Re: [PATCH bpf-next 2/2] libbpf: handle ENOTSUPP in libbpf_strerror_r

[Geliang Tang <geliang@kernel.org>]

On Fri, 2024-07-12 at 18:14 +0800, Geliang Tang wrote:
> From: Geliang Tang <tanggeliang@kylinos.cn>
> 
> The errno 95 (ENOTSUP or EOPNOTSUPP) can be recognized by
> strerror_r(),
> but 524 (ENOTSUPP) can't:
> 
>  prog 'basic_alloc3': BPF program load failed: Operation not
> supported
>  prog 'basic_alloc3': failed to load: -95
>  failed to load object 'verifier_arena'
>  FAIL:unexpected_load_failure unexpected error: -95 (errno 95)
> 
>  prog 'inner_map': BPF program load failed: unknown error (-524)
>  prog 'inner_map': failed to load: -524
>  failed to load object 'bloom_filter_map'
>  failed to load BPF skeleton 'bloom_filter_map': -524
>  FAIL:bloom_filter_map__open_and_load unexpected error: -524
> 
> This patch fixes this by handling ENOTSUPP in libbpf_strerror_r().
> With
> this change, the new error string looks like:
> 
>  prog 'inner_map': BPF program load failed: Operation not supported
> (-524)
> 
> Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
> ---
>  tools/lib/bpf/str_error.c | 11 +++++++----
>  tools/lib/bpf/str_error.h |  4 ++++
>  2 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/lib/bpf/str_error.c b/tools/lib/bpf/str_error.c
> index 5e6a1e27ddf9..10597d5124cd 100644
> --- a/tools/lib/bpf/str_error.c
> +++ b/tools/lib/bpf/str_error.c
> @@ -23,10 +23,13 @@ char *libbpf_strerror_r(int err, char *dst, int
> len)
>  	if (ret == -1)
>  		ret = errno;
>  	if (ret) {
> -		if (ret == EINVAL)
> -			/* strerror_r() doesn't recognize this
> specific error */
> -			snprintf(dst, len, "unknown error (%d)", err
> < 0 ? err : -err);
> -		else
> +		if (ret == EINVAL) {
> +			if (err == ENOTSUPP)

Shouldn't use "err" directly here, should use "err < 0 ? -err : err"
instead. I prefer to add an unsigned variable "no" in v2:

	unsigned int no = err < 0 ? -err : err;

And use "switch-case" for future expansion:
	
	switch (no) {
	case ENOTSUPP:

> +				snprintf(dst, len, "Operation not
> supported (%d)", -err);

No need to use "Operation not supported (-524)" here, just "Operation
not supported" is better.

		snprintf(dst, len, "Operation not supported");

> +			else
> +				/* strerror_r() doesn't recognize
> this specific error */
> +				snprintf(dst, len, "unknown error
> (%d)", err < 0 ? err : -err);

Then here:

		snprintf(dst, len, "unknown error (-%u)", no);

Changes Requested.

Will send a v2 soon.

Thanks,
-Geliang

> +		} else
>  			snprintf(dst, len, "ERROR:
> strerror_r(%d)=%d", err, ret);
>  	}
>  	return dst;
> diff --git a/tools/lib/bpf/str_error.h b/tools/lib/bpf/str_error.h
> index 626d7ffb03d6..c41f6ba133cf 100644
> --- a/tools/lib/bpf/str_error.h
> +++ b/tools/lib/bpf/str_error.h
> @@ -4,6 +4,10 @@
>  
>  #define STRERR_BUFSIZE  128
>  
> +#ifndef ENOTSUPP
> +#define ENOTSUPP 524
> +#endif
> +
>  char *libbpf_strerror_r(int err, char *dst, int len);
>  
>  #endif /* __LIBBPF_STR_ERROR_H */