+/* 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/filehdr.h"
+#include "filesys/directory.h"
+#include "devices/disk.h"
+
+/* Filesystem.
+
+ The filesystem consists of a set of files. Each file has a
+ header, represented by struct filehdr, that is stored by
+ itself in a single sector (see filehdr.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 header 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 header 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 header.
+
+ The filesystem implemented here has the following limitations:
+
+ - No synchronization. Concurrent accesses will interfere
+ with one another.
+
+ - 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.
+
+ - No indirect blocks. This limits maximum file size to the
+ number of sector pointers that fit in a single sector
+ times the size of a sector, or 126 * 512 == 63 kB given
+ 32-bit sizes and 512-byte sectors.
+
+ - No nested 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.
+
+ Note: for the purposes of the "user processes" assignment
+ (project 2), please treat all the code in the filesys
+ directory as a black box. No changes should be needed. For
+ that project, a single lock external to the filesystem code
+ suffices. */
+
+/* File header sectors for system files. */
+#define FREE_MAP_SECTOR 0 /* Free map file header sector. */
+#define ROOT_DIR_SECTOR 1 /* Root directory file header sector. */
+
+/* Root directory. */
+#define NUM_DIR_ENTRIES 10 /* Maximum number of directory entries. */
+#define ROOT_DIR_FILE_SIZE /* Root directory file size in bytes. */ \
+ (sizeof (struct dir_entry) * NUM_DIR_ENTRIES)
+
+/* The disk that contains the filesystem. */
+struct disk *filesys_disk;
+
+/* The free map and root directory files.
+ These files are opened by filesys_init() and never closed. */