1. Final Project: ThreadOS File System
Joe McCarthy
CSS 430: Operating Systems - ThreadOS File System

2. ThreadOS Superblock & Inodes
int totalBlocks;
int totalInodes;
int freeList;
Block #0
Free
Block #x
Free
Block #y
Free
Block #z
Inode #0 32bytes
Inode #1
Block #1
Inode #15
/ root
directory
Block #2
Inode #inodeBlocks -1
Block #(totalBlocks – 1)
CSS 430: Operating Systems - ThreadOS File System

3. ThreadOS Root Directory (“/”)
Entry[] fsizes fnames
(iNumber)
Directory()
Initialize “/” directory
bytes2directory( byte[] data )
Populate directory with byte[] retrieved from disk
directory2bytes()
Converts directory information into byte[]
ialloc( String filename )
Allocate an iNumber for filename
ifree( short iNumber )
Deallocate the iNumber
namei( String filename )
Return filename’s iNumber 1 2 3 4 5 6 7 8 9 10
inodeBlock-1 1 4 5 6 9 /
init
fsck
clri
motd
mount
mknod
passwd
umount
checklist
fsdblb
config
getty
CSS 430: Operating Systems - ThreadOS File System

4. CSS430 ThreadOS File System
int fd = SysLib.open(“fileA”, mode);
SysLib.read(fd, …);
A simplified structure of Unix file system
TCB 1 2 3 31
stdin
stdout
Inode:
length
count 1
direct[11]
indirect
stderr
struct file:
count 1
inode
Disk
ftEnt[32] per-thread file table
FileTable
Inode
CSS 430: Operating Systems - ThreadOS File System

5. CSS 430: Operating Systems - ThreadOS File System
public class FileSystem {
private SuperBlock superblock;
private Directory directory;
private FileTable filetable;
public FileSystem( int diskBlocks ) {
superblock = new SuperBlock( diskBlocks );
directory = new Directory( superblock.inodeBlocks );
filetable = new FileTable( directory );
FileTableEntry dirEnt = open( "/", "r" );
int dirSize = fsize( dirEnt );
if ( dirSize > 0 ) {
byte[] dirData = new byte[dirSize];
read( dirEnt, dirData );
directory.bytes2directory( dirData ); }
close( dirEnt );
...
SuperBlock
SysLib.rawread( 0, byte[] )
Directory
SysLib.rawread( 1, byte[] )
Disk
FileTable
CSS 430: Operating Systems - ThreadOS File System

6. CSS 430: Operating Systems - ThreadOS File System
public class FileSystem {
private SuperBlock superblock;
private Directory directory;
private FileTable filetable;
...
void sync()
boolean format( int files )
FileTableEntry open( String filename, String mode )
boolean close( FileTableEntry ftEnt )
int fsize( FileTableEntry ftEnt )
int read( FileTableEntry ftEnt, byte[] buffer )
int write( FileTableEntry ftEnt, byte[] buffer )
boolean delete( String filename )
int seek( FileTableEntry ftEnt,
int offset, int whence ) }
SuperBlock
SysLib.rawread( 0, byte[] )
Directory
SysLib.rawread( 1, byte[] )
Disk
FileTable
CSS 430: Operating Systems - ThreadOS File System

7. CSS 430: Operating Systems - ThreadOS File System
SuperBlock
DISK
public class SuperBlock {
private final int defaultInodeBlocks = 64;
public int totalBlocks;
public int inodeBlocks;
public int freeList;
public SuperBlock( int diskSize ) {
byte[] superBlock = new byte[Disk.blockSize];
SysLib.rawread( 0, superBlock );
totalBlocks = SysLib.bytes2int( superBlock, 0 );
inodeBlocks = SysLib.bytes2int( superBlock, 4 );
freeList = SysLib.bytes2int( superBlock, 8 );
if ( totalBlocks == diskSize
&& inodeBlocks > 0
&& freeList >= 2 )
return;
else {
totalBlocks = diskSize;
SysLib.cerr( "Formatting\n" );
format(); }
...
Superblock
int totalBlocks;
int inodeBlocks;
int freeList;
Block #0
Inode blocks
Data blocks
CSS 430: Operating Systems - ThreadOS File System

