text: // On-disk file system format.
  // Both the kernel and user programs use this header file.
  
  #define ROOTINO	1	// root i-number
  #define BSIZE	512	// block size
  
  // Disk layout:
  // [boot block |super block |log |inode blocks |free bit map |data blocks]
  //
  // mkfs computes the super block and builds an initial file system.
  // The super block describes the disk layout
  
  struct superblock {
  	uint size;			// Size of file system image (in blocks)
  	uint nblocks;		// Number of data blocks
  	uint ninodes;		// Number of inodes
  	uint nlog;			// Number of log blocks
  	uint logstart;		// Block number of first log block
  	uint inodestart;	// Block number of first inode block
  	uint bmapstart;		// Block number of first free map block
  };
  
  #define NDIRECT		12
  #define NINDIRECT	(BSIZE / sizeof(uint))
  #define MAXFILE		(NDIRECT + NINDIRECT)
  
  // On-disk inode structure
  struct dinode {
  	short type;			// File type
  	short major;		// Major device number (T_DEV only)
  	short minor;		// Minor device number (T_DEV only)
  	short nlink;		// Number of links to inode in fs
  	uint size;			// Size of file (in bytes)
  	uint addrs[NDIRECT+1];	// Data block address
  };
  
  #define T_DIR		1	// Directory
  #define T_FILE		2	// File
  #define T_DEV		3	// Special device
  #define T_SYMLINK	4	// Symlink
  
  // Inodes per block
  #define IPB			(BSIZE / sizeof(struct dinode))
  
  // Block containing inode i
  #define IBLOCK(i, sb)	((i) / IPB + sb.inodestart)
  
  // Bitmap bits per block
  #define BPB			(BSIZE * 8)
  
  // Block of free map containing bit for block b
  #define BBLOCK(b, sb)	(b/BPB + sb.bmapstart)
  
  // Directory is a file containing a sequence of dirent structures
  #define DIRSIZ	14
  
  struct dirent {
  	ushort inum;
  	char name[DIRSIZ];
  };
  