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Date: Thu, 22 Apr 2021 11:40:42 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Yonghong Song <yhs@...com>
Cc: Andrii Nakryiko <andrii@...nel.org>, bpf <bpf@...r.kernel.org>,
Networking <netdev@...r.kernel.org>,
Alexei Starovoitov <ast@...com>,
Daniel Borkmann <daniel@...earbox.net>,
Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 06/17] libbpf: refactor BTF map definition parsing
On Thu, Apr 22, 2021 at 8:33 AM Yonghong Song <yhs@...com> wrote:
>
>
>
> On 4/16/21 1:23 PM, Andrii Nakryiko wrote:
> > Refactor BTF-defined maps parsing logic to allow it to be nicely reused by BPF
> > static linker. Further, at least for BPF static linker, it's important to know
> > which attributes of a BPF map were defined explicitly, so provide a bit set
> > for each known portion of BTF map definition. This allows BPF static linker to
> > do a simple check when dealing with extern map declarations.
> >
> > The same capabilities allow to distinguish attributes explicitly set to zero
> > (e.g., __uint(max_entries, 0)) vs the case of not specifying it at all (no
> > max_entries attribute at all). Libbpf is currently not utilizing that, but it
> > could be useful for backwards compatibility reasons later.
> >
> > Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
> > ---
> > tools/lib/bpf/libbpf.c | 256 ++++++++++++++++++--------------
> > tools/lib/bpf/libbpf_internal.h | 32 ++++
> > 2 files changed, 177 insertions(+), 111 deletions(-)
> >
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index a0e6d6bc47f3..f6f4126389ac 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -2025,255 +2025,262 @@ static int build_map_pin_path(struct bpf_map *map, const char *path)
> > return bpf_map__set_pin_path(map, buf);
> > }
> >
> > -
> > -static int parse_btf_map_def(struct bpf_object *obj,
> > - struct bpf_map *map,
> > - const struct btf_type *def,
> > - bool strict, bool is_inner,
> > - const char *pin_root_path)
> > +int parse_btf_map_def(const char *map_name, struct btf *btf,
> > + const struct btf_type *def_t, bool strict,
> > + struct btf_map_def *map_def, struct btf_map_def *inner_def)
> > {
> > const struct btf_type *t;
> > const struct btf_member *m;
> > + bool is_inner = inner_def == NULL;
> > int vlen, i;
> >
> > - vlen = btf_vlen(def);
> > - m = btf_members(def);
> > + vlen = btf_vlen(def_t);
> > + m = btf_members(def_t);
> > for (i = 0; i < vlen; i++, m++) {
> > - const char *name = btf__name_by_offset(obj->btf, m->name_off);
> > + const char *name = btf__name_by_offset(btf, m->name_off);
> >
> [...]
