Finish basics of new paging module

src/memory/paging/mapping.rs

@@ -0,0 +1,24 @@
+use memory::Frame;
+use super::Page;
+use super::entry::{EntryFlags, PRESENT};
+use memory::FrameAllocator;
+use super::table::P4;
+
+pub fn map<A>(page: &Page, flags: EntryFlags, allocator: &mut A)
+    where A: FrameAllocator
+{
+    let frame = allocator.allocate_frame().expect("out of memory");
+    map_to(page, frame, flags, allocator)
+}
+
+pub fn map_to<A>(page: &Page, frame: Frame, flags: EntryFlags, allocator: &mut A)
+    where A: FrameAllocator
+{
+    let p4 = unsafe { &mut *P4 };
+    let mut p3 = p4.next_table_create(page.p4_index(), allocator);
+    let mut p2 = p3.next_table_create(page.p3_index(), allocator);
+    let mut p1 = p2.next_table_create(page.p2_index(), allocator);
+
+    assert!(!p1[page.p1_index()].flags().contains(PRESENT));
+    p1[page.p1_index()].set(frame, flags | PRESENT);
+}