tools/bpftool: use version from the kernel source tree

Bpftool determines it's own version based on the kernel
version, which is picked from the linux/version.h header.

It's strange to use the version of the installed kernel
headers, and makes much more sense to use the version
of the actual source tree, where bpftool sources are.

Fix this by building kernelversion target and use
the resulting string as bpftool version.

Example:
before:

$ bpftool version
bpftool v4.14.6

after:
$ bpftool version
bpftool v4.15.0-rc3

$bpftool version --json
{"version":"4.15.0-rc3"}

Signed-off-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/Makefile

@@ -23,6 +23,8 @@ endif
 
 LIBBPF = $(BPF_PATH)libbpf.a
 
+BPFTOOL_VERSION=$(shell make --no-print-directory -sC ../../.. kernelversion)
+
 $(LIBBPF): FORCE
 	$(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(OUTPUT) $(OUTPUT)libbpf.a FEATURES_DUMP=$(FEATURE_DUMP_EXPORT)
 
@@ -38,6 +40,7 @@ CC = gcc
 CFLAGS += -O2
 CFLAGS += -W -Wall -Wextra -Wno-unused-parameter -Wshadow
 CFLAGS += -D__EXPORTED_HEADERS__ -I$(srctree)/tools/include/uapi -I$(srctree)/tools/include -I$(srctree)/tools/lib/bpf -I$(srctree)/kernel/bpf/
+CFLAGS += -DBPFTOOL_VERSION='"$(BPFTOOL_VERSION)"'
 LIBS = -lelf -lbfd -lopcodes $(LIBBPF)
 
 INSTALL ?= install

tools/bpf/bpftool/main.c

@@ -38,7 +38,6 @@
 #include <errno.h>
 #include <getopt.h>
 #include <linux/bpf.h>
-#include <linux/version.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -95,21 +94,13 @@ static int do_help(int argc, char **argv)
 
 static int do_version(int argc, char **argv)
 {
-	unsigned int version[3];
-
-	version[0] = LINUX_VERSION_CODE >> 16;
-	version[1] = LINUX_VERSION_CODE >> 8 & 0xf;
-	version[2] = LINUX_VERSION_CODE & 0xf;
-
 	if (json_output) {
 		jsonw_start_object(json_wtr);
 		jsonw_name(json_wtr, "version");
-		jsonw_printf(json_wtr, "\"%u.%u.%u\"",
+		jsonw_printf(json_wtr, "\"%s\"", BPFTOOL_VERSION);
-			     version[0], version[1], version[2]);
 		jsonw_end_object(json_wtr);
 	} else {
-		printf("%s v%u.%u.%u\n", bin_name,
+		printf("%s v%s\n", bin_name, BPFTOOL_VERSION);
-		       version[0], version[1], version[2]);
 	}
 	return 0;
 }