rockbox/firmware/drivers/fat.c

/***************************************************************************
 *             __________               __   ___.
 *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
 *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
 *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
 *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
 *                     \/            \/     \/    \/            \/
 * $Id$
 *
 * Copyright (C) 2002 by Linus Nielsen Feltzing
 *
 * All files in this archive are subject to the GNU General Public License.
 * See the file COPYING in the source tree root for full license agreement.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ****************************************************************************/

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
#include <ctype.h>
#include <stdbool.h>
#include "fat.h"
#include "ata.h"
#include "debug.h"
#include "panic.h"
#include "system.h"
#include "timefuncs.h"

#define BYTES2INT16(array,pos) \
          (array[pos] | (array[pos+1] << 8 ))
#define BYTES2INT32(array,pos) \
          (array[pos] | (array[pos+1] << 8 ) | \
          (array[pos+2] << 16 ) | (array[pos+3] << 24 ))

#define FATTYPE_FAT12       0
#define FATTYPE_FAT16       1
#define FATTYPE_FAT32       2

/* BPB offsets; generic */
#define BS_JMPBOOT          0
#define BS_OEMNAME          3
#define BPB_BYTSPERSEC      11
#define BPB_SECPERCLUS      13
#define BPB_RSVDSECCNT      14
#define BPB_NUMFATS         16
#define BPB_ROOTENTCNT      17
#define BPB_TOTSEC16        19
#define BPB_MEDIA           21
#define BPB_FATSZ16         22
#define BPB_SECPERTRK       24
#define BPB_NUMHEADS        26
#define BPB_HIDDSEC         28
#define BPB_TOTSEC32        32

/* fat12/16 */
#define BS_DRVNUM           36
#define BS_RESERVED1        37
#define BS_BOOTSIG          38
#define BS_VOLID            39
#define BS_VOLLAB           43
#define BS_FILSYSTYPE       54

/* fat32 */
#define BPB_FATSZ32         36
#define BPB_EXTFLAGS        40
#define BPB_FSVER           42
#define BPB_ROOTCLUS        44
#define BPB_FSINFO          48
#define BPB_BKBOOTSEC       50
#define BS_32_DRVNUM        64
#define BS_32_BOOTSIG       66
#define BS_32_VOLID         67
#define BS_32_VOLLAB        71
#define BS_32_FILSYSTYPE    82

#define BPB_LAST_WORD       510


/* attributes */
#define FAT_ATTR_LONG_NAME   (FAT_ATTR_READ_ONLY | FAT_ATTR_HIDDEN | \
                              FAT_ATTR_SYSTEM | FAT_ATTR_VOLUME_ID)
#define FAT_ATTR_LONG_NAME_MASK (FAT_ATTR_READ_ONLY | FAT_ATTR_HIDDEN | \
                                 FAT_ATTR_SYSTEM | FAT_ATTR_VOLUME_ID | \
                                 FAT_ATTR_DIRECTORY | FAT_ATTR_ARCHIVE )

#define FATDIR_NAME          0
#define FATDIR_ATTR          11
#define FATDIR_NTRES         12
#define FATDIR_CRTTIMETENTH  13
#define FATDIR_CRTTIME       14
#define FATDIR_CRTDATE       16
#define FATDIR_LSTACCDATE    18
#define FATDIR_FSTCLUSHI     20
#define FATDIR_WRTTIME       22
#define FATDIR_WRTDATE       24
#define FATDIR_FSTCLUSLO     26
#define FATDIR_FILESIZE      28

#define FATLONG_ORDER        0
#define FATLONG_TYPE         12
#define FATLONG_CHKSUM       13

#define CLUSTERS_PER_FAT_SECTOR (SECTOR_SIZE / 4)
#define DIR_ENTRIES_PER_SECTOR  (SECTOR_SIZE / DIR_ENTRY_SIZE)
#define DIR_ENTRY_SIZE       32
#define NAME_BYTES_PER_ENTRY 13
#define FAT_BAD_MARK         0x0ffffff7
#define FAT_EOF_MARK         0x0ffffff8

struct fsinfo {
    unsigned int freecount; /* last known free cluster count */
    unsigned int nextfree;  /* first cluster to start looking for free
                               clusters, or 0xffffffff for no hint */
};
/* fsinfo offsets */
#define FSINFO_FREECOUNT 488
#define FSINFO_NEXTFREE  492

struct bpb
{
    char bs_oemname[9];  /* OEM string, ending with \0 */
    int bpb_bytspersec;  /* Bytes per sectory, typically 512 */
    unsigned int bpb_secperclus;  /* Sectors per cluster */
    int bpb_rsvdseccnt;  /* Number of reserved sectors */
    int bpb_numfats;     /* Number of FAT structures, typically 2 */
    int bpb_rootentcnt;  /* Number of dir entries in the root */
    int bpb_totsec16;    /* Number of sectors on the volume (old 16-bit) */
    int bpb_media;       /* Media type (typically 0xf0 or 0xf8) */
    int bpb_fatsz16;     /* Number of used sectors per FAT structure */
    int bpb_secpertrk;   /* Number of sectors per track */
    int bpb_numheads;    /* Number of heads */
    int bpb_hiddsec;     /* Hidden sectors before the volume */
    unsigned int bpb_totsec32;    /* Number of sectors on the volume
                                     (new 32-bit) */
    int last_word;       /* 0xAA55 */

    /**** FAT12/16 specific *****/
    int bs_drvnum;       /* Drive number */
    int bs_bootsig;      /* Is 0x29 if the following 3 fields are valid */
    unsigned int bs_volid; /* Volume ID */
    char bs_vollab[12];    /* Volume label, 11 chars plus \0 */
    char bs_filsystype[9]; /* File system type, 8 chars plus \0 */

    /**** FAT32 specific *****/
    int bpb_fatsz32;
    int bpb_extflags;
    int bpb_fsver;
    int bpb_rootclus;
    int bpb_fsinfo;
    int bpb_bkbootsec;

    /* variables for internal use */
    unsigned int fatsize;
    unsigned int totalsectors;
    unsigned int rootdirsector;
    unsigned int firstdatasector;
    unsigned int startsector;
    unsigned int dataclusters;
    struct fsinfo fsinfo;
};

static struct bpb fat_bpb;

static int first_sector_of_cluster(int cluster);
static int bpb_is_sane(void);
static void *cache_fat_sector(int secnum);
static int create_dos_name(unsigned char *name, unsigned char *newname);
static unsigned int find_free_cluster(unsigned int start);

#define FAT_CACHE_SIZE 0x20
#define FAT_CACHE_MASK (FAT_CACHE_SIZE-1)

struct fat_cache_entry
{
    int secnum;
    bool inuse;
    bool dirty;
};

static char fat_cache_sectors[FAT_CACHE_SIZE][SECTOR_SIZE];
static struct fat_cache_entry fat_cache[FAT_CACHE_SIZE];

