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SubjectRe: [Xen-devel] xen/mem-reservation API and out-of-tree kernel modules
On Thu, 31 Jan 2019, Oleksandr Andrushchenko wrote:
> Hello,
>
> I am working on porting an out-of-tree kernel driver to the kernel
> 5.0 and that driver uses functionality provided by
> drivers/xen/mem-reservation.c
> module.  Since commit [1] it is not possible to build a kernel module
> which uses mem-reservation API as xen_scrub_pages variable, which is
> checked in
> xenmem_reservation_scrub_page, became a kernel module parameter and is
> now only
> accessible for built-in modules:
>
> static inline void xenmem_reservation_scrub_page(struct page *page)
> ^^^^^^^^^^^^^
> {
>     if (xen_scrub_pages)
>         ^^^^^^^^^^^^^^^
>         clear_highpage(page);
> }
>
> This results in link-time warning:
>
>     WARNING: "xen_scrub_pages" [yourmodule.ko] undefined!
>
> and thus not allowing the module to run. At the moment I can only see a
> possible fix
> for this by making the following change:
>
> diff --git a/drivers/xen/mem-reservation.c b/drivers/xen/mem-reservation.c
> index 3782cf070338..85fecfec50e1 100644
> --- a/drivers/xen/mem-reservation.c
> +++ b/drivers/xen/mem-reservation.c
> @@ -18,6 +18,7 @@
>
>  bool __read_mostly xen_scrub_pages =
> IS_ENABLED(CONFIG_XEN_SCRUB_PAGES_DEFAULT);
>  core_param(xen_scrub_pages, xen_scrub_pages, bool, 0);
> +EXPORT_SYMBOL(xen_scrub_pages);
>
> but this looks a bit unusual for the kernel?
>
> I am looking for community advice here and help
>
> Thank you,
> Oleksandr
>
> [1]
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=197ecb3802c04499d8ff4f8cb28f6efa008067db

The alternative would be to turn xenmem_reservation_scrub_page into a
regular function (not a static inline)?
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