Re: selftests/vm madv_populate.c test

[Shuah Khan]

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@vm-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