/* sectors cache for longname use */
static unsigned char lastsector[SECTOR_SIZE];
static unsigned char lastsector2[SECTOR_SIZE];

static int sec2cluster(unsigned int sec)
{
    if ( sec < fat_bpb.firstdatasector )
    {
        DEBUGF( "sec2cluster() - Bad sector number (%d)\n", sec);
        return -1;
    }

    return ((sec - fat_bpb.firstdatasector) / fat_bpb.bpb_secperclus) + 2;
}

static int cluster2sec(int cluster)
{
    int max_cluster = fat_bpb.totalsectors -
        fat_bpb.firstdatasector / fat_bpb.bpb_secperclus + 1;
    
    if(cluster > max_cluster)
    {
        DEBUGF( "cluster2sec() - Bad cluster number (%d)\n",
                cluster);
        return -1;
    }

    return first_sector_of_cluster(cluster);
}

static int first_sector_of_cluster(int cluster)
{
    return (cluster - 2) * fat_bpb.bpb_secperclus + fat_bpb.firstdatasector;
}

int fat_startsector(void)
{
    return fat_bpb.startsector;
}

void fat_size(unsigned int* size, unsigned int* free)
{
    if (size)
        *size = fat_bpb.dataclusters * fat_bpb.bpb_secperclus / 2;
    if (free)
        *free = fat_bpb.fsinfo.freecount * fat_bpb.bpb_secperclus / 2;
}

int fat_mount(int startsector)
{
    unsigned char buf[SECTOR_SIZE];
    int err;
    int datasec;
    unsigned int i;

    for(i = 0;i < FAT_CACHE_SIZE;i++)
    {
        fat_cache[i].secnum = 8; /* We use a "safe" sector just in case */
        fat_cache[i].inuse = false;
        fat_cache[i].dirty = false;
    }

    /* Read the sector */
    err = ata_read_sectors(startsector,1,buf);
    if(err)
    {
        DEBUGF( "fat_mount() - Couldn't read BPB (error code %d)\n", err);
        return -1;
    }

    memset(&fat_bpb, 0, sizeof(struct bpb));
    fat_bpb.startsector = startsector;
    
    strncpy(fat_bpb.bs_oemname, &buf[BS_OEMNAME], 8);
    fat_bpb.bs_oemname[8] = 0;

    fat_bpb.bpb_bytspersec = BYTES2INT16(buf,BPB_BYTSPERSEC);
    fat_bpb.bpb_secperclus = buf[BPB_SECPERCLUS];
    fat_bpb.bpb_rsvdseccnt = BYTES2INT16(buf,BPB_RSVDSECCNT);
    fat_bpb.bpb_numfats    = buf[BPB_NUMFATS];
    fat_bpb.bpb_totsec16   = BYTES2INT16(buf,BPB_TOTSEC16);
    fat_bpb.bpb_media      = buf[BPB_MEDIA];
    fat_bpb.bpb_fatsz16    = BYTES2INT16(buf,BPB_FATSZ16);
    fat_bpb.bpb_fatsz32    = BYTES2INT32(buf,BPB_FATSZ32);
    fat_bpb.bpb_secpertrk  = BYTES2INT16(buf,BPB_SECPERTRK);
    fat_bpb.bpb_numheads   = BYTES2INT16(buf,BPB_NUMHEADS);
    fat_bpb.bpb_hiddsec    = BYTES2INT32(buf,BPB_HIDDSEC);
    fat_bpb.bpb_totsec32   = BYTES2INT32(buf,BPB_TOTSEC32);
    fat_bpb.last_word      = BYTES2INT16(buf,BPB_LAST_WORD);

    /* calculate a few commonly used values */
    if (fat_bpb.bpb_fatsz16 != 0)
        fat_bpb.fatsize = fat_bpb.bpb_fatsz16;
    else
        fat_bpb.fatsize = fat_bpb.bpb_fatsz32;

    if (fat_bpb.bpb_totsec16 != 0)
        fat_bpb.totalsectors = fat_bpb.bpb_totsec16;
    else
        fat_bpb.totalsectors = fat_bpb.bpb_totsec32;
    fat_bpb.firstdatasector = fat_bpb.bpb_rsvdseccnt +
        fat_bpb.bpb_numfats * fat_bpb.fatsize;

    /* Determine FAT type */
    datasec = fat_bpb.totalsectors - fat_bpb.firstdatasector;
    fat_bpb.dataclusters = datasec / fat_bpb.bpb_secperclus;

#ifdef TEST_FAT
    /*
      we are sometimes testing with "illegally small" fat32 images,
      so we don't use the proper fat32 test case for test code
    */
    if ( fat_bpb.bpb_fatsz16 )
#else
    if ( fat_bpb.dataclusters < 65525 )
#endif
    {
        DEBUGF("This is not FAT32. Go away!\n");
        return -2;
    }

    fat_bpb.bpb_extflags  = BYTES2INT16(buf,BPB_EXTFLAGS);
    fat_bpb.bpb_fsver     = BYTES2INT16(buf,BPB_FSVER);
    fat_bpb.bpb_rootclus  = BYTES2INT32(buf,BPB_ROOTCLUS);
    fat_bpb.bpb_fsinfo    = BYTES2INT16(buf,BPB_FSINFO);
    fat_bpb.bpb_bkbootsec = BYTES2INT16(buf,BPB_BKBOOTSEC);
    fat_bpb.bs_drvnum     = buf[BS_32_DRVNUM];
    fat_bpb.bs_bootsig    = buf[BS_32_BOOTSIG];

    if(fat_bpb.bs_bootsig == 0x29)
    {
        fat_bpb.bs_volid = BYTES2INT32(buf,BS_32_VOLID);
        strncpy(fat_bpb.bs_vollab, &buf[BS_32_VOLLAB], 11);
        strncpy(fat_bpb.bs_filsystype, &buf[BS_32_FILSYSTYPE], 8);
    }

    if (bpb_is_sane() < 0)
    {
        DEBUGF( "fat_mount() - BPB is not sane\n");
        return -3;
    }

    fat_bpb.rootdirsector = cluster2sec(fat_bpb.bpb_rootclus);

    /* Read the fsinfo sector */
    err = ata_read_sectors(startsector + fat_bpb.bpb_fsinfo, 1, buf);
    if (err)
    {
        DEBUGF( "fat_mount() - Couldn't read FSInfo (error code %d)\n", err);
        return -4;
    }
    fat_bpb.fsinfo.freecount = BYTES2INT32(buf, FSINFO_FREECOUNT);
    fat_bpb.fsinfo.nextfree = BYTES2INT32(buf, FSINFO_NEXTFREE);

