On 7/7/21 1:32 AM, Song Liu wrote:
On Tue, Jul 6, 2021 at 10:24 AM Martynas Pumputis <m@xxxxxxxxx> wrote:When loading a BPF program with a pinned map, the loader checks whether the pinned map can be reused, i.e. their properties match. To derive such of the pinned map, the loader invokes BPF_OBJ_GET_INFO_BY_FD and then does the comparison. Unfortunately, on < 4.12 kernels the BPF_OBJ_GET_INFO_BY_FD is not available, so loading the program fails with the following error: libbpf: failed to get map info for map FD 5: Invalid argument libbpf: couldn't reuse pinned map at '/sys/fs/bpf/tc/globals/cilium_call_policy': parameter mismatch" libbpf: map 'cilium_call_policy': error reusing pinned map libbpf: map 'cilium_call_policy': failed to create: Invalid argument(-22) libbpf: failed to load object 'bpf_overlay.o' To fix this, probe the kernel for BPF_OBJ_GET_INFO_BY_FD support. If it doesn't support, then fallback to derivation of the map properties via /proc/$PID/fdinfo/$MAP_FD. Signed-off-by: Martynas Pumputis <m@xxxxxxxxx>The code looks good to me. Except a checkpatch CHECK: CHECK: Comparison to NULL could be written "!obj" #96: FILE: tools/lib/bpf/libbpf.c:3943: + if (obj == NULL || kernel_supports(obj, FEAT_OBJ_GET_INFO_BY_FD))
Thanks for the review. I will send v2 with the fix.
Also, I think this should target bpf-next tree?
Considering that libbpf is supported on older kernels, w/o this patch it is impossible to use it on < 4.12 kernels for programs with pinned maps. Therefore, I think that this is a fix and thus it should target the bpf tree instead.
Thanks, Song
