Add support for mapping new pages

src/main.rs

@@ -29,7 +29,6 @@ fn init() {
 #[no_mangle]
 pub extern "C" fn _start(boot_info: &'static BootInfo) {
     use crate::vga_buffer::{change_color, Color};
-    use x86_64::{VirtAddr, structures::paging::Translate};
 
     init();
     print!("[ ");
@@ -38,26 +37,6 @@ pub extern "C" fn _start(boot_info: &'static BootInfo) {
     change_color(Color::White, Color::Black);
     println!(" ] Initialized GDT and interrupts");
 
-    let phys_mem_offset = VirtAddr::new(boot_info.physical_memory_offset);
-    let mapper = unsafe { memory::init(phys_mem_offset) };
-
-    let addresses = [
-        // the identity-mapped vga buffer page
-        0xb8000,
-        // some code page
-        0x201008,
-        // some stack page
-        0x0100_0020_1a10,
-        // virtual address mapped to physical address 0
-        boot_info.physical_memory_offset,
-    ];
-
-    for &address in &addresses {
-        let virt = VirtAddr::new(address);
-        let phys = mapper.translate_addr(virt);
-        println!("{:?} -> {:?}", virt, phys);        
-    }
-
     print!("Welcome to ");
     change_color(Color::Blue, Color::Black);
     println!("KarxOS!");

src/memory.rs

@@ -1,4 +1,5 @@
-use x86_64::{VirtAddr, structures::paging::{PageTable, OffsetPageTable}};
+use x86_64::{PhysAddr, VirtAddr, structures::paging::{FrameAllocator, Mapper, OffsetPageTable, Page, PageTable, PhysFrame, Size4KiB}};
+use bootloader::bootinfo::{MemoryMap, MemoryRegionType};
 
 pub unsafe fn init(physical_memory_offset: VirtAddr) -> OffsetPageTable<'static> {
     let level_4_table = active_level_4_table(physical_memory_offset);
@@ -16,3 +17,33 @@ unsafe fn active_level_4_table(physical_memory_offset: VirtAddr) -> &'static mut
 
     &mut *page_table_ptr
 }
+
+pub struct BootInfoFrameAllocator {
+    memory_map: &'static MemoryMap,
+    next: usize,
+}
+
+impl BootInfoFrameAllocator {
+    pub unsafe fn init(memory_map: &'static MemoryMap) -> Self {
+        BootInfoFrameAllocator {
+            memory_map,
+            next: 0
+        }
+    }
+
+    fn usable_frames(&self) -> impl Iterator<Item = PhysFrame> {
+        let regions = self.memory_map.iter();
+        let usable_regions = regions.filter(|r| r.region_type == MemoryRegionType::Usable);
+        let addr_ranges = usable_regions.map(|r| r.range.start_addr()..r.range.end_addr());
+        let frame_addresses = addr_ranges.flat_map(|r| r.step_by(4096));
+        frame_addresses.map(|addr| PhysFrame::containing_address(PhysAddr::new(addr)))
+    }
+}
+
+unsafe impl FrameAllocator<Size4KiB> for BootInfoFrameAllocator {
+    fn allocate_frame(&mut self) -> Option<PhysFrame> {
+        let frame = self.usable_frames().nth(self.next);
+        self.next += 1;
+        frame
+    }
+}