    /* calculate freecount if unset */
    if ( fat_bpb.fsinfo.freecount == 0xffffffff )
    {
        int free = 0;
        for (i = 0; i<fat_bpb.fatsize; i++) {
            unsigned int j;
            unsigned int* fat = cache_fat_sector(i);
            for (j = 0; j < CLUSTERS_PER_FAT_SECTOR; j++) {
                unsigned int c = i * CLUSTERS_PER_FAT_SECTOR + j;
                if ( c > fat_bpb.dataclusters+1 ) /* nr 0 is unused */
                    break;

                if (!(SWAB32(fat[j]) & 0x0fffffff)) {
                    free++;
                    if ( fat_bpb.fsinfo.nextfree == 0xffffffff )
                        fat_bpb.fsinfo.nextfree = c;
                }
            }
        }
        fat_bpb.fsinfo.freecount = free;
    }

    LDEBUGF("Freecount: %d\n",fat_bpb.fsinfo.freecount);
    LDEBUGF("Nextfree: %x\n",fat_bpb.fsinfo.nextfree);
    LDEBUGF("Cluster count: %x\n",fat_bpb.dataclusters);
    LDEBUGF("Sectors per cluster: %d\n",fat_bpb.bpb_secperclus);
    LDEBUGF("FAT sectors: %x\n",fat_bpb.fatsize);

    return 0;
}

static int bpb_is_sane(void)
{
    if(fat_bpb.bpb_bytspersec != 512)
    {
        DEBUGF( "bpb_is_sane() - Error: sector size is not 512 (%d)\n",
                fat_bpb.bpb_bytspersec);
        return -1;
    }
    if(fat_bpb.bpb_secperclus * fat_bpb.bpb_bytspersec > 128*1024)
    {
        DEBUGF( "bpb_is_sane() - Error: cluster size is larger than 128K "
                "(%d * %d = %d)\n",
                fat_bpb.bpb_bytspersec, fat_bpb.bpb_secperclus,
                fat_bpb.bpb_bytspersec * fat_bpb.bpb_secperclus);
        return -2;
    }
    if (fat_bpb.bpb_rsvdseccnt != 32)
    {
        DEBUGF( "bpb_is_sane() - Warning: Reserved sectors is not 32 (%d)\n",
                fat_bpb.bpb_rsvdseccnt);
    }
    if(fat_bpb.bpb_numfats != 2)
    {
        DEBUGF( "bpb_is_sane() - Warning: NumFATS is not 2 (%d)\n",
                fat_bpb.bpb_numfats);
    }
    if(fat_bpb.bpb_media != 0xf0 && fat_bpb.bpb_media < 0xf8)
    {
        DEBUGF( "bpb_is_sane() - Warning: Non-standard "
                "media type (0x%02x)\n",
                fat_bpb.bpb_media);
    }
    if(fat_bpb.last_word != 0xaa55)
    {
        DEBUGF( "bpb_is_sane() - Error: Last word is not "
                "0xaa55 (0x%04x)\n", fat_bpb.last_word);
        return -3;
    }

    if (fat_bpb.fsinfo.freecount >
        (fat_bpb.totalsectors - fat_bpb.firstdatasector)/
        fat_bpb.bpb_secperclus)
    {
        DEBUGF( "bpb_is_sane() - Error: FSInfo.Freecount > disk size "
                 "(0x%04x)\n", fat_bpb.fsinfo.freecount);
        return -4;
    }

    return 0;
}

static void *cache_fat_sector(int fatsector)
{
    int secnum = fatsector + fat_bpb.bpb_rsvdseccnt;
    int cache_index = secnum & FAT_CACHE_MASK;
    struct fat_cache_entry *fce = &fat_cache[cache_index];
    unsigned char *sectorbuf = &fat_cache_sectors[cache_index][0];

    /* Delete the cache entry if it isn't the sector we want */
    if(fce->inuse && fce->secnum != secnum)
    {
        /* Write back if it is dirty */
        if(fce->dirty)
        {
            if(ata_write_sectors(fce->secnum+fat_bpb.startsector, 1,
                                 sectorbuf))
            {
                panicf("cache_fat_sector() - Could not write sector %d\n",
                       secnum);
            }
            if(fat_bpb.bpb_numfats > 1)
            {
                /* Write to the second FAT */
                if(ata_write_sectors(fce->secnum+fat_bpb.startsector+
                                     fat_bpb.fatsize, 1, sectorbuf))
                {
                    panicf("cache_fat_sector() - Could not write sector %d\n",
                           secnum + fat_bpb.fatsize);
                }
            }
        }
        fce->secnum = 8; /* Normally an unused sector */
        fce->dirty = false;
        fce->inuse = false;
    }

    /* Load the sector if it is not cached */
    if(!fce->inuse)
    {
        if(ata_read_sectors(secnum + fat_bpb.startsector,1,
                            sectorbuf))
        {
            DEBUGF( "cache_fat_sector() - Could not read sector %d\n", secnum);
            return NULL;
        }
        fce->inuse = true;
        fce->secnum = secnum;
    }
    return sectorbuf;
}

static unsigned int find_free_cluster(unsigned int startcluster)
{
    unsigned int sector = startcluster / CLUSTERS_PER_FAT_SECTOR;
    unsigned int offset = startcluster % CLUSTERS_PER_FAT_SECTOR;
    unsigned int i;

    /* don't waste time scanning if the disk is already full */
    if (!fat_bpb.fsinfo.freecount)
        return 0;

    for (i = 0; i<fat_bpb.fatsize; i++) {
        unsigned int j;
        unsigned int nr = (i + sector) % fat_bpb.fatsize;
        unsigned int* fat = cache_fat_sector(nr);
        if ( !fat )
            break;
        for (j = 0; j < CLUSTERS_PER_FAT_SECTOR; j++) {
            int k = (j + offset) % CLUSTERS_PER_FAT_SECTOR;
            if (!(SWAB32(fat[k]) & 0x0fffffff)) {
                unsigned int c = nr * CLUSTERS_PER_FAT_SECTOR + k;
                if ( c > fat_bpb.dataclusters+1 ) /* nr 0 is unused */
                    continue;
                LDEBUGF("find_free_cluster(%x) == %x\n",startcluster,c);
                fat_bpb.fsinfo.nextfree = c;
                return c;
            }
        }
        offset = 0;
    }
    LDEBUGF("find_free_cluster(%x) == 0\n",startcluster);
    return 0; /* 0 is an illegal cluster number */
}

static int update_fat_entry(unsigned int entry, unsigned int val)
{
    int sector = entry / CLUSTERS_PER_FAT_SECTOR;
    int offset = entry % CLUSTERS_PER_FAT_SECTOR;
    unsigned int* sec;

