remove unnecessary function

[libfat.git] / source / fatfile.c

/*
 fatfile.c

 Functions used by the newlib disc stubs to interface with
 this library

 Copyright (c) 2006 Michael "Chishm" Chisholm

 Redistribution and use in source and binary forms, with or without modification,
 are permitted provided that the following conditions are met:

  1. Redistributions of source code must retain the above copyright notice,
     this list of conditions and the following disclaimer.
  2. Redistributions in binary form must reproduce the above copyright notice,
     this list of conditions and the following disclaimer in the documentation and/or
     other materials provided with the distribution.
  3. The name of the author may not be used to endorse or promote products derived
     from this software without specific prior written permission.

 THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
 AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE
 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/


#include "fatfile.h"

#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <ctype.h>
#include <unistd.h>
#include <stdio.h>

#include "cache.h"
#include "file_allocation_table.h"
#include "bit_ops.h"
#include "filetime.h"
#include "lock.h"

int _FAT_open_r (struct _reent *r, void *fileStruct, const char *path, int flags, int mode) {
        PARTITION* partition = NULL;
        bool fileExists;
        DIR_ENTRY dirEntry;
        const char* pathEnd;
        uint32_t dirCluster;
        FILE_STRUCT* file = (FILE_STRUCT*) fileStruct;
        partition = _FAT_partition_getPartitionFromPath (path);

        if (partition == NULL) {
                r->_errno = ENODEV;
                return -1;
        }

        // Move the path pointer to the start of the actual path
        if (strchr (path, ':') != NULL) {
                path = strchr (path, ':') + 1;
        }
        if (strchr (path, ':') != NULL) {
                r->_errno = EINVAL;
                return -1;
        }

        // Determine which mode the file is openned for
        if ((flags & 0x03) == O_RDONLY) {
                // Open the file for read-only access
                file->read = true;
                file->write = false;
                file->append = false;
        } else if ((flags & 0x03) == O_WRONLY) {
                // Open file for write only access
                file->read = false;
                file->write = true;
                file->append = false;
        } else if ((flags & 0x03) == O_RDWR) {
                // Open file for read/write access
                file->read = true;
                file->write = true;
                file->append = false;
        } else {
                r->_errno = EACCES;
                return -1;
        }

        // Make sure we aren't trying to write to a read-only disc
        if (file->write && partition->readOnly) {
                r->_errno = EROFS;
                return -1;
        }

        // Search for the file on the disc
        _FAT_lock(&partition->lock);
        fileExists = _FAT_directory_entryFromPath (partition, &dirEntry, path, NULL);

        // The file shouldn't exist if we are trying to create it
        if ((flags & O_CREAT) && (flags & O_EXCL) && fileExists) {
                _FAT_unlock(&partition->lock);
                r->_errno = EEXIST;
                return -1;
        }

        // It should not be a directory if we're openning a file,
        if (fileExists && _FAT_directory_isDirectory(&dirEntry)) {
                _FAT_unlock(&partition->lock);
                r->_errno = EISDIR;
                return -1;
        }

        // We haven't modified the file yet
        file->modified = false;

        // If the file doesn't exist, create it if we're allowed to
        if (!fileExists) {
                if (flags & O_CREAT) {
                        if (partition->readOnly) {
                                // We can't write to a read-only partition
                                _FAT_unlock(&partition->lock);
                                r->_errno = EROFS;
                                return -1;
                        }
                        // Create the file
                        // Get the directory it has to go in
                        pathEnd = strrchr (path, DIR_SEPARATOR);
                        if (pathEnd == NULL) {
                                // No path was specified
                                dirCluster = partition->cwdCluster;
                                pathEnd = path;
                        } else {
                                // Path was specified -- get the right dirCluster
                                // Recycling dirEntry, since it needs to be recreated anyway
                                if (!_FAT_directory_entryFromPath (partition, &dirEntry, path, pathEnd) ||
                                        !_FAT_directory_isDirectory(&dirEntry)) {
                                        _FAT_unlock(&partition->lock);
                                        r->_errno = ENOTDIR;
                                        return -1;
                                }
                                dirCluster = _FAT_directory_entryGetCluster (partition, dirEntry.entryData);
                                // Move the pathEnd past the last DIR_SEPARATOR
                                pathEnd += 1;
                        }
                        // Create the entry data
                        strncpy (dirEntry.filename, pathEnd, MAX_FILENAME_LENGTH - 1);
                        memset (dirEntry.entryData, 0, DIR_ENTRY_DATA_SIZE);

                        // Set the creation time and date
                        dirEntry.entryData[DIR_ENTRY_cTime_ms] = 0;
                        u16_to_u8array (dirEntry.entryData, DIR_ENTRY_cTime, _FAT_filetime_getTimeFromRTC());
                        u16_to_u8array (dirEntry.entryData, DIR_ENTRY_cDate, _FAT_filetime_getDateFromRTC());

