On Wed, Jan 15, 2025 at 2:39 PM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote:
>
> libbpf automatically adjusts autoload for struct_ops programs,
> see libbpf.c:bpf_object_adjust_struct_ops_autoload.
>
> For example, if there is a map:
>
> SEC(".struct_ops.link")
> struct sched_ext_ops ops = {
> .enqueue = foo,
> .tick = bar,
> };
>
> Both 'foo' and 'bar' would be loaded if 'ops' autocreate is true,
> both 'foo' and 'bar' would be skipped if 'ops' autocreate is false.
>
> This means that when veristat processes object file with 'ops',
> it would load 4 programs in total: two programs per each
> 'process_prog' call.
>
> The adjustment occurs at object load time, and libbpf remembers
> association between 'ops' and 'foo'/'bar' at object open time.
> The only way to persuade libbpf to load one of two is to adjust map
> initial value, such that only one program is referenced.
> This patch does exactly that, significantly reducing time to process
> object files with big number of struct_ops programs.
>
> Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
> ---
> tools/testing/selftests/bpf/veristat.c | 39 ++++++++++++++++++++++++++
> 1 file changed, 39 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/veristat.c b/tools/testing/selftests/bpf/veristat.c
> index b47836ee7d4d..23b64faa54ab 100644
> --- a/tools/testing/selftests/bpf/veristat.c
> +++ b/tools/testing/selftests/bpf/veristat.c
> @@ -1103,6 +1103,42 @@ static int guess_prog_type_by_ctx_name(const char *ctx_name,
> return -ESRCH;
> }
>
> +/* Make sure only target program is referenced from struct_ops map,
> + * otherwise libbpf would automatically set autocreate for all
> + * referenced programs.
> + * See libbpf.c:bpf_object_adjust_struct_ops_autoload.
> + */
> +static void mask_unrelated_struct_ops_progs(struct bpf_object *obj,
> + struct bpf_map *map,
> + struct bpf_program *prog)
> +{
> + struct btf *btf = bpf_object__btf(obj);
> + const struct btf_type *t, *mt;
> + struct btf_member *m;
> + int i, ptr_sz, moff;
> + size_t data_sz;
> + void *data;
> +
> + t = btf__type_by_id(btf, bpf_map__btf_value_type_id(map));
> + if (!btf_is_struct(t))
> + return;
> +
> + data = bpf_map__initial_value(map, &data_sz);
> + ptr_sz = min(btf__pointer_size(btf), sizeof(void *));
btf__pointer_size() for .bpf.o should always be 8, so this min is
pointless, I think. I can simplify to just ptr_sz = sizeof(void *)
while applying, if you agree. Let me know.
Other than that looks good.
> + for (i = 0; i < btf_vlen(t); i++) {
> + m = &btf_members(t)[i];
> + mt = btf__type_by_id(btf, m->type);
> + if (!btf_is_ptr(mt))
> + continue;
> + moff = m->offset / 8;
> + if (moff + ptr_sz > data_sz)
> + continue;
> + if (memcmp(data + moff, &prog, ptr_sz) == 0)
> + continue;
> + memset(data + moff, 0, ptr_sz);
> + }
> +}
> +
> static void fixup_obj(struct bpf_object *obj, struct bpf_program *prog, const char *filename)
> {
> struct bpf_map *map;
> @@ -1118,6 +1154,9 @@ static void fixup_obj(struct bpf_object *obj, struct bpf_program *prog, const ch
> case BPF_MAP_TYPE_INODE_STORAGE:
> case BPF_MAP_TYPE_CGROUP_STORAGE:
> break;
> + case BPF_MAP_TYPE_STRUCT_OPS:
> + mask_unrelated_struct_ops_progs(obj, map, prog);
> + break;
> default:
> if (bpf_map__max_entries(map) == 0)
> bpf_map__set_max_entries(map, 1);
> --
> 2.47.1
>