    LDEBUGF("update_fat_entry(%x,%x)\n",entry,val);

    if (entry==val)
        panicf("Creating FAT loop: %x,%x\n",entry,val);

    if ( entry < 2 )
        panicf("Updating reserved FAT entry %d.\n",entry);

    sec = cache_fat_sector(sector);
    if (!sec)
    {
        DEBUGF( "update_entry() - Could not cache sector %d\n", sector);
        return -1;
    }
    fat_cache[sector & FAT_CACHE_MASK].dirty = true;

    if ( val ) {
        if (!(SWAB32(sec[offset]) & 0x0fffffff))
            fat_bpb.fsinfo.freecount--;
    }
    else {
        if (SWAB32(sec[offset]) & 0x0fffffff)
            fat_bpb.fsinfo.freecount++;
    }

    LDEBUGF("update_fat_entry: %d free clusters\n", fat_bpb.fsinfo.freecount);

    /* don't change top 4 bits */
    sec[offset] &= SWAB32(0xf0000000);
    sec[offset] |= SWAB32(val & 0x0fffffff);

    return 0;
}

static int read_fat_entry(unsigned int entry)
{
    int sector = entry / CLUSTERS_PER_FAT_SECTOR;
    int offset = entry % CLUSTERS_PER_FAT_SECTOR;
    unsigned int* sec;

    sec = cache_fat_sector(sector);
    if (!sec)
    {
        DEBUGF( "read_fat_entry() - Could not cache sector %d\n", sector);
        return -1;
    }

    return SWAB32(sec[offset]) & 0x0fffffff;
}

static int get_next_cluster(unsigned int cluster)
{
    int next_cluster;

    next_cluster = read_fat_entry(cluster);

    /* is this last cluster in chain? */
    if ( next_cluster >= FAT_EOF_MARK )
        return 0;
    else
        return next_cluster;
}

static int flush_fat(void)
{
    int i;
    int err;
    unsigned char *sec;
    int secnum;
    unsigned char fsinfo[SECTOR_SIZE];
    unsigned int* intptr;

    LDEBUGF("flush_fat()\n");

    for(i = 0;i < FAT_CACHE_SIZE;i++)
    {
        if(fat_cache[i].inuse && fat_cache[i].dirty)
        {
            secnum = fat_cache[i].secnum + fat_bpb.startsector;
            LDEBUGF("Flushing FAT sector %x\n", secnum);
            sec = fat_cache_sectors[i];

            /* Write to the first FAT */
            err = ata_write_sectors(secnum, 1, sec);
            if(err)
            {
                DEBUGF( "flush_fat() - Couldn't write"
                        " sector (%d)\n", secnum);
                return -1;
            }

            if(fat_bpb.bpb_numfats > 1 )
            {
                /* Write to the second FAT */
                err = ata_write_sectors(secnum + fat_bpb.fatsize, 1, sec);
                if (err)
                {
                    DEBUGF( "flush_fat() - Couldn't write"
                             " sector (%d)\n", secnum + fat_bpb.fatsize);
                    return -2;
                }
            }
            fat_cache[i].dirty = false;
        }
    }

    /* update fsinfo */
    err = ata_read_sectors(fat_bpb.startsector + fat_bpb.bpb_fsinfo, 1,fsinfo);
    if (err)
    {
        DEBUGF( "flush_fat() - Couldn't read FSInfo (error code %d)\n", err);
        return -3;
    }
    intptr = (int*)&(fsinfo[FSINFO_FREECOUNT]);
    *intptr = SWAB32(fat_bpb.fsinfo.freecount);

    intptr = (int*)&(fsinfo[FSINFO_NEXTFREE]);
    *intptr = SWAB32(fat_bpb.fsinfo.nextfree);

    err = ata_write_sectors(fat_bpb.startsector + fat_bpb.bpb_fsinfo,1,fsinfo);
    if (err)
    {
        DEBUGF( "flush_fat() - Couldn't write FSInfo (error code %d)\n", err);
        return -4;
    }

    return 0;
}

#ifdef HAVE_RTC
static void fat_time(unsigned short* date,
                     unsigned short* time,
                     unsigned short* tenth )
{
    struct tm* tm = get_time();

    if (date)
        *date = ((tm->tm_year - 80) << 9) |
            ((tm->tm_mon + 1) << 5) |
            tm->tm_mday;

    if (time)
        *time = (tm->tm_hour << 11) |
            (tm->tm_min << 5) |
            (tm->tm_sec >> 1);

    if (tenth)
        *tenth = (tm->tm_sec & 1) * 100;
}
#endif

static int write_long_name(struct fat_file* file,
                           unsigned int firstentry,
                           unsigned int numentries,
                           unsigned char* name,
                           unsigned char* shortname)
{
    unsigned char buf[SECTOR_SIZE];
    unsigned char* entry;
    unsigned int idx = firstentry % DIR_ENTRIES_PER_SECTOR;
    unsigned int sector = firstentry / DIR_ENTRIES_PER_SECTOR;
    unsigned int i, j=0;
    unsigned char chksum = 0;
    int nameidx=0, namelen = strlen(name);
    int rc;

    LDEBUGF("write_long_name(file:%x, first:%d, num:%d, name:%s)\n",
            file->firstcluster, firstentry, numentries, name);

    rc = fat_seek(file, sector);
    if (rc<0)
        return -1;

    rc = fat_readwrite(file, 1, buf, false);
    if (rc<1)
        return -2;

    /* calculate shortname checksum */
    for (i=11; i>0; i--)
        chksum = ((chksum & 1) ? 0x80 : 0) + (chksum >> 1) + shortname[j++];

    /* calc position of last name segment */
    if ( namelen > NAME_BYTES_PER_ENTRY )
        for (nameidx=0;
             nameidx < (namelen - NAME_BYTES_PER_ENTRY);
             nameidx += NAME_BYTES_PER_ENTRY);

    for (i=0; i < numentries; i++) {
        /* new sector? */
        if ( idx >= DIR_ENTRIES_PER_SECTOR ) {
            /* update current sector */
            rc = fat_seek(file, sector);
            if (rc<0)
                return -3;

            rc = fat_readwrite(file, 1, buf, true);
            if (rc<1)
                return -4;

            /* read next sector */
            rc = fat_readwrite(file, 1, buf, false);
            if (rc<0) {
                LDEBUGF("Failed writing new sector: %d\n",rc);
                return -5;
            }
            if (rc==0)
                /* end of dir */
                memset(buf, 0, sizeof buf);

            sector++;
            idx = 0;
        }

        entry = buf + idx * DIR_ENTRY_SIZE;

        /* verify this entry is free */
        if (entry[0] && entry[0] != 0xe5 )
            panicf("Dir entry %d in sector %x is not free! "
                   "%02x %02x %02x %02x",
                   idx, sector,
                   entry[0], entry[1], entry[2], entry[3]);

        memset(entry, 0, DIR_ENTRY_SIZE);
        if ( i+1 < numentries ) {
            /* longname entry */
            int k, l = nameidx;

            entry[FATLONG_ORDER] = numentries-i-1;
            if (i==0) {
                /* mark this as last long entry */
                entry[FATLONG_ORDER] |= 0x40;

