selftests/net: mv bpf/nat6to4.c to net folder

There are some issues with the bpf/nat6to4.c building.

1. It use TEST_CUSTOM_PROGS, which will add the nat6to4.o to
kselftest-list file and run by common run_tests.
2. When building the test via `make -C tools/testing/selftests/
TARGETS="net"`, the nat6to4.o will be build in selftests/net/bpf/
folder. But in test udpgro_frglist.sh it refers to ../bpf/nat6to4.o.
The correct path should be ./bpf/nat6to4.o.
3. If building the test via `make -C tools/testing/selftests/ TARGETS="net"
install`. The nat6to4.o will be installed to kselftest_install/net/
folder. Then the udpgro_frglist.sh should refer to ./nat6to4.o.

To fix the confusing test path, let's just move the nat6to4.c to net folder
and build it as TEST_GEN_FILES.

Fixes: edae34a3ed92 ("selftests net: add UDP GRO fraglist + bpf self-tests")
Tested-by: Björn Töpel <[e-mail]>
Signed-off-by: Hangbin Liu <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Paolo Abeni <[e-mail]>

tools/testing/selftests/net/Makefile

···
 TEST_PROGS += sctp_vrf.sh
 TEST_GEN_FILES += sctp_hello
 TEST_GEN_FILES += csum
+TEST_GEN_FILES += nat6to4.o
 
 TEST_FILES := settings
 
 include ../lib.mk
 
-include bpf/Makefile
-
 $(OUTPUT)/reuseport_bpf_numa: LDLIBS += -lnuma
 $(OUTPUT)/tcp_mmap: LDLIBS += -lpthread
 $(OUTPUT)/tcp_inq: LDLIBS += -lpthread
 $(OUTPUT)/bind_bhash: LDLIBS += -lpthread
+
+# Rules to generate bpf obj nat6to4.o
+CLANG ?= clang
+SCRATCH_DIR := $(OUTPUT)/tools
+BUILD_DIR := $(SCRATCH_DIR)/build
+BPFDIR := $(abspath ../../../lib/bpf)
+APIDIR := $(abspath ../../../include/uapi)
+
+CCINCLUDE += -I../bpf
+CCINCLUDE += -I../../../../usr/include/
+CCINCLUDE += -I$(SCRATCH_DIR)/include
+
+BPFOBJ := $(BUILD_DIR)/libbpf/libbpf.a
+
+MAKE_DIRS := $(BUILD_DIR)/libbpf
+$(MAKE_DIRS):
+	mkdir -p $@
+
+# Get Clang's default includes on this system, as opposed to those seen by
+# '-target bpf'. This fixes "missing" files on some architectures/distros,
+# such as asm/byteorder.h, asm/socket.h, asm/sockios.h, sys/cdefs.h etc.
+#
+# Use '-idirafter': Don't interfere with include mechanics except where the
+# build would have failed anyways.
+define get_sys_includes
+$(shell $(1) $(2) -v -E - </dev/null 2>&1 \
+	| sed -n '/<...> search starts here:/,/End of search list./{ s| \(/.*\)|-idirafter \1|p }') \
+$(shell $(1) $(2) -dM -E - </dev/null | grep '__riscv_xlen ' | awk '{printf("-D__riscv_xlen=%d -D__BITS_PER_LONG=%d", $$3, $$3)}')
+endef
+
+ifneq ($(CROSS_COMPILE),)
+CLANG_TARGET_ARCH = --target=$(notdir $(CROSS_COMPILE:%-=%))
+endif
+
+CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG),$(CLANG_TARGET_ARCH))
+
+$(OUTPUT)/nat6to4.o: nat6to4.c $(BPFOBJ) | $(MAKE_DIRS)
+	$(CLANG) -O2 -target bpf -c $< $(CCINCLUDE) $(CLANG_SYS_INCLUDES) -o $@
+
+$(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)		       \
+	   $(APIDIR)/linux/bpf.h					       \
+	   | $(BUILD_DIR)/libbpf
+	$(MAKE) $(submake_extras) -C $(BPFDIR) OUTPUT=$(BUILD_DIR)/libbpf/     \
+		    EXTRA_CFLAGS='-g -O0'				       \
+		    DESTDIR=$(SCRATCH_DIR) prefix= all install_headers
+
+EXTRA_CLEAN := $(SCRATCH_DIR)

