/*
 * fat_write.c
 *
 * R/W (V)FAT 12/16/32 filesystem implementation by Donggeun Kim
 *
 * SPDX-License-Identifier:     GPL-2.0+
 */

#include <common.h>
#include <command.h>
#include <config.h>
#include <fat.h>
#include <asm/byteorder.h>
#include <part.h>
#include <linux/ctype.h>
#include <div64.h>
#include <linux/math64.h>
#include "fat.c"

static void uppercase(char *str, int len)
{
        int i;

        for (i = 0; i < len; i++) {
                *str = toupper(*str);
                str++;
        }
}

static int total_sector;
static int disk_write(__u32 block, __u32 nr_blocks, void *buf)
{
        ulong ret;

        if (!cur_dev)
                return -1;

        if (cur_part_info.start + block + nr_blocks >
                cur_part_info.start + total_sector) {
                printf("error: overflow occurs\n");
                return -1;
        }

        ret = blk_dwrite(cur_dev, cur_part_info.start + block, nr_blocks, buf);
        if (nr_blocks && ret == 0)
                return -1;

        return ret;
}

/*
 * Set short name in directory entry
 */
static void set_name(dir_entry *dirent, const char *filename)
{
        char s_name[VFAT_MAXLEN_BYTES];
        char *period;
        int period_location, len, i, ext_num;

        if (filename == NULL)
                return;

        len = strlen(filename);
        if (len == 0)
                return;

        strcpy(s_name, filename);
        uppercase(s_name, len);

        period = strchr(s_name, '.');
        if (period == NULL) {
                period_location = len;
                ext_num = 0;
        } else {
                period_location = period - s_name;
                ext_num = len - period_location - 1;
        }

        /* Pad spaces when the length of file name is shorter than eight */
        if (period_location < 8) {
                memcpy(dirent->name, s_name, period_location);
                for (i = period_location; i < 8; i++)
                        dirent->name[i] = ' ';
        } else if (period_location == 8) {
                memcpy(dirent->name, s_name, period_location);
        } else {
                memcpy(dirent->name, s_name, 6);
                dirent->name[6] = '~';
                dirent->name[7] = '1';
        }

        if (ext_num < 3) {
                memcpy(dirent->ext, s_name + period_location + 1, ext_num);
                for (i = ext_num; i < 3; i++)
                        dirent->ext[i] = ' ';
        } else
                memcpy(dirent->ext, s_name + period_location + 1, 3);

        debug("name : %s\n", dirent->name);
        debug("ext : %s\n", dirent->ext);
}

static __u8 num_of_fats;
/*
 * Write fat buffer into block device
 */
static int flush_dirty_fat_buffer(fsdata *mydata)
{
        int getsize = FATBUFBLOCKS;
        __u32 fatlength = mydata->fatlength;
        __u8 *bufptr = mydata->fatbuf;
        __u32 startblock = mydata->fatbufnum * FATBUFBLOCKS;

        debug("debug: evicting %d, dirty: %d\n", mydata->fatbufnum,
              (int)mydata->fat_dirty);

        if ((!mydata->fat_dirty) || (mydata->fatbufnum == -1))
                return 0;

        /* Cap length if fatlength is not a multiple of FATBUFBLOCKS */
        if (startblock + getsize > fatlength)
                getsize = fatlength - startblock;

        startblock += mydata->fat_sect;

        /* Write FAT buf */
        if (disk_write(startblock, getsize, bufptr) < 0) {
                debug("error: writing FAT blocks\n");
                return -1;
        }

        if (num_of_fats == 2) {
                /* Update corresponding second FAT blocks */
                startblock += mydata->fatlength;
                if (disk_write(startblock, getsize, bufptr) < 0) {
                        debug("error: writing second FAT blocks\n");
                        return -1;
                }
        }
        mydata->fat_dirty = 0;

        return 0;
}

/*
 * Set the file name information from 'name' into 'slotptr',
 */
static int str2slot(dir_slot *slotptr, const char *name, int *idx)
{
        int j, end_idx = 0;

