paging: add basic bitmap frame allocator

1 files changed, 53 insertions, 17 deletions

diff --git a/src/mm/pma.rs b/src/mm/pma.rs
index aa5e193..af789e8 100644
--- a/src/mm/pma.rs
+++ b/src/mm/pma.rs
@@ -1,4 +1,4 @@
-use crate::defs::Mem;
+use crate::defs::{self, Mem};
 use core::ffi::c_void;
 use core::{ptr, slice};
 // this is POC code, it will be ugly
@@ -6,26 +6,62 @@ use core::{ptr, slice};
 extern "C" {
 	pub fn ___KERNEL_END__();
 }
-/// Bitmap for physical frames. to get around the chicken-egg problem, we provide a provisional
-/// bitmap of fixed length in the startup code.
-pub struct PFMap {
-	bm: &'static mut [u8],
-	skip: usize, // pfn to skip (because they are already used by the initial kernel image)
-	end: usize,  // pfn limit
+
+type BitU8 = u8;
+/// Bitmap for physical frames
+pub struct FMap {
+	pub bm: &'static mut [BitU8],
+	// skip over the kernel image and the bitmap itself.
+	pub skip_byte: usize,
 }
 
-// TODO PMA initialization : needs to singleton
+pub enum PMAError{
+	DoubleFree
+}
 
-impl PFMap {}
+impl FMap {
+	pub fn new() -> Self {
+		let map_start = ___KERNEL_END__ as usize;
+		let fmap = Self {
+			bm: unsafe { slice::from_raw_parts_mut(map_start as *mut u8, Mem::PHY_BM_SIZE) },
+			// looks ugly, perhaps FIXME
+			// We'll waste several frames for the sake of easy alignment
+			skip_byte: 1 + ((map_start >> Mem::PAGE_SHIFT) / 8),
+		};
+		fmap
+	}
 
-pub struct Frame {
-	pfn: usize,
-}
+	/// return : index to the bitmap u8 , bit mask to retrive the bit.
+	fn locate_bit(addr: usize) -> Option<(usize, u8)> {
+		if addr >= Mem::PHY_TOP {
+			return None
+		}
+		let pn = addr >> Mem::PAGE_SHIFT;
+		let idx = pn / 8;
+		let mask:u8 = 1 << (pn % 8);
+		Some((idx, mask))
+	}
 
-impl Frame {
-	pub fn addr(&self) -> usize {
-		self.pfn << Mem::PAGE_SHIFT
+	pub fn alloc_frame(&mut self) -> usize {
+		for i in self.skip_byte..self.bm.len() {
+			if self.bm[i] == 0xff {
+				continue
+			}
+			todo!()
+		}
+		0
+	}
+
+	pub fn dealloc_frame(&mut self) -> Result<(),PMAError>{
+		Ok(())
 	}
-}
 
-// pub struct PageAlloctor;
+	pub fn init(&mut self) {
+		for i in 0..self.skip_byte {
+			self.bm[i] = 0xff;
+		}
+		for i in self.skip_byte..self.bm.len() {
+			self.bm[i] = 0;
+		}
+	}
+}