static inline void set_page_ext(struct page *pg, struct xen_netbk *netbk,
				unsigned int idx)
{
	unsigned int group = netbk - xen_netbk;
	union page_ext ext = { .e = { .group = group + 1, .idx = idx } };

	BUILD_BUG_ON(sizeof(ext) > sizeof(ext.mapping));
	pg->mapping = ext.mapping;
}
static inline void set_page_ext(struct page *pg, struct xen_netbk *netbk,
				unsigned int idx)
{
	unsigned int group = netbk - xen_netbk;
	union page_ext ext = { .e = { .group = group + 1, .idx = idx } };

	BUILD_BUG_ON(sizeof(ext) > sizeof(ext.mapping));
	pg->mapping = ext.mapping;
}