Re: [PATCH 6/7] selftests: only compile userfaultfd for x86 and powperpc

[Michael Ellerman <mpe@ellerman.id.au>]

On Fri, 2015-08-14 at 21:43 +0800, Bamvor Jian Zhang wrote:
> Signed-off-by: Bamvor Jian Zhang <bamvor.zhangjian@linaro.org>
> ---
>  tools/testing/selftests/vm/Makefile | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
> index bb888c6..4dd6e4f 100644
> --- a/tools/testing/selftests/vm/Makefile
> +++ b/tools/testing/selftests/vm/Makefile
> @@ -1,5 +1,15 @@
>  # Makefile for vm selftests
>  
> +uname_M := $(shell uname -m 2>/dev/null || echo not)
> +ARCH ?= $(shell echo $(uname_M) | sed -e s/i.86/i386/ -e s/ppc.*/powerpc/)
> +
> +ifeq ($(ARCH),powerpc)
> +support_userfaultfd = yes
> +endif
> +ifeq ($(ARCH),x86)
> +support_userfaultfd = yes
> +endif
> +
>  CFLAGS = -Wall
>  BINARIES = compaction_test
>  BINARIES += hugepage-mmap
> @@ -9,7 +19,9 @@ BINARIES += mlock2-tests
>  BINARIES += on-fault-limit
>  BINARIES += thuge-gen
>  BINARIES += transhuge-stress
> +ifdef support_userfaultfd
>  BINARIES += userfaultfd
> +endif
>  
>  all: $(BINARIES)
>  %: %.c


This is nasty. It means when userfaultfd gets implemented for other arches
someone has to remember to update the logic here, which they won't.

Instead the C program should just do nothing when __NR_userfaultfd is not defined, eg:

#ifdef __NR_userfaultfd

int main(int argc, char **argv)
{
	...
}

#else

int main(void)
{
	printf("skip: Skipping userfaultfd test\n");
	return 0;
}
#endif


This way when the syscall is implemented for other arches the test will just
start working.

cheers