[PATCH bpf-next] libbpf: make libbpf.map source of truth for libbpf version

[Andrii Nakryiko <andriin@fb.com>]

Currently libbpf version is specified in 2 places: libbpf.map and
Makefile. They easily get out of sync and it's very easy to update one,
but forget to update another one. In addition, Github projection of
libbpf has to maintain its own version which has to be remembered to be
kept in sync manually, which is very error-prone approach.

This patch makes libbpf.map a source of truth for libbpf version and
uses shell invocation to parse out correct full and major libbpf version
to use during build. Now we need to make sure that once new release
cycle starts, we need to add (initially) empty section to libbpf.map
with correct latest version.

This also will make it possible to keep Github projection consistent
with kernel sources version of libbpf by adopting similar parsing of
version from libbpf.map.

Cc: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 tools/lib/bpf/Makefile   | 12 +++++-------
 tools/lib/bpf/libbpf.map |  3 +++
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index 9312066a1ae3..d9afc8509725 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -1,9 +1,10 @@
 # SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
 # Most of this file is copied from tools/lib/traceevent/Makefile
 
-BPF_VERSION = 0
-BPF_PATCHLEVEL = 0
-BPF_EXTRAVERSION = 4
+BPF_FULL_VERSION = $(shell \
+	grep -E 'LIBBPF_([0-9]+)\.([0-9]+)\.([0-9]+) \{' libbpf.map | \
+	tail -n1 | cut -d'_' -f2 | cut -d' ' -f1)
+BPF_VERSION = $(firstword $(subst ., ,$(BPF_FULL_VERSION)))
 
 MAKEFLAGS += --no-print-directory
 
@@ -79,15 +80,12 @@ export prefix libdir src obj
 libdir_SQ = $(subst ','\'',$(libdir))
 libdir_relative_SQ = $(subst ','\'',$(libdir_relative))
 
+LIBBPF_VERSION	= $(BPF_FULL_VERSION)
 VERSION		= $(BPF_VERSION)
-PATCHLEVEL	= $(BPF_PATCHLEVEL)
-EXTRAVERSION	= $(BPF_EXTRAVERSION)
 
 OBJ		= $@
 N		=
 
-LIBBPF_VERSION	= $(BPF_VERSION).$(BPF_PATCHLEVEL).$(BPF_EXTRAVERSION)
-
 LIB_TARGET	= libbpf.a libbpf.so.$(LIBBPF_VERSION)
 LIB_FILE	= libbpf.a libbpf.so*
 PC_FILE		= libbpf.pc
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index f9d316e873d8..4e72df8e98ba 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -184,3 +184,6 @@ LIBBPF_0.0.4 {
 		perf_buffer__new_raw;
 		perf_buffer__poll;
 } LIBBPF_0.0.3;
+
+LIBBPF_0.0.5 {
+} LIBBPF_0.0.4;
-- 
2.17.1