linux-kernel - Re: [RFC PATCH bpf-next] libbpf: print character arrays as strings if possible

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Message-ID: <b49224dbc89bd304a5c20eef4430dfea40f4b6a5.camel@gmail.com>
Date: Wed, 24 Apr 2024 16:33:27 -0700
From: Eduard Zingerman <eddyz87@...il.com>
To: Quentin Deslandes <qde@...cy.de>, bpf@...r.kernel.org
Cc: Andrii Nakryiko <andrii@...nel.org>, Alexei Starovoitov
 <ast@...nel.org>,  Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,  Yonghong Song
 <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, KP
 Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo
 <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
 linux-kernel@...r.kernel.org,  kernel-team@...a.com
Subject: Re: [RFC PATCH bpf-next] libbpf: print character arrays as strings
 if possible

On Sat, 2024-04-13 at 23:39 +0200, Quentin Deslandes wrote:
> Introduce the new print_strings flag in btf_dump_type_data_opts. If
> enabled, libbpf will print character arrays as strings if they meet the
> following conditions:
> - Contains a nul-termination character ('\0')
> - Contains only printable characters before the nul-termination character
> 
> If print_strings is set to false (default value), the existing
> behavior remains unchanged.
> 
> With print_strings=false:
> .str_array = (__u8[14])[
>     'H',
>     'e',
>     'l',
>     'l',
>     'o',
> ],
> 
> With print_strings=true:
> .str_array = (__u8[14])"Hello",
> 
> Signed-off-by: Quentin Deslandes <qde@...cy.de>
> ---

Hi Quentin,

Thank you for this patch, sorry for the delay reviewing it.
Could you please also add a few tests in
tools/testing/selftests/bpf/prog_tests/btf_dump.c ?

[...]

> @@ -2021,6 +2022,21 @@ static int btf_dump_var_data(struct btf_dump *d,
>  	return btf_dump_dump_type_data(d, NULL, t, type_id, data, 0, 0);
>  }
> 
> +static bool btf_dump_isprint_str(const char *data, unsigned int len)
> +{
> +	unsigned int i;
> +
> +	for (i = 0; i < len; ++i) {
> +		if (data[i] == '\0')
> +			return true;
> +
> +		if (!isprint(data[i]))
> +			return false;

Would it make sense to use isprint_l() and specify something like C locale? 

> +	}
> +
> +	return false;
> +}
> +
>  static int btf_dump_array_data(struct btf_dump *d,
>  			       const struct btf_type *t,
>  			       __u32 id,
> @@ -2047,8 +2063,14 @@ static int btf_dump_array_data(struct btf_dump *d,
>  		 * char arrays, so if size is 1 and element is
>  		 * printable as a char, we'll do that.
>  		 */
> -		if (elem_size == 1)
> +		if (elem_size == 1) {
>  			d->typed_dump->is_array_char = true;
> +			if (d->typed_dump->print_strings &&
> +					btf_dump_isprint_str(data, array->nelems)) {
> +				btf_dump_type_values(d, "\"%s\"", data);

Note: this would have to deal with escape sequences,
otherwise strings containing '\' would be printed incorrectly.

> +				return 0;
> +			}
> +		}
>  	}
> 
>  	/* note that we increment depth before calling btf_dump_print() below;

[...]