Re: [PATCH bpf-next] libbpf: add extra BPF_PROG_TYPE check to bpf_object__probe_loading

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

On Fri, Jun 18, 2021 at 4:13 PM jjedwa165
<jonathan.edwards@165gc.onmicrosoft.com> wrote:
>
> eBPF has been backported for RHEL 7 w/ kernel 3.10-940+ [0]. However
> only the following program types are supported [1]
>
> BPF_PROG_TYPE_KPROBE
> BPF_PROG_TYPE_TRACEPOINT
> BPF_PROG_TYPE_PERF_EVENT
>
> For libbpf this causes an EINVAL return during the bpf_object__probe_loading
> call which only checks to see if programs of type BPF_PROG_TYPE_SOCKET_FILTER
> can load.
>
> The following will try BPF_PROG_TYPE_TRACEPOINT as a fallback attempt before
> erroring out. BPF_PROG_TYPE_KPROBE was not a good candidate because on some
> kernels it requires knowledge of the LINUX_VERSION_CODE.
>
> [0] https://www.redhat.com/en/blog/introduction-ebpf-red-hat-enterprise-linux-7
> [1] https://access.redhat.com/articles/3550581
>
> Signed-off-by: jjedwa165 <jonathan.edwards@165gc.onmicrosoft.com>
> ---

LGTM, but please re-submit with your real first and last name in
Signed-off-by. Also add my ack:

Acked-by: Andrii Nakryiko <andrii@kernel.org>

>  tools/lib/bpf/libbpf.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 48c0ade05..1e04ce724 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -4000,6 +4000,10 @@ bpf_object__probe_loading(struct bpf_object *obj)
>         attr.license = "GPL";
>
>         ret = bpf_load_program_xattr(&attr, NULL, 0);
> +       if (ret < 0) {
> +               attr.prog_type = BPF_PROG_TYPE_TRACEPOINT;
> +               ret = bpf_load_program_xattr(&attr, NULL, 0);
> +       }
>         if (ret < 0) {
>                 ret = errno;
>                 cp = libbpf_strerror_r(ret, errmsg, sizeof(errmsg));
> --
> 2.17.1
>