libbpf: Add getter for program size

This adds a new getter for the BPF program size (in bytes). This is useful
for a caller that is trying to predict how much memory will be locked by
loading a BPF object into the kernel.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/157333185272.88376.10996937115395724683.stgit@toke.dk

tools/lib/bpf/libbpf.c

@@ -4782,6 +4782,11 @@ int bpf_program__fd(const struct bpf_program *prog)
 	return bpf_program__nth_fd(prog, 0);
 }
 
+size_t bpf_program__size(const struct bpf_program *prog)
+{
+	return prog->insns_cnt * sizeof(struct bpf_insn);
+}
+
 int bpf_program__set_prep(struct bpf_program *prog, int nr_instances,
 			  bpf_program_prep_t prep)
 {

tools/lib/bpf/libbpf.h

@@ -214,6 +214,9 @@ LIBBPF_API void bpf_program__set_ifindex(struct bpf_program *prog,
 LIBBPF_API const char *bpf_program__title(const struct bpf_program *prog,
 					  bool needs_copy);
 
+/* returns program size in bytes */
+LIBBPF_API size_t bpf_program__size(const struct bpf_program *prog);
+
 LIBBPF_API int bpf_program__load(struct bpf_program *prog, char *license,
 				 __u32 kern_version);
 LIBBPF_API int bpf_program__fd(const struct bpf_program *prog);

tools/lib/bpf/libbpf.map

@@ -203,4 +203,5 @@ LIBBPF_0.0.6 {
 		bpf_program__get_type;
 		bpf_program__is_tracing;
 		bpf_program__set_tracing;
+		bpf_program__size;
 } LIBBPF_0.0.5;