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tools: bpftool: add basic probe capability, probe syscall availability
Add a new component and command for bpftool, in order to probe the
system to dump a set of eBPF-related parameters so that users can know
what features are available on the system.
Parameters are dumped in plain or JSON output (with -j/-p options).
The current patch introduces probing of one simple parameter:
availability of the bpf() system call. Later commits
will add other probes.
Sample output:
# bpftool feature probe kernel
Scanning system call availability...
bpf() syscall is available
# bpftool --json --pretty feature probe kernel
{
"syscall_config": {
"have_bpf_syscall": true
}
}
The optional "kernel" keyword enforces probing of the current system,
which is the only possible behaviour at this stage. It can be safely
omitted.
The feature comes with the relevant man page, but bash completion will
come in a dedicated commit.
v3:
- Do not probe kernel version. Contrarily to what is written below for
v2, we can have the kernel version retrieved in libbpf instead of
bpftool (in the patch adding probing for program types).
v2:
- Remove C-style macros output from this patch.
- Even though kernel version is no longer needed for testing kprobes
availability, note that we still collect it in this patch so that
bpftool gets able to probe (in next patches) older kernels as well.
Signed-off-by: 
Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>