+
+extern struct page *phys_to_page(const unsigned long phys);
+extern struct page *__virt_to_page(const unsigned long virt);
+#define virt_to_page(addr) __virt_to_page((const unsigned long) addr)
+
+/*
+ * Bits 0 through 3 are taken
+ */
+#define PTE_FILE_MAX_BITS 28
+
+#define pte_to_pgoff(pte) ((pte).pte_low >> 4)
+
+#define pgoff_to_pte(off) \
+ ((pte_t) { ((off) << 4) + _PAGE_FILE })