                /* pad name with 0xffff  */
                for (k=1; k<12; k++) entry[k] = 0xff;
                for (k=14; k<26; k++) entry[k] = 0xff;
                for (k=28; k<32; k++) entry[k] = 0xff;
            };
            /* set name */
            for (k=0; k<5 && l <= namelen; k++) {
                entry[k*2 + 1] = name[l++];
                entry[k*2 + 2] = 0;
            }
            for (k=0; k<6 && l <= namelen; k++) {
                entry[k*2 + 14] = name[l++];
                entry[k*2 + 15] = 0;
            }
            for (k=0; k<2 && l <= namelen; k++) {
                entry[k*2 + 28] = name[l++];
                entry[k*2 + 29] = 0;
            }

            entry[FATDIR_ATTR] = FAT_ATTR_LONG_NAME;
            entry[FATDIR_FSTCLUSLO] = 0;
            entry[FATLONG_TYPE] = 0;
            entry[FATLONG_CHKSUM] = chksum;
            LDEBUGF("Longname entry %d: %.13s\n", idx, name+nameidx);
        }
        else {
            /* shortname entry */
            unsigned short date=0, time=0, tenth=0;
            LDEBUGF("Shortname entry: %.13s\n", shortname);
            strncpy(entry + FATDIR_NAME, shortname, 11);
            entry[FATDIR_ATTR] = 0;
            entry[FATDIR_NTRES] = 0;

#ifdef HAVE_RTC
            fat_time(&date, &time, &tenth);
#endif
            entry[FATDIR_CRTTIMETENTH] = tenth;
            *(unsigned short*)(entry + FATDIR_CRTTIME) = SWAB16(time);
            *(unsigned short*)(entry + FATDIR_WRTTIME) = SWAB16(time);
            *(unsigned short*)(entry + FATDIR_CRTDATE) = SWAB16(date);
            *(unsigned short*)(entry + FATDIR_WRTDATE) = SWAB16(date);
            *(unsigned short*)(entry + FATDIR_LSTACCDATE) = SWAB16(date);
        }
        idx++;
        nameidx -= NAME_BYTES_PER_ENTRY;
    }

    /* update last sector */
    rc = fat_seek(file, sector);
    if (rc<0)
        return -5;

    rc = fat_readwrite(file, 1, buf, true);
    if (rc<1)
        return -6;
    
    return 0;
}

static int add_dir_entry(struct fat_dir* dir,
                         struct fat_file* file,
                         char* name)
{
    unsigned char buf[SECTOR_SIZE];
    unsigned char shortname[16];
    int err;
    unsigned int sector;
    bool done = false;
    bool eof = false;
    bool last = false;
    int entries_needed, entries_found = 0;
    int namelen = strlen(name);
    int firstentry;

    LDEBUGF( "add_dir_entry(%s,%x)\n",
             name, file->firstcluster);

    /* create dos name */
    if (create_dos_name(name, shortname) < 0)
        return -1;

    /* one dir entry needed for every 13 bytes of filename,
       plus one entry for the short name */
    entries_needed = namelen / NAME_BYTES_PER_ENTRY + 1;
    if (namelen % NAME_BYTES_PER_ENTRY)
        entries_needed++;

 restart:
    firstentry = 0;

    err=fat_seek(&dir->file, 0);
    if (err<0)
        return -1;

    for (sector=0; !done; sector++)
    {
        unsigned int i;

        err = 0;
        if (!eof) {
            err = fat_readwrite(&dir->file, 1, buf, false);
        }
        if (err==0) {
            /* eof: add new sector */
            eof = true;

            memset(buf, 0, sizeof buf);
            LDEBUGF("Adding new sector to dir\n");
            err=fat_seek(&dir->file, sector);
            if (err<0)
                return -2;

            /* add sectors (we must clear the whole cluster) */
            do {
                err = fat_readwrite(&dir->file, 1, buf, true);
                if (err<1)
                    return -3;
            } while (dir->file.sectornum < (int)fat_bpb.bpb_secperclus);
        }
        if (err<0) {
            DEBUGF( "add_dir_entry() - Couldn't read dir"
                    " (error code %d)\n", err);
            return -4;
        }

        /* look for free slots */
        for (i=0; i < DIR_ENTRIES_PER_SECTOR && !done; i++)
        {
            unsigned char firstbyte = buf[i * DIR_ENTRY_SIZE];
            switch (firstbyte) {
            case 0: /* end of dir */
                entries_found = entries_needed;
                LDEBUGF("Found last entry %d\n", 
                        sector * DIR_ENTRIES_PER_SECTOR + i);
                done = true;
                break;

            case 0xe5: /* free entry */
                entries_found++;
                LDEBUGF("Found free entry %d (%d/%d)\n",
                        sector * DIR_ENTRIES_PER_SECTOR + i,
                        entries_found, entries_needed);
                break;

            default:
                entries_found = 0;

                /* check that our intended shortname doesn't already exist */
                if (!strncmp(shortname, buf + i * DIR_ENTRY_SIZE, 12)) {
                    /* filename exists already. make a new one */
                    snprintf(shortname+8, 4, "%03X", (unsigned)rand() & 0xfff);
                    LDEBUGF("Duplicate shortname, changing to %s\n",
                            shortname);

                    /* name has changed, we need to restart search */
                    goto restart;
                }
                break;
            }

            if (!firstentry && (entries_found == entries_needed)) {
                firstentry = sector * DIR_ENTRIES_PER_SECTOR + i;

                /* if we're not extending the dir,
                   we must go back to first free entry */
                if (done)
                    last = true;
                else
                    firstentry -= (entries_needed - 1);
            }
        }
    }

    sector = firstentry / DIR_ENTRIES_PER_SECTOR;
    LDEBUGF("Adding longname to entry %d in sector %d\n",
            firstentry, sector);

    err = write_long_name(&dir->file, firstentry, 
                          entries_needed, name, shortname);
    if (err < 0)
        return -5;

    /* remember where the shortname dir entry is located */
    file->direntry = firstentry + entries_needed - 1;
    file->direntries = entries_needed;
    file->dircluster = dir->file.firstcluster;
    LDEBUGF("Added new dir entry %d, using %d slots.\n",
            file->direntry, file->direntries);

    /* advance the end-of-dir marker? */
    if (last)
    {
        unsigned int lastentry = firstentry + entries_needed;

        LDEBUGF("Updating end-of-dir entry %d\n",lastentry);

        if (lastentry % DIR_ENTRIES_PER_SECTOR)
        {
            int idx = (lastentry % DIR_ENTRIES_PER_SECTOR) * DIR_ENTRY_SIZE;

            err=fat_seek(&dir->file, lastentry / DIR_ENTRIES_PER_SECTOR);
            if (err<0)
                return -6;

            err = fat_readwrite(&dir->file, 1, buf, false);
            if (err<1)
                return -7;

