot modify > This message is harmless. The commit that adds NLM_F_EXCL is a bug fix. Without it, the kernel returns 0 when it should return -EEXIST. It's just that the kernel complains loudly for the latter case through extack. User needs EEXIST to detect whether it installed the qdisc or not. To see how this affects the system, run ./test_progs -t tc_bpf after installing clsact using: tc qdisc add dev lo clsact Before this fix is added, it will remove the system qdisc as bpf_tc_hook_create returns 0, after the fix it detects the presence of the existing qdisc using -EEXIST and disables the bpf_tc_hook_destroy call before exit. I would suggest handling the error explicitly, and using libbpf_set_print to filter it out. See the example in tools/testing/selftests/bpf/test_progs.c. > I found that commit a1bd8104a9f1c1a5b9cd0f698c886296749a0ce9 is You probably meant bbf29d3a2e49e482d5267311798aec42f00e88f3? I cannot find this commit. > causing this problem, and removing the NLM_F_EXCL resolves the issue. > Is this the expected behavior and I'm doing something wrong? -- Kartikeya
