Re: [PATCH bpf-next v2 7/9] samples/bpf: install libbpf headers when building

API headers from libbpf should not be accessed directly from the source
directory. Instead, they should be exported with "make install_headers".
Make sure that samples/bpf/Makefile installs the headers properly when
building.

The object compiled from and exported by libbpf are now placed into a
subdirectory of sample/bpf/ instead of remaining in tools/lib/bpf/. We
attempt to remove this directory on "make clean". However, the "clean"
target re-enters the samples/bpf/ directory from the root of the
repository ("$(MAKE) -C ../../ M=$(CURDIR) clean"), in such a way that
$(srctree) and $(src) are not defined, making it impossible to use
$(LIBBPF_OUTPUT) and $(LIBBPF_DESTDIR) in the recipe. So we only attempt
to clean $(CURDIR)/libbpf, which is the default value.

We also change the output directory for bpftool, to place the generated
objects under samples/bpf/bpftool/ instead of building in bpftool's
directory directly. Doing so, we make sure bpftool reuses the libbpf
library previously compiled and installed.

Signed-off-by: Quentin Monnet <redacted>
---
 samples/bpf/Makefile | 36 ++++++++++++++++++++++++++----------
 1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 4dc20be5fb96..7de602c2c705 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile

@@ -59,7 +59,11 @@ tprogs-y += xdp_redirect
 tprogs-y += xdp_monitor

 # Libbpf dependencies
-LIBBPF = $(TOOLS_PATH)/lib/bpf/libbpf.a
+LIBBPF_SRC = $(TOOLS_PATH)/lib/bpf
+LIBBPF_OUTPUT = $(abspath $(BPF_SAMPLES_PATH))/libbpf
+LIBBPF_DESTDIR = $(LIBBPF_OUTPUT)
+LIBBPF_INCLUDE = $(LIBBPF_DESTDIR)/include
+LIBBPF = $(LIBBPF_OUTPUT)/libbpf.a

 CGROUP_HELPERS := ../../tools/testing/selftests/bpf/cgroup_helpers.o
 TRACE_HELPERS := ../../tools/testing/selftests/bpf/trace_helpers.o

@@ -198,7 +202,7 @@ TPROGS_CFLAGS += -Wstrict-prototypes

 TPROGS_CFLAGS += -I$(objtree)/usr/include
 TPROGS_CFLAGS += -I$(srctree)/tools/testing/selftests/bpf/
-TPROGS_CFLAGS += -I$(srctree)/tools/lib/
+TPROGS_CFLAGS += -I$(LIBBPF_INCLUDE)
 TPROGS_CFLAGS += -I$(srctree)/tools/include
 TPROGS_CFLAGS += -I$(srctree)/tools/perf
 TPROGS_CFLAGS += -DHAVE_ATTR_TEST=0

@@ -268,16 +272,28 @@ all:
 clean:
        $(MAKE) -C ../../ M=$(CURDIR) clean
        @find $(CURDIR) -type f -name '*~' -delete
+       @/bin/rm -rf $(CURDIR)/libbpf $(CURDIR)/bpftool

-$(LIBBPF): FORCE
+$(LIBBPF): FORCE | $(LIBBPF_OUTPUT) $(LIBBPF_INCLUDE)
 # Fix up variables inherited from Kbuild that tools/ build system won't like
-       $(MAKE) -C $(dir $@) RM='rm -rf' EXTRA_CFLAGS="$(TPROGS_CFLAGS)" \
-               LDFLAGS=$(TPROGS_LDFLAGS) srctree=$(BPF_SAMPLES_PATH)/../../ O=
+       $(MAKE) -C $(LIBBPF_SRC) RM='rm -rf' EXTRA_CFLAGS="$(TPROGS_CFLAGS)" \
+               LDFLAGS=$(TPROGS_LDFLAGS) srctree=$(BPF_SAMPLES_PATH)/../../ \
+               O= OUTPUT=$(LIBBPF_OUTPUT)/ DESTDIR=$(LIBBPF_DESTDIR) prefix= \
+               $@ install_headers

 BPFTOOLDIR := $(TOOLS_PATH)/bpf/bpftool
-BPFTOOL := $(BPFTOOLDIR)/bpftool
-$(BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile)
-           $(MAKE) -C $(BPFTOOLDIR) srctree=$(BPF_SAMPLES_PATH)/../../
+BPFTOOL_OUTPUT := $(abspath $(BPF_SAMPLES_PATH))/bpftool
+BPFTOOL := $(BPFTOOL_OUTPUT)/bpftool
+$(BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile) \
+           | $(BPFTOOL_OUTPUT)
+           $(MAKE) -C $(BPFTOOLDIR) srctree=$(BPF_SAMPLES_PATH)/../../ \
+               OUTPUT=$(BPFTOOL_OUTPUT)/ \
+               LIBBPF_OUTPUT=$(LIBBPF_OUTPUT) \
+               LIBBPF_DESTDIR=$(LIBBPF_DESTDIR)
+
+$(LIBBPF_OUTPUT) $(LIBBPF_INCLUDE) $(BPFTOOL_OUTPUT):
+       $(call msg,MKDIR,$@)
+       $(Q)mkdir -p $@

 $(obj)/syscall_nrs.h:  $(obj)/syscall_nrs.s FORCE
        $(call filechk,offsets,__SYSCALL_NRS_H__)

@@ -367,7 +383,7 @@ $(obj)/%.bpf.o: $(src)/%.bpf.c $(obj)/vmlinux.h $(src)/xdp_sample.bpf.h $(src)/x
        $(Q)$(CLANG) -g -O2 -target bpf -D__TARGET_ARCH_$(SRCARCH) \
                -Wno-compare-distinct-pointer-types -I$(srctree)/include \
                -I$(srctree)/samples/bpf -I$(srctree)/tools/include \
-               -I$(srctree)/tools/lib $(CLANG_SYS_INCLUDES) \
+               -I$(LIBBPF_INCLUDE) $(CLANG_SYS_INCLUDES) \
                -c $(filter %.bpf.c,$^) -o $@

 LINKED_SKELS := xdp_redirect_cpu.skel.h xdp_redirect_map_multi.skel.h \

@@ -404,7 +420,7 @@ $(obj)/%.o: $(src)/%.c
        @echo "  CLANG-bpf " $@
        $(Q)$(CLANG) $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(BPF_EXTRA_CFLAGS) \
                -I$(obj) -I$(srctree)/tools/testing/selftests/bpf/ \
-               -I$(srctree)/tools/lib/ \
+               -I$(LIBBPF_INCLUDE) \
                -D__KERNEL__ -D__BPF_TRACING__ -Wno-unused-value -Wno-pointer-sign \
                -D__TARGET_ARCH_$(SRCARCH) -Wno-compare-distinct-pointer-types \
                -Wno-gnu-variable-sized-type-not-at-end \
--

2.30.2