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

From: [email-masked]
Date: Fri, 9 Sep 2022 10:16:28 -0700

On 09/09, Wang Yufen wrote:
> Move snprintf and len check to common helper pathname_concat() to make the
> code simpler.

> Signed-off-by: Wang Yufen <[email-masked]>
> ---
>   tools/lib/bpf/libbpf.c | 74  
> ++++++++++++++++++--------------------------------
>   1 file changed, 27 insertions(+), 47 deletions(-)

> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 5854b92..238a03e 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -2096,20 +2096,31 @@ static bool get_map_field_int(const char  
> *map_name, const struct btf *btf,
>   	return true;
>   }

> -static int build_map_pin_path(struct bpf_map *map, const char *path)
> +static int pathname_concat(const char *path, const char *name, char *buf)
>   {
> -	char buf[PATH_MAX];
>   	int len;

> -	if (!path)
> -		path = "/sys/fs/bpf";
> -
> -	len = snprintf(buf, PATH_MAX, "%s/%s", path, bpf_map__name(map));
> +	len = snprintf(buf, PATH_MAX, "%s/%s", path, name);
>   	if (len < 0)
>   		return -EINVAL;
>   	else if (len >= PATH_MAX)
>   		return -ENAMETOOLONG;

> +	return 0;
> +}
> +
> +static int build_map_pin_path(struct bpf_map *map, const char *path)
> +{
> +	char buf[PATH_MAX];
> +	int err;
> +
> +	if (!path)
> +		path = "/sys/fs/bpf";
> +
> +	err = pathname_concat(path, bpf_map__name(map), buf);
> +	if (err)
> +		return err;
> +
>   	return bpf_map__set_pin_path(map, buf);
>   }

> @@ -7959,17 +7970,8 @@ 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;

[..]

> +			if (pathname_concat(path, bpf_map__name(map), buf))
>   				goto err_unpin_maps;
> -			}

You're breaking error reporting here and in a bunch of other places.
Should be:

err = pathname_concat();
if (err)
	goto err_unpin_maps;

I have the same attitude towards this patch as the first one in the
series: not worth it. Nothing is currently broken, the code as is relatively
readable, this version is not much simpler, it just looks slightly different
taste-wise..

How about this: if you really want to push this kind of cleanup, send
selftests that exercise all these error cases? :-)

>   			sanitize_pin_path(buf);
>   			pin_path = buf;
>   		} else if (!map->pin_path) {
> @@ -8007,14 +8009,9 @@ 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);
> +			if (err)
> +				return err;
>   			sanitize_pin_path(buf);
>   			pin_path = buf;
>   		} else if (!map->pin_path) {
> @@ -8032,6 +8029,7 @@ 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)
> @@ -8043,17 +8041,8 @@ 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;
> +		if (pathname_concat(path, prog->name, buf))
>   			goto err_unpin_programs;
> -		} else if (len >= PATH_MAX) {
> -			err = -ENAMETOOLONG;
> -			goto err_unpin_programs;
> -		}

>   		err = bpf_program__pin(prog, buf);
>   		if (err)
> @@ -8064,13 +8053,7 @@ 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))
>   			continue;

>   		bpf_program__unpin(prog, buf);
> @@ -8089,13 +8072,10 @@ 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);
> +		if (err)
> +			return libbpf_err(err);

>   		err = bpf_program__unpin(prog, buf);
>   		if (err)
> --
> 1.8.3.1