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 3:48 PM, Okash Khawaja <osk@fb.com> wrote:
> 
> On Wed, Jun 20, 2018 at 11:40:19PM +0100, Song Liu wrote:
>> 
>> 
>>> 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? 
> No real reason. It looked like this file was following a convention of
> keeping statics together. I'll put them back in place if no one objects.

I see. Let's keep this patch as-is then. 

Thanks,
Song

> 
>> 
>> Other than this,
>> 
>> Acked-by: Song Liu <songliubraving@fb.com>
> Thanks
> 
>> 
>>> -
>>> 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