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Date: Tue, 2 Jul 2019 12:18:48 -0700
From: Y Song <ys114321@...il.com>
To: Andrii Nakryiko <andriin@...com>
Cc: andrii.nakryiko@...il.com, Alexei Starovoitov <ast@...com>,
Daniel Borkmann <daniel@...earbox.net>,
bpf <bpf@...r.kernel.org>, netdev <netdev@...r.kernel.org>,
Song Liu <songliubraving@...com>
Subject: Re: [PATCH v2 bpf-next 1/4] libbpf: capture value in BTF type info
for BTF-defined map defs
On Fri, Jun 28, 2019 at 8:26 AM Andrii Nakryiko <andriin@...com> wrote:
>
> Change BTF-defined map definitions to capture compile-time integer
> values as part of BTF type definition, to avoid split of key/value type
> information and actual type/size/flags initialization for maps.
>
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
> tools/lib/bpf/libbpf.c | 58 ++++++++++++++++++++----------------------
> 1 file changed, 28 insertions(+), 30 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 6e6ebef11ba3..9e099ecb2c2b 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -1028,40 +1028,40 @@ static const struct btf_type *skip_mods_and_typedefs(const struct btf *btf,
> }
> }
>
> -static bool get_map_field_int(const char *map_name,
> - const struct btf *btf,
> +/*
> + * Fetch integer attribute of BTF map definition. Such attributes are
> + * represented using a pointer to an array, in which dimensionality of array
> + * encodes specified integer value. E.g., int (*type)[BPF_MAP_TYPE_ARRAY];
> + * encodes `type => BPF_MAP_TYPE_ARRAY` key/value pair completely using BTF
> + * type definition, while using only sizeof(void *) space in ELF data section.
> + */
> +static bool get_map_field_int(const char *map_name, const struct btf *btf,
> const struct btf_type *def,
> - const struct btf_member *m,
> - const void *data, __u32 *res) {
> + const struct btf_member *m, __u32 *res) {
> const struct btf_type *t = skip_mods_and_typedefs(btf, m->type);
> const char *name = btf__name_by_offset(btf, m->name_off);
> - __u32 int_info = *(const __u32 *)(const void *)(t + 1);
> + const struct btf_array *arr_info;
> + const struct btf_type *arr_t;
>
> - if (BTF_INFO_KIND(t->info) != BTF_KIND_INT) {
> - pr_warning("map '%s': attr '%s': expected INT, got %u.\n",
> + if (BTF_INFO_KIND(t->info) != BTF_KIND_PTR) {
> + pr_warning("map '%s': attr '%s': expected PTR, got %u.\n",
> map_name, name, BTF_INFO_KIND(t->info));
> return false;
> }
> - if (t->size != 4 || BTF_INT_BITS(int_info) != 32 ||
> - BTF_INT_OFFSET(int_info)) {
> - pr_warning("map '%s': attr '%s': expected 32-bit non-bitfield integer, "
> - "got %u-byte (%d-bit) one with bit offset %d.\n",
> - map_name, name, t->size, BTF_INT_BITS(int_info),
> - BTF_INT_OFFSET(int_info));
> - return false;
> - }
> - if (BTF_INFO_KFLAG(def->info) && BTF_MEMBER_BITFIELD_SIZE(m->offset)) {
> - pr_warning("map '%s': attr '%s': bitfield is not supported.\n",
> - map_name, name);
> +
> + arr_t = btf__type_by_id(btf, t->type);
> + if (!arr_t) {
> + pr_warning("map '%s': attr '%s': type [%u] not found.\n",
> + map_name, name, t->type);
> return false;
> }
> - if (m->offset % 32) {
> - pr_warning("map '%s': attr '%s': unaligned fields are not supported.\n",
> - map_name, name);
> + if (BTF_INFO_KIND(arr_t->info) != BTF_KIND_ARRAY) {
> + pr_warning("map '%s': attr '%s': expected ARRAY, got %u.\n",
> + map_name, name, BTF_INFO_KIND(arr_t->info));
> return false;
> }
> -
> - *res = *(const __u32 *)(data + m->offset / 8);
> + arr_info = (const void *)(arr_t + 1);
> + *res = arr_info->nelems;
Here, we use number of array elements (__u32 type) as the value.
But we have
#define __int(name, val) int (*name)[val]
which suggests that "val" have type "int".
Do you think using __uint(name, val) may be more consistent?
If this is something to be enforced, it may be worthwhile to check
array element type should be __uint, just in case that in the
future we have different array element type (e.g., int)
for different purpose.
> return true;
> }
>
> @@ -1074,7 +1074,6 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj,
> const struct btf_var_secinfo *vi;
> const struct btf_var *var_extra;
> const struct btf_member *m;
> - const void *def_data;
> const char *map_name;
> struct bpf_map *map;
> int vlen, i;
> @@ -1131,7 +1130,6 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj,
> pr_debug("map '%s': at sec_idx %d, offset %zu.\n",
> map_name, map->sec_idx, map->sec_offset);
>
> - def_data = data->d_buf + vi->offset;
> vlen = BTF_INFO_VLEN(def->info);
> m = (const void *)(def + 1);
> for (i = 0; i < vlen; i++, m++) {
> @@ -1144,19 +1142,19 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj,
> }
> if (strcmp(name, "type") == 0) {
> if (!get_map_field_int(map_name, obj->btf, def, m,
> - def_data, &map->def.type))
> + &map->def.type))
> return -EINVAL;
> pr_debug("map '%s': found type = %u.\n",
> map_name, map->def.type);
> } else if (strcmp(name, "max_entries") == 0) {
> if (!get_map_field_int(map_name, obj->btf, def, m,
> - def_data, &map->def.max_entries))
> + &map->def.max_entries))
> return -EINVAL;
> pr_debug("map '%s': found max_entries = %u.\n",
> map_name, map->def.max_entries);
> } else if (strcmp(name, "map_flags") == 0) {
> if (!get_map_field_int(map_name, obj->btf, def, m,
> - def_data, &map->def.map_flags))
> + &map->def.map_flags))
> return -EINVAL;
> pr_debug("map '%s': found map_flags = %u.\n",
> map_name, map->def.map_flags);
> @@ -1164,7 +1162,7 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj,
> __u32 sz;
>
> if (!get_map_field_int(map_name, obj->btf, def, m,
> - def_data, &sz))
> + &sz))
> return -EINVAL;
> pr_debug("map '%s': found key_size = %u.\n",
> map_name, sz);
> @@ -1207,7 +1205,7 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj,
> __u32 sz;
>
> if (!get_map_field_int(map_name, obj->btf, def, m,
> - def_data, &sz))
> + &sz))
> return -EINVAL;
> pr_debug("map '%s': found value_size = %u.\n",
> map_name, sz);
> --
> 2.17.1
>
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