AttachXDP failed on Ubuntu 20.04, kernel version is 5.4 about ebpf

[loveyacper]

In features/prog.go, it says XDP is supported from version 4.8 :

var haveProgramTypeMatrix = internal.FeatureMatrix[ebpf.ProgramType]{
	...
	ebpf.XDP:           {Version: "4.8"},
        ...
}

But AttachXDP call haveBPFLink, which report error if kernel version is older than 5.7 :

var haveBPFLink = internal.NewFeatureTest("bpf_link", "5.7", func() error {
	...
        return err
})

[florianl]

Hi @loveyacper

The eBPF program type XDP was introduced earlier (with 4.8 iirc) than bpf_link (5.7). As a consequence, bpf_link is expected to not be available on a 5.4 kernel.
You can still load XDP programs, but you have to use another method, like ip link set .... This package cilium/ebpf focuses on everything around the eBPF syscall - therefore it does not cover the loading via ip link set ....
A package, that supports loading of XDP on kernels that do not have support for bpf_link is jsimonetti/rtnetlink/v2#LinkService.Set.
Feel free to checkout https://gist.github.com/florianl/935cfcbeeee209537d8303165dab41e0 as an example for this.

[loveyacper]

@florianl I tried and it worked. I appreciate your helpful and timely reply.