> > }
> > else if (strcmp(name, "values") == 0) {
> > + char inner_map_name[128];
> > int err;
> >
> > if (is_inner) {
> > pr_warn("map '%s': multi-level inner maps not supported.\n",
> > - map->name);
> > + map_name);
> > return -ENOTSUP;
> > }
> > if (i != vlen - 1) {
> > pr_warn("map '%s': '%s' member should be last.\n",
> > - map->name, name);
> > + map_name, name);
> > return -EINVAL;
> > }
> > - if (!bpf_map_type__is_map_in_map(map->def.type)) {
> > + if (!bpf_map_type__is_map_in_map(map_def->map_type)) {
> > pr_warn("map '%s': should be map-in-map.\n",
> > - map->name);
> > + map_name);
> > return -ENOTSUP;
> > }
> > - if (map->def.value_size && map->def.value_size != 4) {
> > + if (map_def->value_size && map_def->value_size != 4) {
> > pr_warn("map '%s': conflicting value size %u != 4.\n",
> > - map->name, map->def.value_size);
> > + map_name, map_def->value_size);
> > return -EINVAL;
> > }
> > - map->def.value_size = 4;
> > - t = btf__type_by_id(obj->btf, m->type);
> > + map_def->value_size = 4;
> > + t = btf__type_by_id(btf, m->type);
> > if (!t) {
> > pr_warn("map '%s': map-in-map inner type [%d] not found.\n",
> > - map->name, m->type);
> > + map_name, m->type);
> > return -EINVAL;
> > }
> > if (!btf_is_array(t) || btf_array(t)->nelems) {
> > pr_warn("map '%s': map-in-map inner spec is not a zero-sized array.\n",
> > - map->name);
> > + map_name);
> > return -EINVAL;
> > }
> > - t = skip_mods_and_typedefs(obj->btf, btf_array(t)->type,
> > - NULL);
> > + t = skip_mods_and_typedefs(btf, btf_array(t)->type, NULL);
> > if (!btf_is_ptr(t)) {
> > pr_warn("map '%s': map-in-map inner def is of unexpected kind %s.\n",
> > - map->name, btf_kind_str(t));
> > + map_name, btf_kind_str(t));
> > return -EINVAL;
> > }
> > - t = skip_mods_and_typedefs(obj->btf, t->type, NULL);
> > + t = skip_mods_and_typedefs(btf, t->type, NULL);
> > if (!btf_is_struct(t)) {
> > pr_warn("map '%s': map-in-map inner def is of unexpected kind %s.\n",
> > - map->name, btf_kind_str(t));
> > + map_name, btf_kind_str(t));
> > return -EINVAL;
> > }
> >
> > - map->inner_map = calloc(1, sizeof(*map->inner_map));
> > - if (!map->inner_map)
> > - return -ENOMEM;
> > - map->inner_map->fd = -1;
> > - map->inner_map->sec_idx = obj->efile.btf_maps_shndx;
>
> The refactoring didn't set map->inner_map->sec_idx. I guess since
> inner_map is only used internally by libbpf, so it does not
> have a user visible sec_idx and hence useless? It is worthwhile to
> mention in the commit message for this difference, I think.
>
> > - map->inner_map->name = malloc(strlen(map->name) +
> > - sizeof(".inner") + 1);
> > - if (!map->inner_map->name)
> > - return -ENOMEM;
> > - sprintf(map->inner_map->name, "%s.inner", map->name);
> > -
> > - err = parse_btf_map_def(obj, map->inner_map, t, strict,
> > - true /* is_inner */, NULL);
> > + snprintf(inner_map_name, sizeof(inner_map_name), "%s.inner", map_name);
> > + err = parse_btf_map_def(inner_map_name, btf, t, strict, inner_def, NULL);
> > if (err)
> > return err;
> > +
> > + map_def->parts |= MAP_DEF_INNER_MAP;
> > } else if (strcmp(name, "pinning") == 0) {
> > __u32 val;
> > - int err;
> >
> > if (is_inner) {
> > - pr_debug("map '%s': inner def can't be pinned.\n",
> > - map->name);
> > + pr_warn("map '%s': inner def can't be pinned.\n", map_name);
> > return -EINVAL;
> > }
> > - if (!get_map_field_int(map->name, obj->btf, m, &val))
> > + if (!get_map_field_int(map_name, btf, m, &val))
> > return -EINVAL;
> > - pr_debug("map '%s': found pinning = %u.\n",
> > - map->name, val);
> > -
> > - if (val != LIBBPF_PIN_NONE &&
