Re: [PATCH bpf-next 2/3] bpf: btf: add btf json print functionality

[Quentin Monnet <quentin.monnet@netronome.com>]

Hi Okash,

2018-06-20 13:30 UTC-0700 ~ Okash Khawaja <osk@fb.com>
> This consumes functionality exported in the previous patch. It does the
> main job of printing with BTF data. This is used in the following patch
> to provide a more readable output of a map's dump. It relies on
> json_writer to do json printing. Below is sample output where map keys
> are ints and values are of type struct A:
> 
> typedef int int_type;
> enum E {
>         E0,
>         E1,
> };
> 
> struct B {
>         int x;
>         int y;
> };
> 
> struct A {
>         int m;
>         unsigned long long n;
>         char o;
>         int p[8];
>         int q[4][8];
>         enum E r;
>         void *s;
>         struct B t;
>         const int u;
>         int_type v;
>         unsigned int w1: 3;
>         unsigned int w2: 3;
> };
> 
> $ sudo bpftool map dump -p id 14
> [{
>         "key": 0
>     },{
>         "value": {
>             "m": 1,
>             "n": 2,
>             "o": "c",
>             "p": [15,16,17,18,15,16,17,18
>             ],
>             "q": [[25,26,27,28,25,26,27,28
>                 ],[35,36,37,38,35,36,37,38
>                 ],[45,46,47,48,45,46,47,48
>                 ],[55,56,57,58,55,56,57,58
>                 ]
>             ],
>             "r": 1,
>             "s": 0x7ffff6f70568,

Hexadecimal values, without quotes, are not valid JSON. Please stick to
decimal values.

>             "t": {
>                 "x": 5,
>                 "y": 10
>             },
>             "u": 100,
>             "v": 20,
>             "w1": 0x7,
>             "w2": 0x3
>         }
>     }
> ]
> 
> This patch uses json's {} and [] to imply struct/union and array. More
> explicit information can be added later. For example, a command line
> option can be introduced to print whether a key or value is struct
> or union, name of a struct etc. This will however come at the expense
> of duplicating info when, for example, printing an array of structs.
> enums are printed as ints without their names.
> 
> Signed-off-by: Okash Khawaja <osk@fb.com>
> Acked-by: Martin KaFai Lau <kafai@fb.com>
> 
> ---
>  tools/bpf/bpftool/btf_dumper.c |  247 +++++++++++++++++++++++++++++++++++++++++
>  tools/bpf/bpftool/btf_dumper.h |   18 ++
>  2 files changed, 265 insertions(+)
> 
> --- /dev/null
> +++ b/tools/bpf/bpftool/btf_dumper.c
> @@ -0,0 +1,247 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (c) 2018 Facebook */
> +
> +#include <linux/btf.h>
> +#include <linux/err.h>
> +#include <stdio.h> /* for (FILE *) used by json_writer */
> +#include <linux/bitops.h>
> +#include <string.h>
> +#include <ctype.h>
> +
> +#include "btf.h"
> +#include "json_writer.h"
> +
> +#define BITS_PER_BYTE_MASK (BITS_PER_BYTE - 1)
> +#define BITS_PER_BYTE_MASKED(bits) ((bits) & BITS_PER_BYTE_MASK)
> +#define BITS_ROUNDDOWN_BYTES(bits) ((bits) >> 3)
> +#define BITS_ROUNDUP_BYTES(bits) \
> +	(BITS_ROUNDDOWN_BYTES(bits) + !!BITS_PER_BYTE_MASKED(bits))
> +
> +static int btf_dumper_do_type(const struct btf *btf, uint32_t type_id,
> +		uint8_t bit_offset, const void *data, json_writer_t *jw);
> +
> +static void btf_dumper_ptr(const void *data, json_writer_t *jw)
> +{
> +	jsonw_printf(jw, "%p", *((uintptr_t *)data));
> +}
> +
> +static int btf_dumper_modifier(const struct btf *btf, uint32_t type_id,
> +		const void *data, json_writer_t *jw)
> +{
> +	int32_t actual_type_id = btf__resolve_type(btf, type_id);
> +	int ret;
> +
> +	if (actual_type_id < 0)
> +		return actual_type_id;
> +
> +	ret = btf_dumper_do_type(btf, actual_type_id, 0, data, jw);
> +
> +	return ret;
> +}
> +
> +static void btf_dumper_enum(const void *data, json_writer_t *jw)
> +{
> +	jsonw_printf(jw, "%d", *((int32_t *)data));
> +}
> +
> +static int btf_dumper_array(const struct btf *btf, uint32_t type_id,
> +		const void *data, json_writer_t *jw)
> +{
> +	const struct btf_type *t = btf__type_by_id(btf, type_id);
> +	struct btf_array *arr = (struct btf_array *)(t + 1);
> +	int64_t elem_size;
> +	uint32_t i;
> +	int ret;
> +
> +	elem_size = btf__resolve_size(btf, arr->type);
> +	if (elem_size < 0)
> +		return elem_size;
> +
> +	jsonw_start_array(jw);
> +	for (i = 0; i < arr->nelems; i++) {
> +		ret = btf_dumper_do_type(btf, arr->type, 0,
> +				data + (i * elem_size), jw);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	jsonw_end_array(jw);
> +
> +	return 0;
> +}
> +
> +static void btf_dumper_int_bits(uint32_t int_type, uint8_t bit_offset,
> +		const void *data, json_writer_t *jw)
> +{
> +	uint16_t total_bits_offset;
> +	uint32_t bits = BTF_INT_BITS(int_type);

