[PATCH v2 net-next 04/14] selftests: net: add a generic rule for BPF skeletons

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

net/bpf.mk builds the BPF programs of the networking selftests, but a
test that loads its program through a bpftool-generated skeleton has to
bring its own rule for the header. Add a pattern rule that generates
$(OUTPUT)/<name>.skel.h from $(OUTPUT)/<name>.bpf.o. BPFTOOL selects the
bpftool binary and defaults to the one in PATH. When bpftool fails, the
rule removes the partial header, so a later build does not take it as
up to date.

xskxceiver, which moves to net/lib in the next patch, is the first user.

Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
---
 tools/testing/selftests/net/bpf.mk | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/testing/selftests/net/bpf.mk b/tools/testing/selftests/net/bpf.mk
index a4f6755dd894..0eca0c5de5b5 100644
--- a/tools/testing/selftests/net/bpf.mk
+++ b/tools/testing/selftests/net/bpf.mk
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 # Rules to generate bpf objs
 CLANG ?= clang
+BPFTOOL ?= bpftool
 SCRATCH_DIR := $(OUTPUT)/tools
 BUILD_DIR := $(SCRATCH_DIR)/build
 BPFDIR := $(top_srcdir)/tools/lib/bpf
@@ -42,6 +43,11 @@ $(BPF_PROG_OBJS): $(OUTPUT)/%.o : %.c $(BPFOBJ) | $(MAKE_DIRS)
 	$(Q)$(CLANG) -O2 -g --target=bpf $(CCINCLUDE) $(CLANG_SYS_INCLUDES) \
 	-c $< -o $@
 
+$(OUTPUT)/%.skel.h: $(OUTPUT)/%.bpf.o
+	$(call msg,GEN-SKEL,,$@)
+	$(Q)$(BPFTOOL) gen skeleton $< name $(notdir $*) > $@ || \
+		{ rm -f $@; exit 1; }
+
 $(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)		       \
 	   $(APIDIR)/linux/bpf.h					       \
 	   | $(BUILD_DIR)/libbpf
-- 
2.43.0