Add unmap function

src/main.rs

@@ -228,6 +228,16 @@ unsafe fn new_tables<A: Arch>(areas: &'static [MemoryArea]) {
         flush_all.consume(flush);
     }
     flush_all.flush();
+
+    let flush_all = PageFlushAll::new();
+    for i in 0..16 {
+        let virt = VirtualAddress::new(MEGABYTE + i * A::PAGE_SIZE);
+        let flush = mapper.unmap(
+            virt,
+        ).expect("failed to unmap page");
+        flush_all.consume(flush);
+    }
+    flush_all.flush();
 }
 
 unsafe fn inner<A: Arch>() {

src/page/mapper.rs

@@ -78,4 +78,27 @@ impl<'f, A: Arch, F: FrameAllocator> PageMapper<'f, A, F> {
             }
         }
     }
+
+    pub unsafe fn unmap(&mut self, virt: VirtualAddress) -> Option<PageFlush<A>> {
+        let (old, flush) = self.unmap_phys(virt)?;
+        self.allocator.free_one(old.address());
+        Some(flush)
+    }
+
+    pub unsafe fn unmap_phys(&mut self, virt: VirtualAddress) -> Option<(PageEntry<A>, PageFlush<A>)> {
+        //TODO: verify virt is aligned
+        let mut table = self.table();
+        //TODO: unmap parents
+        loop {
+            let i = table.index_of(virt)?;
+            if table.level() == 0 {
+                let entry_opt = table.entry(i);
+                table.set_entry(i, PageEntry::new(0));
+                let entry = entry_opt?;
+                return Some((entry, PageFlush::new(virt)));
+            } else {
+                table = table.next(i)?;
+            }
+        }
+    }
 }