Plans for supporting the libxdp protocol for attaching XDP component programs?

[thediveo]

Please forgive me in case I've missed this feature, but looking especially at link.go I'm under the impression that this isn't supported yet.

libxdp's README.org and especially libxdp/protocol.org describe a protocol that allows to modularize XDP programs into what I think is called "components". As this is done in user space, libxdp documents the protocol behind it, not least that other implementation (such as a Go native, non-libxdp/cgo) can successfully interoperate with libxdp.

Are there any plans on supporting the component feature in the cilium/ebpf module?

[ti-mo]

libxdp is a project built on top of libbpf, so another Go library could implement the same approach on top of ebpf-go. libxdp takes a highly opinionated approach, so for the same reason libxdp exists as a separate library from libbpf, ebpf-go is unlikely to ever implement a similar concept directly.

@dylandreimerink was working on an AF_XDP implementation some time ago, not sure if this is related.

[wenlxie]

@ti-mo @dylandreimerink Does libxdp (for attach multiple xdp prog) supported already? Thanks
With this, we can support to integrate 3rd party xdp programs like xdpcap to cilium xdp.

[dylandreimerink]

We do not support it "out of the box". However, you should be able to use the library to perform all of the steps. If I recall correctly you have to load your XDP program as an extention type program making sure to specify the correct kernel data type to attach to and attach program. And finally do the actual replacing of a dummy function in the dispatcher with your XDP program with a freplace link.

I suggest taking a look at the libxdp code to see how everything needs to be wired up, but all of the building blocks are there I believe.

[wenlxie]

@dylandreimerink thanks, I will take a look

[wenlxie]

@dylandreimerink
I am trying to have a Poc for cilium to support multiple xdp progs which works like xdp-tools
https://github.com/xdp-project/xdp-tools/tree/master/xdp-loader

I loaded the main prog xdp-dispatcher as XDP type.

	dispatcher, err := bpf.LoadCollectionSpec(option.Config.StateDir + "/xdp-dispatcher.o")
	if err != nil {
		return nil, fmt.Errorf("loading eBPF xdp-dispatcher ELF: %w", err)
	}
	l.Debugf("Loaded spec for xdp dispatcher:%+v", dispatcher)

	maincoll, err := bpf.LoadCollection(dispatcher, ebpf.CollectionOptions{})
	if err != nil {
		l.WithError(err).Errorf("Couldn't load xdp-dispatcher, err:%v", err)
		return nil, fmt.Errorf("Couldn't load xdp-dispatcher, err:%v", err)
	}

Then I load bpf_xdp.o of cilium as extention type.

1. LoadSpec from the objPath
2. Set the cil_xdp_entry prog to be extention type:

			prog.AttachTarget = maincoll.Programs["xdp_dispatcher"]
			prog.Type = ebpf.Extension
			prog.AttachType = ebpf.AttachNone
			prog.AttachTo = "prog0"
			spec.Programs[name] = prog

But when I load the bpf_xdp.o to kernel by bpf.LoadCollection, it shows the error

level=debug msg="Loading Collection into kernel" device=eth0 ifindex=86 objPath=/var/run/cilium/state/bpf_xdp.o subsys=datapath-loader
Verifier error: program cil_xdp_entry: load program: invalid argument
Verifier log: load program: invalid argument:
	processed 271 insns (limit 1000000) max_states_per_insn 0 total_states 22 peak_states 22 mark_read 6
level=fatal msg="Failed to compile XDP program" error="loading eBPF collection into the kernel: program cil_xdp_entry: load program: invalid argument" subsys=datapath-loader

4. Then I try to load a simple xdp prog as the extention type, then there is no invalid argument errors.

5. So I am not sure what's the error in bpf_xdp.o, any suggestions?

6. Another question is:
   bpf_xdp.o has lots of tailcalls, do you know how to set the type/attach type/AttachTarget of these tailed programs?

Appreciate that if you can help to have a check. Thanks