8. CSS 430: Operating Systems - ThreadOS File System
SuperBlock
DISK
public class SuperBlock {
private final int defaultInodeBlocks = 64;
public int totalBlocks;
public int inodeBlocks;
public int freeList;
...
void sync()
/* write totalBlocks, inodeBlocks, freelist
to disk */
void format()
void format( int numBlocks )
public int getFreeBlock()
/* dequeue top block
in freelist */
public boolean returnBlock( int oldBlockNumber )
/* enqueue oldBlockNumber
to top of freelist */ }
Superblock
int totalBlocks;
int inodeBlocks;
int freeList;
Block #0
Inode #0 32bytes …
Block #1
Inode #15 … … …
Block # (inodeBlocks
/ 16) + 1
Inode #inodeBlocks-1 … …
Data blocks:
CSS 430: Operating Systems - ThreadOS File System

9. CSS 430: Operating Systems - ThreadOS File System
SuperBlock.format(16)
DISK
public class SuperBlock {
private final int defaultInodeBlocks = 64;
public int totalBlocks;
public int inodeBlocks;
public int freeList;
...
void format()
void format( int numBlocks )
/* initialize Inodes, free blocks */ }
Superblock
totalBlocks = 1000
inodeBlocks = 16
freeList = 2
Block #0
Inode #0 32bytes …
Block #1
Inode #15 3
Block #2 4
Block #3 … … … -1
Block #999
CSS 430: Operating Systems - ThreadOS File System

10. CSS 430: Operating Systems - ThreadOS File System
Directory
public class Directory {
private static int maxChars = 30; // the max characters of each file name
private int fsizes[]; // the actual size of each file name
private char fnames[][]; // file names in characters
public Directory ( int maxInumber ) { // a default constructor
fsizes = new int[maxInumber]; // maxInumber = max # files
for ( int i = 0; i < maxInumber; i++ ) // all file sizes set to 0
fsizes[i] = 0;
fnames = new char[maxInumber][maxChars];
String root = "/"; // entry (inode) 0 is "/"
fsizes[0] = root.length();
root.getChars( 0, fsizes[0], fnames[0], 0 ); }
...
CSS 430: Operating Systems - ThreadOS File System

11. CSS 430: Operating Systems - ThreadOS File System
Directory
public class Directory {
private static int maxChars = 30; // the max characters of each file name
private int fsizes[]; // the actual size of each file name
private char fnames[][]; // file names in characters
...
public void bytes2directory( byte[] data ) {
int offset = 0;
for ( int i = 0; i < fsizes.length; i++, offset += 4 )
fsizes[i] = SysLib.bytes2int( data, offset );
for ( int i = 0; i < fnames.length; i++, offset += maxChars * 2 ) {
String fname = new String( data, offset, maxChars * 2 );
fname.getChars( 0, fsizes[i], fnames[i], 0 ); }
public byte[] directory2bytes()
public short ialloc ( String filename )
/* allocate Inode for filename (-1 if none) */
public boolean ifree ( short iNumber )
/* deallocate Inode # iNumber */
public short namei( String filename )
/* find Inode for filename (-1 if none) */
CSS 430: Operating Systems - ThreadOS File System

12. CSS 430: Operating Systems - ThreadOS File System
FileTable
public class FileTable { // File Structure Table
private Vector table; // the actual entity of File Structure Table
private Directory dir; // the root directory
public FileTable ( Directory directory ) { // a default constructor
table = new Vector(); // instantiate a file table
dir = directory; // instantiate the root directory }
public synchronized FileTableEntry falloc( String fname, String mode )
// allocate a new file table entry for this file name
// allocate/retrieve and register the corresponding inode using dir
// increment this inode's count
// immediately write back this inode to the disk
// return a reference to this file table entry
public synchronized boolean ffree( FileTableEntry e ) {
// receive a file table entry reference
// save the corresponding inode to the disk
// free this file table entry.
// return true if this file table entry found in table
public synchronized boolean fempty() {
return table.isEmpty(); // return if table is empty
} // should be called before a format
CSS 430: Operating Systems - ThreadOS File System

