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/*
* Copyright (C) 2009,2010 Matthias Treydte <mt@waldheinz.de>
*
* This library is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published
* by the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*
* This library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library; If not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
package de.waldheinz.fs.fat;
import de.waldheinz.fs.BlockDevice;
import java.io.IOException;
/**
* The FAT32 File System Information Sector.
*
* @author Matthias Treydte <waldheinz at gmail.com>
* @see http://en.wikipedia.org/wiki/File_Allocation_Table#FS_Information_Sector
*/
final class FsInfoSector extends Sector {
/**
* The offset to the free cluster count value in the FS info sector.
*/
public static final int FREE_CLUSTERS_OFFSET = 0x1e8;
/**
* The offset to the "last allocated cluster" value in this sector.
*/
public static final int LAST_ALLOCATED_OFFSET = 0x1ec;
/**
* The offset to the signature of this sector.
*/
public static final int SIGNATURE_OFFSET = 0x1fe;
private FsInfoSector(BlockDevice device, long offset) {
super(device, offset, BootSector.SIZE);
}
/**
* Reads a {@code FsInfoSector} as specified by the given
* {@code Fat32BootSector}.
*
* @param bs the boot sector that specifies where the FS info sector is
* stored
* @return the FS info sector that was read
* @throws IOException on read error
* @see Fat32BootSector#getFsInfoSectorNr()
*/
public static FsInfoSector read(Fat32BootSector bs) throws IOException {
final FsInfoSector result =
new FsInfoSector(bs.getDevice(), offset(bs));
result.read();
result.verify();
return result;
}
/**
* Creates an new {@code FsInfoSector} where the specified
* {@code Fat32BootSector} indicates it should be.
*
* @param bs the boot sector specifying the FS info sector storage
* @return the FS info sector instance that was created
* @throws IOException on write error
* @see Fat32BootSector#getFsInfoSectorNr()
*/
public static FsInfoSector create(Fat32BootSector bs) throws IOException {
final int offset = offset(bs);
if (offset == 0) throw new IOException(
"creating a FS info sector at offset 0 is strange");
final FsInfoSector result =
new FsInfoSector(bs.getDevice(), offset(bs));
result.init();
result.write();
return result;
}
private static int offset(Fat32BootSector bs) {
return bs.getFsInfoSectorNr() * bs.getBytesPerSector();
}
/**
* Sets the number of free clusters on the file system stored at
* {@link #FREE_CLUSTERS_OFFSET}.
*
* @param value the new free cluster count
* @see Fat#getFreeClusterCount()
*/
public void setFreeClusterCount(long value) {
if (getFreeClusterCount() == value) return;
set32(FREE_CLUSTERS_OFFSET, value);
}
/**
* Returns the number of free clusters on the file system as sepcified by
* the 32-bit value at {@link #FREE_CLUSTERS_OFFSET}.
*
* @return the number of free clusters
* @see Fat#getFreeClusterCount()
*/
public long getFreeClusterCount() {
return get32(FREE_CLUSTERS_OFFSET);
}
/**
* Sets the last allocated cluster that was used in the {@link Fat}.
*
* @param value the FAT's last allocated cluster number
* @see Fat#getLastAllocatedCluster()
*/
public void setLastAllocatedCluster(long value) {
if (getLastAllocatedCluster() == value) return;
super.set32(LAST_ALLOCATED_OFFSET, value);
}
/**
* Returns the last allocated cluster number of the {@link Fat} of the
* file system this FS info sector is part of.
*
* @return the last allocated cluster number
* @see Fat#getLastAllocatedCluster()
*/
public long getLastAllocatedCluster() {
return super.get32(LAST_ALLOCATED_OFFSET);
}
private void init() {
buffer.position(0x00);
buffer.put((byte) 0x52);
buffer.put((byte) 0x52);
buffer.put((byte) 0x61);
buffer.put((byte) 0x41);
/* 480 reserved bytes */
buffer.position(0x1e4);
buffer.put((byte) 0x72);
buffer.put((byte) 0x72);
buffer.put((byte) 0x41);
buffer.put((byte) 0x61);
setFreeClusterCount(-1);
setLastAllocatedCluster(Fat.FIRST_CLUSTER);
buffer.position(SIGNATURE_OFFSET);
buffer.put((byte) 0x55);
buffer.put((byte) 0xaa);
markDirty();
}
private void verify() throws IOException {
if (!(get8(SIGNATURE_OFFSET) == 0x55) ||
!(get8(SIGNATURE_OFFSET + 1) == 0xaa)) {
throw new IOException("invalid FS info sector signature");
}
}
@Override
public String toString() {
return FsInfoSector.class.getSimpleName() +
" [freeClusterCount=" + getFreeClusterCount() + //NOI18N
", lastAllocatedCluster=" + getLastAllocatedCluster() + //NOI18N
", offset=" + getOffset() + //NOI18N
", dirty=" + isDirty() + //NOI18N
"]"; //NOI18N
}
}
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