On 2024-02-21 10:51, Quentin Deslandes wrote:

On 2024-02-18 18:39, David Ahern wrote:

quoted

On 2/14/24 1:42 AM, Quentin Deslandes wrote:

quoted

+	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?

I've settled on a slightly different solution: the BPF socket-local code is gated
by ENABLE_BPF_SKSTORAGE_SUPPORT instead of HAVE_LIBBPF. If libbpf-0.5+ is available,
and HAVE_LIBBPF is defined, ENABLE_BPF_SKSTORAGE_SUPPORT will be defined in ss,
enabling this feature. If HAVE_LIBBPF is defined but libbpf-0.5+ is not available,
a compile warning will be printed, ENABLE_BPF_SKSTORAGE_SUPPORT won't be defined in
ss, and ss will be compiled without socket-local storage support.

This will ensure that:
- Features relying on HAVE_LIBBPF in ss don't have to comply with the same requirements
  as the BPF socket-local storage support (because iproute2 only requires libbpf-0.1+).
- This change won't prevent iproute2 as a whole from being compiled.

This seems much more reasonable than using #error and failing the whole build. I'll
send a v9 with these changes.

Regards,
Quentin Deslandes