Re: [bpf-next v3 1/2] libbpf: Add pathname_concat() helper

[Andrii Nakryiko]

On Sun, Sep 18, 2022 at 7:28 PM Wang Yufen <wangyufen@xxxxxxxxxx> wrote:
>
> Move snprintf and len check to common helper pathname_concat() to make the
> code simpler.
>
> Signed-off-by: Wang Yufen <wangyufen@xxxxxxxxxx>
> ---
>  tools/lib/bpf/libbpf.c | 76 +++++++++++++++++++-------------------------------
>  1 file changed, 29 insertions(+), 47 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 3ad1392..43a530d 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -2096,19 +2096,30 @@ static bool get_map_field_int(const char *map_name, const struct btf *btf,
>         return true;
>  }
>
> +static int pathname_concat(const char *path, const char *name, char *buf, size_t buflen)
> +{
> +       int len;
> +
> +       len = snprintf(buf, buflen, "%s/%s", path, name);
> +       if (len < 0)
> +               return -EINVAL;
> +       if (len >= buflen)
> +               return -ENAMETOOLONG;
> +
> +       return 0;
> +}
> +
>  static int build_map_pin_path(struct bpf_map *map, const char *path)
>  {
>         char buf[PATH_MAX];
> -       int len;
> +       int err;
>
>         if (!path)
>                 path = "/sys/fs/bpf";
>
> -       len = snprintf(buf, PATH_MAX, "%s/%s", path, bpf_map__name(map));
> -       if (len < 0)
> -               return -EINVAL;
> -       else if (len >= PATH_MAX)
> -               return -ENAMETOOLONG;
> +       err = pathname_concat(path, bpf_map__name(map), buf, PATH_MAX);

sizeof(buf) instead of PATH_MAX?

> +       if (err)
> +               return err;
>
>         return bpf_map__set_pin_path(map, buf);
>  }
> @@ -7961,17 +7972,9 @@ int bpf_object__pin_maps(struct bpf_object *obj, const char *path)
>                         continue;
>
>                 if (path) {
> -                       int len;
> -
> -                       len = snprintf(buf, PATH_MAX, "%s/%s", path,
> -                                      bpf_map__name(map));
> -                       if (len < 0) {
> -                               err = -EINVAL;
> -                               goto err_unpin_maps;
> -                       } else if (len >= PATH_MAX) {
> -                               err = -ENAMETOOLONG;
> +                       err = pathname_concat(path, bpf_map__name(map), buf, PATH_MAX);

same, let's not hardcode constants we don't need to hardcode, just do
sizeof(buf)

> +                       if (err)
>                                 goto err_unpin_maps;
> -                       }
>                         sanitize_pin_path(buf);
>                         pin_path = buf;
>                 } else if (!map->pin_path) {
> @@ -8009,14 +8012,9 @@ int bpf_object__unpin_maps(struct bpf_object *obj, const char *path)
>                 char buf[PATH_MAX];
>
>                 if (path) {
> -                       int len;
> -
> -                       len = snprintf(buf, PATH_MAX, "%s/%s", path,
> -                                      bpf_map__name(map));
> -                       if (len < 0)
> -                               return libbpf_err(-EINVAL);
> -                       else if (len >= PATH_MAX)
> -                               return libbpf_err(-ENAMETOOLONG);
> +                       err = pathname_concat(path, bpf_map__name(map), buf, PATH_MAX);

ditto here and all the cases below

> +                       if (err)
> +                               return err;
>                         sanitize_pin_path(buf);
>                         pin_path = buf;
>                 } else if (!map->pin_path) {
> @@ -8034,6 +8032,7 @@ int bpf_object__unpin_maps(struct bpf_object *obj, const char *path)
>  int bpf_object__pin_programs(struct bpf_object *obj, const char *path)
>  {
>         struct bpf_program *prog;
> +       char buf[PATH_MAX];
>         int err;
>
>         if (!obj)
> @@ -8045,17 +8044,9 @@ int bpf_object__pin_programs(struct bpf_object *obj, const char *path)
>         }
>
>         bpf_object__for_each_program(prog, obj) {
> -               char buf[PATH_MAX];
> -               int len;
> -
> -               len = snprintf(buf, PATH_MAX, "%s/%s", path, prog->name);
> -               if (len < 0) {
> -                       err = -EINVAL;
> -                       goto err_unpin_programs;
> -               } else if (len >= PATH_MAX) {
> -                       err = -ENAMETOOLONG;
> +               err = pathname_concat(path, prog->name, buf, PATH_MAX);
> +               if (err)
>                         goto err_unpin_programs;
> -               }
>
>                 err = bpf_program__pin(prog, buf);
>                 if (err)
> @@ -8066,13 +8057,7 @@ int bpf_object__pin_programs(struct bpf_object *obj, const char *path)
>
>  err_unpin_programs:
>         while ((prog = bpf_object__prev_program(obj, prog))) {
> -               char buf[PATH_MAX];
> -               int len;
> -
> -               len = snprintf(buf, PATH_MAX, "%s/%s", path, prog->name);
> -               if (len < 0)
> -                       continue;
> -               else if (len >= PATH_MAX)
> +               if (pathname_concat(path, prog->name, buf, PATH_MAX))
>                         continue;
>
>                 bpf_program__unpin(prog, buf);
> @@ -8091,13 +8076,10 @@ int bpf_object__unpin_programs(struct bpf_object *obj, const char *path)
>
>         bpf_object__for_each_program(prog, obj) {
>                 char buf[PATH_MAX];
> -               int len;
>
> -               len = snprintf(buf, PATH_MAX, "%s/%s", path, prog->name);
> -               if (len < 0)
> -                       return libbpf_err(-EINVAL);
> -               else if (len >= PATH_MAX)
> -                       return libbpf_err(-ENAMETOOLONG);
> +               err = pathname_concat(path, prog->name, buf, PATH_MAX);
> +               if (err)
> +                       return libbpf_err(err);
>
>                 err = bpf_program__unpin(prog, buf);
>                 if (err)
> --
> 1.8.3.1
>