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

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Date:	Tue, 8 Sep 2015 17:15:29 +0800
From:	Bamvor Zhang Jian <bamvor.zhangjian@...aro.org>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	linux-kernel@...r.kernel.org, Mark Brown <broonie@...nel.org>,
	khilman@...aro.org, tyler.baker@...aro.org,
	shuahkh@....samsung.com, Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 6/7] selftests: only compile userfaultfd for x86 and
 powperpc

Hi, Michael

I thought I reply to you, but ...

On 08/31/2015 11:26 AM, Michael Ellerman wrote:
> On Fri, 2015-08-14 at 21:43 +0800, Bamvor Jian Zhang wrote:
>> Signed-off-by: Bamvor Jian Zhang <bamvor.zhangjian@...aro.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
> 
>
When read the following code, It seems that sometimes __NR_userfaultfd is not
defined but the syscall is exist. I am not sure why these piece is needed.
cc'd c

#ifndef __NR_userfaultfd
#ifdef __x86_64__
#define __NR_userfaultfd 323
#elif defined(__i386__)
#define __NR_userfaultfd 374
#elif defined(__powewrpc__)
#define __NR_userfaultfd 364
#else
#error "missing __NR_userfaultfd definition"
#endif
#endif

Do you mean that we should remove the above code?

regards

bamvor
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