On 15 November 2023 03:45:41 GMT-05:00, Alan Maguire <alan.maguire@xxxxxxxxxx> wrote:
>On 14/11/2023 05:10, Quentin Monnet wrote:
>> 2023-11-12 12:49 UTC+0000 ~ Alan Maguire <alan.maguire@xxxxxxxxxx>
>>> Provide a way to dump BTF metadata info via bpftool; this
>>> consists of BTF size, header fields and kind layout info
>>> (if available); for example
>>>
>>> $ bpftool btf dump file vmlinux format meta
>>> size 5161076
>>> magic 0xeb9f
>>> version 1
>>> flags 0x1
>>> hdr_len 40
>>> type_len 3036368
>>> type_off 0
>>> str_len 2124588
>>> str_off 3036368
>>> kind_layout_len 80
>>> kind_layout_off 5160956
>>> crc 0x64af901b
>>> base_crc 0x0
>>> kind 0 UNKNOWN flags 0x0 info_sz 0 elem_sz 0
>>> kind 1 INT flags 0x0 info_sz 0 elem_sz 0
>>> kind 2 PTR flags 0x0 info_sz 0 elem_sz 0
>>> kind 3 ARRAY flags 0x0 info_sz 0 elem_sz 0
>>> kind 4 STRUCT flags 0x35 info_sz 0 elem_sz 0
>>> ...
>>>
>>> JSON output is also supported:
>>>
>>> $ bpftool -j btf dump file vmlinux format meta
>>> {"size":5161076,"header":{"magic":60319,"version":1,"flags":1,"hdr_len":40,"type_len":3036368,"type_off":0,"str_len":2124588,"str_off":3036368,"kind_layout_len":80,"kind_layout_offset":5160956,"crc":1689227291,"base_crc":0},"kind_layouts":[{"kind":0,"name":"UNKNOWN","flags":0,"info_sz":0,"elem_sz":0},{"kind":1,"name":"INT","flags":0,"info_sz":0,"elem_sz":0},{"kind":2,"name":"PTR","flags":0,"info_sz":0,"elem_sz":0},{"kind":3,"name":"ARRAY","flags":0,"info_sz":0,"elem_sz":0},{"kind":4,"name":"STRUCT","flags":53,"info_sz":0,"elem_sz":0},{"kind":5,"name":"UNION","flags":0,"info_sz":0,"elem_sz":0},{"kind":6,"name":"ENUM","flags":60319,"info_sz":1,"elem_sz":1},{"kind":7,"name":"FWD","flags":40,"info_sz":0,"elem_sz":0},{"kind":8,"name":"TYPEDEF","flags":0,"info_sz":0,"elem_sz":0},{"kind":9,"name":"VOLATILE","flags":0,"info_sz":0,"elem_sz":0},{"kind":10,"name":"CONST","flags":0,"info_sz":0,"elem_sz":0},{"kind":11,"name":"RESTRICT","flags":1,"info_sz":0,"elem_sz":0},{"kind":12,"name":"FUNC","flags":0,"info_sz":0,"elem_sz":0},{"kind":13,"name":"FUNC_PROTO","flags":80,"info_sz":0,"elem_sz":0},{"kind":14,"name":"VAR","flags":0,"info_sz":0,"elem_sz":0},{"kind":15,"name":"DATASEC","flags":0,"info_sz":0,"elem_sz":0},{"kind":16,"name":"FLOAT","flags":53,"info_sz":0,"elem_sz":0},{"kind":17,"name":"DECL_TAG","flags":0,"info_sz":0,"elem_sz":0},{"kind":18,"name":"TYPE_TAG","flags":11441,"info_sz":3,"elem_sz":0},{"kind":19,"name":"ENUM64","flags":0,"info_sz":0,"elem_sz":0}]}
>>>
>>> Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
>>> ---
>>> tools/bpf/bpftool/bash-completion/bpftool | 2 +-
>>> tools/bpf/bpftool/btf.c | 91 ++++++++++++++++++++++-
>>> 2 files changed, 90 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/tools/bpf/bpftool/bash-completion/bpftool b/tools/bpf/bpftool/bash-completion/bpftool
>>> index 6e4f7ce6bc01..157c3afd8247 100644
>>> --- a/tools/bpf/bpftool/bash-completion/bpftool
>>> +++ b/tools/bpf/bpftool/bash-completion/bpftool
>>> @@ -937,7 +937,7 @@ _bpftool()
>>> return 0
>>> ;;
>>> format)
>>> - COMPREPLY=( $( compgen -W "c raw" -- "$cur" ) )
>>> + COMPREPLY=( $( compgen -W "c raw meta" -- "$cur" ) )
>>> ;;
>>> *)
>>> # emit extra options
>>> diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
>>> index 91fcb75babe3..208f3a587534 100644
>>> --- a/tools/bpf/bpftool/btf.c
>>> +++ b/tools/bpf/bpftool/btf.c
>>> @@ -504,6 +504,88 @@ static int dump_btf_c(const struct btf *btf,
>>> return err;
>>> }
>>>
>>> +static int dump_btf_meta(const struct btf *btf)
>>> +{
>>> + const struct btf_header *hdr;
>>> + const struct btf_kind_layout *k;
>>> + __u8 i, nr_kinds = 0;
>>> + const void *data;
>>> + __u32 data_sz;
>>> +
>>> + data = btf__raw_data(btf, &data_sz);
>>> + if (!data)
>>> + return -ENOMEM;
>>> + hdr = data;
>>> + if (json_output) {
>>> + jsonw_start_object(json_wtr); /* btf metadata object */
>>
>> Nit: Please make sure to be consistent when aligning these comments:
>> there are several occurrences with spaces (here three spaces), several
>> ones with tabs. For these, I'd prefer tabs to align the start and end
>> comments for a given object/array, although I don't really using a
>> single space as well as long as we keep it consistent.
