netdev - Re: [bpf-next 1/2] libbpf: Add make_path_and_pin() helper for bpf_xxx_

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Date:   Fri, 9 Sep 2022 10:06:27 -0700
From:   sdf@...gle.com
To:     Wang Yufen <wangyufen@...wei.com>
Cc:     andrii@...nel.org, ast@...nel.org, daniel@...earbox.net,
        martin.lau@...ux.dev, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, haoluo@...gle.com,
        jolsa@...nel.org, paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, davem@...emloft.net, kuba@...nel.org,
        hawk@...nel.org, nathan@...nel.org, ndesaulniers@...gle.com,
        trix@...hat.com, bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [bpf-next 1/2] libbpf: Add make_path_and_pin() helper for bpf_xxx__pin()

On 09/09, Wang Yufen wrote:
> Move make path, check path and pin to the common helper  
> make_path_and_pin() to make
> the code simpler.

Idk, I guess I'll defer to Andrii here; I won't really call it simpler.
The code just looks different and looses some observability (see below).

> Signed-off-by: Wang Yufen <wangyufen@...wei.com>
> ---
>   tools/lib/bpf/libbpf.c | 56  
> ++++++++++++++++++++++----------------------------
>   1 file changed, 24 insertions(+), 32 deletions(-)

> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 3ad1392..5854b92 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -7755,16 +7755,11 @@ static int check_path(const char *path)
>   	return err;
>   }

> -int bpf_program__pin(struct bpf_program *prog, const char *path)
> +static int make_path_and_pin(int fd, const char *path)
>   {
>   	char *cp, errmsg[STRERR_BUFSIZE];
>   	int err;

> -	if (prog->fd < 0) {
> -		pr_warn("prog '%s': can't pin program that wasn't loaded\n",  
> prog->name);
> -		return libbpf_err(-EINVAL);
> -	}
> -
>   	err = make_parent_dir(path);
>   	if (err)
>   		return libbpf_err(err);
> @@ -7773,12 +7768,27 @@ int bpf_program__pin(struct bpf_program *prog,  
> const char *path)
>   	if (err)
>   		return libbpf_err(err);

> -	if (bpf_obj_pin(prog->fd, path)) {
> +	if (bpf_obj_pin(fd, path)) {
>   		err = -errno;
>   		cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg));
> -		pr_warn("prog '%s': failed to pin at '%s': %s\n", prog->name, path,  
> cp);
> +		pr_warn("failed to pin at '%s': %s\n", path, cp);

This seems to be making logging worse?
We went from "can't pin 'program name' to 'path': ENOENT" to "can't pin
to 'path': ENOENT". You can deduce the program name from the path, but
why not keep the proper log message?

>   		return libbpf_err(err);
>   	}
> +	return 0;
> +}
> +
> +int bpf_program__pin(struct bpf_program *prog, const char *path)
> +{
> +	int err;
> +
> +	if (prog->fd < 0) {
> +		pr_warn("prog '%s': can't pin program that wasn't loaded\n",  
> prog->name);
> +		return libbpf_err(-EINVAL);
> +	}
> +
> +	err = make_path_and_pin(prog->fd, path);
> +	if (err)
> +		return libbpf_err(err);

>   	pr_debug("prog '%s': pinned at '%s'\n", prog->name, path);
>   	return 0;
> @@ -7838,32 +7848,20 @@ int bpf_map__pin(struct bpf_map *map, const char  
> *path)
>   		map->pin_path = strdup(path);
>   		if (!map->pin_path) {
>   			err = -errno;
> -			goto out_err;
> +			cp = libbpf_strerror_r(-err, errmsg, sizeof(errmsg));
> +			pr_warn("failed to pin map: %s\n", cp);
> +			return libbpf_err(err);
>   		}
>   	}

> -	err = make_parent_dir(map->pin_path);
> -	if (err)
> -		return libbpf_err(err);
> -
> -	err = check_path(map->pin_path);
> +	err = make_path_and_pin(map->fd, map->pin_path);
>   	if (err)
>   		return libbpf_err(err);

> -	if (bpf_obj_pin(map->fd, map->pin_path)) {
> -		err = -errno;
> -		goto out_err;
> -	}
> -
>   	map->pinned = true;
>   	pr_debug("pinned map '%s'\n", map->pin_path);

>   	return 0;
> -
> -out_err:
> -	cp = libbpf_strerror_r(-err, errmsg, sizeof(errmsg));
> -	pr_warn("failed to pin map: %s\n", cp);
> -	return libbpf_err(err);
>   }

>   int bpf_map__unpin(struct bpf_map *map, const char *path)
> @@ -9611,19 +9609,13 @@ int bpf_link__pin(struct bpf_link *link, const  
> char *path)

>   	if (link->pin_path)
>   		return libbpf_err(-EBUSY);
> -	err = make_parent_dir(path);
> -	if (err)
> -		return libbpf_err(err);
> -	err = check_path(path);
> -	if (err)
> -		return libbpf_err(err);

>   	link->pin_path = strdup(path);
>   	if (!link->pin_path)
>   		return libbpf_err(-ENOMEM);

> -	if (bpf_obj_pin(link->fd, link->pin_path)) {
> -		err = -errno;
> +	err = make_path_and_pin(link->fd, path);
> +	if (err) {
>   		zfree(&link->pin_path);
>   		return libbpf_err(err);
>   	}
> --
> 1.8.3.1