Nit: Please use reverse-Christmas-tree here.

As for patch 3 you also have a number of continuation lines not aligned
on the opening parenthesis from the first line, throughout the patch
(please consider running checkpatch in "--strict" mode for the list).

> +	uint16_t bytes_to_copy;
> +	uint16_t bits_to_copy;
> +	uint8_t upper_bits;
> +	union {
> +		uint64_t u64_num;
> +		uint8_t u8_nums[8];
> +	} print_num;
> +
> +	total_bits_offset = bit_offset + BTF_INT_OFFSET(int_type);
> +	data += BITS_ROUNDDOWN_BYTES(total_bits_offset);
> +	bit_offset = BITS_PER_BYTE_MASKED(total_bits_offset);
> +	bits_to_copy = bits + bit_offset;
> +	bytes_to_copy = BITS_ROUNDUP_BYTES(bits_to_copy);
> +
> +	print_num.u64_num = 0;
> +	memcpy(&print_num.u64_num, data, bytes_to_copy);
> +
> +	upper_bits = BITS_PER_BYTE_MASKED(bits_to_copy);
> +	if (upper_bits) {
> +		uint8_t mask = (1 << upper_bits) - 1;
> +
> +		print_num.u8_nums[bytes_to_copy - 1] &= mask;
> +	}
> +
> +	print_num.u64_num >>= bit_offset;
> +
> +	jsonw_printf(jw, "0x%llx", print_num.u64_num);
> +}
> +
> +static int btf_dumper_int(const struct btf_type *t, uint8_t bit_offset,
> +		const void *data, json_writer_t *jw)
> +{
> +	uint32_t *int_type = (uint32_t *)(t + 1);
> +	uint32_t bits = BTF_INT_BITS(*int_type);
> +	int ret = 0;
> +
> +	/* if this is bit field */
> +	if (bit_offset || BTF_INT_OFFSET(*int_type) ||
> +			BITS_PER_BYTE_MASKED(bits)) {
> +		btf_dumper_int_bits(*int_type, bit_offset, data, jw);
> +		return ret;
> +	}
> +
> +	switch (BTF_INT_ENCODING(*int_type)) {
> +	case 0:
> +		if (BTF_INT_BITS(*int_type) == 64)
> +			jsonw_printf(jw, "%lu", *((uint64_t *)data));
> +		else if (BTF_INT_BITS(*int_type) == 32)
> +			jsonw_printf(jw, "%u", *((uint32_t *)data));
> +		else if (BTF_INT_BITS(*int_type) == 16)
> +			jsonw_printf(jw, "%hu", *((uint16_t *)data));
> +		else if (BTF_INT_BITS(*int_type) == 8)
> +			jsonw_printf(jw, "%hhu", *((uint8_t *)data));
> +		else
> +			btf_dumper_int_bits(*int_type, bit_offset, data, jw);
> +		break;
> +	case BTF_INT_SIGNED:
> +		if (BTF_INT_BITS(*int_type) == 64)
> +			jsonw_printf(jw, "%ld", *((int64_t *)data));
> +		else if (BTF_INT_BITS(*int_type) == 32)
> +			jsonw_printf(jw, "%d", *((int32_t *)data));
> +		else if (BTF_INT_BITS(*int_type) ==  16)
> +			jsonw_printf(jw, "%hd", *((int16_t *)data));
> +		else if (BTF_INT_BITS(*int_type) ==  8)
> +			jsonw_printf(jw, "%hhd", *((int8_t *)data));
> +		else
> +			btf_dumper_int_bits(*int_type, bit_offset, data, jw);
> +		break;
> +	case BTF_INT_CHAR:
> +		if (*((char *)data) == '\0')
> +			jsonw_null(jw);
> +		else if (isprint(*((char *)data)))
> +			jsonw_printf(jw, "\"%c\"", *((char *)data));
> +		else
> +			jsonw_printf(jw, "%hhx", *((char *)data));
> +		break;
> +	case BTF_INT_BOOL:
> +		jsonw_bool(jw, *((int *)data));
> +		break;
> +	default:
> +		/* shouldn't happen */
> +		ret = -EINVAL;
> +		break;
> +	}
> +
> +	return ret;
> +}
> +