        for (j = 0; j <= 8; j += 2) {
                if (name[*idx] == 0x00) {
                        slotptr->name0_4[j] = 0;
                        slotptr->name0_4[j + 1] = 0;
                        end_idx++;
                        goto name0_4;
                }
                slotptr->name0_4[j] = name[*idx];
                (*idx)++;
                end_idx++;
        }
        for (j = 0; j <= 10; j += 2) {
                if (name[*idx] == 0x00) {
                        slotptr->name5_10[j] = 0;
                        slotptr->name5_10[j + 1] = 0;
                        end_idx++;
                        goto name5_10;
                }
                slotptr->name5_10[j] = name[*idx];
                (*idx)++;
                end_idx++;
        }
        for (j = 0; j <= 2; j += 2) {
                if (name[*idx] == 0x00) {
                        slotptr->name11_12[j] = 0;
                        slotptr->name11_12[j + 1] = 0;
                        end_idx++;
                        goto name11_12;
                }
                slotptr->name11_12[j] = name[*idx];
                (*idx)++;
                end_idx++;
        }

        if (name[*idx] == 0x00)
                return 1;

        return 0;
/* Not used characters are filled with 0xff 0xff */
name0_4:
        for (; end_idx < 5; end_idx++) {
                slotptr->name0_4[end_idx * 2] = 0xff;
                slotptr->name0_4[end_idx * 2 + 1] = 0xff;
        }
        end_idx = 5;
name5_10:
        end_idx -= 5;
        for (; end_idx < 6; end_idx++) {
                slotptr->name5_10[end_idx * 2] = 0xff;
                slotptr->name5_10[end_idx * 2 + 1] = 0xff;
        }
        end_idx = 11;
name11_12:
        end_idx -= 11;
        for (; end_idx < 2; end_idx++) {
                slotptr->name11_12[end_idx * 2] = 0xff;
                slotptr->name11_12[end_idx * 2 + 1] = 0xff;
        }

        return 1;
}

static int is_next_clust(fsdata *mydata, dir_entry *dentptr);
static void flush_dir_table(fsdata *mydata, dir_entry **dentptr);

/*
 * Fill dir_slot entries with appropriate name, id, and attr
 * The real directory entry is returned by 'dentptr'
 */
static void
fill_dir_slot(fsdata *mydata, dir_entry **dentptr, const char *l_name)
{
        __u8 temp_dir_slot_buffer[MAX_LFN_SLOT * sizeof(dir_slot)];
        dir_slot *slotptr = (dir_slot *)temp_dir_slot_buffer;
        __u8 counter = 0, checksum;
        int idx = 0, ret;

        /* Get short file name checksum value */
        checksum = mkcksum((*dentptr)->name, (*dentptr)->ext);

        do {
                memset(slotptr, 0x00, sizeof(dir_slot));
                ret = str2slot(slotptr, l_name, &idx);
                slotptr->id = ++counter;
                slotptr->attr = ATTR_VFAT;
                slotptr->alias_checksum = checksum;
                slotptr++;
        } while (ret == 0);

        slotptr--;
        slotptr->id |= LAST_LONG_ENTRY_MASK;

        while (counter >= 1) {
                if (is_next_clust(mydata, *dentptr)) {
                        /* A new cluster is allocated for directory table */
                        flush_dir_table(mydata, dentptr);
                }
                memcpy(*dentptr, slotptr, sizeof(dir_slot));
                (*dentptr)++;
                slotptr--;
                counter--;
        }

        if (is_next_clust(mydata, *dentptr)) {
                /* A new cluster is allocated for directory table */
                flush_dir_table(mydata, dentptr);
        }
}

static __u32 dir_curclust;

/*
 * Extract the full long filename starting at 'retdent' (which is really
 * a slot) into 'l_name'. If successful also copy the real directory entry
 * into 'retdent'
 * If additional adjacent cluster for directory entries is read into memory,
 * then 'get_contents_vfatname_block' is copied into 'get_dentfromdir_block' and
 * the location of the real directory entry is returned by 'retdent'
 * Return 0 on success, -1 otherwise.
 */
static int
get_long_file_name(fsdata *mydata, int curclust, __u8 *cluster,
              dir_entry **retdent, char *l_name)
{
        dir_entry *realdent;
        dir_slot *slotptr = (dir_slot *)(*retdent);
        dir_slot *slotptr2 = NULL;
        __u8 *buflimit = cluster + mydata->sect_size * ((curclust == 0) ?
                                                        PREFETCH_BLOCKS :
                                                        mydata->clust_size);
        __u8 counter = (slotptr->id & ~LAST_LONG_ENTRY_MASK) & 0xff;
        int idx = 0, cur_position = 0;

