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Date:   Fri, 15 Oct 2021 18:06:13 +0200
From:   David Hildenbrand <>
To:     Shuah Khan <>
Subject: Re: selftests/vm madv_populate.c test

On 15.10.21 17:47, David Hildenbrand wrote:
> On 15.10.21 17:45, Shuah Khan wrote:
>> 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
>>> 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.
> Did you also install Linux headers? I assume no, correct?

What happens in your environment when compiling and running the
memfd_secret test?

If assume you'll see a "skip" when executing, because it might also
refer to the local version of linux headers and although it builds, it
really cannot build something "functional". It just doesn't add a
"#warning" to make that obvious.


David / dhildenb

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