org.jscsi.target.storage

Class RandomAccessStorageModule

java.lang.Object

org.jscsi.target.storage.RandomAccessStorageModule

All Implemented Interfaces:

IStorageModule

Direct Known Subclasses:

SynchronizedRandomAccessStorageModule

public class RandomAccessStorageModule
extends Object
implements IStorageModule

Instances of this class can be used for persistent storage of data. They are backed by a RandomAccessFile, which will immediately write all changes in the data to hard-disk.

This class is not thread-safe.

Author:

Andreas Ergenzinger

See Also:

RandomAccessFile

Nested Class Summary

Nested classes/interfaces inherited from interface org.jscsi.target.storage.IStorageModule

IStorageModule.STORAGEKIND

Field Summary

Fields

Modifier and Type	Field and Description
protected long	sizeInBlocks The size of the medium in blocks.

Fields inherited from interface org.jscsi.target.storage.IStorageModule

VIRTUAL_BLOCK_SIZE

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	RandomAccessStorageModule(long sizeInBlocks, RandomAccessFile randomAccessFile) Creates a new RandomAccessStorageModule backed by the specified file.

Method Summary

Methods

Modifier and Type	Method and Description
int	checkBounds(long logicalBlockAddress, int transferLengthInBlocks) This method can be used for checking if a (series of) I/O operations will result in an IOException due to trying to access blocks outside the medium's boundaries.
void	close() Closes the backing RandomAccessFile.
long	getSizeInBlocks() Returns the storage space size in bytes divided by the block size in bytes (rounded down).
static IStorageModule	open(File file, long storageLength, boolean create, IStorageModule.STORAGEKIND kind) This is the build method for creating instances of RandomAccessStorageModule.
void	read(byte[] bytes, int bytesOffset, int length, long storageIndex) Copies bytes from storage to the passed byte array.
void	write(byte[] bytes, int bytesOffset, int length, long storageIndex) Saves part of the passed byte array's content.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

sizeInBlocks

protected final long sizeInBlocks

The size of the medium in blocks.

See Also:

IStorageModule.VIRTUAL_BLOCK_SIZE

Constructor Detail

RandomAccessStorageModule

protected RandomAccessStorageModule(long sizeInBlocks,
                         RandomAccessFile randomAccessFile)
                             throws FileNotFoundException

Creates a new RandomAccessStorageModule backed by the specified file. If no such file exists, a FileNotFoundException will be thrown.

Parameters:

sizeInBlocks - blocksize for this module

randomAccessFile - the path to the file serving as storage medium

Throws:

FileNotFoundException - if the specified file does not exist

Method Detail

read

public void read(byte[] bytes,
        int bytesOffset,
        int length,
        long storageIndex)
          throws IOException

Copies bytes from storage to the passed byte array.

Specified by:

read in interface IStorageModule

Parameters:

bytes - the array into which the data will be copied

bytesOffset - the position of the first byte in bytes, which will be filled with data from storage

length - the number of bytes to copy

storageIndex - the position of the first byte to be copied

Throws:

IOException

write

public void write(byte[] bytes,
         int bytesOffset,
         int length,
         long storageIndex)
           throws IOException

Saves part of the passed byte array's content.

Specified by:

write in interface IStorageModule

Parameters:

bytes - the source of the data to be stored

bytesOffset - offset of the first byte to be stored

length - the number of bytes to be copied

storageIndex - byte offset in the storage area

Throws:

IOException

getSizeInBlocks

public final long getSizeInBlocks()

Returns the storage space size in bytes divided by the block size in bytes (rounded down).

Specified by:

getSizeInBlocks in interface IStorageModule

Returns:

the virtual amount of storage blocks available

checkBounds

public final int checkBounds(long logicalBlockAddress,
              int transferLengthInBlocks)

This method can be used for checking if a (series of) I/O operations will result in an IOException due to trying to access blocks outside the medium's boundaries.

The SCSI standard requires checking for these boundary violations right after receiving a read or write command, so that an appropriate error message can be returned to the initiator. Therefore this method must be called prior to each read or write sequence.

The values returned by this method and their meaning with regard to the interval [0, IStorageModule.getSizeInBlocks() - 1] are shown in the following table:

Return Value	Meaning
0	no boundaries are violated
1	the logicalBlockAddress parameter lies outside of the interval
2	the interval [logicalBlockAddress, logicalBlockAddress + transferLengthInBlocks] lies outside of the interval, or transferLengthInBlocks is negative

Note that the parameters of this method are referring to blocks, not to byte indices.

Specified by:

checkBounds in interface IStorageModule

Parameters:

logicalBlockAddress - the index of the first block of data to be read or written

transferLengthInBlocks - the total number of consecutive blocks about to be read or written

Returns:

see table in description

close

public final void close()
                 throws IOException

Closes the backing RandomAccessFile.

Specified by:

close in interface IStorageModule

Throws:

IOException - if an I/O Error occurs

open

public static final IStorageModule open(File file,
                  long storageLength,
                  boolean create,
                  IStorageModule.STORAGEKIND kind)
                                 throws IOException

This is the build method for creating instances of RandomAccessStorageModule. If there is no file to be found at the specified filePath, then a FileNotFoundException will be thrown.

Parameters:

file - a path leading to the file serving as storage medium

storageLength - length of storage (if not already existing)

create - should the storage be created

Returns:

a new instance of RandomAccessStorageModule

Throws:

IOException