[bpf-next,v2,05/12] tools: libbpf: expose the prog type guessing from section name logic

libbpf can guess program type based on ELF section names.  As libbpf
becomes more popular its association between section name strings and
types becomes more of a standard.  Allow libbpf users to use the same
logic for matching strings to types, e.g. when the string originates
from command line.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
---
 tools/lib/bpf/libbpf.c | 43 ++++++++++++++++++++++++------------------
 tools/lib/bpf/libbpf.h |  3 +++
 2 files changed, 28 insertions(+), 18 deletions(-)

Jakub Kicinski <jakub.kicinski@netronome.com> [Mon, 2018-07-09 11:01 -0700]:
> libbpf can guess program type based on ELF section names.  As libbpf
> becomes more popular its association between section name strings and
> types becomes more of a standard.  Allow libbpf users to use the same
> logic for matching strings to types, e.g. when the string originates
> from command line.
> 
> Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
> Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
> ---
>  tools/lib/bpf/libbpf.c | 43 ++++++++++++++++++++++++------------------
>  tools/lib/bpf/libbpf.h |  3 +++
>  2 files changed, 28 insertions(+), 18 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 38ed3e92e393..30f3e58bd563 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -2081,25 +2081,33 @@ static const struct {
>  #undef BPF_S_PROG_SEC
>  #undef BPF_SA_PROG_SEC
>  
> -static int bpf_program__identify_section(struct bpf_program *prog)
> +int libbpf_prog_type_by_string(const char *name, enum bpf_prog_type *prog_type,
> +			       enum bpf_attach_type *expected_attach_type)
>  {
>  	int i;
>  
> -	if (!prog->section_name)
> -		goto err;
> -
> -	for (i = 0; i < ARRAY_SIZE(section_names); i++)
> -		if (strncmp(prog->section_name, section_names[i].sec,
> -			    section_names[i].len) == 0)
> -			return i;
> -
> -err:
> -	pr_warning("failed to guess program type based on section name %s\n",
> -		   prog->section_name);
> +	if (!name)
> +		return -1;

Should it return -EINVAL? It can help in bpf_prog_load_xattr below:

			err = bpf_program__identify_section(prog, &prog_type,
							    &expected_attach_type);
			if (err < 0) {
				...
				return err;
			}


>  
> +	for (i = 0; i < ARRAY_SIZE(section_names); i++) {
> +		if (strncmp(name, section_names[i].sec, section_names[i].len))
> +			continue;
> +		*prog_type = section_names[i].prog_type;
> +		*expected_attach_type = section_names[i].expected_attach_type;
> +		return 0;
> +	}
>  	return -1;

Same here.

>  }
>  
> +static int
> +bpf_program__identify_section(struct bpf_program *prog,
> +			      enum bpf_prog_type *prog_type,
> +			      enum bpf_attach_type *expected_attach_type)
> +{
> +	return libbpf_prog_type_by_string(prog->section_name, prog_type,
> +					  expected_attach_type);
> +}
> +
>  int bpf_map__fd(struct bpf_map *map)
>  {
>  	return map ? map->fd : -EINVAL;
> @@ -2230,7 +2238,6 @@ int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,
>  	enum bpf_prog_type prog_type;
>  	struct bpf_object *obj;
>  	struct bpf_map *map;
> -	int section_idx;
>  	int err;
>  
>  	if (!attr)
> @@ -2252,14 +2259,14 @@ int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,
>  		prog->prog_ifindex = attr->ifindex;
>  		expected_attach_type = attr->expected_attach_type;
>  		if (prog_type == BPF_PROG_TYPE_UNSPEC) {
> -			section_idx = bpf_program__identify_section(prog);
> -			if (section_idx < 0) {
> +			err = bpf_program__identify_section(prog, &prog_type,
> +							    &expected_attach_type);
> +			if (err < 0) {
> +				pr_warning("failed to guess program type based on section name %s\n",
> +					   prog->section_name);
>  				bpf_object__close(obj);
>  				return -EINVAL;
>  			}
> -			prog_type = section_names[section_idx].prog_type;
> -			expected_attach_type =
> -				section_names[section_idx].expected_attach_type;
>  		}
>  
>  		bpf_program__set_type(prog, prog_type);
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 564f4be9bae0..617dacfc6704 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -92,6 +92,9 @@ int bpf_object__set_priv(struct bpf_object *obj, void *priv,
>  			 bpf_object_clear_priv_t clear_priv);
>  void *bpf_object__priv(struct bpf_object *prog);
>  
> +int libbpf_prog_type_by_string(const char *name, enum bpf_prog_type *prog_type,

Nit:

I think it should be either:
  int libbpf_prog_type_by_title(const char *title, enum bpf_prog_type *prog_type,

(to be consistent with bpf_program__title())),

or:
  int libbpf_prog_type_by_name(const char *name, enum bpf_prog_type *prog_type,

(to have function name consistent with argument name and with
bpf_program->name).

IMO "name" is better since it's used across API many times and will be
more consistent, when "title" is used just once (IMO
bpf_program__title() should have been called bpf_program__name() to be
consistent with bpf_map__name() and others, not sure if it's fine to
change now).

> +			       enum bpf_attach_type *expected_attach_type);
> +
>  /* Accessors of bpf_program */
>  struct bpf_program;
>  struct bpf_program *bpf_program__next(struct bpf_program *prog,
> -- 
> 2.17.1
>