netdev - [PATCH bpf-next v3 02/10] tools: bpftool: install libbpf headers instead of including the dir

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Date:   Sun,  3 Oct 2021 20:22:00 +0100
From:   Quentin Monnet <quentin@...valent.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Quentin Monnet <quentin@...valent.com>
Subject: [PATCH bpf-next v3 02/10] tools: bpftool: install libbpf headers instead of including the dir

Bpftool relies on libbpf, therefore it relies on a number of headers
from the library and must be linked against the library. The Makefile
for bpftool exposes these objects by adding tools/lib as an include
directory ("-I$(srctree)/tools/lib"). This is a working solution, but
this is not the cleanest one. The risk is to involuntarily include
objects that are not intended to be exposed by the libbpf.

The headers needed to compile bpftool should in fact be "installed" from
libbpf, with its "install_headers" Makefile target. In addition, there
is one header which is internal to the library and not supposed to be
used by external applications, but that bpftool uses anyway.

Adjust the Makefile in order to install the header files properly before
compiling bpftool. Also copy the additional internal header file
(nlattr.h), but call it out explicitly. Build (and install headers) in a
subdirectory under bpftool/ instead of tools/lib/bpf/. When descending
from a parent Makefile, this is configurable by setting the OUTPUT,
LIBBPF_OUTPUT and LIBBPF_DESTDIR variables.

Also adjust the Makefile for BPF selftests, so as to reuse the (host)
libbpf compiled earlier and to avoid compiling a separate version of the
library just for bpftool.

Signed-off-by: Quentin Monnet <quentin@...valent.com>
Acked-by: Andrii Nakryiko <andrii@...nel.org>
---
 tools/bpf/bpftool/Makefile           | 26 +++++++++++++++-----------
 tools/testing/selftests/bpf/Makefile |  2 ++
 2 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
index 1fcf5b01a193..ef5219e0e233 100644
--- a/tools/bpf/bpftool/Makefile
+++ b/tools/bpf/bpftool/Makefile
@@ -17,16 +17,16 @@ endif
 BPF_DIR = $(srctree)/tools/lib/bpf/
 
 ifneq ($(OUTPUT),)
-  LIBBPF_OUTPUT = $(OUTPUT)/libbpf/
-  LIBBPF_PATH = $(LIBBPF_OUTPUT)
-  BOOTSTRAP_OUTPUT = $(OUTPUT)/bootstrap/
+  _OUTPUT := $(OUTPUT)
 else
-  LIBBPF_OUTPUT =
-  LIBBPF_PATH = $(BPF_DIR)
-  BOOTSTRAP_OUTPUT = $(CURDIR)/bootstrap/
+  _OUTPUT := $(CURDIR)
 endif
+BOOTSTRAP_OUTPUT := $(_OUTPUT)/bootstrap/
+LIBBPF_OUTPUT := $(_OUTPUT)/libbpf/
+LIBBPF_DESTDIR := $(LIBBPF_OUTPUT)
+LIBBPF_INCLUDE := $(LIBBPF_DESTDIR)/include
 
-LIBBPF = $(LIBBPF_PATH)libbpf.a
+LIBBPF = $(LIBBPF_OUTPUT)libbpf.a
 LIBBPF_BOOTSTRAP_OUTPUT = $(BOOTSTRAP_OUTPUT)libbpf/
 LIBBPF_BOOTSTRAP = $(LIBBPF_BOOTSTRAP_OUTPUT)libbpf.a
 
@@ -37,8 +37,13 @@ endif
 $(LIBBPF_OUTPUT) $(BOOTSTRAP_OUTPUT) $(LIBBPF_BOOTSTRAP_OUTPUT):
 	$(QUIET_MKDIR)mkdir -p $@
 
+# We need to copy nlattr.h which is not otherwise exported by libbpf, but still
+# required by bpftool.
 $(LIBBPF): FORCE | $(LIBBPF_OUTPUT)
-	$(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(LIBBPF_OUTPUT) $(LIBBPF_OUTPUT)libbpf.a
+	$(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(LIBBPF_OUTPUT) \
+		DESTDIR=$(LIBBPF_DESTDIR) prefix= $(LIBBPF) install_headers
+	$(call QUIET_INSTALL, bpf/nlattr.h)
+	$(Q)install -m 644 -t $(LIBBPF_INCLUDE)/bpf/ $(BPF_DIR)nlattr.h
 
 $(LIBBPF_BOOTSTRAP): FORCE | $(LIBBPF_BOOTSTRAP_OUTPUT)
 	$(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(LIBBPF_BOOTSTRAP_OUTPUT) \
@@ -60,10 +65,10 @@ CFLAGS += -W -Wall -Wextra -Wno-unused-parameter -Wno-missing-field-initializers
 CFLAGS += $(filter-out -Wswitch-enum -Wnested-externs,$(EXTRA_WARNINGS))
 CFLAGS += -DPACKAGE='"bpftool"' -D__EXPORTED_HEADERS__ \
 	-I$(if $(OUTPUT),$(OUTPUT),.) \
+	-I$(LIBBPF_INCLUDE) \
 	-I$(srctree)/kernel/bpf/ \
 	-I$(srctree)/tools/include \
 	-I$(srctree)/tools/include/uapi \
-	-I$(srctree)/tools/lib \
 	-I$(srctree)/tools/perf
 CFLAGS += -DBPFTOOL_VERSION='"$(BPFTOOL_VERSION)"'
 ifneq ($(EXTRA_CFLAGS),)
@@ -167,8 +172,7 @@ $(OUTPUT)%.bpf.o: skeleton/%.bpf.c $(OUTPUT)vmlinux.h $(LIBBPF)
 	$(QUIET_CLANG)$(CLANG) \
 		-I$(if $(OUTPUT),$(OUTPUT),.) \
 		-I$(srctree)/tools/include/uapi/ \
-		-I$(LIBBPF_PATH) \
-		-I$(srctree)/tools/lib \
+		-I$(LIBBPF_INCLUDE) \
 		-g -O2 -Wall -target bpf -c $< -o $@ && $(LLVM_STRIP) -g $@
 
 $(OUTPUT)%.skel.h: $(OUTPUT)%.bpf.o $(BPFTOOL_BOOTSTRAP)
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 326ea75ce99e..5432bfc99740 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -209,6 +209,8 @@ $(DEFAULT_BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile)    \
 		    CC=$(HOSTCC) LD=$(HOSTLD)				       \
 		    EXTRA_CFLAGS='-g -O0'				       \
 		    OUTPUT=$(HOST_BUILD_DIR)/bpftool/			       \
+		    LIBBPF_OUTPUT=$(HOST_BUILD_DIR)/libbpf/		       \
+		    LIBBPF_DESTDIR=$(HOST_SCRATCH_DIR)/			       \
 		    prefix= DESTDIR=$(HOST_SCRATCH_DIR)/ install
 
 all: docs
-- 
2.30.2