        if (counter > VFAT_MAXSEQ) {
                debug("Error: VFAT name is too long\n");
                return -1;
        }

        while ((__u8 *)slotptr < buflimit) {
                if (counter == 0)
                        break;
                if (((slotptr->id & ~LAST_LONG_ENTRY_MASK) & 0xff) != counter)
                        return -1;
                slotptr++;
                counter--;
        }

        if ((__u8 *)slotptr >= buflimit) {
                if (curclust == 0)
                        return -1;
                curclust = get_fatent(mydata, dir_curclust);
                if (CHECK_CLUST(curclust, mydata->fatsize)) {
                        debug("curclust: 0x%x\n", curclust);
                        printf("Invalid FAT entry\n");
                        return -1;
                }

                dir_curclust = curclust;

                if (get_cluster(mydata, curclust, get_contents_vfatname_block,
                                mydata->clust_size * mydata->sect_size) != 0) {
                        debug("Error: reading directory block\n");
                        return -1;
                }

                slotptr2 = (dir_slot *)get_contents_vfatname_block;
                while (counter > 0) {
                        if (((slotptr2->id & ~LAST_LONG_ENTRY_MASK)
                            & 0xff) != counter)
                                return -1;
                        slotptr2++;
                        counter--;
                }

                /* Save the real directory entry */
                realdent = (dir_entry *)slotptr2;
                while ((__u8 *)slotptr2 > get_contents_vfatname_block) {
                        slotptr2--;
                        slot2str(slotptr2, l_name, &idx);
                }
        } else {
                /* Save the real directory entry */
                realdent = (dir_entry *)slotptr;
        }

        do {
                slotptr--;
                if (slot2str(slotptr, l_name, &idx))
                        break;
        } while (!(slotptr->id & LAST_LONG_ENTRY_MASK));

        l_name[idx] = '\0';
        if (*l_name == DELETED_FLAG)
                *l_name = '\0';
        else if (*l_name == aRING)
                *l_name = DELETED_FLAG;
        downcase(l_name);

        /* Return the real directory entry */
        *retdent = realdent;

        if (slotptr2) {
                memcpy(get_dentfromdir_block, get_contents_vfatname_block,
                        mydata->clust_size * mydata->sect_size);
                cur_position = (__u8 *)realdent - get_contents_vfatname_block;
                *retdent = (dir_entry *) &get_dentfromdir_block[cur_position];
        }

        return 0;
}

/*
 * Set the entry at index 'entry' in a FAT (12/16/32) table.
 */
static int set_fatent_value(fsdata *mydata, __u32 entry, __u32 entry_value)
{
        __u32 bufnum, offset, off16;
        __u16 val1, val2;

        switch (mydata->fatsize) {
        case 32:
                bufnum = entry / FAT32BUFSIZE;
                offset = entry - bufnum * FAT32BUFSIZE;
                break;
        case 16:
                bufnum = entry / FAT16BUFSIZE;
                offset = entry - bufnum * FAT16BUFSIZE;
                break;
        case 12:
                bufnum = entry / FAT12BUFSIZE;
                offset = entry - bufnum * FAT12BUFSIZE;
                break;
        default:
                /* Unsupported FAT size */
                return -1;
        }

        /* Read a new block of FAT entries into the cache. */
        if (bufnum != mydata->fatbufnum) {
                int getsize = FATBUFBLOCKS;
                __u8 *bufptr = mydata->fatbuf;
                __u32 fatlength = mydata->fatlength;
                __u32 startblock = bufnum * FATBUFBLOCKS;

                /* Cap length if fatlength is not a multiple of FATBUFBLOCKS */
                if (startblock + getsize > fatlength)
                        getsize = fatlength - startblock;

                if (flush_dirty_fat_buffer(mydata) < 0)
                        return -1;

                startblock += mydata->fat_sect;

                if (disk_read(startblock, getsize, bufptr) < 0) {
                        debug("Error reading FAT blocks\n");
                        return -1;
                }
                mydata->fatbufnum = bufnum;
        }

