Add an AreaFrameAllocator

src/memory/area_frame_allocator.rs

@@ -0,0 +1,67 @@
+use memory::Frame;
+use multiboot2::{MemoryAreaIter, MemoryArea};
+
+/// A frame allocator that uses the memory areas from the multiboot information structure as
+/// source. The {kernel, multiboot}_{start, end} fields are used to avoid returning memory that is
+/// already in use.
+///
+/// `kernel_end` and `multiboot_end` are _inclusive_ bounds.
+pub struct AreaFrameAllocator {
+    next_free_frame: Frame,
+    current_area: Option<&'static MemoryArea>,
+    areas: MemoryAreaIter,
+    kernel_start: Frame,
+    kernel_end: Frame,
+    multiboot_start: Frame,
+    multiboot_end: Frame,
+}
+
+impl AreaFrameAllocator {
+    pub fn new(kernel_start: usize, kernel_end: usize, multiboot_start: usize, multiboot_end: usize,
+        memory_areas: MemoryAreaIter) -> AreaFrameAllocator
+    {
+        let mut allocator = AreaFrameAllocator {
+            next_free_frame: Frame::containing_address(0),
+            current_area: None,
+            areas: memory_areas,
+            kernel_start: Frame::containing_address(kernel_start),
+            kernel_end: Frame::containing_address(kernel_end),
+            multiboot_start: Frame::containing_address(multiboot_start),
+            multiboot_end: Frame::containing_address(multiboot_end),
+        };
+        allocator.choose_next_area();
+        allocator
+    }
+
+    pub fn allocate_frame(&mut self) -> Option<Frame> {
+        match self.current_area {
+            None => None,
+            Some(area) => {
+                let frame = self.next_free_frame;
+                let current_area_last_frame = {
+                    let address = area.base_addr + area.length - 1;
+                    Frame::containing_address(address as usize)
+                };
+
+                if frame > current_area_last_frame {
+                    self.choose_next_area()
+                } else if frame >= self.kernel_start && frame <= self.kernel_end {
+                    self.next_free_frame = Frame{ number: self.kernel_end.number + 1 }
+                } else if frame >= self.multiboot_start && frame <= self.multiboot_end {
+                    self.next_free_frame = Frame{ number: self.multiboot_end.number + 1 }
+                } else {
+                    self.next_free_frame.number += 1;
+                    return Some(frame);
+                }
+                self.allocate_frame()
+            }
+        }
+    }
+
+    fn choose_next_area(&mut self) {
+        self.current_area = self.areas.clone().filter(|area| {
+            let address = area.base_addr + area.length - 1;
+            Frame::containing_address(address as usize) >= self.next_free_frame
+        }).min_by(|area| area.base_addr);
+    }
+}

src/memory/mod.rs

@@ -1,3 +1,7 @@
+pub use self::area_frame_allocator::AreaFrameAllocator;
+
+mod area_frame_allocator;
+
 pub const PAGE_SIZE: usize = 4096;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]