create & open efs.

easy-fs/src/dirty.rs

@@ -0,0 +1,54 @@
+use super::BlockDevice;
+use super::BLOCK_SZ;
+use alloc::sync::Arc;
+use core::marker::PhantomData;
+
+pub struct Dirty<T> {
+    block_id: usize,
+    block_cache: [u8; BLOCK_SZ],
+    offset: usize,
+    block_device: Arc<dyn BlockDevice>,
+    phantom: PhantomData<T>,
+}
+
+impl<T> Dirty<T> where T: Sized {
+    pub fn new(block_id: usize, offset: usize, block_device: Arc<dyn BlockDevice>) -> Self {
+        Self {
+            block_id,
+            block_cache: {
+                let mut cache = [0u8; BLOCK_SZ];
+                block_device.read_block(block_id as usize, &mut cache);
+                cache
+            },
+            offset,
+            block_device,
+            phantom: PhantomData,
+        }
+    }
+    pub fn get_mut(&mut self) -> &mut T {
+        let type_size = core::mem::size_of::<T>();
+        // assert that the struct is inside a block
+        assert!(self.offset + type_size <= BLOCK_SZ);
+        let start_addr = &self.block_cache[self.offset] as *const _ as usize;
+        unsafe { &mut *(start_addr as *mut T) }
+    }
+    pub fn read(&self) -> &T {
+        let type_size = core::mem::size_of::<T>();
+        // assert that the struct is inside a block
+        assert!(self.offset + type_size <= BLOCK_SZ);
+        let start_addr = &self.block_cache[self.offset] as *const _ as usize;
+        unsafe { &*(start_addr as *const T) }
+    }
+    pub fn modify(&mut self, f: impl Fn(&mut T)) {
+        f(self.get_mut());
+    }
+    pub fn write_back(&mut self) {
+        self.block_device.write_block(self.block_id as usize, &self.block_cache);
+    }
+}
+
+impl<T> Drop for Dirty<T> {
+    fn drop(&mut self) {
+        self.write_back();
+    }
+}