> +static int btf_dumper_struct(const struct btf *btf, uint32_t type_id,
> +		const void *data, json_writer_t *jw)
> +{
> +	const struct btf_type *t = btf__type_by_id(btf, type_id);
> +	struct btf_member *m;
> +	int ret = 0;
> +	int i, vlen;
> +
> +	if (t == NULL)
> +		return -EINVAL;
> +
> +	vlen = BTF_INFO_VLEN(t->info);
> +	jsonw_start_object(jw);
> +	m = (struct btf_member *)(t + 1);
> +
> +	for (i = 0; i < vlen; i++) {
> +		jsonw_name(jw, btf__name_by_offset(btf, m[i].name_off));
> +		ret = btf_dumper_do_type(btf, m[i].type,
> +				BITS_PER_BYTE_MASKED(m[i].offset),
> +				data + BITS_ROUNDDOWN_BYTES(m[i].offset), jw);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	jsonw_end_object(jw);
> +
> +	return 0;
> +}
> +
> +static int btf_dumper_do_type(const struct btf *btf, uint32_t type_id,
> +		uint8_t bit_offset, const void *data, json_writer_t *jw)
> +{
> +	const struct btf_type *t = btf__type_by_id(btf, type_id);
> +	int ret = 0;
> +
> +	switch (BTF_INFO_KIND(t->info)) {
> +	case BTF_KIND_INT:
> +		ret = btf_dumper_int(t, bit_offset, data, jw);
> +		break;
> +	case BTF_KIND_STRUCT:
> +	case BTF_KIND_UNION:
> +		ret = btf_dumper_struct(btf, type_id, data, jw);
> +		break;
> +	case BTF_KIND_ARRAY:
> +		ret = btf_dumper_array(btf, type_id, data, jw);
> +		break;
> +	case BTF_KIND_ENUM:
> +		btf_dumper_enum(data, jw);
> +		break;
> +	case BTF_KIND_PTR:
> +		btf_dumper_ptr(data, jw);
> +		break;
> +	case BTF_KIND_UNKN:
> +		jsonw_printf(jw, "(unknown)");
> +		break;
> +	case BTF_KIND_FWD:
> +		/* map key or value can't be forward */
> +		ret = -EINVAL;
> +		break;
> +	case BTF_KIND_TYPEDEF:
> +	case BTF_KIND_VOLATILE:
> +	case BTF_KIND_CONST:
> +	case BTF_KIND_RESTRICT:
> +		ret = btf_dumper_modifier(btf, type_id, data, jw);
> +		break;
> +	default:
> +		jsonw_printf(jw, "(unsupported-kind");
> +		ret = -EINVAL;
> +		break;
> +	}
> +
> +	return ret;
> +}
> +
> +int32_t btf_dumper_type(const struct btf *btf, json_writer_t *jw,
> +		uint32_t type_id, const void *data)
> +{
> +	if (!jw)
> +		return -EINVAL;
> +
> +	return btf_dumper_do_type(btf, type_id, 0, data, jw);
> +}
> --- /dev/null
> +++ b/tools/bpf/bpftool/btf_dumper.h
> @@ -0,0 +1,18 @@
> +/* SPDX-License-Identifier: GPL-2.0 */

I believe SPDX tag in header files should use C++ style comments (//)?

> +/* Copyright (c) 2018 Facebook */
> +
> +#ifndef BTF_DUMPER_H
> +#define BTF_DUMPER_H
> +
> +/* btf_dumper_type - json print data along with type information
> + * @btf: btf instance initialised via btf__new()
> + * @jw: json writer used for printing
> + * @type_id: index in btf->types array. this points to the type to be dumped
> + * @data: pointer the actual data, i.e. the values to be printed
> + *
> + * Returns zero on success and negative error code otherwise
> + */
> +int32_t btf_dumper_type(const struct btf *btf, json_writer_t *jw,
> +		uint32_t type_id, void *data);
> +
> +#endif
> 

Thanks,
Quentin