                        if (!_FAT_directory_addEntry (partition, &dirEntry, dirCluster)) {
                                _FAT_unlock(&partition->lock);
                                r->_errno = ENOSPC;
                                return -1;
                        }

                        // File entry is modified
                        file->modified = true;
                } else {
                        // file doesn't exist, and we aren't creating it
                        _FAT_unlock(&partition->lock);
                        r->_errno = ENOENT;
                        return -1;
                }
        }

        file->filesize = u8array_to_u32 (dirEntry.entryData, DIR_ENTRY_fileSize);

        /* Allow LARGEFILEs with undefined results
        // Make sure that the file size can fit in the available space
        if (!(flags & O_LARGEFILE) && (file->filesize >= (1<<31))) {
                r->_errno = EFBIG;
                return -1;
        }
        */

        // Make sure we aren't trying to write to a read-only file
        if (file->write && !_FAT_directory_isWritable(&dirEntry)) {
                _FAT_unlock(&partition->lock);
                r->_errno = EROFS;
                return -1;
        }

        // Associate this file with a particular partition
        file->partition = partition;

        file->startCluster = _FAT_directory_entryGetCluster (partition, dirEntry.entryData);

        // Truncate the file if requested
        if ((flags & O_TRUNC) && file->write && (file->startCluster != 0)) {
                _FAT_fat_clearLinks (partition, file->startCluster);
                file->startCluster = CLUSTER_FREE;
                file->filesize = 0;
                // File is modified since we just cut it all off
                file->modified = true;
        }

        // Remember the position of this file's directory entry
        file->dirEntryStart = dirEntry.dataStart;               // Points to the start of the LFN entries of a file, or the alias for no LFN
        file->dirEntryEnd = dirEntry.dataEnd;

        // Reset read/write pointer
        file->currentPosition = 0;
        file->rwPosition.cluster = file->startCluster;
        file->rwPosition.sector =  0;
        file->rwPosition.byte = 0;

        if (flags & O_APPEND) {
                file->append = true;

                // Set append pointer to the end of the file
                file->appendPosition.cluster = _FAT_fat_lastCluster (partition, file->startCluster);
                file->appendPosition.sector = (file->filesize % partition->bytesPerCluster) / BYTES_PER_READ;
                file->appendPosition.byte = file->filesize % BYTES_PER_READ;

                // Check if the end of the file is on the end of a cluster
                if ( (file->filesize > 0) && ((file->filesize % partition->bytesPerCluster)==0) ){
                        // Set flag to allocate a new cluster
                        file->appendPosition.sector = partition->sectorsPerCluster;
                        file->appendPosition.byte = 0;
                }
        } else {
                file->append = false;
                // Use something sane for the append pointer, so the whole file struct contains known values
                file->appendPosition = file->rwPosition;
        }

        file->inUse = true;

        // Insert this file into the double-linked list of open files
        partition->openFileCount += 1;
        if (partition->firstOpenFile) {
                file->nextOpenFile = partition->firstOpenFile;
                partition->firstOpenFile->prevOpenFile = file;
        } else {
                file->nextOpenFile = NULL;
        }
        file->prevOpenFile = NULL;
        partition->firstOpenFile = file;

        _FAT_unlock(&partition->lock);

        /*FILE *fp;
        fp=__sfp(r);
        fp->_file = (int) file;
        setvbuf(fp,NULL,_IONBF,0);*/
        return (int) file;
}

/*
Synchronizes the file data to disc.
Does no locking of its own -- lock the partition before calling.
Returns 0 on success, an error code on failure.
*/
int _FAT_syncToDisc (FILE_STRUCT* file) {
        uint8_t dirEntryData[DIR_ENTRY_DATA_SIZE];

        if (!file || !file->inUse) {
                return EBADF;
        }

        if (file->write && file->modified) {
                // Load the old entry
                _FAT_cache_readPartialSector (file->partition->cache, dirEntryData,
                        _FAT_fat_clusterToSector(file->partition, file->dirEntryEnd.cluster) + file->dirEntryEnd.sector,
                        file->dirEntryEnd.offset * DIR_ENTRY_DATA_SIZE, DIR_ENTRY_DATA_SIZE);

                // Write new data to the directory entry
                // File size
                u32_to_u8array (dirEntryData, DIR_ENTRY_fileSize, file->filesize);

                // Start cluster
                u16_to_u8array (dirEntryData, DIR_ENTRY_cluster, file->startCluster);
                u16_to_u8array (dirEntryData, DIR_ENTRY_clusterHigh, file->startCluster >> 16);