        /* Mark as dirty */
        mydata->fat_dirty = 1;

        /* Set the actual entry */
        switch (mydata->fatsize) {
        case 32:
                ((__u32 *) mydata->fatbuf)[offset] = cpu_to_le32(entry_value);
                break;
        case 16:
                ((__u16 *) mydata->fatbuf)[offset] = cpu_to_le16(entry_value);
                break;
        case 12:
                off16 = (offset * 3) / 4;

                switch (offset & 0x3) {
                case 0:
                        val1 = cpu_to_le16(entry_value) & 0xfff;
                        ((__u16 *)mydata->fatbuf)[off16] &= ~0xfff;
                        ((__u16 *)mydata->fatbuf)[off16] |= val1;
                        break;
                case 1:
                        val1 = cpu_to_le16(entry_value) & 0xf;
                        val2 = (cpu_to_le16(entry_value) >> 4) & 0xff;

                        ((__u16 *)mydata->fatbuf)[off16] &= ~0xf000;
                        ((__u16 *)mydata->fatbuf)[off16] |= (val1 << 12);

                        ((__u16 *)mydata->fatbuf)[off16 + 1] &= ~0xff;
                        ((__u16 *)mydata->fatbuf)[off16 + 1] |= val2;
                        break;
                case 2:
                        val1 = cpu_to_le16(entry_value) & 0xff;
                        val2 = (cpu_to_le16(entry_value) >> 8) & 0xf;

                        ((__u16 *)mydata->fatbuf)[off16] &= ~0xff00;
                        ((__u16 *)mydata->fatbuf)[off16] |= (val1 << 8);

                        ((__u16 *)mydata->fatbuf)[off16 + 1] &= ~0xf;
                        ((__u16 *)mydata->fatbuf)[off16 + 1] |= val2;
                        break;
                case 3:
                        val1 = cpu_to_le16(entry_value) & 0xfff;
                        ((__u16 *)mydata->fatbuf)[off16] &= ~0xfff0;
                        ((__u16 *)mydata->fatbuf)[off16] |= (val1 << 4);
                        break;
                default:
                        break;
                }

                break;
        default:
                return -1;
        }

        return 0;
}

/*
 * Determine the next free cluster after 'entry' in a FAT (12/16/32) table
 * and link it to 'entry'. EOC marker is not set on returned entry.
 */
static __u32 determine_fatent(fsdata *mydata, __u32 entry)
{
        __u32 next_fat, next_entry = entry + 1;

        while (1) {
                next_fat = get_fatent(mydata, next_entry);
                if (next_fat == 0) {
                        /* found free entry, link to entry */
                        set_fatent_value(mydata, entry, next_entry);
                        break;
                }
                next_entry++;
        }
        debug("FAT%d: entry: %08x, entry_value: %04x\n",
               mydata->fatsize, entry, next_entry);

        return next_entry;
}

/*
 * Write at most 'size' bytes from 'buffer' into the specified cluster.
 * Return 0 on success, -1 otherwise.
 */
static int
set_cluster(fsdata *mydata, __u32 clustnum, __u8 *buffer,
             unsigned long size)
{
        __u32 idx = 0;
        __u32 startsect;
        int ret;

        if (clustnum > 0)
                startsect = mydata->data_begin +
                                clustnum * mydata->clust_size;
        else
                startsect = mydata->rootdir_sect;

        debug("clustnum: %d, startsect: %d\n", clustnum, startsect);

        if ((unsigned long)buffer & (ARCH_DMA_MINALIGN - 1)) {
                ALLOC_CACHE_ALIGN_BUFFER(__u8, tmpbuf, mydata->sect_size);

                printf("FAT: Misaligned buffer address (%p)\n", buffer);

                while (size >= mydata->sect_size) {
                        memcpy(tmpbuf, buffer, mydata->sect_size);
                        ret = disk_write(startsect++, 1, tmpbuf);
                        if (ret != 1) {
                                debug("Error writing data (got %d)\n", ret);
                                return -1;
                        }