            /* clear last entry */
            buf[idx] = 0;

            err=fat_seek(&dir->file, lastentry / DIR_ENTRIES_PER_SECTOR);
            if (err<0)
                return -8;
            
            /* we must clear entire last cluster */
            do {
                err = fat_readwrite(&dir->file, 1, buf, true);
                if (err<1)
                    return -9;
                memset(buf, 0, sizeof buf);
            } while (dir->file.sectornum < (int)fat_bpb.bpb_secperclus);
        }
        else
        {
            /* add a new sector/cluster for last entry */
            memset(buf, 0, sizeof buf);
            do {
                err = fat_readwrite(&dir->file, 1, buf, true);
                if (err<1)
                    return -10;
            } while (dir->file.sectornum < (int)fat_bpb.bpb_secperclus);
        }
    }

    return 0;
}

unsigned char char2dos(unsigned char c)
{
    switch(c)
    {
        case 0xe5: /* Special kanji character */
            c = 0x05;
            break;
        case 0x20:
        case 0x22:
        case 0x2a:
        case 0x2b:
        case 0x2c:
        case 0x2e:
        case 0x3a:
        case 0x3b:
        case 0x3c:
        case 0x3d:
        case 0x3e:
        case 0x3f:
        case 0x5b:
        case 0x5c:
        case 0x5d:
        case 0x7c:
            /* Illegal name */
            c = 0;
            break;
                
        default:
            if(c < 0x20)
            {
                /* Illegal name */
                c = 0;
            }
            break;
    }
    return c;
}

static int create_dos_name(unsigned char *name, unsigned char *newname)
{
    int i,j;

    /* Name part */
    for (i=0, j=0; name[i] && (j < 8); i++)
    {
        unsigned char c = char2dos(name[i]);
        if (c)
            newname[j++] = toupper(c);
    }
    while (j < 8)
        newname[j++] = ' ';

    /* Extension part */
    snprintf(newname+8, 4, "%03X", (unsigned)rand() & 0xfff);

    return 0;
}

static int update_file_size( struct fat_file* file, int size )
{
    unsigned char buf[SECTOR_SIZE];
    int sector = file->direntry / DIR_ENTRIES_PER_SECTOR;
    unsigned char* entry =
        buf + DIR_ENTRY_SIZE * (file->direntry % DIR_ENTRIES_PER_SECTOR);
    unsigned int* sizeptr;
    unsigned short* clusptr;
    struct fat_file dir;
    int err;

    LDEBUGF("update_file_size(cluster:%x entry:%d size:%d)\n",
            file->firstcluster, file->direntry, size);

    /* create a temporary file handle for the dir holding this file */
    err = fat_open(file->dircluster, &dir, NULL);
    if (err<0)
        return -1;

    err = fat_seek( &dir, sector );
    if (err<0)
        return -2;

    err = fat_readwrite(&dir, 1, buf, false);
    if (err<1)
        return -3;

    if (!entry[0] || entry[0] == 0xe5)
        panicf("Updating size on empty dir entry %d\n", file->direntry);
        
    clusptr = (short*)(entry + FATDIR_FSTCLUSHI);
    *clusptr = SWAB16(file->firstcluster >> 16);
    
    clusptr = (short*)(entry + FATDIR_FSTCLUSLO);
    *clusptr = SWAB16(file->firstcluster & 0xffff);

    sizeptr = (int*)(entry + FATDIR_FILESIZE);
    *sizeptr = SWAB32(size);

#ifdef HAVE_RTC
    {
        unsigned short date=0, time=0;
        fat_time(&date, &time, NULL);
        *(unsigned short*)(entry + FATDIR_WRTTIME) = SWAB16(time);
        *(unsigned short*)(entry + FATDIR_WRTDATE) = SWAB16(date);
        *(unsigned short*)(entry + FATDIR_LSTACCDATE) = SWAB16(date);
    }
#endif

    err = fat_seek( &dir, sector );
    if (err<0)
        return -4;

    err = fat_readwrite(&dir, 1, buf, true);
    if (err<1)
        return -5;

    return 0;
}

static int parse_direntry(struct fat_direntry *de, unsigned char *buf)
{
    int i=0,j=0;
    memset(de, 0, sizeof(struct fat_direntry));
    de->attr = buf[FATDIR_ATTR];
    de->crttimetenth = buf[FATDIR_CRTTIMETENTH];
    de->crtdate = BYTES2INT16(buf,FATDIR_CRTDATE);
    de->crttime = BYTES2INT16(buf,FATDIR_CRTTIME);
    de->wrtdate = BYTES2INT16(buf,FATDIR_WRTDATE);
    de->wrttime = BYTES2INT16(buf,FATDIR_WRTTIME);
    de->filesize = BYTES2INT32(buf,FATDIR_FILESIZE);
    de->firstcluster = BYTES2INT16(buf,FATDIR_FSTCLUSLO) |
                      (BYTES2INT16(buf,FATDIR_FSTCLUSHI) << 16);

    /* fix the name */
    for (i=0; (i<8) && (buf[FATDIR_NAME+i] != ' '); i++)
        de->name[j++] = buf[FATDIR_NAME+i];
    if ( buf[FATDIR_NAME+8] != ' ' ) {
        de->name[j++] = '.';
        for (i=8; (i<11) && (buf[FATDIR_NAME+i] != ' '); i++)
            de->name[j++] = buf[FATDIR_NAME+i];
    }
    return 1;
}

int fat_open(unsigned int startcluster,
             struct fat_file *file,
             struct fat_dir* dir)
{
    file->firstcluster = startcluster;
    file->lastcluster = startcluster;
    file->lastsector = 0;
    file->sectornum = 0;
    file->eof = false;

    /* remember where the file's dir entry is located */
    if ( dir ) {
        file->direntry = dir->entry - 1;
        file->direntries = dir->entrycount;
        file->dircluster = dir->file.firstcluster;
    }
    LDEBUGF("fat_open(%x), entry %d\n",startcluster,file->direntry);
    return 0;
}

int fat_create_file(char* name,
                    struct fat_file* file,
                    struct fat_dir* dir)
{
    int err;

    LDEBUGF("fat_create_file(\"%s\",%x,%x)\n",name,file,dir);
    err = add_dir_entry(dir, file, name);
    if (!err) {
        file->firstcluster = 0;
        file->lastcluster = 0;
        file->lastsector = 0;
        file->sectornum = 0;
        file->eof = false;
    }

    return err;
}

int fat_truncate(struct fat_file *file)
{
    /* truncate trailing clusters */
    int next;
    int last = file->lastcluster;

