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423 lines
13 KiB
C
423 lines
13 KiB
C
/*
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file_allocation_table.c
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Reading, writing and manipulation of the FAT structure on
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a FAT partition
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Copyright (c) 2006 Michael "Chishm" Chisholm
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Redistribution and use in source and binary forms, with or without modification,
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are permitted provided that the following conditions are met:
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1. Redistributions of source code must retain the above copyright notice,
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this list of conditions and the following disclaimer.
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2. Redistributions in binary form must reproduce the above copyright notice,
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this list of conditions and the following disclaimer in the documentation and/or
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other materials provided with the distribution.
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3. The name of the author may not be used to endorse or promote products derived
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from this software without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
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WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
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AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE
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LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "file_allocation_table.h"
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#include "partition.h"
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#include <string.h>
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/*
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Gets the cluster linked from input cluster
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*/
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uint32_t _FAT_fat_nextCluster( PARTITION* partition, uint32_t cluster )
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{
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uint32_t nextCluster = CLUSTER_FREE;
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sec_t sector;
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int offset;
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if ( cluster == CLUSTER_FREE )
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{
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return CLUSTER_FREE;
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}
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switch ( partition->filesysType )
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{
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case FS_UNKNOWN:
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return CLUSTER_ERROR;
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break;
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case FS_FAT12:
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{
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u32 nextCluster_h;
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sector = partition->fat.fatStart + ( ( ( cluster * 3 ) / 2 ) / BYTES_PER_READ );
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offset = ( ( cluster * 3 ) / 2 ) % BYTES_PER_READ;
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_FAT_cache_readLittleEndianValue ( partition->cache, &nextCluster, sector, offset, sizeof( u8 ) );
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offset++;
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if ( offset >= BYTES_PER_READ )
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{
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offset = 0;
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sector++;
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}
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nextCluster_h = 0;
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_FAT_cache_readLittleEndianValue ( partition->cache, &nextCluster_h, sector, offset, sizeof( u8 ) );
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nextCluster |= ( nextCluster_h << 8 );
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if ( cluster & 0x01 )
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{
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nextCluster = nextCluster >> 4;
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}
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else
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{
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nextCluster &= 0x0FFF;
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}
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if ( nextCluster >= 0x0FF7 )
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{
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nextCluster = CLUSTER_EOF;
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}
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break;
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}
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case FS_FAT16:
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sector = partition->fat.fatStart + ( ( cluster << 1 ) / BYTES_PER_READ );
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offset = ( cluster % ( BYTES_PER_READ >> 1 ) ) << 1;
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_FAT_cache_readLittleEndianValue ( partition->cache, &nextCluster, sector, offset, sizeof( u16 ) );
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if ( nextCluster >= 0xFFF7 )
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{
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nextCluster = CLUSTER_EOF;
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}
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break;
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case FS_FAT32:
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sector = partition->fat.fatStart + ( ( cluster << 2 ) / BYTES_PER_READ );
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offset = ( cluster % ( BYTES_PER_READ >> 2 ) ) << 2;
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_FAT_cache_readLittleEndianValue ( partition->cache, &nextCluster, sector, offset, sizeof( u32 ) );
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if ( nextCluster >= 0x0FFFFFF7 )
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{
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nextCluster = CLUSTER_EOF;
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}
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break;
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default:
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return CLUSTER_ERROR;
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break;
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}
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return nextCluster;
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}
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/*
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writes value into the correct offset within a partition's FAT, based
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on the cluster number.