                // Modification time and date
                u16_to_u8array (dirEntryData, DIR_ENTRY_mTime, _FAT_filetime_getTimeFromRTC());
                u16_to_u8array (dirEntryData, DIR_ENTRY_mDate, _FAT_filetime_getDateFromRTC());

                // Access date
                u16_to_u8array (dirEntryData, DIR_ENTRY_aDate, _FAT_filetime_getDateFromRTC());

                // Set archive attribute
                dirEntryData[DIR_ENTRY_attributes] |= ATTRIB_ARCH;

                // Write the new entry
                _FAT_cache_writePartialSector (file->partition->cache, dirEntryData,
                        _FAT_fat_clusterToSector(file->partition, file->dirEntryEnd.cluster) + file->dirEntryEnd.sector,
                        file->dirEntryEnd.offset * DIR_ENTRY_DATA_SIZE, DIR_ENTRY_DATA_SIZE);

                // Flush any sectors in the disc cache
                if (!_FAT_cache_flush(file->partition->cache)) {
                        return EIO;
                }
        }

        file->modified = false;

        return 0;
}


int _FAT_close_r (struct _reent *r, int fd) {
        FILE_STRUCT* file = (FILE_STRUCT*)  fd;
        int ret = 0;

        if (!file->inUse) {
                r->_errno = EBADF;
                return -1;
        }

        _FAT_lock(&file->partition->lock);

        ret = _FAT_syncToDisc (file);
        if (ret != 0) {
                r->_errno = ret;
                ret = -1;
        }

        file->inUse = false;

        // Remove this file from the double-linked list of open files
        file->partition->openFileCount -= 1;
        if (file->nextOpenFile) {
                file->nextOpenFile->prevOpenFile = file->prevOpenFile;
        }
        if (file->prevOpenFile) {
                file->prevOpenFile->nextOpenFile = file->nextOpenFile;
        } else {
                file->partition->firstOpenFile = file->nextOpenFile;
        }

        _FAT_unlock(&file->partition->lock);

        return ret;
}

ssize_t _FAT_read_r (struct _reent *r, int fd, char *ptr, size_t len) {
        FILE_STRUCT* file = (FILE_STRUCT*)  fd;
        PARTITION* partition;
        CACHE* cache;
        FILE_POSITION position;
        uint32_t tempNextCluster;
        unsigned int tempVar;
        size_t remain;
        bool flagNoError = true;

        // Short circuit cases where len is 0 (or less)
        if (len <= 0) {
                return 0;
        }

        // Make sure we can actually read from the file
        if ((file == NULL) || !file->inUse || !file->read) {
                r->_errno = EBADF;
                return -1;
        }

        partition = file->partition;
        _FAT_lock(&partition->lock);

        // Don't try to read if the read pointer is past the end of file
        if (file->currentPosition >= file->filesize || file->startCluster == CLUSTER_FREE) {
                r->_errno = EOVERFLOW;
                _FAT_unlock(&partition->lock);
                return 0;
        }

        // Don't read past end of file
        if (len + file->currentPosition > file->filesize) {
                r->_errno = EOVERFLOW;
                len = file->filesize - file->currentPosition;
        }

        remain = len;
        position = file->rwPosition;
        cache = file->partition->cache;

        // Align to sector
        tempVar = BYTES_PER_READ - position.byte;
        if (tempVar > remain) {
                tempVar = remain;
        }

        if ((tempVar < BYTES_PER_READ) && flagNoError)
        {
                _FAT_cache_readPartialSector ( cache, ptr, _FAT_fat_clusterToSector (partition, position.cluster) + position.sector,
                        position.byte, tempVar);

                remain -= tempVar;
                ptr += tempVar;

                position.byte += tempVar;
                if (position.byte >= BYTES_PER_READ) {
                        position.byte = 0;
                        position.sector++;
                }
        }

        // align to cluster
        // tempVar is number of sectors to read
        if (remain > (partition->sectorsPerCluster - position.sector) * BYTES_PER_READ) {
                tempVar = partition->sectorsPerCluster - position.sector;
        } else {
                tempVar = remain / BYTES_PER_READ;
        }

        if ((tempVar > 0) && flagNoError) {
                if (! _FAT_cache_getSectors (cache, _FAT_fat_clusterToSector (partition, position.cluster) + position.sector,
                        tempVar, ptr))
                {
                        flagNoError = false;
                        r->_errno = EIO;
                } else {
                        ptr += tempVar * BYTES_PER_READ;
                        remain -= tempVar * BYTES_PER_READ;
                        position.sector += tempVar;
                }
        }