    LDEBUGF("fat_truncate(%x, %x)\n", file->firstcluster, last);

    for ( last = get_next_cluster(last); last; last = next ) {
        next = get_next_cluster(last);
        update_fat_entry(last,0);
    }
    if (file->lastcluster)
        update_fat_entry(file->lastcluster,FAT_EOF_MARK);

    return 0;
}

int fat_closewrite(struct fat_file *file, int size)
{
    LDEBUGF("fat_closewrite(size=%d)\n",size);

    if (!size) {
        /* empty file */
        if ( file->firstcluster ) {
            update_fat_entry(file->firstcluster, 0);
            file->firstcluster = 0;
        }
    }

    if (file->dircluster)
        if (update_file_size(file, size) < 0)
            return -1;

    flush_fat();

#ifdef TEST_FAT
    if ( file->firstcluster ) {
        /* debug */
        int count = 0;
        int len;
        int next;
        for ( next = file->firstcluster; next;
              next = get_next_cluster(next) )
            LDEBUGF("cluster %d: %x\n", count++, next);
        len = count * fat_bpb.bpb_secperclus * SECTOR_SIZE;
        LDEBUGF("File is %d clusters (chainlen=%d, size=%d)\n",
                count, len, size );
        if ( len > size + fat_bpb.bpb_secperclus * SECTOR_SIZE)
            panicf("Cluster chain is too long\n");
        if ( len < size )
            panicf("Cluster chain is too short\n");
    }
#endif

    return 0;
}

static int free_direntries(int dircluster, int startentry, int numentries)
{
    unsigned char buf[SECTOR_SIZE];
    struct fat_file dir;
    unsigned int entry = startentry - numentries + 1;
    unsigned int sector = entry / DIR_ENTRIES_PER_SECTOR;
    int i;
    int err;

    /* create a temporary file handle for the dir holding this file */
    err = fat_open(dircluster, &dir, NULL);
    if (err<0)
        return -1;

    err = fat_seek( &dir, sector );
    if (err<0)
        return -2;

    err = fat_readwrite(&dir, 1, buf, false);
    if (err<1)
        return -3;

    for (i=0; i < numentries; i++) {
        LDEBUGF("Clearing dir entry %d (%d/%d)\n",
                entry, i+1, numentries);
        buf[(entry % DIR_ENTRIES_PER_SECTOR) * DIR_ENTRY_SIZE] = 0xe5;
        entry++;

        if ( (entry % DIR_ENTRIES_PER_SECTOR) == 0 ) {
            /* flush this sector */
            err = fat_seek(&dir, sector);
            if (err<0)
                return -4;

            err = fat_readwrite(&dir, 1, buf, true);
            if (err<1)
                return -5;

            if ( i+1 < numentries ) {
                /* read next sector */
                err = fat_readwrite(&dir, 1, buf, false);
                if (err<1)
                    return -6;
            }
            sector++;
        }
    }

    if ( entry % DIR_ENTRIES_PER_SECTOR ) {
        /* flush this sector */
        err = fat_seek(&dir, sector);
        if (err<0)
            return -7;
            
        err = fat_readwrite(&dir, 1, buf, true);
        if (err<1)
            return -8;
    }

    return 0;
}

int fat_remove(struct fat_file* file)
{
    int next, last = file->firstcluster;

    LDEBUGF("fat_remove(%x)\n",last);

    while ( last ) {
        next = get_next_cluster(last);
        update_fat_entry(last,0);
        last = next;
    }

    if ( file->dircluster )
        if ( free_direntries(file->dircluster, 
                             file->direntry, 
                             file->direntries) < 0 )
            return -1;

    file->firstcluster = 0;
    file->dircluster = 0;

    return 0;
}

int fat_rename(struct fat_file* file, 
               unsigned char* newname,
               int size)
{
    int err;
    struct fat_dir dir;
    struct fat_file newfile = *file;

    if ( !file->dircluster ) {
        DEBUGF("File has no dir cluster!\n");
        return -1;
    }

    /* create a temporary file handle */
    err = fat_opendir(&dir, file->dircluster);
    if (err<0)
        return -2;

    /* create new name */
    err = add_dir_entry(&dir, &newfile, newname);
    if (err<0)
        return -3;

    /* write size and cluster link */
    err = update_file_size(&newfile, size);
    if (err<0)
        return -4;

    /* remove old name */
    err = free_direntries(file->dircluster, file->direntry, file->direntries);
    if (err<0)
        return -5;

    err = flush_fat();
    if (err<0)
        return -6;

    return 0;
}


static int next_write_cluster(struct fat_file* file,
                              int oldcluster,
                              int* newsector)
{
    int cluster = 0;
    int sector;

    LDEBUGF("next_write_cluster(%x,%x)\n",file->firstcluster, oldcluster);

    if (oldcluster)
        cluster = get_next_cluster(oldcluster);

    if (!cluster) {
        if (oldcluster)
            cluster = find_free_cluster(oldcluster+1);
        else
            cluster = find_free_cluster(fat_bpb.fsinfo.nextfree);

        if (cluster) {
            if (oldcluster)
                update_fat_entry(oldcluster, cluster); 
            else
                file->firstcluster = cluster;
            update_fat_entry(cluster, FAT_EOF_MARK); 
        }
        else {
#ifdef TEST_FAT
            if (fat_bpb.fsinfo.freecount>0)
                panicf("There is free space, but find_free_cluster() "
                       "didn't find it!\n");
#endif
            DEBUGF("next_write_cluster(): Disk full!\n");
            return 0;
        }
    }
    sector = cluster2sec(cluster);
    if (sector<0)
        return 0;

    *newsector = sector;
    return cluster;
}

static bool transfer( unsigned int start, int count, char* buf, bool write )
{
    int err;

    LDEBUGF("transfer(s=%x, c=%x, %s)\n",start, count, write?"write":"read");
    if (write) {
        if (start < fat_bpb.firstdatasector)
            panicf("Writing before data\n");
        err = ata_write_sectors(start, count, buf);
    }
    else
        err = ata_read_sectors(start, count, buf);
    if (err) {
        DEBUGF( "transfer() - Couldn't %s sector %x"
                " (error code %d)\n", 
                write ? "write":"read", start, err);
        return false;
    }
    return true;
}


int fat_readwrite( struct fat_file *file, int sectorcount, 
                   void* buf, bool write )
{
    int cluster = file->lastcluster;
    int sector = file->lastsector;
    int numsec = file->sectornum;
    bool eof = file->eof;
    int first=0, last=0;
    int i;

    LDEBUGF( "fat_readwrite(file:%x,count:0x%x,buf:%x,%s)\n",
             file->firstcluster,sectorcount,buf,write?"write":"read");
    LDEBUGF( "fat_readwrite: sec=%x numsec=%d eof=%d\n",
             sector,numsec, eof?1:0);

    if ( eof && !write)
        return 0;

