Re: Mutli-directory module Makefiles

Masahiro Yamada
2018-01-25T13:09:25Z

2018-01-23 6:46 GMT+09:00 Jakub Kicinski <kubakici@wp.pl>:
> Hi!
>
> in drivers/net/ethernet/netronome/nfp there is a module which is built
> from C sources in 4 directories. What is the best way to handle that?
>
> Currently we just add all the objects in one Makefile:
>
> nfp-objs := \
> nfpcore/nfp6000_pcie.o \
> nfpcore/nfp_cppcore.o \
> etc.

I recommend you to refactor the Makefile,
adding Makefiles into nfpcore, nic, flower, bpf sub-directories.

Also, ifeq is ugly,
can you rewrite like follows?

nfp-$(CONFIG_NFP_APP_FLOWER) += flower/
nfp-$(CONFIG_BPF_SYSCALL) += bpf/
nfp-$(CONFIG_NFP_DEBUG) += nfp_net_debugfs.o

> However, this makes it impossible to build a single object in subdirs:
>
> $ make drivers/net/ethernet/netronome/nfp/nfpcore/nfp_cppcore.o
> scripts/Makefile.build:45: drivers/net/ethernet/netronome/nfp/nfpcore/Makefile: No such file or directory
> make[2]: *** No rule to make target 'drivers/net/ethernet/netronome/nfp/nfpcore/Makefile'. Stop.
>
> Documentation/kbuild/modules.txt also contains an unclear remark that
> this is not recommended (or is it about the use of $(src)?):
>
> --- 4.3 Several Subdirectories
> ...
> To build the module complex.ko, we then need the following
> kbuild file:
>
> --> filename: Kbuild
> obj-m := complex.o
> complex-y := src/complex_main.o
> complex-y += src/hal/hardwareif.o
>
> ccflags-y := -I$(src)/include
> ccflags-y += -I$(src)/src/hal/include
>
> As you can see, kbuild knows how to handle object files located
> in other directories. The trick is to specify the directory
> relative to the kbuild file's location. **That being said, this
> is NOT recommended practice.**
>
> Making the include optional would work:
>
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> @@ -42,7 +42,7 @@ save-cflags := $(CFLAGS)
> # The filename Kbuild has precedence over Makefile
> kbuild-dir := $(if $(filter /%,$(src)),$(src),$(srctree)/$(src))
> kbuild-file := $(if $(wildcard $(kbuild-dir)/Kbuild),$(kbuild-dir)/Kbuild,$(kbuild-dir)/Makefile)
> -include $(kbuild-file)
> +-include $(kbuild-file)
>
> # If the save-* variables changed error out
> ifeq ($(KBUILD_NOPEDANTIC),)
>
> Or we could create empty Makefiles in subdirectories... Is there a
> better way of handling this? Which is preferred?

--
Best Regards
Masahiro Yamada