usbloadergx/source/libfat/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.

 2009-10-23 oggzee: fixes for cluster aligned file size (write, truncate, seek)
*/


#include "fatfile.h"

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

#include "fat_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 );

    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 );

    if ( file->write )
    {
        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_readSectors ( 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_readSectors ( 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_readSectors ( 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;
}

// if current position is on the cluster border and more data has to be written
// then get next cluster or allocate next cluster
// this solves the over-allocation problems when file size is aligned to cluster size
// return true on succes, false on error
static bool _FAT_check_position_for_next_cluster( struct _reent *r,
        FILE_POSITION *position, PARTITION* partition, size_t remain, bool *flagNoError )
{
    uint32_t tempNextCluster;
    // do nothing if no more data to write
    if ( remain == 0 ) return true;
    if ( flagNoError && *flagNoError == false ) return false;
    if ( ( remain < 0 ) || ( position->sector > partition->sectorsPerCluster ) )
    {
        // invalid arguments - internal error
        r->_errno = EINVAL;
        goto err;
    }
    if ( position->sector == partition->sectorsPerCluster )
    {
        // need to advance to next cluster
        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;
            goto err;
        }
        position->sector = 0;
        position->cluster = tempNextCluster;
    }
    return true;
err:
    if ( flagNoError ) *flagNoError = false;
    return false;
}

/*
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;
    unsigned int sector;

    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;
            }

            sector = _FAT_fat_clusterToSector ( partition, position.cluster ) + position.sector;
            _FAT_cache_writeSectors ( cache, sector, 1, zeroBuffer );

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

        if ( !_FAT_check_position_for_next_cluster( r, &position, partition, remain, NULL ) )
        {
            // error already marked
            return false;
        }

        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
    _FAT_check_position_for_next_cluster( r, &position, partition, remain, &flagNoError );

    // 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 && tempVar < partition->sectorsPerCluster ) && flagNoError )
    {
        if ( !_FAT_cache_writeSectors ( 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;
        }
    }

    // Write whole clusters
    while ( ( remain >= partition->bytesPerCluster ) && flagNoError )
    {
        // allocate next cluster
        _FAT_check_position_for_next_cluster( r, &position, partition, remain, &flagNoError );
        if ( !flagNoError ) break;
        // set indexes to the current position
        uint32_t chunkEnd = position.cluster;
        uint32_t nextChunkStart = position.cluster;
        size_t chunkSize = partition->bytesPerCluster;
        FILE_POSITION next_position = position;

        // group consecutive clusters
        while ( flagNoError &&
#ifdef LIMIT_SECTORS
                ( chunkSize + partition->bytesPerCluster <= LIMIT_SECTORS * BYTES_PER_READ ) &&
#endif
                ( chunkSize + partition->bytesPerCluster < remain ) )
        {
            // pretend to use up all sectors in next_position
            next_position.sector = partition->sectorsPerCluster;
            // get or allocate next cluster
            _FAT_check_position_for_next_cluster( r, &next_position, partition,
                                                  remain - chunkSize, &flagNoError );
            if ( !flagNoError ) break; // exit loop on error
            nextChunkStart = next_position.cluster;
            if ( nextChunkStart != chunkEnd + 1 ) break; // exit loop if not consecutive
            chunkEnd = nextChunkStart;
            chunkSize += partition->bytesPerCluster;
        }

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

        if ( ( chunkEnd != nextChunkStart ) && _FAT_fat_isValidCluster( partition, nextChunkStart ) )
        {
            // new cluster is already allocated (because it was not consecutive)
            position.cluster = nextChunkStart;
            position.sector = 0;
        }
        else
        {
            // Allocate a new cluster when next writing the file
            position.cluster = chunkEnd;
            position.sector = partition->sectorsPerCluster;
        }
    }

    // allocate next cluster if needed
    _FAT_check_position_for_next_cluster( r, &position, partition, remain, &flagNoError );

    // Write remaining sectors
    tempVar = remain / BYTES_PER_READ; // Number of sectors left
    if ( ( tempVar > 0 ) && flagNoError )
    {
        if ( !_FAT_cache_writeSectors ( 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
    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 where the correct cluster is
        // how many clusters from start of file
        clusCount = position / partition->bytesPerCluster;
        cluster = file->startCluster;
        if ( position >= file->currentPosition )
        {
            // start from current cluster
            int currentCount = file->currentPosition / partition->bytesPerCluster;
            if ( file->rwPosition.sector == partition->sectorsPerCluster )
            {
                currentCount--;
            }
            clusCount -= currentCount;
            cluster = file->rwPosition.cluster;
        }
        // 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;

        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;
}

typedef int ( *_frag_append_t )( void *ff, u32 offset, u32 sector, u32 count );

int _FAT_get_fragments ( const char *path, _frag_append_t append_fragment, void *callback_data )
{
    struct _reent r;
    FILE_STRUCT file;
    PARTITION* partition;
    u32 cluster;
    u32 sector;
    u32 offset; // in sectors
    u32 size;   // in sectors
    int ret = -1;
    int fd;

    fd = _FAT_open_r ( &r, &file, path, O_RDONLY, 0 );
    if ( fd == -1 ) return -1;
    if ( fd != ( int )&file ) return -1;

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

    size = file.filesize / BYTES_PER_READ;
    cluster = file.startCluster;
    offset = 0;

    do
    {
        if ( !_FAT_fat_isValidCluster( partition, cluster ) )
        {
            // invalid cluster
            goto out;
        }
        // add cluster to fileinfo
        sector = _FAT_fat_clusterToSector( partition, cluster );
        if ( append_fragment( callback_data, offset, sector, partition->sectorsPerCluster ) )
        {
            // too many fragments
            goto out;
        }
        offset += partition->sectorsPerCluster;
        cluster = _FAT_fat_nextCluster ( partition, cluster );
    }
    while ( offset < size );

    // set size
    append_fragment( callback_data, size, 0, 0 );
    // success
    ret = 0;

out:
    _FAT_unlock( &partition->lock );
    _FAT_close_r( &r, fd );
    return ret;
}