        // Move onto next cluster
        // It should get to here without reading anything if a cluster is due to be allocated
        if ((position.sector >= partition->sectorsPerCluster) && flagNoError) {
                tempNextCluster = _FAT_fat_nextCluster(partition, position.cluster);
                if ((remain == 0) && (tempNextCluster == CLUSTER_EOF)) {
                        position.sector = partition->sectorsPerCluster;
                } else if (!_FAT_fat_isValidCluster(partition, tempNextCluster)) {
                        r->_errno = EIO;
                        flagNoError = false;
                } else {
                        position.sector = 0;
                        position.cluster = tempNextCluster;
                }
        }

        // Read in whole clusters, contiguous blocks at a time
        while ((remain >= partition->bytesPerCluster) && flagNoError) {
                uint32_t chunkEnd;
                uint32_t nextChunkStart = position.cluster;
                size_t chunkSize = 0;

                do {
                        chunkEnd = nextChunkStart;
                        nextChunkStart = _FAT_fat_nextCluster (partition, chunkEnd);
                        chunkSize += partition->bytesPerCluster;
                } while ((nextChunkStart == chunkEnd + 1) &&
#ifdef LIMIT_SECTORS
                        (chunkSize + partition->bytesPerCluster <= LIMIT_SECTORS * BYTES_PER_READ) &&
#endif
                        (chunkSize + partition->bytesPerCluster <= remain));

                if (!_FAT_cache_getSectors (cache, _FAT_fat_clusterToSector (partition, position.cluster),
                                chunkSize / BYTES_PER_READ, ptr))
                {
                        flagNoError = false;
                        r->_errno = EIO;
                        break;
                }
                ptr += chunkSize;
                remain -= chunkSize;

                // Advance to next cluster
                if ((remain == 0) && (nextChunkStart == CLUSTER_EOF)) {
                        position.sector = partition->sectorsPerCluster;
                        position.cluster = chunkEnd;
                } else if (!_FAT_fat_isValidCluster(partition, nextChunkStart)) {
                        r->_errno = EIO;
                        flagNoError = false;
                } else {
                        position.sector = 0;
                        position.cluster = nextChunkStart;
                }
        }

        // Read remaining sectors
        tempVar = remain / BYTES_PER_READ; // Number of sectors left
        if ((tempVar > 0) && flagNoError) {
                if (!_FAT_cache_getSectors (cache, _FAT_fat_clusterToSector (partition, position.cluster),
                        tempVar, ptr))
                {
                        flagNoError = false;
                        r->_errno = EIO;
                } else {
                        ptr += tempVar * BYTES_PER_READ;
                        remain -= tempVar * BYTES_PER_READ;
                        position.sector += tempVar;
                }
        }

        // Last remaining sector
        // Check if anything is left
        if ((remain > 0) && flagNoError) {
                _FAT_cache_readPartialSector ( cache, ptr,
                        _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, 0, remain);
                position.byte += remain;
                remain = 0;
        }

        // Length read is the wanted length minus the stuff not read
        len = len - remain;

        // Update file information
        file->rwPosition = position;
        file->currentPosition += len;

        _FAT_unlock(&partition->lock);
        return len;
}

/*
Extend a file so that the size is the same as the rwPosition
*/
static bool _FAT_file_extend_r (struct _reent *r, FILE_STRUCT* file) {
        PARTITION* partition = file->partition;
        CACHE* cache = file->partition->cache;
        FILE_POSITION position;
        uint8_t zeroBuffer [BYTES_PER_READ] = {0};
        uint32_t remain;
        uint32_t tempNextCluster;

        position.byte = file->filesize % BYTES_PER_READ;
        position.sector = (file->filesize % partition->bytesPerCluster) / BYTES_PER_READ;
        // It is assumed that there is always a startCluster
        // This will be true when _FAT_file_extend_r is called from _FAT_write_r
        position.cluster = _FAT_fat_lastCluster (partition, file->startCluster);

        remain = file->currentPosition - file->filesize;

        if ((remain > 0) && (file->filesize > 0) && (position.sector == 0) && (position.byte  == 0)) {
                // Get a new cluster on the edge of a cluster boundary
                tempNextCluster = _FAT_fat_linkFreeCluster(partition, position.cluster);
                if (!_FAT_fat_isValidCluster(partition, tempNextCluster)) {
                        // Couldn't get a cluster, so abort
                        r->_errno = ENOSPC;
                        return false;
                }
                position.cluster = tempNextCluster;
                position.sector = 0;
        }

        if (remain + position.byte < BYTES_PER_READ) {
                // Only need to clear to the end of the sector
                _FAT_cache_writePartialSector (cache, zeroBuffer,
                        _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, position.byte, remain);
                position.byte += remain;
        } else {
                if (position.byte > 0) {
                        _FAT_cache_writePartialSector (cache, zeroBuffer,
                                _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, position.byte,
                                BYTES_PER_READ - position.byte);
                        remain -= (BYTES_PER_READ - position.byte);
                        position.byte = 0;
                        position.sector ++;
                }

                while (remain >= BYTES_PER_READ) {
                        if (position.sector >= partition->sectorsPerCluster) {
                                position.sector = 0;
                                // Ran out of clusters so get a new one
                                tempNextCluster = _FAT_fat_linkFreeCluster(partition, position.cluster);
                                if (!_FAT_fat_isValidCluster(partition, tempNextCluster)) {
                                        // Couldn't get a cluster, so abort
                                        r->_errno = ENOSPC;
                                        return false;
                                }
                                position.cluster = tempNextCluster;
                        }

