Re: [PATCH bpf-next 1/3] bpf: btf: export btf types and name by offset from lib

[Song Liu <songliubraving@fb.com>]

> On Jun 20, 2018, at 1:30 PM, Okash Khawaja <osk@fb.com> wrote:
> 
> This patch introduces btf__resolve_type() function and exports two
> existing functions from libbpf. btf__resolve_type follows modifier
> types like const and typedef until it hits a type which actually takes
> up memory, and then returns it. This function follows similar pattern
> to btf__resolve_size but instead of computing size, it just returns
> the type.
> 
> These  functions will be used in the followig patch which parses
> information inside array of `struct btf_type *`. btf_name_by_offset is
> used for printing variable names.
> 
> Signed-off-by: Okash Khawaja <osk@fb.com>
> Acked-by: Martin KaFai Lau <kafai@fb.com>
> 
> ---
> tools/lib/bpf/btf.c |   65 ++++++++++++++++++++++++++++++++++++----------------
> tools/lib/bpf/btf.h |    3 ++
> 2 files changed, 48 insertions(+), 20 deletions(-)
> 
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -17,6 +17,11 @@
> 
> #define BTF_MAX_NR_TYPES 65535
> 
> +#define IS_MODIFIER(k) (((k) == BTF_KIND_TYPEDEF) || \
> +		((k) == BTF_KIND_VOLATILE) || \
> +		((k) == BTF_KIND_CONST) || \
> +		((k) == BTF_KIND_RESTRICT))
> +
> static struct btf_type btf_void;
> 
> struct btf {
> @@ -33,14 +38,6 @@ struct btf {
> 	int fd;
> };
> 
> -static const char *btf_name_by_offset(const struct btf *btf, uint32_t offset)
> -{
> -	if (offset < btf->hdr->str_len)
> -		return &btf->strings[offset];
> -	else
> -		return NULL;
> -}
> -
> static int btf_add_type(struct btf *btf, struct btf_type *t)
> {
> 	if (btf->types_size - btf->nr_types < 2) {
> @@ -190,15 +187,6 @@ static int btf_parse_type_sec(struct btf
> 	return 0;
> }
> 
> -static const struct btf_type *btf_type_by_id(const struct btf *btf,
> -					     uint32_t type_id)
> -{
> -	if (type_id > btf->nr_types)
> -		return NULL;
> -
> -	return btf->types[type_id];
> -}

nit: Why do we need to move these two functions to later of the file? 

Other than this,

Acked-by: Song Liu <songliubraving@fb.com>

> -
> static bool btf_type_is_void(const struct btf_type *t)
> {
> 	return t == &btf_void || BTF_INFO_KIND(t->info) == BTF_KIND_FWD;
> @@ -234,7 +222,7 @@ int64_t btf__resolve_size(const struct b
> 	int64_t size = -1;
> 	int i;
> 
> -	t = btf_type_by_id(btf, type_id);
> +	t = btf__type_by_id(btf, type_id);
> 	for (i = 0; i < MAX_RESOLVE_DEPTH && !btf_type_is_void_or_null(t);
> 	     i++) {
> 		size = btf_type_size(t);
> @@ -259,7 +247,7 @@ int64_t btf__resolve_size(const struct b
> 			return -EINVAL;
> 		}
> 
> -		t = btf_type_by_id(btf, type_id);
> +		t = btf__type_by_id(btf, type_id);
> 	}
> 
> 	if (size < 0)
> @@ -271,6 +259,26 @@ int64_t btf__resolve_size(const struct b
> 	return nelems * size;
> }
> 
> +int32_t btf__resolve_type(const struct btf *btf, uint32_t type_id)
> +{
> +	const struct btf_type *t;
> +	int depth = 0;
> +
> +	t = btf__type_by_id(btf, type_id);
> +	while (depth < MAX_RESOLVE_DEPTH &&
> +			!btf_type_is_void_or_null(t) &&
> +			IS_MODIFIER(BTF_INFO_KIND(t->info))) {
> +		type_id = t->type;
> +		t = btf__type_by_id(btf, type_id);
> +		depth++;
> +	}
> +
> +	if (depth == MAX_RESOLVE_DEPTH || btf_type_is_void_or_null(t))
> +		return -EINVAL;
> +
> +	return type_id;
> +}
> +
> int32_t btf__find_by_name(const struct btf *btf, const char *type_name)
> {
> 	uint32_t i;
> @@ -280,7 +288,7 @@ int32_t btf__find_by_name(const struct b
> 
> 	for (i = 1; i <= btf->nr_types; i++) {
> 		const struct btf_type *t = btf->types[i];
> -		const char *name = btf_name_by_offset(btf, t->name_off);
> +		const char *name = btf__name_by_offset(btf, t->name_off);
> 
> 		if (name && !strcmp(type_name, name))
> 			return i;
> @@ -371,3 +379,20 @@ int btf__fd(const struct btf *btf)
> {
> 	return btf->fd;
> }
> +
> +const char *btf__name_by_offset(const struct btf *btf, uint32_t offset)
> +{
> +	if (offset < btf->hdr->str_len)
> +		return &btf->strings[offset];
> +	else
> +		return NULL;
> +}
> +
> +const struct btf_type *btf__type_by_id(const struct btf *btf,
> +					     uint32_t type_id)
> +{
> +	if (type_id > btf->nr_types)
> +		return NULL;
> +
> +	return btf->types[type_id];
> +}
> --- a/tools/lib/bpf/btf.h
> +++ b/tools/lib/bpf/btf.h
> @@ -17,6 +17,9 @@ void btf__free(struct btf *btf);
> struct btf *btf__new(uint8_t *data, uint32_t size, btf_print_fn_t err_log);
> int32_t btf__find_by_name(const struct btf *btf, const char *type_name);
> int64_t btf__resolve_size(const struct btf *btf, uint32_t type_id);
> +int32_t btf__resolve_type(const struct btf *btf, uint32_t type_id);
> int btf__fd(const struct btf *btf);
> +const char *btf__name_by_offset(const struct btf *btf, uint32_t offset);
> +const struct btf_type *btf__type_by_id(const struct btf *btf, uint32_t type_id);
> 
> #endif
>