Re: [PATCH iproute2] libbpf: fix attach of prog with multiple sections

On Wed, Jul 21, 2021 at 04:47:14PM +0200, Martynas Pumputis wrote:

quoted

quoted

diff --git a/lib/bpf_libbpf.c b/lib/bpf_libbpf.c
index d05737a4..f76b90d2 100644
--- a/lib/bpf_libbpf.c
+++ b/lib/bpf_libbpf.c

@@ -267,10 +267,12 @@ static int load_bpf_object(struct bpf_cfg_in *cfg)
         }

         bpf_object__for_each_program(p, obj) {
+               bool prog_to_attach = !prog && cfg->section &&
+                       !strcmp(get_bpf_program__section_name(p), cfg->section);

This is still problematic, because one section can have multiple BPF
programs. I.e., it's possible two define two or more XDP BPF programs
all with SEC("xdp") and libbpf works just fine with that. I suggest
moving users to specify the program name (i.e., C function name
representing the BPF program). All the xdp_mycustom_suffix namings are
a hack and will be rejected by libbpf 1.0, so it would be great to get
a head start on fixing this early on.

Thanks for bringing this up. Currently, there is no way to specify a
function name with "tc exec bpf" (only a section name via the "sec" arg). So
probably, we should just add another arg to specify the function name.

How about add a "prog" arg to load specified program name and mark
"sec" as not recommended? To keep backwards compatibility we just load the
first program in the section.

Thanks
Hangbin