Re: [PATCH bpf-next v3 1/7] samples: bpf: refactor hbm program with libbpf

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Tue, Nov 24, 2020 at 1:03 AM Daniel T. Lee <danieltimlee@gmail.com> wrote:
>
> This commit refactors the existing cgroup programs with libbpf
> bpf loader. Since bpf_program__attach doesn't support cgroup program
> attachment, this explicitly attaches cgroup bpf program with
> bpf_program__attach_cgroup(bpf_prog, cg1).
>
> Also, to change attach_type of bpf program, this uses libbpf's
> bpf_program__set_expected_attach_type helper to switch EGRESS to
> INGRESS. To keep bpf program attached to the cgroup hierarchy even
> after the exit, this commit uses the BPF_LINK_PINNING to pin the link
> attachment even after it is closed.
>
> Besides, this program was broken due to the typo of BPF MAP definition.
> But this commit solves the problem by fixing this from 'queue_stats' map
> struct hvm_queue_stats -> hbm_queue_stats.
>
> Fixes: 36b5d471135c ("selftests/bpf: samples/bpf: Split off legacy stuff from bpf_helpers.h")
> Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
> ---
> Changes in v2:
>  - restore read_trace_pipe2
>  - remove unnecessary return code and cgroup fd compare
>  - add static at global variable and remove unused variable
>  - change cgroup path with unified controller (/unified/)
>  - add link pinning to prevent cleaning up on process exit
>
> Changes in v3:
>  - cleanup bpf_link, bpf_object and cgroup fd both on success and error
>  - remove link NULL cleanup since __destroy() can handle
>  - fix cgroup test on cgroup fd cleanup
>
>  samples/bpf/.gitignore     |   3 +
>  samples/bpf/Makefile       |   2 +-
>  samples/bpf/do_hbm_test.sh |  32 +++++------
>  samples/bpf/hbm.c          | 111 ++++++++++++++++++++-----------------
>  samples/bpf/hbm_kern.h     |   2 +-
>  5 files changed, 78 insertions(+), 72 deletions(-)
>

Thanks for the nice clean up! I've applied the series to bpf-next. If
Martin finds any other problems, those can be fixed in a follow up
patch(es). But see also below about find_program_by_title().

> -       if (ret) {
> -               printf("ERROR: bpf_prog_load_xattr failed for: %s\n", prog);
> -               printf("  Output from verifier:\n%s\n------\n", bpf_log_buf);
> -               ret = -1;
> -       } else {
> -               ret = map_fd;
> +       bpf_prog = bpf_object__find_program_by_title(obj, "cgroup_skb/egress");

It would be good to avoid using find_program_by_title(), as it's going
to get deprecated and eventually removed. Looking up by section name
("title") is ambiguous now that libbpf supports many BPF programs per
same section. There is find_program_by_name() which looks program by
its C function name. I suggest using it.


> +       if (!bpf_prog) {
> +               printf("ERROR: finding a prog in obj file failed\n");
> +               goto err;
> +       }
> +