CSE 461 File Systems Project II solved

Description

Class Filesys: public Sdisk
{
Public :
Filesys(string diskname, int numberofblocks, int blocksize);
int fsclose();
int fssynch();
int newfile(string file);
int rmfile(string file);
int getfirstblock(string file);
int addblock(string file, string block);
int delblock(string file, int blocknumber);
int readblock(string file, int blocknumber, string& buffer);
int writeblock(string file, int blocknumber, string buffer);
int nextblock(string file, int blocknumber);
Private :
int rootsize;           // maximum number of entries in ROOT
int fatsize;            // number of blocks occupied by FAT
vector<string> filename;   // filenames in ROOT
vector<int> firstblock; // firstblocks in ROOT
vector<int> fat;             // FAT
};

An explanation of the member functions follows :

• Filesys()

  This constructor reads from the sdisk and either opens the existing file system on the disk or creates one for an empty disk. Recall the sdisk is a file of characters which we will manipulate as a raw hard disk drive. This file is logically divided up into number_of_blocks many blocks where each block has block_size many characters. Information is first read from block 1 to determine if an existing file system is on the disk. If a filesystem exists, it is opened and made available. Otherwise, the file system is created.The module creates a file system on the sdisk by creating an intial FAT and ROOT. A file system on the disk will have the following segments:

   

  Block 0	ROOT
  Blocks 1 -> n	FAT
  Blocks (n+1) -> (number_of_blocks-1)	Data Blocks

  The file system consists of two primary data objects. The directory is a file that consists of information about files and sub-directories. The root directory contains a list of file (and directory) names along with a block number of the first block in the file (or directory). (Of course, other information about the file such as creation date, ownership, permissions, etc. may also be maintained.) ROOT (root directory) for the above example may look something like

   

  file1	3
  file2	7
  file3	10

  The FAT is an array of block numbers indexed one entry for every block. Every file in the file system is made up of blocks, and the component blocks are maintained as linked lists within the FAT. FAT[0], the entry for the first block of the FAT, is used as a pointer to the first free (unused) block in the file system. Consider the following FAT for a file system with 16 blocks. 

  Block 0	ROOT 6
  Block 1	FAT 0
  Block 2	FAT 0
  Block 3	4
  Block 4	5
  Block 5	0
  Block 6	8
  Block 7	9
  Block 8	13
  Block 9	0
  Block 10	11
  Block 11	12
  Block 12	0
  Block 13	14
  Block 14	15
  Block 15	0

  In the example above, the FAT has 3 files. The free list of blocks begins at entry 0 and consists of blocks 6, 8, 13, 14, 15. Block 0 on the disk contains the root directory and is used in the FAT for the free list. Block 1 and Block 2 on the disk contains the FAT. File 1 contains blocks 3, 4 and 5; File 2 contains blocks 7 and 9; File 3 contains blocks 10, 11, and 12. Note that a “0” denotes the end-of-file or “last block”.

  PROBLEM : What should the value of FAT_size be in terms of blocks if a file system is to be created on the disk? Assume that we use a decimal numbering system where every digit requires one byte of information and is in the set [0..9].

  Both FAT and ROOT are stored in memory AND on the disk. Any changes made to either structure in memory must also be immediately written to the disk.

   

• fssynch

  This module writes FAT and ROOT to the sdisk. It should be used every time FAT and ROOT are modified. 

• fsclose

  This module writes FAT and ROOT to the sdisk (closing the sdisk). 

• newfile(file)

  This function adds an entry for the string file in ROOT with an initial first block of 0 (empty). It returns error codes of 1 if successful and 0 otherwise (no room or file already exists). 

• rmfile(file)

  This function removes the entry file from ROOT if the file is empty (first block is 0). It returns error codes of 1 if successful and 0 otherwise (not empty or file does not exist). 

• getfirstblock(file)

  This function returns the block number of the first block in file. It returns the error code of 0 if the file does not exist. 

• addblock(file,buffer)

  This function adds a block of data stored in the string buffer to the end of file F and returns the block number. It returns error code 0 if the file does not exist, and returns -1 if there are no available blocks (file system is full!). 

• delblock(file,blocknumber)

  The function removes block numbered blocknumber from file and returns an error code of 1 if successful and 0 otherwise. 

• readblock(file,blocknumber,buffer)

  gets block numbered blocknumber from file and stores the data in the string buffer. It returns an error code of 1 if successful and 0 otherwise. 

• writeblock(file,blocknumber,buffer)

  writes the buffer to the block numbered blocknumber in file. It returns an appropriate error code. 

• nextblock(file,blocknumber)

  returns the number of the block that follows blocknumber in file. It will return 0 if blocknumber is the last block and -1 if some other error has occurred (such as file is not in the root directory, or blocknumber is not a block in file.)IMPLEMENTATION GUIDELINES : It is essential that your software satisfies the specifications. These will be the only functions (in your system) which physically access the sdisk.

   

  1. A test main program will be provided on the class website.