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384 lines
11 KiB
C
384 lines
11 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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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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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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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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}
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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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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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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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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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_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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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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} else {
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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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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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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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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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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 an error
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partition->fat.firstFree = firstFree;
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return CLUSTER_ERROR;
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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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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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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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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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_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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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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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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// 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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uint32_t nextCluster;
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if (chainLength == 0) {
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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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} else {
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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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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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_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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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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/*-----------------------------------------------------------------
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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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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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if (_FAT_fat_nextCluster(partition, curCluster) == CLUSTER_FREE) {
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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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