                        buffer += mydata->sect_size;
                        size -= mydata->sect_size;
                }
        } else if (size >= mydata->sect_size) {
                idx = size / mydata->sect_size;
                ret = disk_write(startsect, idx, buffer);
                if (ret != idx) {
                        debug("Error writing data (got %d)\n", ret);
                        return -1;
                }

                startsect += idx;
                idx *= mydata->sect_size;
                buffer += idx;
                size -= idx;
        }

        if (size) {
                ALLOC_CACHE_ALIGN_BUFFER(__u8, tmpbuf, mydata->sect_size);

                memcpy(tmpbuf, buffer, size);
                ret = disk_write(startsect, 1, tmpbuf);
                if (ret != 1) {
                        debug("Error writing data (got %d)\n", ret);
                        return -1;
                }
        }

        return 0;
}

/*
 * Find the first empty cluster
 */
static int find_empty_cluster(fsdata *mydata)
{
        __u32 fat_val, entry = 3;

        while (1) {
                fat_val = get_fatent(mydata, entry);
                if (fat_val == 0)
                        break;
                entry++;
        }

        return entry;
}

/*
 * Write directory entries in 'get_dentfromdir_block' to block device
 */
static void flush_dir_table(fsdata *mydata, dir_entry **dentptr)
{
        int dir_newclust = 0;

        if (set_cluster(mydata, dir_curclust,
                    get_dentfromdir_block,
                    mydata->clust_size * mydata->sect_size) != 0) {
                printf("error: wrinting directory entry\n");
                return;
        }
        dir_newclust = find_empty_cluster(mydata);
        set_fatent_value(mydata, dir_curclust, dir_newclust);
        if (mydata->fatsize == 32)
                set_fatent_value(mydata, dir_newclust, 0xffffff8);
        else if (mydata->fatsize == 16)
                set_fatent_value(mydata, dir_newclust, 0xfff8);
        else if (mydata->fatsize == 12)
                set_fatent_value(mydata, dir_newclust, 0xff8);

        dir_curclust = dir_newclust;

        if (flush_dirty_fat_buffer(mydata) < 0)
                return;

        memset(get_dentfromdir_block, 0x00,
                mydata->clust_size * mydata->sect_size);

        *dentptr = (dir_entry *) get_dentfromdir_block;
}

/*
 * Set empty cluster from 'entry' to the end of a file
 */
static int clear_fatent(fsdata *mydata, __u32 entry)
{
        __u32 fat_val;

        while (!CHECK_CLUST(entry, mydata->fatsize)) {
                fat_val = get_fatent(mydata, entry);
                if (fat_val != 0)
                        set_fatent_value(mydata, entry, 0);
                else
                        break;

                entry = fat_val;
        }

        /* Flush fat buffer */
        if (flush_dirty_fat_buffer(mydata) < 0)
                return -1;

        return 0;
}

/*
 * Write at most 'maxsize' bytes from 'buffer' into
 * the file associated with 'dentptr'
 * Update the number of bytes written in *gotsize and return 0
 * or return -1 on fatal errors.
 */
static int
set_contents(fsdata *mydata, dir_entry *dentptr, __u8 *buffer,
              loff_t maxsize, loff_t *gotsize)
{
        loff_t filesize = FAT2CPU32(dentptr->size);
        unsigned int bytesperclust = mydata->clust_size * mydata->sect_size;
        __u32 curclust = START(dentptr);
        __u32 endclust = 0, newclust = 0;
        loff_t actsize;

        *gotsize = 0;
        debug("Filesize: %llu bytes\n", filesize);

        if (maxsize > 0 && filesize > maxsize)
                filesize = maxsize;

        debug("%llu bytes\n", filesize);

        if (!curclust) {
                if (filesize) {
                        debug("error: nonempty clusterless file!\n");
                        return -1;
                }
                return 0;
        }

        actsize = bytesperclust;
        endclust = curclust;
        do {
                /* search for consecutive clusters */
                while (actsize < filesize) {
                        newclust = determine_fatent(mydata, endclust);

                        if ((newclust - 1) != endclust)
                                goto getit;

                        if (CHECK_CLUST(newclust, mydata->fatsize)) {
                                debug("newclust: 0x%x\n", newclust);
                                debug("Invalid FAT entry\n");
                                return 0;
                        }
                        endclust = newclust;
                        actsize += bytesperclust;
                }

