netdev - Re: [PATCH net 1/3] selftests: net: remove dependency on ebpf tests

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Message-ID: <6cb2ddf941698e2feb780dfae9325e98cd39d7a9.camel@redhat.com>
Date: Thu, 25 Jan 2024 16:19:04 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
	netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>,  Jakub Kicinski <kuba@...nel.org>, Shuah Khan
 <shuah@...nel.org>, Willem de Bruijn <willemb@...gle.com>, Lucas Karpinski
 <lkarpins@...hat.com>,  linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net 1/3] selftests: net: remove dependency on ebpf tests

On Thu, 2024-01-25 at 09:27 -0500, Willem de Bruijn wrote:
> Paolo Abeni wrote:
> > On Wed, 2024-01-24 at 20:10 -0500, Willem de Bruijn wrote:
> > > Paolo Abeni wrote:
> > > > Several net tests requires an XDP program build under the ebpf
> > > > directory, and error out if such program is not available.
> > > > 
> > > > That makes running successful net test hard, let's duplicate into the
> > > > net dir the [very small] program, re-using the existing rules to build
> > > > it, and finally dropping the bogus dependency.
> > > > 
> > > > Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> > > > ---
> > > >  tools/testing/selftests/net/Makefile          |  5 +++--
> > > >  tools/testing/selftests/net/udpgro.sh         |  4 ++--
> > > >  tools/testing/selftests/net/udpgro_bench.sh   |  4 ++--
> > > >  tools/testing/selftests/net/udpgro_frglist.sh |  6 +++---
> > > >  tools/testing/selftests/net/udpgro_fwd.sh     |  2 +-
> > > >  tools/testing/selftests/net/veth.sh           |  4 ++--
> > > >  tools/testing/selftests/net/xdp_dummy.c       | 13 +++++++++++++
> > > >  7 files changed, 26 insertions(+), 12 deletions(-)
> > > >  create mode 100644 tools/testing/selftests/net/xdp_dummy.c
> > > > 
> > > > diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
> > > > index 50818075e566..304d8b852ef0 100644
> > > > --- a/tools/testing/selftests/net/Makefile
> > > > +++ b/tools/testing/selftests/net/Makefile
> > > > @@ -84,6 +84,7 @@ TEST_PROGS += sctp_vrf.sh
> > > >  TEST_GEN_FILES += sctp_hello
> > > >  TEST_GEN_FILES += csum
> > > >  TEST_GEN_FILES += nat6to4.o
> > > > +TEST_GEN_FILES += xdp_dummy.o
> > > >  TEST_GEN_FILES += ip_local_port_range
> > > >  TEST_GEN_FILES += bind_wildcard
> > > >  TEST_PROGS += test_vxlan_mdb.sh
> > > > @@ -104,7 +105,7 @@ $(OUTPUT)/tcp_inq: LDLIBS += -lpthread
> > > >  $(OUTPUT)/bind_bhash: LDLIBS += -lpthread
> > > >  $(OUTPUT)/io_uring_zerocopy_tx: CFLAGS += -I../../../include/
> > > >  
> > > > -# Rules to generate bpf obj nat6to4.o
> > > > +# Rules to generate bpf objs
> > > >  CLANG ?= clang
> > > >  SCRATCH_DIR := $(OUTPUT)/tools
> > > >  BUILD_DIR := $(SCRATCH_DIR)/build
> > > > @@ -139,7 +140,7 @@ endif
> > > >  
> > > >  CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG),$(CLANG_TARGET_ARCH))
> > > >  
> > > > -$(OUTPUT)/nat6to4.o: nat6to4.c $(BPFOBJ) | $(MAKE_DIRS)
> > > > +$(OUTPUT)/nat6to4.o $(OUTPUT)/xdp_dummy.o: $(OUTPUT)/%.o : %.c $(BPFOBJ) | $(MAKE_DIRS)
> > > >  	$(CLANG) -O2 --target=bpf -c $< $(CCINCLUDE) $(CLANG_SYS_INCLUDES) -o $@
> > > 
> > > is the "$(OUTPUT)/%.o :" intentional or a leftover from editing?
> > 
> > Is intentional and AFAICS required to let this rule being selected when
> > the output directory is not an empty string (the target and the pre-req
> > will be in different directories).
> 
> Thanks. I don't understand why. Sorry to harp on this small point, but
> you've verified that the build fails without? Is it perhaps due to that
> "$(MAKE_DIRS)" order-only-prerequisite? But nat6to4 on its own did not
> need this.

I tried quite a bit of permutation (all others failing) before
selecting this one (shame on me, with a stackoverflow hint [!!!]).

But I finally found the relevant documentation reference:

https://www.gnu.org/software/make/manual/make.html#Static-Pattern

A simpler wildcard rule would not be enough, as the already existing
wildcard used to build plain c files will take precedence.

nat6to4 did not need this fancy syntax, as it was a simple, single
target single pre-req rule - that takes precedence on the mentioned
wildcard.

Please let me know if the above clarifies a bit the scenario.

Cheers,

Paolo