netdev - Re: [PATCH iproute2 v8 1/3] ss: add support for BPF socket-local storage

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Message-ID: <5615212b-736d-4a91-8951-ddb9bc90049b@naccy.de>
Date: Wed, 21 Feb 2024 10:51:46 +0100
From: Quentin Deslandes <qde@...cy.de>
To: David Ahern <dsahern@...il.com>, netdev@...r.kernel.org
Cc: Martin KaFai Lau <martin.lau@...nel.org>,
 Stephen Hemminger <stephen@...workplumber.org>, kernel-team@...a.com,
 Matthieu Baerts <matttbe@...nel.org>
Subject: Re: [PATCH iproute2 v8 1/3] ss: add support for BPF socket-local
 storage

On 2024-02-18 18:39, David Ahern wrote:
> On 2/14/24 1:42 AM, Quentin Deslandes wrote:
>> +	if (info.type != BPF_MAP_TYPE_SK_STORAGE) {
>> +		fprintf(stderr, "ss: BPF map with ID %s has type '%s', expecting 'sk_storage'\n",
>> +			optarg, libbpf_bpf_map_type_str(info.type));
>> +		close(fd);
>> +		return -1;
>> +	}
> 
> ss.c: In function ‘bpf_map_opts_load_info’:
> ss.c:3448:33: warning: implicit declaration of function
> ‘libbpf_bpf_map_type_str’ [-Wimplicit-function-declaration]
>  3448 |                         optarg, libbpf_bpf_map_type_str(info.type));
>       |                                 ^~~~~~~~~~~~~~~~~~~~~~~
> ss.c:3447:68: warning: format ‘%s’ expects argument of type ‘char *’,
> but argument 4 has type ‘int’ [-Wformat=]
>  3447 |                 fprintf(stderr, "ss: BPF map with ID %s has type
> '%s', expecting 'sk_storage'\n",
>       |                                                                   ~^
>       |                                                                    |
>       |
>   char *
>       |                                                                   %d
>  3448 |                         optarg, libbpf_bpf_map_type_str(info.type));
>       |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>       |                                 |
>       |                                 int
>     CC       lnstat_util.o
>     LINK     lnstat
>     LINK     ss
> /usr/bin/ld: ss.o: in function `main':
> 
> 
> Ubuntu 22.04 has libbpf-0.5 installed. I suspect version hook is needed.
> e.g., something like this (but with the relevant version numbers):
> 
> #if (LIBBPF_MAJOR_VERSION > 0) || (LIBBPF_MINOR_VERSION >= 7)

After checking, all the libbpf symbols I use require at least libbpf-0.5, except
for this one which was introduced in libbpf-1.0. Hence, I will print the type ID
instead of the string. IMO printing the string representation of the type doesn't
add enough value to justify adding a version hook.

However, I see the minimum required version for libbpf is 0.1, but this
series requires 0.5. I would check the version in ss and #error if
the requirements are not met, but I'm not sure this is the right way to do it.
What do you think?

Regards,
Quentin Deslandes