                        _FAT_disc_writeSectors (partition->disc,
                                _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, 1, zeroBuffer);

                        remain -= BYTES_PER_READ;
                        position.sector ++;
                }

                if (position.sector >= partition->sectorsPerCluster) {
                        position.sector = 0;
                        tempNextCluster = _FAT_fat_nextCluster(partition, position.cluster);
                        if ((tempNextCluster == CLUSTER_EOF) || (tempNextCluster == CLUSTER_FREE)) {
                                // Ran out of clusters so get a new one
                                tempNextCluster = _FAT_fat_linkFreeCluster(partition, position.cluster);
                        }
                        if (!_FAT_fat_isValidCluster(partition, tempNextCluster)) {
                                // Couldn't get a cluster, so abort
                                r->_errno = ENOSPC;
                                return false;
                        }
                        position.cluster = tempNextCluster;
                }

                if (remain > 0) {
                        _FAT_cache_writePartialSector (cache, zeroBuffer,
                                _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, 0, remain);
                        position.byte = remain;
                }
        }

        file->rwPosition = position;
        file->filesize = file->currentPosition;
        return true;
}


ssize_t _FAT_write_r (struct _reent *r, int fd, const char *ptr, size_t len) {
        FILE_STRUCT* file = (FILE_STRUCT*)  fd;
        PARTITION* partition;
        CACHE* cache;
        FILE_POSITION position;
        uint32_t tempNextCluster;
        unsigned int tempVar;
        size_t remain;
        bool flagNoError = true;
        bool flagAppending = false;

        // Make sure we can actually write to the file
        if ((file == NULL) || !file->inUse || !file->write) {
                r->_errno = EBADF;
                return -1;
        }

        partition = file->partition;
        cache = file->partition->cache;
        _FAT_lock(&partition->lock);

        // Only write up to the maximum file size, taking into account wrap-around of ints
        if (remain + file->filesize > FILE_MAX_SIZE || len + file->filesize < file->filesize) {
                len = FILE_MAX_SIZE - file->filesize;
        }
        remain = len;

        // Short circuit cases where len is 0 (or less)
        if (len <= 0) {
                _FAT_unlock(&partition->lock);
                return 0;
        }

        // Get a new cluster for the start of the file if required
        if (file->startCluster == CLUSTER_FREE) {
                tempNextCluster = _FAT_fat_linkFreeCluster (partition, CLUSTER_FREE);
                if (!_FAT_fat_isValidCluster(partition, tempNextCluster)) {
                        // Couldn't get a cluster, so abort immediately
                        _FAT_unlock(&partition->lock);
                        r->_errno = ENOSPC;
                        return -1;
                }
                file->startCluster = tempNextCluster;

                // Appending starts at the begining for a 0 byte file
                file->appendPosition.cluster = file->startCluster;
                file->appendPosition.sector = 0;
                file->appendPosition.byte = 0;

                file->rwPosition.cluster = file->startCluster;
                file->rwPosition.sector =  0;
                file->rwPosition.byte = 0;
        }

        if (file->append) {
                position = file->appendPosition;
                flagAppending = true;
        } else {
                // If the write pointer is past the end of the file, extend the file to that size
                if (file->currentPosition > file->filesize) {
                        if (!_FAT_file_extend_r (r, file)) {
                                _FAT_unlock(&partition->lock);
                                return -1;
                        }
                }

                // Write at current read pointer
                position = file->rwPosition;

                // If it is writing past the current end of file, set appending flag
                if (len + file->currentPosition > file->filesize) {
                        flagAppending = true;
                }
        }

        // Move onto next cluster if needed
        if (position.sector >= partition->sectorsPerCluster) {
                position.sector = 0;
                tempNextCluster = _FAT_fat_nextCluster(partition, position.cluster);
                if ((tempNextCluster == CLUSTER_EOF) || (tempNextCluster == CLUSTER_FREE)) {
                        // Ran out of clusters so get a new one
                        tempNextCluster = _FAT_fat_linkFreeCluster(partition, position.cluster);
                }
                if (!_FAT_fat_isValidCluster(partition, tempNextCluster)) {
                        // Couldn't get a cluster, so abort
                        r->_errno = ENOSPC;
                        flagNoError = false;
                } else {
                        position.cluster = tempNextCluster;
                }
        }