                /* set remaining bytes */
                actsize = filesize;
                if (set_cluster(mydata, curclust, buffer, (int)actsize) != 0) {
                        debug("error: writing cluster\n");
                        return -1;
                }
                *gotsize += actsize;

                /* Mark end of file in FAT */
                if (mydata->fatsize == 12)
                        newclust = 0xfff;
                else if (mydata->fatsize == 16)
                        newclust = 0xffff;
                else if (mydata->fatsize == 32)
                        newclust = 0xfffffff;
                set_fatent_value(mydata, endclust, newclust);

                return 0;
getit:
                if (set_cluster(mydata, curclust, buffer, (int)actsize) != 0) {
                        debug("error: writing cluster\n");
                        return -1;
                }
                *gotsize += actsize;
                filesize -= actsize;
                buffer += actsize;

                if (CHECK_CLUST(newclust, mydata->fatsize)) {
                        debug("newclust: 0x%x\n", newclust);
                        debug("Invalid FAT entry\n");
                        return 0;
                }
                actsize = bytesperclust;
                curclust = endclust = newclust;
        } while (1);
}

/*
 * Set start cluster in directory entry
 */
static void set_start_cluster(const fsdata *mydata, dir_entry *dentptr,
                                __u32 start_cluster)
{
        if (mydata->fatsize == 32)
                dentptr->starthi =
                        cpu_to_le16((start_cluster & 0xffff0000) >> 16);
        dentptr->start = cpu_to_le16(start_cluster & 0xffff);
}

/*
 * Fill dir_entry
 */
static void fill_dentry(fsdata *mydata, dir_entry *dentptr,
        const char *filename, __u32 start_cluster, __u32 size, __u8 attr)
{
        set_start_cluster(mydata, dentptr, start_cluster);
        dentptr->size = cpu_to_le32(size);

        dentptr->attr = attr;

        set_name(dentptr, filename);
}

/*
 * Check whether adding a file makes the file system to
 * exceed the size of the block device
 * Return -1 when overflow occurs, otherwise return 0
 */
static int check_overflow(fsdata *mydata, __u32 clustnum, loff_t size)
{
        __u32 startsect, sect_num, offset;

        if (clustnum > 0) {
                startsect = mydata->data_begin +
                                clustnum * mydata->clust_size;
        } else {
                startsect = mydata->rootdir_sect;
        }

        sect_num = div_u64_rem(size, mydata->sect_size, &offset);

        if (offset != 0)
                sect_num++;

        if (startsect + sect_num > cur_part_info.start + total_sector)
                return -1;
        return 0;
}

/*
 * Check if adding several entries exceed one cluster boundary
 */
static int is_next_clust(fsdata *mydata, dir_entry *dentptr)
{
        int cur_position;

        cur_position = (__u8 *)dentptr - get_dentfromdir_block;

        if (cur_position >= mydata->clust_size * mydata->sect_size)
                return 1;
        else
                return 0;
}

static dir_entry *empty_dentptr;
/*
 * Find a directory entry based on filename or start cluster number
 * If the directory entry is not found,
 * the new position for writing a directory entry will be returned
 */
static dir_entry *find_directory_entry(fsdata *mydata, int startsect,
        char *filename, dir_entry *retdent, __u32 start)
{
        __u32 curclust = (startsect - mydata->data_begin) / mydata->clust_size;

        debug("get_dentfromdir: %s\n", filename);

        while (1) {
                dir_entry *dentptr;

                int i;

                if (get_cluster(mydata, curclust, get_dentfromdir_block,
                            mydata->clust_size * mydata->sect_size) != 0) {
                        printf("Error: reading directory block\n");
                        return NULL;
                }

                dentptr = (dir_entry *)get_dentfromdir_block;

                dir_curclust = curclust;

                for (i = 0; i < DIRENTSPERCLUST; i++) {
                        char s_name[14], l_name[VFAT_MAXLEN_BYTES];

