libbpf: Sync progs autoload with maps autocreate for struct_ops maps

Automatically select which struct_ops programs to load depending on
which struct_ops maps are selected for automatic creation.
E.g. for the BPF code below:

    SEC("struct_ops/test_1") int BPF_PROG(foo) { ... }
    SEC("struct_ops/test_2") int BPF_PROG(bar) { ... }

    SEC(".struct_ops.link")
    struct test_ops___v1 A = {
        .foo = (void *)foo
    };

    SEC(".struct_ops.link")
    struct test_ops___v2 B = {
        .foo = (void *)foo,
        .bar = (void *)bar,
    };

And the following libbpf API calls:

    bpf_map__set_autocreate(skel->maps.A, true);
    bpf_map__set_autocreate(skel->maps.B, false);

The autoload would be enabled for program 'foo' and disabled for
program 'bar'.

During load, for each struct_ops program P, referenced from some
struct_ops map M:
- set P.autoload = true if M.autocreate is true for some M;
- set P.autoload = false if M.autocreate is false for all M;
- don't change P.autoload, if P is not referenced from any map.

Do this after bpf_object__init_kern_struct_ops_maps()
to make sure that shadow vars assignment is done.
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240306104529.6453-9-eddyz87@gmail.com

tools/lib/bpf/libbpf.c

@@ -1031,6 +1031,48 @@ static bool is_valid_st_ops_program(struct bpf_object *obj,
 	return false;
 }
 
+/* For each struct_ops program P, referenced from some struct_ops map M,
+ * enable P.autoload if there are Ms for which M.autocreate is true,
+ * disable P.autoload if for all Ms M.autocreate is false.
+ * Don't change P.autoload for programs that are not referenced from any maps.
+ */
+static int bpf_object_adjust_struct_ops_autoload(struct bpf_object *obj)
+{
+	struct bpf_program *prog, *slot_prog;
+	struct bpf_map *map;
+	int i, j, k, vlen;
+
+	for (i = 0; i < obj->nr_programs; ++i) {
+		int should_load = false;
+		int use_cnt = 0;
+
+		prog = &obj->programs[i];
+		if (prog->type != BPF_PROG_TYPE_STRUCT_OPS)
+			continue;
+
+		for (j = 0; j < obj->nr_maps; ++j) {
+			map = &obj->maps[j];
+			if (!bpf_map__is_struct_ops(map))
+				continue;
+
+			vlen = btf_vlen(map->st_ops->type);
+			for (k = 0; k < vlen; ++k) {
+				slot_prog = map->st_ops->progs[k];
+				if (prog != slot_prog)
+					continue;
+
+				use_cnt++;
+				if (map->autocreate)
+					should_load = true;
+			}
+		}
+		if (use_cnt)
+			prog->autoload = should_load;
+	}
+
+	return 0;
+}
+
 /* Init the map's fields that depend on kern_btf */
 static int bpf_map__init_kern_struct_ops(struct bpf_map *map)
 {
@@ -8175,6 +8217,7 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch
 	err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);
 	err = err ? : bpf_object__sanitize_maps(obj);
 	err = err ? : bpf_object__init_kern_struct_ops_maps(obj);
+	err = err ? : bpf_object_adjust_struct_ops_autoload(obj);
 	err = err ? : bpf_object__relocate(obj, obj->btf_custom_path ? : target_btf_path);
 	err = err ? : bpf_object__sanitize_and_load_btf(obj);
 	err = err ? : bpf_object__create_maps(obj);