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>

7 files changed, 66 insertions, 0 deletions

diff --git a/tools/bpf/bpftool/Documentation/bpftool-cgroup.rst b/tools/bpf/bpftool/Documentation/bpftool-cgroup.rst
index d07ccf8a23f7..d43fce568ef7 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-cgroup.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-cgroup.rst
@@ -142,5 +142,6 @@ SEE ALSO
 	**bpftool**\ (8),
 	**bpftool-prog**\ (8),
 	**bpftool-map**\ (8),
+	**bpftool-feature**\ (8),
 	**bpftool-net**\ (8),
 	**bpftool-perf**\ (8)
diff --git a/tools/bpf/bpftool/Documentation/bpftool-feature.rst b/tools/bpf/bpftool/Documentation/bpftool-feature.rst
new file mode 100644
index 000000000000..40ac13c0b782
--- /dev/null
+++ b/tools/bpf/bpftool/Documentation/bpftool-feature.rst
@@ -0,0 +1,60 @@
+===============
+bpftool-feature
+===============
+-------------------------------------------------------------------------------
+tool for inspection of eBPF-related parameters for Linux kernel or net device
+-------------------------------------------------------------------------------
+
+:Manual section: 8
+
+SYNOPSIS
+========
+
+	**bpftool** [*OPTIONS*] **feature** *COMMAND*
+
+	*OPTIONS* := { { **-j** | **--json** } [{ **-p** | **--pretty** }] }
+
+	*COMMANDS* := { **probe** | **help** }
+
+MAP COMMANDS
+=============
+
+|	**bpftool** **feature probe** [**kernel**]
+|	**bpftool** **feature help**
+
+DESCRIPTION
+===========
+	**bpftool feature probe** [**kernel**]
+		  Probe the running kernel and dump a number of eBPF-related
+		  parameters, such as availability of the **bpf()** system call.
+
+		  Keyword **kernel** can be omitted.
+
+	**bpftool feature help**
+		  Print short help message.
+
+OPTIONS
+=======
+	-h, --help
+		  Print short generic help message (similar to **bpftool help**).
+
+	-v, --version
+		  Print version number (similar to **bpftool version**).
+
+	-j, --json
+		  Generate JSON output. For commands that cannot produce JSON, this
+		  option has no effect.
+
+	-p, --pretty
+		  Generate human-readable JSON output. Implies **-j**.
+
+SEE ALSO
+========
+	**bpf**\ (2),
+	**bpf-helpers**\ (7),
+	**bpftool**\ (8),
+	**bpftool-prog**\ (8),
+	**bpftool-map**\ (8),
+	**bpftool-cgroup**\ (8),
+	**bpftool-net**\ (8),
+	**bpftool-perf**\ (8)
diff --git a/tools/bpf/bpftool/Documentation/bpftool-map.rst b/tools/bpf/bpftool/Documentation/bpftool-map.rst
index 0584c31d3fe2..5c984ffc9f01 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-map.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-map.rst
@@ -256,5 +256,6 @@ SEE ALSO
 	**bpftool**\ (8),
 	**bpftool-prog**\ (8),
 	**bpftool-cgroup**\ (8),
+	**bpftool-feature**\ (8),
 	**bpftool-net**\ (8),
 	**bpftool-perf**\ (8)
diff --git a/tools/bpf/bpftool/Documentation/bpftool-net.rst b/tools/bpf/bpftool/Documentation/bpftool-net.rst
index ed87c9b619ad..779dab3650ee 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-net.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-net.rst
@@ -142,4 +142,5 @@ SEE ALSO
 	**bpftool-prog**\ (8),
 	**bpftool-map**\ (8),
 	**bpftool-cgroup**\ (8),
+	**bpftool-feature**\ (8),
 	**bpftool-perf**\ (8)
diff --git a/tools/bpf/bpftool/Documentation/bpftool-perf.rst b/tools/bpf/bpftool/Documentation/bpftool-perf.rst
index f4c5e5538bb8..bca5590a80d0 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-perf.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-perf.rst
@@ -84,4 +84,5 @@ SEE ALSO
 	**bpftool-prog**\ (8),
 	**bpftool-map**\ (8),
 	**bpftool-cgroup**\ (8),
+	**bpftool-feature**\ (8),
 	**bpftool-net**\ (8)
diff --git a/tools/bpf/bpftool/Documentation/bpftool-prog.rst b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
index 58c8369b77dd..13b56102f528 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-prog.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
@@ -258,5 +258,6 @@ SEE ALSO
 	**bpftool**\ (8),
 	**bpftool-map**\ (8),
 	**bpftool-cgroup**\ (8),
+	**bpftool-feature**\ (8),
 	**bpftool-net**\ (8),
 	**bpftool-perf**\ (8)
diff --git a/tools/bpf/bpftool/Documentation/bpftool.rst b/tools/bpf/bpftool/Documentation/bpftool.rst
index e1677e81ed59..27153bb816ac 100644
--- a/tools/bpf/bpftool/Documentation/bpftool.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool.rst
@@ -72,5 +72,6 @@ SEE ALSO
 	**bpftool-prog**\ (8),
 	**bpftool-map**\ (8),
 	**bpftool-cgroup**\ (8),
+	**bpftool-feature**\ (8),
 	**bpftool-net**\ (8),
 	**bpftool-perf**\ (8)