Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> writes: > On Tue, Jan 21, 2020 at 04:37:31PM +0100, Toke Høiland-Jørgensen wrote: >> Alexei Starovoitov <ast@xxxxxxxxxx> writes: >> >> > The last few month BPF community has been discussing an approach to call >> > chaining, since exiting bpt_tail_call() mechanism used in production XDP >> > programs has plenty of downsides. The outcome of these discussion was a >> > conclusion to implement dynamic re-linking of BPF programs. Where rootlet XDP >> > program attached to a netdevice can programmatically define a policy of >> > execution of other XDP programs. Such rootlet would be compiled as normal XDP >> > program and provide a number of placeholder global functions which later can be >> > replaced with future XDP programs. BPF trampoline, function by function >> > verification were building blocks towards that goal. The patch 1 is a final >> > building block. It introduces dynamic program extensions. A number of >> > improvements like more flexible function by function verification and better >> > libbpf api will be implemented in future patches. >> >> This is great, thank you! I'll go play around with it; couldn't spot >> anything obvious from eye-balling the code, except that yeah, it does >> need a more flexible libbpf api :) >> >> One thing that's not obvious to me: How can userspace tell which >> programs replace which functions after they are loaded? Is this put into >> prog_tags in struct bpf_prog_info, or? > > good point. Would be good to extend bpf_prog_info. Since prog-to-prog > connection is unidirectional the bpf_prog_info of extension prog will be able > to say which original program it's replacing. Yeah, that'll do. I can live with having to enumerate all programs and backtrack to the attached XDP program to figure out its component parts. > bpftool prog show will be able to print all this data. I think > fenry/fexit progs would need the same bpf_prog_info extension. > attach_prog_id + attach_btf_id would be enough. Yes, please. I actually assumed this was already there for fentry/fexit, which is why I was puzzled I couldn't find where this series hooked into that. I'll just wait for such an extension to show up, then :) > In the mean time I can try to hack drgn script to do the same. That would be great, thanks! -Toke
