Re: [PATCH bpf] libbpf: fix XDP program load regression for old kernels

On Thu, Sep 24, 2020 at 10:34 AM Alexei Starovoitov
[off-list ref] wrote:

On Thu, Sep 24, 2020 at 10:18 AM Andrii Nakryiko [off-list ref] wrote:

quoted

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 <redacted>
Reported-by: Udip Pant <redacted>
Fixes: dc8698cac7aa ("libbpf: Add support for BPF XDP link")
Signed-off-by: Andrii Nakryiko <redacted>

Applied. Thanks

Thanks!

Looks like libbpf CI needs to add a few old kernels.

Yeah. We have 4.9 which is very old and only a few selftests can even
succeed there. Then we jump to 5.5, which is too recent to detect this
issue. This issue happened on 4.15, would that be a good version to
stick to? Any opinions?