Add `pointed_frame` and `set` methods to `Entry`

src/memory/mod.rs

@@ -1,4 +1,5 @@
 pub use self::area_frame_allocator::AreaFrameAllocator;
+use self::paging::PhysicalAddress;
 
 mod area_frame_allocator;
 mod paging;
@@ -14,6 +15,10 @@ impl Frame {
     fn containing_address(address: usize) -> Frame {
         Frame{ number: address / PAGE_SIZE }
     }
+
+    fn start_address(&self) -> PhysicalAddress {
+        self.number * PAGE_SIZE
+    }
 }
 
 pub trait FrameAllocator {

src/memory/paging/entry.rs

@@ -14,6 +14,21 @@ impl Entry {
     pub fn flags(&self) -> EntryFlags {
         EntryFlags::from_bits_truncate(self.0)
     }
+
+    pub fn pointed_frame(&self) -> Option<Frame> {
+        if self.flags().contains(PRESENT) {
+            Some(Frame::containing_address(
+                self.0 as usize & 0x000fffff_fffff000
+            ))
+        } else {
+            None
+        }
+    }
+
+    pub fn set(&mut self, frame: Frame, flags: EntryFlags) {
+        assert!(frame.start_address() & !0x000fffff_fffff000 == 0);
+        self.0 = (frame.start_address() as u64) | flags.bits();
+    }
 }
 
 bitflags! {