        // Align to sector
        tempVar = BYTES_PER_READ - position.byte;
        if (tempVar > remain) {
                tempVar = remain;
        }

        if ((tempVar < BYTES_PER_READ) && flagNoError) {
                // Write partial sector to disk
                _FAT_cache_writePartialSector (cache, ptr,
                        _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, position.byte, tempVar);

                remain -= tempVar;
                ptr += tempVar;
                position.byte += tempVar;


                // Move onto next sector
                if (position.byte >= BYTES_PER_READ) {
                        position.byte = 0;
                        position.sector ++;
                }
        }

        // Align to cluster
        // tempVar is number of sectors to write
        if (remain > (partition->sectorsPerCluster - position.sector) * BYTES_PER_READ) {
                tempVar = partition->sectorsPerCluster - position.sector;
        } else {
                tempVar = remain / BYTES_PER_READ;
        }

        if ((tempVar > 0) && flagNoError) {
                if (!_FAT_disc_writeSectors (partition->disc,
                        _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, tempVar, ptr))
                {
                        flagNoError = false;
                        r->_errno = EIO;
                } else {
                        ptr += tempVar * BYTES_PER_READ;
                        remain -= tempVar * BYTES_PER_READ;
                        position.sector += tempVar;
                }
        }

        if ((position.sector >= partition->sectorsPerCluster) && flagNoError && (remain > 0)) {
                position.sector = 0;
                tempNextCluster = _FAT_fat_nextCluster(partition, position.cluster);
                if ((tempNextCluster == CLUSTER_EOF) || (tempNextCluster == CLUSTER_FREE)) {
                        // Ran out of clusters so get a new one
                        tempNextCluster = _FAT_fat_linkFreeCluster(partition, position.cluster);
                }
                if (!_FAT_fat_isValidCluster(partition, tempNextCluster)) {
                        // Couldn't get a cluster, so abort
                        r->_errno = ENOSPC;
                        flagNoError = false;
                } else {
                        position.cluster = tempNextCluster;
                }
        }

        // Write whole clusters
        while ((remain >= partition->bytesPerCluster) && flagNoError) {
                uint32_t chunkEnd;
                uint32_t nextChunkStart = position.cluster;
                size_t chunkSize = 0;

                do {
                        chunkEnd = nextChunkStart;
                        nextChunkStart = _FAT_fat_nextCluster (partition, chunkEnd);
                        if ((nextChunkStart == CLUSTER_EOF) || (nextChunkStart == CLUSTER_FREE)) {
                                // Ran out of clusters so get a new one
                                nextChunkStart = _FAT_fat_linkFreeCluster(partition, chunkEnd);
                        }
                        if (!_FAT_fat_isValidCluster(partition, nextChunkStart)) {
                                // Couldn't get a cluster, so abort
                                r->_errno = ENOSPC;
                                flagNoError = false;
                        } else {
                                chunkSize += partition->bytesPerCluster;
                        }
                } while (flagNoError && (nextChunkStart == chunkEnd + 1) &&
#ifdef LIMIT_SECTORS
                        (chunkSize + partition->bytesPerCluster <= LIMIT_SECTORS * BYTES_PER_READ) &&
#endif
                        (chunkSize + partition->bytesPerCluster <= remain));

                if ( !_FAT_disc_writeSectors (partition->disc, _FAT_fat_clusterToSector(partition, position.cluster),
                        chunkSize / BYTES_PER_READ, ptr))
                {
                        flagNoError = false;
                        r->_errno = EIO;
                        break;
                }
                ptr += chunkSize;
                remain -= chunkSize;

                if (_FAT_fat_isValidCluster(partition, nextChunkStart)) {
                        position.cluster = nextChunkStart;
                } else {
                        // Allocate a new cluster when next writing the file
                        position.cluster = chunkEnd;
                        position.sector = partition->sectorsPerCluster;
                }
        }

        // Write remaining sectors
        tempVar = remain / BYTES_PER_READ; // Number of sectors left
        if ((tempVar > 0) && flagNoError) {
                if (!_FAT_disc_writeSectors (partition->disc, _FAT_fat_clusterToSector (partition, position.cluster),
                        tempVar, ptr))
                {
                        flagNoError = false;
                        r->_errno = EIO;
                } else {
                        ptr += tempVar * BYTES_PER_READ;
                        remain -= tempVar * BYTES_PER_READ;
                        position.sector += tempVar;
                }
        }