tools/testing/selftests/net/bpf/Makefile

···
-# SPDX-License-Identifier: GPL-2.0
-
-CLANG ?= clang
-SCRATCH_DIR := $(OUTPUT)/tools
-BUILD_DIR := $(SCRATCH_DIR)/build
-BPFDIR := $(abspath ../../../lib/bpf)
-APIDIR := $(abspath ../../../include/uapi)
-
-CCINCLUDE += -I../../bpf
-CCINCLUDE += -I../../../../../usr/include/
-CCINCLUDE += -I$(SCRATCH_DIR)/include
-
-BPFOBJ := $(BUILD_DIR)/libbpf/libbpf.a
-
-MAKE_DIRS := $(BUILD_DIR)/libbpf $(OUTPUT)/bpf
-$(MAKE_DIRS):
-	mkdir -p $@
-
-TEST_CUSTOM_PROGS = $(OUTPUT)/bpf/nat6to4.o
-all: $(TEST_CUSTOM_PROGS)
-
-# Get Clang's default includes on this system, as opposed to those seen by
-# '-target bpf'. This fixes "missing" files on some architectures/distros,
-# such as asm/byteorder.h, asm/socket.h, asm/sockios.h, sys/cdefs.h etc.
-#
-# Use '-idirafter': Don't interfere with include mechanics except where the
-# build would have failed anyways.
-define get_sys_includes
-$(shell $(1) $(2) -v -E - </dev/null 2>&1 \
-	| sed -n '/<...> search starts here:/,/End of search list./{ s| \(/.*\)|-idirafter \1|p }') \
-$(shell $(1) $(2) -dM -E - </dev/null | grep '__riscv_xlen ' | awk '{printf("-D__riscv_xlen=%d -D__BITS_PER_LONG=%d", $$3, $$3)}')
-endef
-
-ifneq ($(CROSS_COMPILE),)
-CLANG_TARGET_ARCH = --target=$(notdir $(CROSS_COMPILE:%-=%))
-endif
-
-CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG),$(CLANG_TARGET_ARCH))
-
-$(TEST_CUSTOM_PROGS): $(OUTPUT)/%.o: %.c $(BPFOBJ) | $(MAKE_DIRS)
-	$(CLANG) -O2 -target bpf -c $< $(CCINCLUDE) $(CLANG_SYS_INCLUDES) -o $@
-
-$(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)		       \
-	   $(APIDIR)/linux/bpf.h					       \
-	   | $(BUILD_DIR)/libbpf
-	$(MAKE) $(submake_extras) -C $(BPFDIR) OUTPUT=$(BUILD_DIR)/libbpf/     \
-		    EXTRA_CFLAGS='-g -O0'				       \
-		    DESTDIR=$(SCRATCH_DIR) prefix= all install_headers
-
-EXTRA_CLEAN := $(TEST_CUSTOM_PROGS) $(SCRATCH_DIR)
-

tools/testing/selftests/net/udpgro_frglist.sh

···
 
 	ip -n "${PEER_NS}" link set veth1 xdp object ${BPF_FILE} section xdp
 	tc -n "${PEER_NS}" qdisc add dev veth1 clsact
-	tc -n "${PEER_NS}" filter add dev veth1 ingress prio 4 protocol ipv6 bpf object-file ../bpf/nat6to4.o section schedcls/ingress6/nat_6  direct-action
-	tc -n "${PEER_NS}" filter add dev veth1 egress prio 4 protocol ip bpf object-file ../bpf/nat6to4.o section schedcls/egress4/snat4 direct-action
+	tc -n "${PEER_NS}" filter add dev veth1 ingress prio 4 protocol ipv6 bpf object-file nat6to4.o section schedcls/ingress6/nat_6  direct-action
+	tc -n "${PEER_NS}" filter add dev veth1 egress prio 4 protocol ip bpf object-file nat6to4.o section schedcls/egress4/snat4 direct-action
         echo ${rx_args}
 	ip netns exec "${PEER_NS}" ./udpgso_bench_rx ${rx_args} -r &
 
···
 	exit -1
 fi
 
-if [ ! -f bpf/nat6to4.o ]; then
-	echo "Missing nat6to4 helper. Build bpfnat6to4.o selftest first"
+if [ ! -f nat6to4.o ]; then
+	echo "Missing nat6to4 helper. Build bpf nat6to4.o selftest first"
 	exit -1
 fi