> > - val != LIBBPF_PIN_BY_NAME) {
> > + if (val != LIBBPF_PIN_NONE && val != LIBBPF_PIN_BY_NAME) {
> > pr_warn("map '%s': invalid pinning value %u.\n",
> > - map->name, val);
> > + map_name, val);
> > return -EINVAL;
> > }
> > - if (val == LIBBPF_PIN_BY_NAME) {
> > - err = build_map_pin_path(map, pin_root_path);
> > - if (err) {
> > - pr_warn("map '%s': couldn't build pin path.\n",
> > - map->name);
> > - return err;
> > - }
> > - }
> > + map_def->pinning = val;
> > + map_def->parts |= MAP_DEF_PINNING;
> > } else {
> > if (strict) {
> > - pr_warn("map '%s': unknown field '%s'.\n",
> > - map->name, name);
> > + pr_warn("map '%s': unknown field '%s'.\n", map_name, name);
> > return -ENOTSUP;
> > }
> > - pr_debug("map '%s': ignoring unknown field '%s'.\n",
> > - map->name, name);
> > + pr_debug("map '%s': ignoring unknown field '%s'.\n", map_name, name);
> > }
> > }
> >
> > - if (map->def.type == BPF_MAP_TYPE_UNSPEC) {
> > - pr_warn("map '%s': map type isn't specified.\n", map->name);
> > + if (map_def->map_type == BPF_MAP_TYPE_UNSPEC) {
> > + pr_warn("map '%s': map type isn't specified.\n", map_name);
> > return -EINVAL;
> > }
> >
> > return 0;
> > }
> >
> > +static void fill_map_from_def(struct bpf_map *map, const struct btf_map_def *def)
> > +{
> [...]
> > +}
> > +
> > static int bpf_object__init_user_btf_map(struct bpf_object *obj,
> > const struct btf_type *sec,
> > int var_idx, int sec_idx,
> > const Elf_Data *data, bool strict,
> > const char *pin_root_path)
> > {
> > + struct btf_map_def map_def = {}, inner_def = {};
> > const struct btf_type *var, *def;
> > const struct btf_var_secinfo *vi;
> > const struct btf_var *var_extra;
> > const char *map_name;
> > struct bpf_map *map;
> > + int err;
> >
> > vi = btf_var_secinfos(sec) + var_idx;
> > var = btf__type_by_id(obj->btf, vi->type);
> > @@ -2327,7 +2334,34 @@ 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);
> >
> > - return parse_btf_map_def(obj, map, def, strict, false, pin_root_path);
> > + err = parse_btf_map_def(map->name, obj->btf, def, strict, &map_def, &inner_def);
> > + if (err)
> > + return err;
> > +
> > + fill_map_from_def(map, &map_def);
> > +
> > + if (map_def.pinning == LIBBPF_PIN_BY_NAME) {
> > + err = build_map_pin_path(map, pin_root_path);
> > + if (err) {
> > + pr_warn("map '%s': couldn't build pin path.\n", map->name);
> > + return err;
> > + }
> > + }
> > +
> > + if (map_def.parts & MAP_DEF_INNER_MAP) {
> > + map->inner_map = calloc(1, sizeof(*map->inner_map));
> > + if (!map->inner_map)
> > + return -ENOMEM;
> > + map->inner_map->fd = -1;
>
> missing set map->inner_map->sec_idx here.
I'll add it back here, but it was never really necessary. More for the
completeness sake. sec_idx is used only to match relo to a map, and
this inner_map is never matched and never referenced by a relocation.
>
> > + map->inner_map->name = malloc(strlen(map_name) + sizeof(".inner") + 1);
> > + if (!map->inner_map->name)
> > + return -ENOMEM;
> > + sprintf(map->inner_map->name, "%s.inner", map_name);
> > +
> > + fill_map_from_def(map->inner_map, &inner_def);
> > + }
> > +
> > + return 0;
> > }
> >
> > static int bpf_object__init_user_btf_maps(struct bpf_object *obj, bool strict,
> > diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> > index 92b7eae10c6d..17883073710c 100644
> > --- a/tools/lib/bpf/libbpf_internal.h
> > +++ b/tools/lib/bpf/libbpf_internal.h
> > @@ -138,6 +138,38 @@ static inline __u32 btf_type_info(int kind, int vlen, int kflag)
> > return (kflag << 31) | (kind << 24) | vlen;
> > }
> >
> [...]
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