feat: allocator: block: implement reserver function

kernel/src/vspace/allocator/block.rs

@@ -47,6 +47,10 @@ impl<const N: usize> RamBlock<N> {
     }
 
     fn insert(&mut self, start: PhysAddr, size: usize) -> Result<&mut Option<Block>, ()> {
+        if size == 0 {
+            return Err(());
+        }
+
         for block in self.blocks.iter_mut() {
             if block.is_none() {
                 *block = Some(Block { start, size });
@@ -102,12 +106,42 @@ impl<const N: usize> RamBlock<N> {
 
         None
     }
+
+    pub fn reserve(&mut self, start: PhysAddr, size: usize) {
+        // NOTE: only support inclusive range
+        let victim = self
+            .blocks
+            .iter_mut()
+            .find(|block| block.is_some_and(|b| b.start_addr() <= start && start < b.end_addr()));
+
+        if victim.is_none() {
+            return;
+        }
+        let victim = victim.unwrap();
+
+        if let Some(block) = victim.take() {
+            let region_start = block.start_addr();
+            let region_end = block.end_addr();
+
+            let before_size = (start - region_start).as_usize();
+            let after_size = (region_end - (start + size)).as_usize();
+
+            // insert larger block first, then before block, then after block
+            if after_size > before_size {
+                // we could safely assert that before_size > 0 here
+                let _ = self.insert(start + size, after_size);
+                let _ = self.insert(region_start, before_size);
+            } else {
+                let _ = self.insert(region_start, before_size);
+                let _ = self.insert(start + size, after_size);
+            }
+        }
+    }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
-    use log::debug;
 
     #[test_case]
     fn test_block() {
@@ -150,4 +184,28 @@ mod tests {
         let ptr = blk.alloc(Layout::from_size_align(1, 1).unwrap());
         assert_eq!(ptr, None);
     }
+
+    #[test_case]
+    fn test_block_reserve() {
+        let mut blk = RamBlock::<4>::new();
+        blk.dealloc(PhysAddr(0), 100);
+
+        blk.reserve(PhysAddr(0), 10);
+        let ptr = blk.alloc(Layout::from_size_align(10, 1).unwrap());
+        assert_eq!(ptr, Some(PhysAddr(10)));
+
+        blk.reserve(PhysAddr(90), 10);
+        let ptr = blk.alloc(Layout::from_size_align(70, 1).unwrap());
+        assert_eq!(ptr, Some(PhysAddr(0x14)));
+
+        blk.dealloc(PhysAddr(0), 30);
+        blk.reserve(PhysAddr(10), 10);
+        let ptr = blk.alloc(Layout::from_size_align(10, 1).unwrap());
+        assert_eq!(ptr, Some(PhysAddr(0)));
+        let ptr = blk.alloc(Layout::from_size_align(10, 1).unwrap());
+        assert_eq!(ptr, Some(PhysAddr(20)));
+
+        let ptr = blk.alloc(Layout::from_size_align(1, 1).unwrap());
+        assert_eq!(ptr, None);
+    }
 }

kernel/src/vspace/allocator/freelist.rs

@@ -116,10 +116,9 @@ impl FreeList {
     }
 
     pub fn reserve(&mut self, start: PhysAddr, size: usize) {
+        // NOTE: only support inclusive range
         if let Some((region, _)) = self.alloc_node(|region| {
-            let left = max(region.start_addr(), start);
-            let right = min(region.end_addr(), start + size);
-            (left < right).some(|| (), ())
+            (region.start_addr() <= start && start < region.end_addr()).some(|| (), ())
         }) {
             let region_start = region.start_addr();
             let region_end = region.end_addr();

kernel/src/vspace/allocator/mod.rs

@@ -3,4 +3,5 @@ mod block;
 mod freelist;
 
 pub use bitmap::*;
+pub use block::*;
 pub use freelist::*;