                        l_name[0] = '\0';
                        if (dentptr->name[0] == DELETED_FLAG) {
                                dentptr++;
                                if (is_next_clust(mydata, dentptr))
                                        break;
                                continue;
                        }
                        if ((dentptr->attr & ATTR_VOLUME)) {
                                if (vfat_enabled &&
                                    (dentptr->attr & ATTR_VFAT) &&
                                    (dentptr->name[0] & LAST_LONG_ENTRY_MASK)) {
                                        get_long_file_name(mydata, curclust,
                                                     get_dentfromdir_block,
                                                     &dentptr, l_name);
                                        debug("vfatname: |%s|\n", l_name);
                                } else {
                                        /* Volume label or VFAT entry */
                                        dentptr++;
                                        if (is_next_clust(mydata, dentptr))
                                                break;
                                        continue;
                                }
                        }
                        if (dentptr->name[0] == 0) {
                                debug("Dentname == NULL - %d\n", i);
                                empty_dentptr = dentptr;
                                return NULL;
                        }

                        get_name(dentptr, s_name);

                        if (strcmp(filename, s_name)
                            && strcmp(filename, l_name)) {
                                debug("Mismatch: |%s|%s|\n",
                                        s_name, l_name);
                                dentptr++;
                                if (is_next_clust(mydata, dentptr))
                                        break;
                                continue;
                        }

                        memcpy(retdent, dentptr, sizeof(dir_entry));

                        debug("DentName: %s", s_name);
                        debug(", start: 0x%x", START(dentptr));
                        debug(", size:  0x%x %s\n",
                              FAT2CPU32(dentptr->size),
                              (dentptr->attr & ATTR_DIR) ?
                              "(DIR)" : "");

                        return dentptr;
                }

                /*
                 * In FAT16/12, the root dir is locate before data area, shows
                 * in following:
                 * -------------------------------------------------------------
                 * | Boot | FAT1 & 2 | Root dir | Data (start from cluster #2) |
                 * -------------------------------------------------------------
                 *
                 * As a result if curclust is in Root dir, it is a negative
                 * number or 0, 1.
                 *
                 */
                if (mydata->fatsize != 32 && (int)curclust <= 1) {
                        /* Current clust is in root dir, set to next clust */
                        curclust++;
                        if ((int)curclust <= 1)
                                continue;       /* continue to find */

                        /* Reach the end of root dir */
                        empty_dentptr = dentptr;
                        return NULL;
                }

                curclust = get_fatent(mydata, dir_curclust);
                if (IS_LAST_CLUST(curclust, mydata->fatsize)) {
                        empty_dentptr = dentptr;
                        return NULL;
                }
                if (CHECK_CLUST(curclust, mydata->fatsize)) {
                        debug("curclust: 0x%x\n", curclust);
                        debug("Invalid FAT entry\n");
                        return NULL;
                }
        }

        return NULL;
}

static int do_fat_write(const char *filename, void *buffer, loff_t size,
                        loff_t *actwrite)
{
        dir_entry *dentptr, *retdent;
        __u32 startsect;
        __u32 start_cluster;
        boot_sector bs;
        volume_info volinfo;
        fsdata datablock;
        fsdata *mydata = &datablock;
        int cursect;
        int ret = -1, name_len;
        char l_filename[VFAT_MAXLEN_BYTES];

        *actwrite = size;
        dir_curclust = 0;

        if (read_bootsectandvi(&bs, &volinfo, &mydata->fatsize)) {
                debug("error: reading boot sector\n");
                return -1;
        }

        total_sector = bs.total_sect;
        if (total_sector == 0)
                total_sector = (int)cur_part_info.size; /* cast of lbaint_t */

        if (mydata->fatsize == 32)
                mydata->fatlength = bs.fat32_length;
        else
                mydata->fatlength = bs.fat_length;

        mydata->fat_sect = bs.reserved;

        cursect = mydata->rootdir_sect
                = mydata->fat_sect + mydata->fatlength * bs.fats;
        num_of_fats = bs.fats;

        mydata->sect_size = (bs.sector_size[1] << 8) + bs.sector_size[0];
        mydata->clust_size = bs.cluster_size;

        if (mydata->fatsize == 32) {
                mydata->data_begin = mydata->rootdir_sect -
                                        (mydata->clust_size * 2);
        } else {
                int rootdir_size;

