Move Frame::start_address to memory/mod.rs and use it in identity_map()

posts/DRAFT-paging.md

@@ -130,18 +130,16 @@ pub fn set(&mut self, frame: Frame, flags: EntryFlags) {
 ```
 The start address of a frame should be page aligned and smaller than 2^52 (since x86 uses 52bit physical addresses). Since an invalid address could mess up the entry, we add an assertion. To actually set the entry, we just need to `or` the start address and the flag bits.
 
-The missing `start_address` function is pretty simple:
+The missing `Frame::start_address` method is pretty simple:
 
 ```rust
-use memory::paging::PhysicalAddress;
+use self::paging::PhysicalAddress;
 
-impl Frame {
-    fn start_address(&self) -> PhysicalAddress {
-        self.number << 12
-    }
+fn start_address(&self) -> PhysicalAddress {
+    self.number * PAGE_SIZE
 }
 ```
-Since we only need it in the entry submodule, we put it in a new `impl Frame` block in `entry.rs`.
+We add it to the `impl Frame` block in `memory/mod.rs`.
 
 ### Page Tables
 To model page tables, we create a basic `Table` struct in a new `table` submodule:
@@ -640,7 +638,7 @@ pub fn identity_map<A>(&mut self,
                        allocator: &mut A)
     where A: FrameAllocator
 {
-    let page = Page { number: frame.number };
+    let page = Page::containing_address(frame.start_address());
     self.map_to(&page, frame, flags, allocator)
 }
 ```

src/memory/mod.rs

@@ -1,4 +1,5 @@
 pub use self::area_frame_allocator::AreaFrameAllocator;
+use self::paging::PhysicalAddress;
 
 pub mod paging;
 mod area_frame_allocator;
@@ -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

@@ -44,9 +44,3 @@ bitflags! {
         const NO_EXECUTE =      1 << 63,
     }
 }
-
-impl Frame {
-    fn start_address(&self) -> PhysicalAddress {
-        self.number << 12
-    }
-}

src/memory/paging/mod.rs

@@ -150,7 +150,7 @@ impl RecursivePageTable {
     pub fn identity_map<A>(&mut self, frame: Frame, flags: EntryFlags, allocator: &mut A)
         where A: FrameAllocator
     {
-        let page = Page { number: frame.number };
+        let page = Page::containing_address(frame.start_address());
         self.map_to(&page, frame, flags, allocator)
     }