linux-kernel - Re: selftests/vm madv

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Date:   Fri, 15 Oct 2021 09:45:01 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: selftests/vm madv_populate.c test

On 9/18/21 1:41 AM, David Hildenbrand wrote:
> On 18.09.21 00:45, Shuah Khan wrote:
>> Hi David,
>>
>> I am running into the following warning when try to build this test:
>>
>> madv_populate.c:334:2: warning: #warning "missing MADV_POPULATE_READ or MADV_POPULATE_WRITE definition" [-Wcpp]
>>     334 | #warning "missing MADV_POPULATE_READ or MADV_POPULATE_WRITE definition"
>>         |  ^~~~~~~
>>
>>
>> I see that the following handling is in place. However there is no
>> other information to explain why the check is necessary.
>>
>> #if defined(MADV_POPULATE_READ) && defined(MADV_POPULATE_WRITE)
>>
>> #else /* defined(MADV_POPULATE_READ) && defined(MADV_POPULATE_WRITE) */
>>
>> #warning "missing MADV_POPULATE_READ or MADV_POPULATE_WRITE definition"
>>
>> I do see these defined in:
>>
>> include/uapi/asm-generic/mman-common.h:#define MADV_POPULATE_READ       22
>> include/uapi/asm-generic/mman-common.h:#define MADV_POPULATE_WRITE      23
>>
>> Is this the case of missing include from madv_populate.c?
> 
> Hi Shuan,
> 
> note that we're including "#include <sys/mman.h>", which in my
> understanding maps to the version installed on your system instead
> of the one in our build environment.ing.
> 
> So as soon as you have a proper kernel + the proper headers installed
> and try to build, it would pick up MADV_POPULATE_READ and
> MADV_POPULATE_WRITE from the updated headers. That makes sense: you
> annot run any MADV_POPULATE_READ/MADV_POPULATE_WRITE tests on a kernel
> that doesn't support it.
> 
> See vm/userfaultfd.c where we do something similar.
> 

Kselftest is for testing the kernel with kernel headers. That is the
reason why there is the dependency on header install.

> 
> As soon as we have a proper environment, it seems to work just fine:
> 
> Linux vm-0 5.15.0-0.rc1.20210915git3ca706c189db.13.fc36.x86_64 #1 SMP Thu Sep 16 11:32:54 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
> [root@...0 linux]# cat /etc/redhat-release
> Fedora release 36 (Rawhide)

This is a distro release. We don't want to have dependency on headers
from the distro to run selftests. Hope this makes sense.

I still see this on my test system running Linux 5.15-rc5.

Can we make this work with kernel headers?

thanks,
-- Shuah