Implement Default trait for structs

src/main.rs

@@ -7,19 +7,22 @@ struct NullFS;
 impl Filesystem for NullFS {}
 
 // This is the total capacity of the backing storage for the file system
-// this includes the space used for the superblock, free object bitmaps, and file data and metadata
-const FS_SIZE_BYTES: u64 = 1u64 * (0b1 << 30) as u64; // 1 GB, toy size
+// this includes the space used for the FSMetadata, free object bitmaps, and file data and metadata
+const FS_SIZE_BYTES: u64 = 1u64 * (0b1 << 30) as u64; // 1 GB
 const BLK_SIZE_BYTES: u64 = 4096u64;
+// some blocks reserved for FSMetadata, free inode and data block bitmaps, and inode table
+const RESERVED_DATA_BLKS: u32 = 3;
 const NUM_DATA_BLKS: u32 = (FS_SIZE_BYTES / BLK_SIZE_BYTES) as u32;
 const FREE_BLK_BMAP_SIZE_BYTES: usize = ((NUM_DATA_BLKS + 7) / 8) as usize;
 
 // Inodes
-const MAX_NUM_INODES: u32 = 10; // toy size
+const MAX_NUM_INODES: u32 = 10;
+const RESERVED_INODES: u32 = 2; // 0: null inode, 1: root
 const FREE_INODE_BMAP_SIZE_BYTES: usize = ((MAX_NUM_INODES + 7) / 8) as usize;
 const NUM_INO_DIRECT_PTR: usize = 12;
 
 // free inode bitmap can begin right after this struct and inode table can follow immediately after
-struct SuperBlock {
+struct FSMetadata {
     ino_count: u32,
     blk_count: u32,
     free_blk_count: u32,
@@ -29,20 +32,25 @@ struct SuperBlock {
     wtime: u64,
 }
 
-impl Default for SuperBlock {
+impl Default for FSMetadata {
     fn default() -> Self {
         Self {
             ino_count: MAX_NUM_INODES,
             blk_count: NUM_DATA_BLKS,
-            free_blk_count: NUM_DATA_BLKS - 3u32, // first three blocks are reserved for FS metadata
-            free_ino_count: MAX_NUM_INODES - 1,   // first inode is reserved for the root
+            free_blk_count: NUM_DATA_BLKS - RESERVED_DATA_BLKS,
+            free_ino_count: MAX_NUM_INODES - RESERVED_INODES,
             super_blk_no: 0,
             mtime: 0,
             wtime: 0,
         }
     }
 }
 
+#[derive(Clone, Copy)]
+struct Block {
+    data: [u8; BLK_SIZE_BYTES as usize],
+}
+
 trait FreeObjectBitmap<const N: usize> {
     fn map(&self) -> &BitArray<[u8; N], Lsb0>;
 
@@ -51,17 +59,25 @@ trait FreeObjectBitmap<const N: usize> {
     }
 }
 
-#[derive(Default)]
 struct FreeBlockBitmap {
     map: BitArray<[u8; FREE_BLK_BMAP_SIZE_BYTES], Lsb0>,
 }
 
+impl Default for FreeBlockBitmap {
+    fn default() -> Self {
+        let mut map = BitArray::default();
+        map[0..(RESERVED_DATA_BLKS as usize)].fill(true);
+        Self { map }
+    }
+}
+
 impl FreeObjectBitmap<FREE_BLK_BMAP_SIZE_BYTES> for FreeBlockBitmap {
     fn map(&self) -> &BitArray<[u8; FREE_BLK_BMAP_SIZE_BYTES], Lsb0> {
         &self.map
     }
 }
 
+#[derive(Clone, Copy)]
 struct Inode {
     ino_id: u64,     // inode number
     size: u64,       // file size
@@ -75,29 +91,50 @@ struct Inode {
     tri_indirect_blk: u32,
 }
 
-#[derive(Default)]
 struct FreeInodeBitmap {
     map: BitArray<[u8; FREE_INODE_BMAP_SIZE_BYTES], Lsb0>,
 }
 
+impl Default for FreeInodeBitmap {
+    fn default() -> Self {
+        let mut map = BitArray::default();
+        map[0..(RESERVED_INODES as usize)].fill(true);
+        Self { map }
+    }
+}
+
 impl FreeObjectBitmap<FREE_INODE_BMAP_SIZE_BYTES> for FreeInodeBitmap {
     fn map(&self) -> &BitArray<[u8; FREE_INODE_BMAP_SIZE_BYTES], Lsb0> {
         &self.map
     }
 }
 
-#[derive(Default)]
 struct FSState {
-    superblk: SuperBlock,
-    free_blks: FreeBlockBitmap,
-    inode_bitmap: FreeInodeBitmap,
-    inodes: Vec<Inode>,
-    blks: Vec<u8>,
+    metadata: FSMetadata,
+    free_inode_bitmap: FreeInodeBitmap,
+    inodes: [Option<Inode>; MAX_NUM_INODES as usize],
+    free_blk_bitmap: FreeBlockBitmap,
+    blks: [Option<Block>; NUM_DATA_BLKS as usize],
 }
 
-impl FSState {
-    fn alloc_inode(&mut self) -> Option<u64> {
-        None
+// we have to implement Default ourselves here
+// because the Default trait is not implemented for static arrays
+// above a certain size
+impl Default for FSState {
+    fn default() -> Self {
+        let mut metadata = FSMetadata::default();
+        let free_inode_bitmap = FreeInodeBitmap::default();
+        let mut inodes = [None; MAX_NUM_INODES as usize];
+        let free_blk_bitmap = FreeBlockBitmap::default();
+        let mut blks = [None; NUM_DATA_BLKS as usize];
+
+        Self {
+            metadata,
+            free_inode_bitmap,
+            inodes,
+            free_blk_bitmap,
+            blks,
+        }
     }
 }