mirror of
https://github.com/wiiu-env/libfat.git
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297 lines
8.3 KiB
C
297 lines
8.3 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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2006-07-11 - Chishm
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* Original release
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2006-07-11 - Chishm
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* Made several fixes related to free clusters, thanks to Loopy
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*/
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#include "file_allocation_table.h"
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#include "partition.h"
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/*
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Gets the cluster linked from input cluster
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*/
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u32 _FAT_fat_nextCluster(PARTITION* partition, u32 cluster)
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{
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u32 nextCluster = CLUSTER_FREE;
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u32 sector;
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int offset;
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switch (partition->filesysType)
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{
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case FS_UNKNOWN:
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nextCluster = CLUSTER_FREE;
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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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_FAT_cache_readPartialSector (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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offset = 0;
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sector++;
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}
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_FAT_cache_readPartialSector (partition->cache, ((u8*)&nextCluster) + sizeof(u8), sector, offset, sizeof(u8));
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if (cluster & 0x01) {
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nextCluster = nextCluster >> 4;
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} else {
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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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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_readPartialSector (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_readPartialSector (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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nextCluster = CLUSTER_FREE;
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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, u32 cluster, u32 value) {
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u32 sector;
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int offset;
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u8 oldValue;
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if ((cluster < 0x0002) || (cluster > partition->fat.lastCluster))
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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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_FAT_cache_readPartialSector (partition->cache, &oldValue, sector, offset, sizeof(u8));
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value = (value << 4) | (oldValue & 0x0F);
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_FAT_cache_writePartialSector (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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offset = 0;
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sector++;
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}
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_FAT_cache_writePartialSector (partition->cache, ((u8*)&value) + sizeof(u8), sector, offset, sizeof(u8));
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} else {
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_FAT_cache_writePartialSector (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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offset = 0;
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sector++;
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}
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_FAT_cache_readPartialSector (partition->cache, &oldValue, sector, offset, sizeof(u8));
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value = ((value >> 8) & 0x0F) | (oldValue & 0xF0);
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_FAT_cache_writePartialSector (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_writePartialSector (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_writePartialSector (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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-----------------------------------------------------------------*/
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u32 _FAT_fat_linkFreeCluster(PARTITION* partition, u32 cluster) {
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u32 firstFree;
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u32 curLink;
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u32 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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return CLUSTER_FREE;
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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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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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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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firstFree++;
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if (firstFree > lastCluster) {
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if (loopedAroundFAT) {
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// If couldn't get a free cluster then return, saying this fact
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partition->fat.firstFree = firstFree;
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return CLUSTER_FREE;
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} else {
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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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_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, u32 cluster) {
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u32 nextCluster;
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if ((cluster < 0x0002) || (cluster > partition->fat.lastCluster))
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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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partition->fat.firstFree = cluster;
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}
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while ((cluster != CLUSTER_EOF) && (cluster != CLUSTER_FREE)) {
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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_lastCluster
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Trace the cluster links until the last one is found
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-----------------------------------------------------------------*/
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u32 _FAT_fat_lastCluster (PARTITION* partition, u32 cluster) {
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while ((_FAT_fat_nextCluster(partition, cluster) != CLUSTER_FREE) && (_FAT_fat_nextCluster(partition, cluster) != CLUSTER_EOF)) {
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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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