                rootdir_size = ((bs.dir_entries[1]  * (int)256 +
                                 bs.dir_entries[0]) *
                                 sizeof(dir_entry)) /
                                 mydata->sect_size;
                mydata->data_begin = mydata->rootdir_sect +
                                        rootdir_size -
                                        (mydata->clust_size * 2);
        }

        mydata->fatbufnum = -1;
        mydata->fat_dirty = 0;
        mydata->fatbuf = memalign(ARCH_DMA_MINALIGN, FATBUFSIZE);
        if (mydata->fatbuf == NULL) {
                debug("Error: allocating memory\n");
                return -1;
        }

        if (disk_read(cursect,
                (mydata->fatsize == 32) ?
                (mydata->clust_size) :
                PREFETCH_BLOCKS, do_fat_read_at_block) < 0) {
                debug("Error: reading rootdir block\n");
                goto exit;
        }
        dentptr = (dir_entry *) do_fat_read_at_block;

        name_len = strlen(filename);
        if (name_len >= VFAT_MAXLEN_BYTES)
                name_len = VFAT_MAXLEN_BYTES - 1;

        memcpy(l_filename, filename, name_len);
        l_filename[name_len] = 0; /* terminate the string */
        downcase(l_filename);

        startsect = mydata->rootdir_sect;
        retdent = find_directory_entry(mydata, startsect,
                                l_filename, dentptr, 0);
        if (retdent) {
                /* Update file size and start_cluster in a directory entry */
                retdent->size = cpu_to_le32(size);
                start_cluster = START(retdent);

                if (start_cluster) {
                        if (size) {
                                ret = check_overflow(mydata, start_cluster,
                                                        size);
                                if (ret) {
                                        printf("Error: %llu overflow\n", size);
                                        goto exit;

                                }
                        }

                        ret = clear_fatent(mydata, start_cluster);
                        if (ret) {
                                printf("Error: clearing FAT entries\n");
                                goto exit;
                        }

                        if (!size)
                                set_start_cluster(mydata, retdent, 0);
                } else if (size) {
                        ret = start_cluster = find_empty_cluster(mydata);
                        if (ret < 0) {
                                printf("Error: finding empty cluster\n");
                                goto exit;
                        }

                        ret = check_overflow(mydata, start_cluster, size);
                        if (ret) {
                                printf("Error: %llu overflow\n", size);
                                goto exit;
                        }

                        set_start_cluster(mydata, retdent, start_cluster);
                }
        } else {
                /* Set short name to set alias checksum field in dir_slot */
                set_name(empty_dentptr, filename);
                fill_dir_slot(mydata, &empty_dentptr, filename);

                if (size) {
                        ret = start_cluster = find_empty_cluster(mydata);
                        if (ret < 0) {
                                printf("Error: finding empty cluster\n");
                                goto exit;
                        }

                        ret = check_overflow(mydata, start_cluster, size);
                        if (ret) {
                                printf("Error: %llu overflow\n", size);
                                goto exit;
                        }
                } else {
                        start_cluster = 0;
                }

                /* Set attribute as archieve for regular file */
                fill_dentry(mydata, empty_dentptr, filename,
                        start_cluster, size, 0x20);

                retdent = empty_dentptr;
        }

        ret = set_contents(mydata, retdent, buffer, size, actwrite);
        if (ret < 0) {
                printf("Error: writing contents\n");
                goto exit;
        }
        debug("attempt to write 0x%llx bytes\n", *actwrite);

        /* Flush fat buffer */
        ret = flush_dirty_fat_buffer(mydata);
        if (ret) {
                printf("Error: flush fat buffer\n");
                goto exit;
        }

        /* Write directory table to device */
        ret = set_cluster(mydata, dir_curclust, get_dentfromdir_block,
                        mydata->clust_size * mydata->sect_size);
        if (ret)
                printf("Error: writing directory entry\n");

exit:
        free(mydata->fatbuf);
        return ret;
}

int file_fat_write(const char *filename, void *buffer, loff_t offset,
                   loff_t maxsize, loff_t *actwrite)
{
        if (offset != 0) {
                printf("Error: non zero offset is currently not supported.\n");
                return -1;
        }

        printf("writing %s\n", filename);
        return do_fat_write(filename, buffer, maxsize, actwrite);
}