        // Last remaining sector
        if ((remain > 0) && flagNoError) {
                if (flagAppending) {
                        _FAT_cache_eraseWritePartialSector ( cache, ptr,
                                _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, 0, remain);
                } else {
                        _FAT_cache_writePartialSector ( cache, ptr,
                                _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, 0, remain);
                }
                position.byte += remain;
                remain = 0;
        }


        // Amount written is the originally requested amount minus stuff remaining
        len = len - remain;

        // Update file information
        file->modified = true;
        if (file->append) {
                // Appending doesn't affect the read pointer
                file->appendPosition = position;
                file->filesize += len;
        } else {
                // Writing also shifts the read pointer
                file->rwPosition = position;
                file->currentPosition += len;
                if (file->filesize < file->currentPosition) {
                        file->filesize = file->currentPosition;
                }
        }

        _FAT_unlock(&partition->lock);

        return len;
}


off_t _FAT_seek_r (struct _reent *r, int fd, off_t pos, int dir) {
        FILE_STRUCT* file = (FILE_STRUCT*)  fd;
        PARTITION* partition;
        uint32_t cluster, nextCluster;
        int clusCount;
        off_t newPosition;
        uint32_t position;

        if ((file == NULL) || (file->inUse == false))    {
                // invalid file
                r->_errno = EBADF;
                return -1;
        }

        partition = file->partition;
        _FAT_lock(&partition->lock);

        switch (dir) {
                case SEEK_SET:
                        newPosition = pos;
                        break;
                case SEEK_CUR:
                        newPosition = (off_t)file->currentPosition + pos;
                        break;
                case SEEK_END:
                        newPosition = (off_t)file->filesize + pos;
                        break;
                default:
                        _FAT_unlock(&partition->lock);
                        r->_errno = EINVAL;
                        return -1;
        }

        if ((pos > 0) && (newPosition < 0)) {
                _FAT_unlock(&partition->lock);
                r->_errno = EOVERFLOW;
                return -1;
        }

        // newPosition can only be larger than the FILE_MAX_SIZE on platforms where
        // off_t is larger than 32 bits.
        if (newPosition < 0 || ((sizeof(newPosition) > 4) && newPosition > (off_t)FILE_MAX_SIZE)) {
                _FAT_unlock(&partition->lock);
                r->_errno = EINVAL;
                return -1;
        }

        position = (uint32_t)newPosition;

        // Only change the read/write position if it is within the bounds of the current filesize,
        // or at the very edge of the file
        if (position <= file->filesize && file->startCluster != CLUSTER_FREE) {
                // Calculate the sector and byte of the current position,
                // and store them
                file->rwPosition.sector = (position % partition->bytesPerCluster) / BYTES_PER_READ;
                file->rwPosition.byte = position % BYTES_PER_READ;

                // Calculate where the correct cluster is
                if ((position >= file->currentPosition) && (file->rwPosition.sector != partition->sectorsPerCluster)) {
                        clusCount = (position / partition->bytesPerCluster) - (file->currentPosition / partition->bytesPerCluster);
                        cluster = file->rwPosition.cluster;
                } else {
                        clusCount = position / partition->bytesPerCluster;
                        cluster = file->startCluster;
                }

                nextCluster = _FAT_fat_nextCluster (partition, cluster);
                while ((clusCount > 0) && (nextCluster != CLUSTER_FREE) && (nextCluster != CLUSTER_EOF)) {
                        clusCount--;
                        cluster = nextCluster;
                        nextCluster = _FAT_fat_nextCluster (partition, cluster);
                }

                // Check if ran out of clusters and it needs to allocate a new one
                if (clusCount > 0) {
                        if ((clusCount == 1) && (file->filesize == position) && (file->rwPosition.sector == 0)) {
                                // Set flag to allocate a new cluster
                                file->rwPosition.sector = partition->sectorsPerCluster;
                                file->rwPosition.byte = 0;
                        } else {
                                _FAT_unlock(&partition->lock);
                                r->_errno = EINVAL;
                                return -1;
                        }
                }

                file->rwPosition.cluster = cluster;
        }

        // Save position
        file->currentPosition = position;

        _FAT_unlock(&partition->lock);
        return position;
}



int _FAT_fstat_r (struct _reent *r, int fd, struct stat *st) {
        FILE_STRUCT* file = (FILE_STRUCT*)  fd;
        PARTITION* partition;
        DIR_ENTRY fileEntry;

        if ((file == NULL) || (file->inUse == false))    {
                // invalid file
                r->_errno = EBADF;
                return -1;
        }

        partition = file->partition;
        _FAT_lock(&partition->lock);

        // Get the file's entry data
        fileEntry.dataStart = file->dirEntryStart;
        fileEntry.dataEnd = file->dirEntryEnd;

        if (!_FAT_directory_entryFromPosition (partition, &fileEntry)) {
                _FAT_unlock(&partition->lock);
                r->_errno = EIO;
                return -1;
        }

