1 files changed, 84 insertions, 0 deletions
diff --git a/src/memory/cached_block.rs b/src/memory/cached_block.rs
new file mode 100644
index 0000000..0c401ff
--- /dev/null
+++ b/src/memory/cached_block.rs
@@ -0,0 +1,84 @@
+use and_then_some::BoolExt;
+use crate::AyaFS;
+use crate::block_device::BLOCK_SIZE;
+use crate::disk::data_block::{Block, DataBlock};
+
+#[derive(Clone)]
+pub struct CachedBlock<T: Block> {
+    pub block: T,
+    pub index: usize,
+    pub dirty: bool,
+}
+
+impl<T: Block> CachedBlock<T> {
+    fn cast<U: Block>(&self) -> CachedBlock<U> {
+        unsafe { std::mem::transmute_copy(&self) }
+    }
+}
+
+pub fn convert_mut<U: Block, T: Block>(input_block: &mut CachedBlock<U>) -> &mut CachedBlock<T> {
+    let ptr = input_block as *const CachedBlock<U> as *mut u8;
+    let block = ptr.cast::<CachedBlock<T>>();
+    unsafe { &mut *block }
+}
+
+pub fn convert<U: Block, T: Block>(input_block: &CachedBlock<U>) -> &CachedBlock<T> {
+    let ptr = input_block as *const CachedBlock<U> as *mut u8;
+    let block = ptr.cast::<CachedBlock<T>>();
+    unsafe { &*block }
+}
+
+impl AyaFS {
+    pub(crate) fn update_block<T: Block>(&mut self, block: CachedBlock<T>) -> bool {
+        if self.cached_blocks.contains(&block.index) {
+            let data_block = convert::<T, DataBlock>(&block).clone();
+            self.cached_blocks.push(block.index, data_block);
+            true
+        } else {
+            false
+        }
+    }
+    pub(crate) fn get_block<T: Block>(&mut self, index: usize) -> Option<&CachedBlock<T>> {
+        self.load_block(index)
+            .and_then(|| self.cached_blocks.get(&index).map(convert::<DataBlock, T>))
+    }
+
+    pub(crate) fn get_block_mut<T: Block>(&mut self, index: usize) -> Option<&mut CachedBlock<T>> {
+        self.load_block(index).and_then(|| {
+            self.cached_blocks
+                .get_mut(&index)
+                .map(convert_mut::<DataBlock, T>)
+        })
+    }
+
+    pub(crate) fn load_block(&mut self, index: usize) -> bool {
+        // 反正我自己保证所有实现了 Block trait 的数据结构都是 4K bytes 长, 来回 cast 没问题
+        // 如果 block cache 里没有这个 block
+        if self.cached_blocks.contains(&index) == false {
+            if self.data_bitmap.query(index) == false {
+                return false;
+            } // 先看这个 block 是不是 valid, 不 valid 直接返回 None
+            let block = DataBlock::default();
+            let buffer = unsafe {
+                std::slice::from_raw_parts_mut(&block as *const DataBlock as *mut u8, BLOCK_SIZE)
+            };
+            self.device.read(index, buffer);
+            let cached_block = CachedBlock {
+                block,
+                index,
+                dirty: false,
+            };
+            if let Some((old_index, old_block)) = self.cached_blocks.push(index, cached_block) {
+                assert_ne!(old_index, index); // 只有 block 不在 cache 里的时候才会插入
+                if old_block.dirty {
+                    let old_block_ptr = &old_block.block as *const DataBlock as *mut u8;
+                    let old_block_buffer =
+                        unsafe { std::slice::from_raw_parts(old_block_ptr, BLOCK_SIZE) };
+                    self.device.write(old_index, old_block_buffer);
+                }
+            } // 如果 valid 就放到 block cache 里, 同时将（可能）被驱逐的 block 依据其是否为脏块进行写回
+        }
+
+        true
+    }
+}