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*/
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static bool _FAT_fat_writeFatEntry ( PARTITION* partition, uint32_t cluster, uint32_t value )
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{
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sec_t sector;
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int offset;
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uint32_t oldValue;
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if ( ( cluster < CLUSTER_FIRST ) || ( cluster > partition->fat.lastCluster /* This will catch CLUSTER_ERROR */ ) )
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{
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return false;
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}
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switch ( partition->filesysType )
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{
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case FS_UNKNOWN:
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return false;
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break;
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case FS_FAT12:
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sector = partition->fat.fatStart + ( ( ( cluster * 3 ) / 2 ) / BYTES_PER_READ );
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offset = ( ( cluster * 3 ) / 2 ) % BYTES_PER_READ;
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if ( cluster & 0x01 )
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{
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_FAT_cache_readLittleEndianValue ( partition->cache, &oldValue, sector, offset, sizeof( u8 ) );
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value = ( value << 4 ) | ( oldValue & 0x0F );
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_FAT_cache_writeLittleEndianValue ( partition->cache, value & 0xFF, sector, offset, sizeof( u8 ) );
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offset++;
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if ( offset >= BYTES_PER_READ )
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{
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offset = 0;
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sector++;
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}
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_FAT_cache_writeLittleEndianValue ( partition->cache, ( value >> 8 ) & 0xFF, sector, offset, sizeof( u8 ) );
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}
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else
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{
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_FAT_cache_writeLittleEndianValue ( partition->cache, value, sector, offset, sizeof( u8 ) );
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offset++;
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if ( offset >= BYTES_PER_READ )
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{
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offset = 0;
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sector++;
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}
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_FAT_cache_readLittleEndianValue ( partition->cache, &oldValue, sector, offset, sizeof( u8 ) );
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value = ( ( value >> 8 ) & 0x0F ) | ( oldValue & 0xF0 );
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_FAT_cache_writeLittleEndianValue ( partition->cache, value, sector, offset, sizeof( u8 ) );
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}
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break;
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case FS_FAT16:
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sector = partition->fat.fatStart + ( ( cluster << 1 ) / BYTES_PER_READ );
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offset = ( cluster % ( BYTES_PER_READ >> 1 ) ) << 1;
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_FAT_cache_writeLittleEndianValue ( partition->cache, value, sector, offset, sizeof( u16 ) );
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break;
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case FS_FAT32:
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sector = partition->fat.fatStart + ( ( cluster << 2 ) / BYTES_PER_READ );
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offset = ( cluster % ( BYTES_PER_READ >> 2 ) ) << 2;
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_FAT_cache_writeLittleEndianValue ( partition->cache, value, sector, offset, sizeof( u32 ) );
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break;
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default:
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return false;
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break;
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}
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return true;
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}
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/*-----------------------------------------------------------------
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gets the first available free cluster, sets it
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to end of file, links the input cluster to it then returns the
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cluster number
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If an error occurs, return CLUSTER_ERROR
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-----------------------------------------------------------------*/
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uint32_t _FAT_fat_linkFreeCluster( PARTITION* partition, uint32_t cluster )
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{
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uint32_t firstFree;
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uint32_t curLink;
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uint32_t lastCluster;
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bool loopedAroundFAT = false;
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lastCluster = partition->fat.lastCluster;
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if ( cluster > lastCluster )
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{
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return CLUSTER_ERROR;
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}
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// Check if the cluster already has a link, and return it if so
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curLink = _FAT_fat_nextCluster( partition, cluster );
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if ( ( curLink >= CLUSTER_FIRST ) && ( curLink <= lastCluster ) )
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{
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return curLink; // Return the current link - don't allocate a new one
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}
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// Get a free cluster
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firstFree = partition->fat.firstFree;
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// Start at first valid cluster
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if ( firstFree < CLUSTER_FIRST )
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{
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firstFree = CLUSTER_FIRST;
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}
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// Search until a free cluster is found
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while ( _FAT_fat_nextCluster( partition, firstFree ) != CLUSTER_FREE )
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{
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firstFree++;
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if ( firstFree > lastCluster )
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{
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if ( loopedAroundFAT )
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{
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// If couldn't get a free cluster then return an error
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partition->fat.firstFree = firstFree;
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return CLUSTER_ERROR;
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}
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else
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{
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// Try looping back to the beginning of the FAT
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// This was suggested by loopy
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firstFree = CLUSTER_FIRST;
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loopedAroundFAT = true;
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}
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}
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}
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partition->fat.firstFree = firstFree;
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if ( ( cluster >= CLUSTER_FIRST ) && ( cluster < lastCluster ) )
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{
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// Update the linked from FAT entry
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_FAT_fat_writeFatEntry ( partition, cluster, firstFree );
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}
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// Create the linked to FAT entry
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_FAT_fat_writeFatEntry ( partition, firstFree, CLUSTER_EOF );
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return firstFree;
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}
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/*-----------------------------------------------------------------
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gets the first available free cluster, sets it
