tools: net: package libynl for use in selftests

Support building the C YNL userspace library into one big static file.
We can then link selftests against it for easy to use C netlink
interface.

Signed-off-by: Mina Almasry <almasrymina@google.com>
Link: https://patch.msgid.link/20240628003253.1694510-14-almasrymina@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/net/ynl/Makefile

@@ -2,9 +2,12 @@
 
 SUBDIRS = lib generated samples
 
-all: $(SUBDIRS)
+all: $(SUBDIRS) libynl.a
 
 samples: | lib generated
+libynl.a: | lib generated
+	@echo -e "\tAR $@"
+	@ar rcs $@ lib/ynl.o generated/*-user.o
 
 $(SUBDIRS):
 	@if [ -f "$@/Makefile" ] ; then \
@@ -17,5 +20,6 @@ clean distclean:
 			$(MAKE) -C $$dir $@; \
 		fi \
 	done
+	rm -f libynl.a
 
 .PHONY: all clean distclean $(SUBDIRS)

tools/net/ynl/lib/Makefile

@@ -14,7 +14,9 @@ include $(wildcard *.d)
 all: ynl.a
 
 ynl.a: $(OBJS)
-	ar rcs $@ $(OBJS)
+	@echo -e "\tAR $@"
+	@ar rcs $@ $(OBJS)
+
 clean:
 	rm -f *.o *.d *~
 	rm -rf __pycache__

tools/testing/selftests/net/ynl.mk

@@ -0,0 +1,21 @@
+# SPDX-License-Identifier: GPL-2.0
+
+# YNL selftest build snippet
+
+# Inputs:
+#
+# YNL_GENS:      families we need in the selftests
+# YNL_PROGS:     TEST_PROGS which need YNL (TODO, none exist, yet)
+# YNL_GEN_FILES: TEST_GEN_FILES which need YNL
+
+YNL_OUTPUTS := $(patsubst %,$(OUTPUT)/%,$(YNL_GEN_FILES))
+
+$(YNL_OUTPUTS): $(OUTPUT)/libynl.a
+$(YNL_OUTPUTS): CFLAGS += \
+	-I$(top_srcdir)/usr/include/ $(KHDR_INCLUDES) \
+	-I$(top_srcdir)/tools/net/ynl/lib/ \
+	-I$(top_srcdir)/tools/net/ynl/generated/
+
+$(OUTPUT)/libynl.a:
+	$(Q)$(MAKE) -C $(top_srcdir)/tools/net/ynl GENS="$(YNL_GENS)" libynl.a
+	$(Q)cp $(top_srcdir)/tools/net/ynl/libynl.a $(OUTPUT)/libynl.a