>>
>>> + jsonw_uint_field(json_wtr, "size", data_sz);
>>> + jsonw_name(json_wtr, "header");
>>> + jsonw_start_object(json_wtr); /* btf header object */
>>> + jsonw_uint_field(json_wtr, "magic", hdr->magic);
>>> + jsonw_uint_field(json_wtr, "version", hdr->version);
>>> + jsonw_uint_field(json_wtr, "flags", hdr->flags);
>>> + jsonw_uint_field(json_wtr, "hdr_len", hdr->hdr_len);
>>> + jsonw_uint_field(json_wtr, "type_len", hdr->type_len);
>>> + jsonw_uint_field(json_wtr, "type_off", hdr->type_off);
>>> + jsonw_uint_field(json_wtr, "str_len", hdr->str_len);
>>> + jsonw_uint_field(json_wtr, "str_off", hdr->str_off);
>>> + } else {
>>> + printf("size %-10d\n", data_sz);
>>> + printf("magic 0x%-10x\nversion %-10d\nflags 0x%-10x\nhdr_len %-10d\n",
>>> + hdr->magic, hdr->version, hdr->flags, hdr->hdr_len);
>>> + printf("type_len %-10d\ntype_off %-10d\n", hdr->type_len, hdr->type_off);
>>> + printf("str_len %-10d\nstr_off %-10d\n", hdr->str_len, hdr->str_off);
>>> + }
>>> +
>>> + if (hdr->hdr_len < sizeof(struct btf_header)) {
>>> + if (json_output) {
>>> + jsonw_end_object(json_wtr); /* header object */
>>> + jsonw_end_object(json_wtr); /* metadata object */
>>
>> Similarly, can you please keep consistent comment strings? "metadata
>> object" here vs. "end metadata" below.
>>
>
>Sure, I'll fix indent consistency/naming and the docs issue in the
>next revision. Thanks!
>
>>> + }
>>> + return 0;
>>> + }
>>> + if (hdr->kind_layout_len > 0 && hdr->kind_layout_off > 0) {
>>> + k = (void *)hdr + hdr->hdr_len + hdr->kind_layout_off;
>>> + nr_kinds = hdr->kind_layout_len / sizeof(*k);
>>> + }
>>> + if (json_output) {
>>> + jsonw_uint_field(json_wtr, "kind_layout_len", hdr->kind_layout_len);
>>> + jsonw_uint_field(json_wtr, "kind_layout_offset", hdr->kind_layout_off);
>>> + jsonw_uint_field(json_wtr, "crc", hdr->crc);
>>> + jsonw_uint_field(json_wtr, "base_crc", hdr->base_crc);
>>> + jsonw_end_object(json_wtr); /* end header object */
>>> +
>>> + if (nr_kinds > 0) {
>>> + jsonw_name(json_wtr, "kind_layouts");
>>> + jsonw_start_array(json_wtr);
>>> + for (i = 0; i < nr_kinds; i++) {
>>> + jsonw_start_object(json_wtr);
>>> + jsonw_uint_field(json_wtr, "kind", i);
>>> + if (i < NR_BTF_KINDS)
>>> + jsonw_string_field(json_wtr, "name", btf_kind_str[i]);
>>
>> I prefer to avoid conditional fields in JSON, especially in an array
>> it's easier to process the JSON if all items have the same structure.
>> Would it make sense to keep the "name" field, but use jsonw_null() (or
>> "UNKNOWN") for the value when there's no name to print?
>>
>
>The only thing about UNKNOWN is that there is a BTF_KIND_UNKN that
>is displayed as UNKNOWN; what about "?" to be consistent with the
>non-json output (or if there's another option of course, we could
>use that for both)? Thanks!
Right, sorry, I realised just after sending my message.
In that case we could just use a 'null' value in JSON with jsonw_null()? The object '{"name": null}' is valid. The question mark is another possibility but requires comparing strings when parsing the JSON.
Thanks,
Quentin
