On Fri, Aug 28, 2020 at 12:37 PM Stanislav Fomichev <sdf@xxxxxxxxxx> wrote:
>
> From: YiFei Zhu <zhuyifei@xxxxxxxxxx>
>
> Added a flag "--metadata" to `bpftool prog list` to dump the metadata
> contents. For some formatting some BTF code is put directly in the
> metadata dumping. Sanity checks on the map and the kind of the btf_type
> to make sure we are actually dumping what we are expecting.
>
> A helper jsonw_reset is added to json writer so we can reuse the same
> json writer without having extraneous commas.
>
> Sample output:
>
> $ bpftool prog --metadata
> 6: cgroup_skb name prog tag bcf7977d3b93787c gpl
> [...]
> btf_id 4
> metadata:
> metadata_a = "foo"
> metadata_b = 1
>
> $ bpftool prog --metadata --json --pretty
> [{
> "id": 6,
> [...]
> "btf_id": 4,
> "metadata": {
> "metadata_a": "foo",
> "metadata_b": 1
> }
> }
> ]
>
> Cc: YiFei Zhu <zhuyifei1999@xxxxxxxxx>
> Signed-off-by: YiFei Zhu <zhuyifei@xxxxxxxxxx>
> Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> ---
> tools/bpf/bpftool/json_writer.c | 6 ++
> tools/bpf/bpftool/json_writer.h | 3 +
> tools/bpf/bpftool/main.c | 10 +++
> tools/bpf/bpftool/main.h | 1 +
> tools/bpf/bpftool/prog.c | 130 ++++++++++++++++++++++++++++++++
> 5 files changed, 150 insertions(+)
>
[...]
> +
> + if (bpf_map_lookup_elem(map_fd, &key, value)) {
> + p_err("metadata map lookup failed: %s", strerror(errno));
> + goto out_free;
> + }
> +
> + err = btf__get_from_id(map_info.btf_id, &btf);
what if the map has no btf_id associated (e.g., because of an old
kernel?); why fail in this case?
> + if (err || !btf) {
> + p_err("metadata BTF get failed: %s", strerror(-err));
> + goto out_free;
> + }
> +
> + t_datasec = btf__type_by_id(btf, map_info.btf_value_type_id);
> + if (BTF_INFO_KIND(t_datasec->info) != BTF_KIND_DATASEC) {
btf_is_datasec(t_datasec)
> + p_err("bad metadata BTF");
> + goto out_free;
> + }
> +
> + vlen = BTF_INFO_VLEN(t_datasec->info);
btf_vlen(t_datasec)
> + vsi = (struct btf_var_secinfo *)(t_datasec + 1);
btf_var_secinfos(t_datasec)
> +
> + /* We don't proceed to check the kinds of the elements of the DATASEC.
> + * The verifier enforce then to be BTF_KIND_VAR.
typo: then -> them
> + */
> +
> + if (json_output) {
> + struct btf_dumper d = {
> + .btf = btf,
> + .jw = json_wtr,
> + .is_plain_text = false,
> + };
> +
> + jsonw_name(json_wtr, "metadata");
> +
> + jsonw_start_object(json_wtr);
> + for (i = 0; i < vlen; i++) {
nit: doing ++vsi here
> + t_var = btf__type_by_id(btf, vsi[i].type);
and vsi->type here and below would look a bit cleaner
> +
> + jsonw_name(json_wtr, btf__name_by_offset(btf, t_var->name_off));
> + err = btf_dumper_type(&d, t_var->type, value + vsi[i].offset);
> + if (err) {
> + p_err("btf dump failed");
> + break;
> + }
> + }
> + jsonw_end_object(json_wtr);
[...]
