Fix regression in libbpf, introduced by XDP link change, which causes XDP
programs to fail to be loaded into kernel due to specified BPF_XDP
expected_attach_type. While kernel doesn't enforce expected_attach_type for
BPF_PROG_TYPE_XDP, some old kernels already support XDP program, but they
don't yet recognize expected_attach_type field in bpf_attr, so setting it to
non-zero value causes program load to fail.

Luckily, libbpf already has a mechanism to deal with such cases, so just make
expected_attach_type optional for XDP programs.

Reported-by: Nikita Shirokov <tehn...@tehnerd.com>
Reported-by: Udip Pant <udipp...@fb.com>
Fixes: dc8698cac7aa ("libbpf: Add support for BPF XDP link")
Signed-off-by: Andrii Nakryiko <andr...@fb.com>
---
 tools/lib/bpf/libbpf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 7253b833576c..e493d6048143 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -6925,7 +6925,7 @@ static const struct bpf_sec_def section_defs[] = {
                                                BPF_XDP_DEVMAP),
        BPF_EAPROG_SEC("xdp_cpumap/",           BPF_PROG_TYPE_XDP,
                                                BPF_XDP_CPUMAP),
-       BPF_EAPROG_SEC("xdp",                   BPF_PROG_TYPE_XDP,
+       BPF_APROG_SEC("xdp",                    BPF_PROG_TYPE_XDP,
                                                BPF_XDP),
        BPF_PROG_SEC("perf_event",              BPF_PROG_TYPE_PERF_EVENT),
        BPF_PROG_SEC("lwt_in",                  BPF_PROG_TYPE_LWT_IN),
-- 
2.24.1

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