+/* This file is derived from source code for the Nachos
+ instructional operating system. The Nachos copyright notice
+ is reproduced in full below. */
+
+/* Copyright (c) 1992-1996 The Regents of the University of California.
+ All rights reserved.
+
+ Permission to use, copy, modify, and distribute this software
+ and its documentation for any purpose, without fee, and
+ without written agreement is hereby granted, provided that the
+ above copyright notice and the following two paragraphs appear
+ in all copies of this software.
+
+ IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO
+ ANY PARTY FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR
+ CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF THIS SOFTWARE
+ AND ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA
+ HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+ THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY
+ WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS IS"
+ BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATION TO
+ PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR
+ MODIFICATIONS.
+*/
+
+#include "filesys/filesys.h"
+#include <bitmap.h>
+#include <debug.h>
+#include <stdio.h>
+#include <string.h>
+#include "filesys/file.h"
+#include "filesys/inode.h"
+#include "filesys/directory.h"
+#include "devices/disk.h"
+
+/* Filesystem.
+
+ For the purposes of the "user processes" and "virtual memory"
+ assignments (projects 2 and 3), please treat all the code in
+ the filesys directory as a black box. No changes should be
+ needed. For those projects, a single lock external to the
+ filesystem code suffices.
+
+ The filesystem consists of a set of files. Each file has a
+ header called an `index node' or `inode', represented by
+ struct inode, that is stored by itself in a single sector (see
+ inode.h). The header contains the file's length in bytes and
+ an array that lists the sector numbers for the file's
+ contents.
+
+ Two files are special. The first special file is the free
+ map, whose inode is always stored in sector 0
+ (FREE_MAP_SECTOR). The free map stores a bitmap (see
+ lib/bitmap.h) that contains one bit for each sector on the
+ disk. Each bit that corresponds to a sector within a file is
+ set to true, and the other bits, which are not part of any
+ file, are set to false.
+
+ The second special file is the root directory, whose inode is
+ always stored in sector 1 (ROOT_DIR_SECTOR). The root
+ directory file stores an array of `struct dir_entry' (see
+ directory.h), each of which, if it is in use, associates a
+ filename with the sector of the file's inode.
+
+ The filesystem implemented here has the following limitations:
+
+ - No synchronization. Concurrent accesses will interfere
+ with one another, so external synchronization is needed.
+
+ - File size is fixed at creation time. Because the root
+ directory is represented as a file, the number of files
+ that may be created is also limited.
+
+ - File data is allocated as a single extent, so that
+ external fragmentation can become a serious problem as a
+ file system is used over time.
+
+ - No subdirectories.
+
+ - Filenames limited to 14 characters.
+
+ - A system crash mid-operation may corrupt the disk in a way
+ that cannot be repaired automatically. No `fsck' tool is
+ provided in any case.
+
+ However one important feature is included:
+
+ - Unix-like semantics for filesys_remove() are implemented.
+ That is, if a file is open when it is removed, its blocks
+ are not deallocated and it may still be accessed by the
+ threads that have it open until the last one closes it. */
+
+/* Sectors of system file inodes. */
+#define FREE_MAP_SECTOR 0 /* Free map file inode sector. */
+#define ROOT_DIR_SECTOR 1 /* Root directory file inode sector. */
+
+/* Root directory. */
+#define NUM_DIR_ENTRIES 10 /* Maximum number of directory entries. */
+
+/* The disk that contains the filesystem. */