netdev - Re: [PATCH bpf] selftests/bpf: make directory prerequisites order-only

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Date:   Wed, 17 Jul 2019 11:10:01 +0200
From:   Ilya Leoshkevich <iii@...ux.ibm.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>, bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>
Subject: Re: [PATCH bpf] selftests/bpf: make directory prerequisites
 order-only

> Am 16.07.2019 um 19:49 schrieb Alexei Starovoitov <alexei.starovoitov@...il.com>:
> 
> On Mon, Jul 15, 2019 at 3:22 PM Daniel Borkmann <daniel@...earbox.net> wrote:
>> 
>> On 7/12/19 3:56 PM, Ilya Leoshkevich wrote:
>>> When directories are used as prerequisites in Makefiles, they can cause
>>> a lot of unnecessary rebuilds, because a directory is considered changed
>>> whenever a file in this directory is added, removed or modified.
>>> 
>>> If the only thing a target is interested in is the existence of the
>>> directory it depends on, which is the case for selftests/bpf, this
>>> directory should be specified as an order-only prerequisite: it would
>>> still be created in case it does not exist, but it would not trigger a
>>> rebuild of a target in case it's considered changed.
>>> 
>>> Signed-off-by: Ilya Leoshkevich <iii@...ux.ibm.com>
>> 
>> Applied, thanks!
> 
> Hi Ilya,
> 
> this commit breaks map_tests.
> To reproduce:
> rm map_tests/tests.h
> make
> tests.h will not be regenerated.
> Please provide a fix asap.
> We cannot ship bpf tree with such failure.

Hi Alexei,

Sorry about this! I actually had the following in my local tree:

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index f1f2b82b8fb8..95795cf5805c 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -231,7 +231,7 @@ ifeq ($(DWARF2BTF),y)
 endif

 PROG_TESTS_H := $(OUTPUT)/prog_tests/tests.h
-test_progs.c: $(PROG_TESTS_H)
+$(OUTPUT)/test_progs: $(PROG_TESTS_H)
 $(OUTPUT)/test_progs: CFLAGS += $(TEST_PROGS_CFLAGS)
 $(OUTPUT)/test_progs: prog_tests/*.c

@@ -258,7 +258,7 @@ MAP_TESTS_DIR = $(OUTPUT)/map_tests
 $(MAP_TESTS_DIR):
 <------>mkdir -p $@
 MAP_TESTS_H := $(MAP_TESTS_DIR)/tests.h
-test_maps.c: $(MAP_TESTS_H)
+$(OUTPUT)/test_maps: $(MAP_TESTS_H)
 $(OUTPUT)/test_maps: CFLAGS += $(TEST_MAPS_CFLAGS)
 MAP_TESTS_FILES := $(wildcard map_tests/*.c)
 $(MAP_TESTS_H): $(MAP_TESTS_FILES) | $(MAP_TESTS_DIR)
@@ -275,7 +275,7 @@ $(MAP_TESTS_H): $(MAP_TESTS_FILES) | $(MAP_TESTS_DIR)
 <------><------> ) > $(MAP_TESTS_H))

 VERIFIER_TESTS_H := $(OUTPUT)/verifier/tests.h
-test_verifier.c: $(VERIFIER_TESTS_H)
+$(OUTPUT)/test_verifier: $(VERIFIER_TESTS_H)
 $(OUTPUT)/test_verifier: CFLAGS += $(TEST_VERIFIER_CFLAGS)

 VERIFIER_TESTS_DIR = $(OUTPUT)/verifier

but did not realise that this is a pre-requisite for my directories change.
I should have tested it separately, then I would have noticed.

Andrii,
Thanks for helping out and providing the fix!

Best regards,
Ilya