[PATCH v2 5/5] linux: Fix sys/mount.h usage with kernel headers

[Florian Weimer]

* Adhemerval Zanella via Libc-alpha:

> Now that kernel exports linux/mount.h and includes it on linux/fs.h,
> its definitions might clash with glibc exports sys/mount.h.  To avoid
> the need to rearrange the Linux header to be always after glibc one,
> the glibc sys/mount.h is changed to:
>
>   1. Undefine the macros also used as enum constants.  This covers prior
>      inclusion of <linux/mount.h> (for instance MS_RDONLY).
>
>   2. Include <linux/mount.h> based on the usual __has_include check
>      (needs to use __has_include ("linux/mount.h") to paper over GCC
>      bugs.
>
>   3. Define enum fsconfig_command only if FSOPEN_CLOEXEC is not defined.
>      (FSOPEN_CLOEXEC should be a very close proxy.)
>
>   4. Define struct mount_attr if MOUNT_ATTR_SIZE_VER0 is not defined.
>      (Added in the same commit on the Linux side.)
>
> This patch also adds some tests to check if including linux/fs.h and
> linux/mount.h after and before sys/mount.h does work.
>
> Checked on x86_64-linux-gnu.

Also built with build-many-glibcs.py.  This version looks good.

There is a gap with old compilers only (those that don't have
__has_include), and if <linux/mount.h> is included after <sys/mount.h>,
but I think that's an acceptable trade-off.

Reviewed-by: Florian Weimer <fweimer@redhat.com>

Thanks,
Florian