13. CSS 430: Operating Systems - ThreadOS File System
FileTable
public synchronized FileTableEntry falloc( String fname, String mode )
short iNumber = -1;
Inode inode = null;
while ( true ) {
iNumber = ( fname.equals( "/" ) ? 0 : dir.namei( fname ) );
if ( iNumber < 0 ) { // file does not exist
// create a new Inode (nothing to retrieve from disk)
} else { // file exists
inode = new Inode( iNumber ); // retrieve inode from disk
if ( mode.compareTo( "r" ) == 0 ) { // mode is "r”
// if inode.flag indicates file is not already open for writing
// break
// else wait until writing is done
} else { /* ... */ } // mode is "w", "w+" or "a” }
inode.count++; // a new FileTableEntry points to it
inode.toDisk( iNumber ); // reflect this inode to disk
FileTableEntry e = new FileTableEntry( inode, iNumber, mode );
table.addElement( e ); // add entry to system-wide FileTable
return e; // return this new file table entry
CSS 430: Operating Systems - ThreadOS File System

14. CSS 430: Operating Systems - ThreadOS File System
Inode
public class Inode {
public final static int iNodeSize = 32; // fixed to 32 bytes
public final static int directSize = 11; // # direct pointers
public int length; // file size in bytes
public short count; // # file-table entries pointing to this
public short flag; // how is this file (inode) being used?
public short direct[] = new short[directSize]; // direct pointers
public short indirect; // an indirect pointer
Inode () { // a default constructor (new file)
length = 0;
count = 0;
flag = 1;
for ( int i = 0; i < directSize; i++ )
direct[i] = -1;
indirect = -1; }
CSS 430: Operating Systems - ThreadOS File System

15. CSS 430: Operating Systems - ThreadOS File System
Inode
DISK
public class Inode {
...
Inode ( short iNumber ) {
int blkNumber = iNumber / ;
byte[] data = new byte[Disk.blockSize];
SysLib.rawread( blkNumber, data );
int offset = ( iNumber % 16 ) * iNodeSize;
length = SysLib.bytes2int( data, offset );
offset += 4;
count = SysLib.bytes2short( data, offset );
offset += 2;
flag = SysLib.bytes2short( data, offset );
for ( int i = 0; i < directSize; i++ ) {
direct[i] = SysLib.bytes2short( data, offset ); }
indirect = SysLib.bytes2short( data, offset );
Superblock
int totalBlocks;
int inodeBlocks;
int freeList;
Inode #0 32bytes …
Inode #15 … …
Inode #inodeBlocks-1 … …
CSS 430: Operating Systems - ThreadOS File System

16. CSS 430: Operating Systems - ThreadOS File System
Inode
DISK
public class Inode {
...
void toDisk( short iNumber )
int findIndexBlock()
boolean registerIndexBlock( short indexBlockNumber )
int findTargetBlock( int offset )
int registerTargetBlock( int offset,
short targetBlockNumber )
byte[] unregisterIndexBlock() }
Superblock
int totalBlocks;
int inodeBlocks;
int freeList;
Inode #0 32bytes …
Inode #15 … …
Inode #inodeBlocks-1 … …
CSS 430: Operating Systems - ThreadOS File System

17. CSS 430: Operating Systems - ThreadOS File System
Opening a File
Test5.java:
int fd = SysLib.open( "css430", "w+" );
SysLib.java:
public static int open( String filename, String mode ) {
String[] args = new String[2];
args[0] = filename;
args[1] = mode;
return Kernel.interrupt( Kernel.INTERRUPT_SOFTWARE, Kernel.OPEN, 0, args ); };
Kernel.java:
case OPEN:
if ( ( myTcb = scheduler.getMyTcb() ) == null )
return ERROR;
else {
String[] s = (String[]) args;
FileTableEntry ftEnt = fs.open( s[0], s[1] );
int fd = myTcb.getFd( ftEnt );
return fd; }
CSS 430: Operating Systems - ThreadOS File System

18. CSS 430: Operating Systems - ThreadOS File System
Opening a File
Kernel.java:
case OPEN:
if ( ( myTcb = scheduler.getMyTcb() ) == null )
return ERROR;
else {
String[] s = (String[]) args;
FileTableEntry ftEnt = fs.open( s[0], s[1] );
int fd = myTcb.getFd( ftEnt );
return fd; }
FileSystem.java:
FileTableEntry open( String filename, String mode ) {
FileTableEntry ftEnt = filetable.falloc( filename, mode );
if ( mode == "w" ) // release all blocks belonging to this file
if ( deallocAllBlocks( ftEnt ) == false )
return null;
return ftEnt; }
CSS 430: Operating Systems - ThreadOS File System