        // Fill in the stat struct
        _FAT_directory_entryStat (partition, &fileEntry, st);

        // Fix stats that have changed since the file was openned
        st->st_ino = (ino_t)(file->startCluster);               // The file serial number is the start cluster
        st->st_size = file->filesize;                                   // File size

        _FAT_unlock(&partition->lock);
        return 0;
}

int _FAT_ftruncate_r (struct _reent *r, int fd, off_t len) {
        FILE_STRUCT* file = (FILE_STRUCT*)  fd;
        PARTITION* partition;
        int ret=0;
        uint32_t newSize = (uint32_t)len;

        if (len < 0) {
                // Trying to truncate to a negative size
                r->_errno = EINVAL;
                return -1;
        }

        if ((sizeof(len) > 4) && len > (off_t)FILE_MAX_SIZE) {
                // Trying to extend the file beyond what FAT supports
                r->_errno = EFBIG;
                return -1;
        }

        if (!file || !file->inUse) {
                // invalid file
                r->_errno = EBADF;
                return -1;
        }

        if (!file->write) {
                // Read-only file
                r->_errno = EINVAL;
                return -1;
        }

        partition = file->partition;
        _FAT_lock(&partition->lock);

        if (newSize > file->filesize) {
                // Expanding the file
                FILE_POSITION savedPosition;
                uint32_t savedOffset;
                // Get a new cluster for the start of the file if required
                if (file->startCluster == CLUSTER_FREE) {
                        uint32_t tempNextCluster = _FAT_fat_linkFreeCluster (partition, CLUSTER_FREE);
                        if (!_FAT_fat_isValidCluster(partition, tempNextCluster)) {
                                // Couldn't get a cluster, so abort immediately
                                _FAT_unlock(&partition->lock);
                                r->_errno = ENOSPC;
                                return -1;
                        }
                        file->startCluster = tempNextCluster;

                        file->rwPosition.cluster = file->startCluster;
                        file->rwPosition.sector =  0;
                        file->rwPosition.byte = 0;
                }
                // Save the read/write pointer
                savedPosition = file->rwPosition;
                savedOffset = file->currentPosition;
                // Set the position to the new size
                file->currentPosition = newSize;
                // Extend the file to the new position
                if (!_FAT_file_extend_r (r, file)) {
                        ret = -1;
                }
                // Set the append position to the new rwPointer
                if (file->append) {
                        file->appendPosition = file->rwPosition;
                }
                // Restore the old rwPointer;
                file->rwPosition = savedPosition;
                file->currentPosition = savedOffset;
        } else if (newSize < file->filesize){
                // Shrinking the file
                if (len == 0) {
                        // Cutting the file down to nothing, clear all clusters used
                        _FAT_fat_clearLinks (partition, file->startCluster);
                        file->startCluster = CLUSTER_FREE;

                        file->appendPosition.cluster = CLUSTER_FREE;
                        file->appendPosition.sector = 0;
                        file->appendPosition.byte = 0;
                } else {
                        // Trimming the file down to the required size
                        unsigned int chainLength;
                        uint32_t lastCluster;

                        // Drop the unneeded end of the cluster chain.
                        // If the end falls on a cluster boundary, drop that cluster too,
                        // then set a flag to allocate a cluster as needed
                        chainLength = ((newSize-1) / partition->bytesPerCluster) + 1;
                        lastCluster = _FAT_fat_trimChain (partition, file->startCluster, chainLength);

                        if (file->append) {
                                file->appendPosition.byte = newSize % BYTES_PER_READ;
                                // Does the end of the file fall on the edge of a cluster?
                                if (newSize % partition->bytesPerCluster == 0) {
                                        // Set a flag to allocate a new cluster
                                        file->appendPosition.sector = partition->sectorsPerCluster;
                                } else {
                                        file->appendPosition.sector = (newSize % partition->bytesPerCluster) / BYTES_PER_READ;
                                }
                                file->appendPosition.cluster = lastCluster;
                        }
                }
        } else {
                // Truncating to same length, so don't do anything
        }

        file->filesize = newSize;
        file->modified = true;

        _FAT_unlock(&partition->lock);
        return ret;
}

int _FAT_fsync_r (struct _reent *r, int fd) {
        FILE_STRUCT* file = (FILE_STRUCT*)  fd;
        int ret = 0;

        if (!file->inUse) {
                r->_errno = EBADF;
                return -1;
        }

        _FAT_lock(&file->partition->lock);

        ret = _FAT_syncToDisc (file);
        if (ret != 0) {
                r->_errno = ret;
                ret = -1;
        }

        _FAT_unlock(&file->partition->lock);

        return ret;
}