    /* find sequential sectors and write them all at once */
    for (i=0; (i < sectorcount) && (sector > -1); i++ ) {
        numsec++;
        if ( numsec > (int)fat_bpb.bpb_secperclus || !cluster ) {
            int oldcluster = cluster;
            if (write)
                cluster = next_write_cluster(file, cluster, &sector);
            else {
                cluster = get_next_cluster(cluster);
                sector = cluster2sec(cluster);
            }
            if (!cluster) {
                eof = true;
                if ( write ) {
                    /* remember last cluster, in case 
                       we want to append to the file */
                    cluster = oldcluster;
                }
            }
            else
                eof = false;
            numsec=1;
        }
        else {
            if (sector)
                sector++;
            else {
                /* look up first sector of file */
                sector = cluster2sec(file->firstcluster);
                numsec=1;
            }
        }

        if (!first)
            first = sector;

        if ( ((sector != first) && (sector != last+1)) || /* not sequential */
             (last-first+1 == 256) ) { /* max 256 sectors per ata request */
            int count = last - first + 1;
            if (!transfer( first + fat_bpb.startsector, count, buf, write ))
                return -2;

            ((char*)buf) += count * SECTOR_SIZE;
            first = sector;
        }

        if ((i == sectorcount-1) && /* last sector requested */
            (!eof))
        {
            int count = sector - first + 1;
            if (!transfer( first + fat_bpb.startsector, 
                           count, buf, write ))
                    return -2;
        }

        last = sector;
    }

    file->lastcluster = cluster;
    file->lastsector = sector;
    file->sectornum = numsec;
    file->eof = eof;

    /* if eof, don't report last block as read/written */
    if (eof)
        i--;

    return i;
}

int fat_seek(struct fat_file *file, unsigned int seeksector )
{
    int clusternum=0, sectornum=0, sector=0;
    int cluster = file->firstcluster;
    int i;

    file->eof = false;
    if (seeksector) {
        /* we need to find the sector BEFORE the requested, since
           the file struct stores the last accessed sector */
        seeksector--;
        clusternum = seeksector / fat_bpb.bpb_secperclus;
        sectornum = seeksector % fat_bpb.bpb_secperclus;

        
        for (i=0; i<clusternum; i++) {
            cluster = get_next_cluster(cluster);
            if (!cluster) {
                DEBUGF("Seeking beyond the end of the file! "
                       "(sector %d, cluster %d)\n", seeksector, i);
                return -1;
            }
        }
        
        sector = cluster2sec(cluster) + sectornum;
    }
    else {
        sectornum = -1;
    }

    LDEBUGF("fat_seek(%x, %x) == %x, %x, %x\n",
            file->firstcluster, seeksector, cluster, sector, sectornum);

    file->lastcluster = cluster;
    file->lastsector = sector;
    file->sectornum = sectornum + 1;
    return 0;
}

int fat_opendir(struct fat_dir *dir, unsigned int startcluster)
{
    int err;

    if (startcluster == 0)
        startcluster = sec2cluster(fat_bpb.rootdirsector);

    err = fat_open(startcluster, &dir->file, NULL);
    if(err)
    {
        DEBUGF( "fat_opendir() - Couldn't open dir"
                " (error code %d)\n", err);
        return -1;
    }

    dir->entry = 0;
    dir->sector = 0;

    return 0;
}

int fat_getnext(struct fat_dir *dir, struct fat_direntry *entry)
{
    bool done = false;
    int i;
    int err;
    unsigned char firstbyte;
    int longarray[20];
    int longs=0;
    int sectoridx=0;
    static unsigned char cached_buf[SECTOR_SIZE];

    dir->entrycount = 0;

    while(!done)
    {
        if ( !(dir->entry % DIR_ENTRIES_PER_SECTOR) || !dir->sector )
        {
            err = fat_readwrite(&dir->file, 1, cached_buf, false);
            if (err==0) {
                /* eof */
                entry->name[0] = 0;
                break;
            }
            if (err<0) {
                DEBUGF( "fat_getnext() - Couldn't read dir"
                        " (error code %d)\n", err);
                return -1;
            }
            dir->sector = dir->file.lastsector;
        }

        for (i = dir->entry % DIR_ENTRIES_PER_SECTOR;
             i < DIR_ENTRIES_PER_SECTOR; i++)
        {
            unsigned int entrypos = i * DIR_ENTRY_SIZE;

            firstbyte = cached_buf[entrypos];
            dir->entry++;

            if (firstbyte == 0xe5) {
                /* free entry */
                sectoridx = 0;
                dir->entrycount = 0;
                continue;
            }

            if (firstbyte == 0) {
                /* last entry */
                entry->name[0] = 0;
                dir->entrycount = 0;
                return 0;
            }

            dir->entrycount++;

            /* longname entry? */
            if ( ( cached_buf[entrypos + FATDIR_ATTR] &
                   FAT_ATTR_LONG_NAME_MASK ) == FAT_ATTR_LONG_NAME ) {
                longarray[longs++] = entrypos + sectoridx;
            }
            else {
                if ( parse_direntry(entry,
                                    &cached_buf[entrypos]) ) {

                    /* don't return volume id entry */
                    if ( entry->attr == FAT_ATTR_VOLUME_ID )
                        continue;

                    /* replace shortname with longname? */
                    if ( longs ) {
                        int j,k,l=0;
                        /* iterate backwards through the dir entries */
                        for (j=longs-1; j>=0; j--) {
                            unsigned char* ptr = cached_buf;
                            int index = longarray[j];
                            /* current or cached sector? */
                            if ( sectoridx >= SECTOR_SIZE ) {
                                if ( sectoridx >= SECTOR_SIZE*2 ) {
                                    if ( ( index >= SECTOR_SIZE ) &&
                                         ( index < SECTOR_SIZE*2 ))
                                        ptr = lastsector;
                                    else
                                        ptr = lastsector2;
                                }
                                else {
                                    if ( index < SECTOR_SIZE )
                                        ptr = lastsector;
                                }

                                index &= SECTOR_SIZE-1;
                            }

                            /* names are stored in unicode, but we
                               only grab the low byte (iso8859-1). */
                            for (k=0; k<5; k++)
                                entry->name[l++] = ptr[index + k*2 + 1];
                            for (k=0; k<6; k++)
                                entry->name[l++] = ptr[index + k*2 + 14];
                            for (k=0; k<2; k++)
                                entry->name[l++] = ptr[index + k*2 + 28];
                        }
                        entry->name[l]=0;
                    }
                    done = true;
                    sectoridx = 0;
                    i++;
                    break;
                }
            }
        }

        /* save this sector, for longname use */
        if ( sectoridx )
            memcpy( lastsector2, cached_buf, SECTOR_SIZE );
        else
            memcpy( lastsector, cached_buf, SECTOR_SIZE );
        sectoridx += SECTOR_SIZE;

    }
    return 0;
}

/* -----------------------------------------------------------------
 * local variables:
 * eval: (load-file "../rockbox-mode.el")
 * end:
 */