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    • Yonghong Song's avatar
      libbpf: Fix bpf_xdp_query() in old kernels · c8ee37bd
      Yonghong Song authored
      Commit 04d58f1b("libbpf: add API to get XDP/XSK supported features")
      added feature_flags to struct bpf_xdp_query_opts. If a user uses
      bpf_xdp_query_opts with feature_flags member, the bpf_xdp_query()
      will check whether 'netdev' family exists or not in the kernel.
      If it does not exist, the bpf_xdp_query() will return -ENOENT.
      
      But 'netdev' family does not exist in old kernels as it is
      introduced in the same patch set as Commit 04d58f1b.
      So old kernel with newer libbpf won't work properly with
      bpf_xdp_query() api call.
      
      To fix this issue, if the return value of
      libbpf_netlink_resolve_genl_family_id() is -ENOENT, bpf_xdp_query()
      will just return 0, skipping the rest of xdp feature query.
      This preserves backward compatibility.
      
      Fixes: 04d58f1b ("libbpf: add API to get XDP/XSK supported features")
      Signed-off-by: default avatarYonghong Song <yhs@fb.com>
      Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
      Link: https://lore.kernel.org/bpf/20230227224943.1153459-1-yhs@fb.com
      c8ee37bd