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to end of file, links the input cluster to it, clears the new
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cluster to 0 valued bytes, then returns the cluster number
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If an error occurs, return CLUSTER_ERROR
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-----------------------------------------------------------------*/
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uint32_t _FAT_fat_linkFreeClusterCleared ( PARTITION* partition, uint32_t cluster )
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{
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uint32_t newCluster;
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uint32_t i;
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uint8_t emptySector[BYTES_PER_READ];
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// Link the cluster
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newCluster = _FAT_fat_linkFreeCluster( partition, cluster );
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if ( newCluster == CLUSTER_FREE || newCluster == CLUSTER_ERROR )
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{
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return CLUSTER_ERROR;
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}
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// Clear all the sectors within the cluster
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memset ( emptySector, 0, BYTES_PER_READ );
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for ( i = 0; i < partition->sectorsPerCluster; i++ )
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{
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_FAT_cache_writeSectors ( partition->cache,
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_FAT_fat_clusterToSector ( partition, newCluster ) + i,
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1, emptySector );
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}
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return newCluster;
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}
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/*-----------------------------------------------------------------
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_FAT_fat_clearLinks
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frees any cluster used by a file
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-----------------------------------------------------------------*/
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bool _FAT_fat_clearLinks ( PARTITION* partition, uint32_t cluster )
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{
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uint32_t nextCluster;
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if ( ( cluster < CLUSTER_FIRST ) || ( cluster > partition->fat.lastCluster /* This will catch CLUSTER_ERROR */ ) )
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return false;
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// If this clears up more space in the FAT before the current free pointer, move it backwards
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if ( cluster < partition->fat.firstFree )
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{
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partition->fat.firstFree = cluster;
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}
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while ( ( cluster != CLUSTER_EOF ) && ( cluster != CLUSTER_FREE ) && ( cluster != CLUSTER_ERROR ) )
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{
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// Store next cluster before erasing the link
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nextCluster = _FAT_fat_nextCluster ( partition, cluster );
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// Erase the link
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_FAT_fat_writeFatEntry ( partition, cluster, CLUSTER_FREE );
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// Move onto next cluster
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cluster = nextCluster;
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}
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return true;
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}
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/*-----------------------------------------------------------------
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_FAT_fat_trimChain
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Drop all clusters past the chainLength.
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If chainLength is 0, all clusters are dropped.
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If chainLength is 1, the first cluster is kept and the rest are
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dropped, and so on.
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Return the last cluster left in the chain.
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-----------------------------------------------------------------*/
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uint32_t _FAT_fat_trimChain ( PARTITION* partition, uint32_t startCluster, unsigned int chainLength )
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{
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uint32_t nextCluster;
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if ( chainLength == 0 )
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{
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// Drop the entire chain
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_FAT_fat_clearLinks ( partition, startCluster );
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return CLUSTER_FREE;
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}
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else
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{
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// Find the last cluster in the chain, and the one after it
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chainLength--;
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nextCluster = _FAT_fat_nextCluster ( partition, startCluster );
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while ( ( chainLength > 0 ) && ( nextCluster != CLUSTER_FREE ) && ( nextCluster != CLUSTER_EOF ) )
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{
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chainLength--;
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startCluster = nextCluster;
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nextCluster = _FAT_fat_nextCluster ( partition, startCluster );
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}
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// Drop all clusters after the last in the chain
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if ( nextCluster != CLUSTER_FREE && nextCluster != CLUSTER_EOF )
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{
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_FAT_fat_clearLinks ( partition, nextCluster );
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}
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// Mark the last cluster in the chain as the end of the file
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_FAT_fat_writeFatEntry ( partition, startCluster, CLUSTER_EOF );
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return startCluster;
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}
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}
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/*-----------------------------------------------------------------
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_FAT_fat_lastCluster
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Trace the cluster links until the last one is found
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-----------------------------------------------------------------*/
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uint32_t _FAT_fat_lastCluster ( PARTITION* partition, uint32_t cluster )
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{
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while ( ( _FAT_fat_nextCluster( partition, cluster ) != CLUSTER_FREE ) && ( _FAT_fat_nextCluster( partition, cluster ) != CLUSTER_EOF ) )
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{
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cluster = _FAT_fat_nextCluster( partition, cluster );
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}
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return cluster;
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}
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/*-----------------------------------------------------------------
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_FAT_fat_freeClusterCount
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Return the number of free clusters available
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-----------------------------------------------------------------*/
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unsigned int _FAT_fat_freeClusterCount ( PARTITION* partition )
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{
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unsigned int count = 0;
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uint32_t curCluster;
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for ( curCluster = CLUSTER_FIRST; curCluster <= partition->fat.lastCluster; curCluster++ )
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{
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if ( _FAT_fat_nextCluster( partition, curCluster ) == CLUSTER_FREE )
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{
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count++;
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}
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}
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return count;
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}
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