[PATCH bpf-next v8] tools/bpf: generate pkg-config file for libbpf

[luca.boccassi@gmail.com]

From: Luca Boccassi <bluca@debian.org>

Generate a libbpf.pc file at build time so that users can rely
on pkg-config to find the library, its CFLAGS and LDFLAGS.

Signed-off-by: Luca Boccassi <bluca@debian.org>
Acked-by: Andrey Ignatov <rdna@fb.com>
---
v2: use QUIET_GEN instead of QUIET_LINK to generate pc file,
    save kernel version in its own variable instead of calling
    make inline
v3: use LIBBPF_VERSION instead of kernel_version
v4: use -I${prefix}/include rather than -I${prefix}/include/bpf
    in the Cflags field as requested, to keep consistency with
    how the headers are used now and to avoid a dependency from
    the pc file to the headers installation
v5: add acked-by, add SPDX line to pc file
v6: remove URL field, generalize Description field
v7: fix build with make OUTPUT=/foo/bar/ by prefixing $(OUTPUT)
    to the pc file variable
v8: rebased on latest bpf-next to solve merge conflict
    (not that indentation looks wrong on 2 lines because the
    "+" added by the diff makes the first tab start at the 8th
    column rather than the 7th, it align once applied though)

 tools/lib/bpf/.gitignore         |  1 +
 tools/lib/bpf/Makefile           | 19 ++++++++++++++++---
 tools/lib/bpf/libbpf.pc.template | 12 ++++++++++++
 3 files changed, 29 insertions(+), 3 deletions(-)
 create mode 100644 tools/lib/bpf/libbpf.pc.template

diff --git a/tools/lib/bpf/.gitignore b/tools/lib/bpf/.gitignore
index 4db74758c674..7d9e182a1f51 100644
--- a/tools/lib/bpf/.gitignore
+++ b/tools/lib/bpf/.gitignore
@@ -1,3 +1,4 @@
 libbpf_version.h
+libbpf.pc
 FEATURE-DUMP.libbpf
 test_libbpf
diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index 5bf8e52c41fc..0fe54fe4cc04 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -90,6 +90,7 @@ 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
 
 # Set compile option CFLAGS
 ifdef EXTRA_CFLAGS
@@ -134,13 +135,14 @@ VERSION_SCRIPT	:= libbpf.map
 
 LIB_TARGET	:= $(addprefix $(OUTPUT),$(LIB_TARGET))
 LIB_FILE	:= $(addprefix $(OUTPUT),$(LIB_FILE))
+PC_FILE		:= $(addprefix $(OUTPUT),$(PC_FILE))
 
 GLOBAL_SYM_COUNT = $(shell readelf -s --wide $(BPF_IN) | \
 			   awk '/GLOBAL/ && /DEFAULT/ && !/UND/ {s++} END{print s}')
 VERSIONED_SYM_COUNT = $(shell readelf -s --wide $(OUTPUT)libbpf.so | \
 			      grep -Eo '[^ ]+@LIBBPF_' | cut -d@ -f1 | sort -u | wc -l)
 
-CMD_TARGETS = $(LIB_TARGET)
+CMD_TARGETS = $(LIB_TARGET) $(PC_FILE)
 
 CXX_TEST_TARGET = $(OUTPUT)test_libbpf
 
@@ -187,6 +189,12 @@ $(OUTPUT)libbpf.a: $(BPF_IN)
 $(OUTPUT)test_libbpf: test_libbpf.cpp $(OUTPUT)libbpf.a
 	$(QUIET_LINK)$(CXX) $(INCLUDES) $^ -lelf -o $@
 
+$(OUTPUT)libbpf.pc:
+	$(QUIET_GEN)sed -e "s|@PREFIX@|$(prefix)|" \
+		-e "s|@LIBDIR@|$(libdir_SQ)|" \
+		-e "s|@VERSION@|$(LIBBPF_VERSION)|" \
+		< libbpf.pc.template > $@
+
 check: check_abi
 
 check_abi: $(OUTPUT)libbpf.so
@@ -223,7 +231,12 @@ install_headers:
 		$(call do_install,libbpf.h,$(prefix)/include/bpf,644);
 		$(call do_install,btf.h,$(prefix)/include/bpf,644);
 
-install: install_lib
+install_pkgconfig: $(PC_FILE)
+	$(call QUIET_INSTALL, $(PC_FILE)) \
+		$(call do_install,$(PC_FILE),$(libdir_SQ)/pkgconfig,644)
+
+
+install: install_lib install_pkgconfig
 
 ### Cleaning rules
 
@@ -233,7 +246,7 @@ config-clean:
 
 clean:
 	$(call QUIET_CLEAN, libbpf) $(RM) $(TARGETS) $(CXX_TEST_TARGET) \
-		*.o *~ *.a *.so *.so.$(VERSION) .*.d .*.cmd LIBBPF-CFLAGS
+		*.o *~ *.a *.so *.so.$(VERSION) .*.d .*.cmd *.pc LIBBPF-CFLAGS
 	$(call QUIET_CLEAN, core-gen) $(RM) $(OUTPUT)FEATURE-DUMP.libbpf
 
 
diff --git a/tools/lib/bpf/libbpf.pc.template b/tools/lib/bpf/libbpf.pc.template
new file mode 100644
index 000000000000..ac17fcef2108
--- /dev/null
+++ b/tools/lib/bpf/libbpf.pc.template
@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+prefix=@PREFIX@
+libdir=@LIBDIR@
+includedir=${prefix}/include
+
+Name: libbpf
+Description: BPF library
+Version: @VERSION@
+Libs: -L${libdir} -lbpf
+Requires.private: libelf
+Cflags: -I${includedir}
-- 
2.20.1