Re: [PATCH bpf-next 3/8] tools: bpftool: add probes for kernel configuration options

2018-12-15 00:56 UTC+0100 ~ Daniel Borkmann [off-list ref]

On 12/13/2018 01:19 PM, Quentin Monnet wrote:

quoted

Add probes to dump a number of options set (or not set) for compiling
the kernel image. These parameters provide information about what BPF
components should be available on the system. A number of them are not
directly related to eBPF, but are in fact used in the kernel as
conditions on which to compile, or not to compile, some of the eBPF
helper functions.

Sample output:

    # bpftool feature probe kernel
    Scanning system configuration...
    ...
    CONFIG_BPF is set to y
    CONFIG_BPF_SYSCALL is set to y
    CONFIG_HAVE_EBPF_JIT is set to y
    ...

    # bpftool --pretty --json feature probe kernel
    {
        "system_config": {
            ...
            "CONFIG_BPF": "y",
            "CONFIG_BPF_SYSCALL": "y",
            "CONFIG_HAVE_EBPF_JIT": "y",
            ...
        }
    }

    # bpftool feature probe kernel macros prefix BPFTOOL_
    /*** System configuration ***/
    ...
    #define BPFTOOL_CONFIG_BPF y
    #define BPFTOOL_CONFIG_BPF_SYSCALL y
    #define BPFTOOL_CONFIG_HAVE_EBPF_JIT y
    ...

Looks reasonable. I think as a user next question that would
follow-up from it would be whether this set of config means
that e.g. requirements for XDP, cgroups bpf, tracing or xyz is
fulfilled. Perhaps it makes sense to split the options[] into
base_options[], bpf_trace_options[], bpf_tc_options[] etc such
that it might become obvious that base_options[] + bpf_tc_options[]
are supported and thus cls_bpf could be used. I'd see this part
here in general more as giving a hint to the user in that some
basic assumptions could be made and providing some info on the
misc ones on what might potentially be missing. Though more
concrete info would come from the actual helper / map / prog
type probing.

Good idea. I admit that the list of options dumped with no explanations
whatsoever is hard to interpret. I'll try to divide the list into
meaningful subsections.