FAT: Add FAT write feature

In some cases, saving data in RAM as a file with FAT format is required.
This patch allows the file to be written in FAT formatted partition.

The usage is similar with reading a file.
First, fat_register_device function is called before file_fat_write function
in order to set target partition.
Then, file_fat_write function is invoked with desired file name,
start ram address for writing data, and file size.

Signed-off-by: Donggeun Kim <dg77.kim@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>

1 files changed, 1090 insertions, 0 deletions

diff --git a/fs/fat/fat_write.c b/fs/fat/fat_write.c
new file mode 100644
index 0000000..4f1772f
--- /dev/null
+++ b/fs/fat/fat_write.c
@@ -0,0 +1,1090 @@
+/*
+ * fat_write.c
+ *
+ * R/W (V)FAT 12/16/32 filesystem implementation by Donggeun Kim
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+#include <common.h>
+#include <command.h>
+#include <config.h>
+#include <fat.h>
+#include <asm/byteorder.h>
+#include <part.h>
+#include "fat.c"
+
+static void uppercase(char *str, int len)
+{
+	int i;
+
+	for (i = 0; i < len; i++) {
+		TOUPPER(*str);
+		str++;
+	}
+}
+
+static int total_sector;
+static int disk_write(__u32 startblock, __u32 getsize, __u8 *bufptr)
+{
+	if (cur_dev == NULL)
+		return -1;
+
+	if (startblock + getsize > total_sector) {
+		printf("error: overflow occurs\n");
+		return -1;
+	}
+
+	startblock += part_offset;
+
+	if (cur_dev->block_read) {
+		return cur_dev->block_write(cur_dev->dev, startblock, getsize,
+					   (unsigned long *) bufptr);
+	}
+	return -1;
+}
+
+/*
+ * 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;
+
+	memcpy(s_name, filename, len);
+	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);
+}
+
+/*
+ * Write fat buffer into block device
+ */
+static int flush_fat_buffer(fsdata *mydata)
+{
+	int getsize = FATBUFBLOCKS;
+	__u32 fatlength = mydata->fatlength;
+	__u8 *bufptr = mydata->fatbuf;
+	__u32 startblock = mydata->fatbufnum * FATBUFBLOCKS;
+
+	fatlength *= mydata->sect_size;
+	startblock += mydata->fat_sect;
+
+	if (getsize > fatlength)
+		getsize = fatlength;
+
+	/* Write FAT buf */
+	if (disk_write(startblock, getsize, bufptr) < 0) {
+		debug("error: writing FAT blocks\n");
+		return -1;
+	}
+
+	return 0;
+}
+
+/*
+ * Get the entry at index 'entry' in a FAT (12/16/32) table.
+ * On failure 0x00 is returned.
+ * When bufnum is changed, write back the previous fatbuf to the disk.
+ */
+static __u32 get_fatent_value(fsdata *mydata, __u32 entry)
+{
+	__u32 bufnum;
+	__u32 off16, offset;
+	__u32 ret = 0x00;
+	__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 ret;
+	}
+
+	debug("FAT%d: entry: 0x%04x = %d, offset: 0x%04x = %d\n",
+	       mydata->fatsize, entry, entry, offset, offset);
+
+	/* 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;
+
+		if (getsize > fatlength)
+			getsize = fatlength;
+
+		fatlength *= mydata->sect_size;	/* We want it in bytes now */
+		startblock += mydata->fat_sect;	/* Offset from start of disk */
+
+		/* Write back the fatbuf to the disk */
+		if (mydata->fatbufnum != -1) {
+			if (flush_fat_buffer(mydata) < 0)
+				return -1;
+		}
+
+		if (disk_read(startblock, getsize, bufptr) < 0) {
+			debug("Error reading FAT blocks\n");
+			return ret;
+		}
+		mydata->fatbufnum = bufnum;
+	}
+
+	/* Get the actual entry from the table */
+	switch (mydata->fatsize) {
+	case 32:
+		ret = FAT2CPU32(((__u32 *) mydata->fatbuf)[offset]);
+		break;
+	case 16:
+		ret = FAT2CPU16(((__u16 *) mydata->fatbuf)[offset]);
+		break;
+	case 12:
+		off16 = (offset * 3) / 4;
+
+		switch (offset & 0x3) {
+		case 0:
+			ret = FAT2CPU16(((__u16 *) mydata->fatbuf)[off16]);
+			ret &= 0xfff;
+			break;
+		case 1:
+			val1 = FAT2CPU16(((__u16 *)mydata->fatbuf)[off16]);
+			val1 &= 0xf000;
+			val2 = FAT2CPU16(((__u16 *)mydata->fatbuf)[off16 + 1]);
+			val2 &= 0x00ff;
+			ret = (val2 << 4) | (val1 >> 12);
+			break;
+		case 2:
+			val1 = FAT2CPU16(((__u16 *)mydata->fatbuf)[off16]);
+			val1 &= 0xff00;
+			val2 = FAT2CPU16(((__u16 *)mydata->fatbuf)[off16 + 1]);
+			val2 &= 0x000f;
+			ret = (val2 << 8) | (val1 >> 8);
+			break;
+		case 3:
+			ret = FAT2CPU16(((__u16 *)mydata->fatbuf)[off16]);
+			ret = (ret & 0xfff0) >> 4;
+			break;
+		default:
+			break;
+		}
+		break;
+	}
+	debug("FAT%d: ret: %08x, entry: %08x, offset: %04x\n",
+	       mydata->fatsize, ret, entry, offset);
+
+	return ret;
+}
+
+#ifdef CONFIG_SUPPORT_VFAT
+/*
+ * 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)
+{
+	dir_slot *slotptr = (dir_slot *)get_vfatname_block;
+	__u8 counter, checksum;
+	int idx = 0, ret;
+	char s_name[16];
+
+	/* Get short file name and checksum value */
+	strncpy(s_name, (*dentptr)->name, 16);
+	checksum = mkcksum(s_name);
+
+	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_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_value(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_vfatname_block,
+				mydata->clust_size * mydata->sect_size) != 0) {
+			debug("Error: reading directory block\n");
+			return -1;
+		}
+
+		slotptr2 = (dir_slot *)get_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_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_vfatname_block,
+			mydata->clust_size * mydata->sect_size);
+		cur_position = (__u8 *)realdent - get_vfatname_block;
+		*retdent = (dir_entry *) &get_dentfromdir_block[cur_position];
+	}
+
+	return 0;
+}
+
+#endif
+
+/*
+ * Set the entry at index 'entry' in a FAT (16/32) table.
+ */
+static int set_fatent_value(fsdata *mydata, __u32 entry, __u32 entry_value)
+{
+	__u32 bufnum, offset;
+
+	switch (mydata->fatsize) {
+	case 32:
+		bufnum = entry / FAT32BUFSIZE;
+		offset = entry - bufnum * FAT32BUFSIZE;
+		break;
+	case 16:
+		bufnum = entry / FAT16BUFSIZE;
+		offset = entry - bufnum * FAT16BUFSIZE;
+		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;
+
+		fatlength *= mydata->sect_size;
+		startblock += mydata->fat_sect;
+
+		if (getsize > fatlength)
+			getsize = fatlength;
+
+		if (mydata->fatbufnum != -1) {
+			if (flush_fat_buffer(mydata) < 0)
+				return -1;
+		}
+
+		if (disk_read(startblock, getsize, bufptr) < 0) {
+			debug("Error reading FAT blocks\n");
+			return -1;
+		}
+		mydata->fatbufnum = bufnum;
+	}
+
+	/* 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;
+	default:
+		return -1;
+	}
+
+	return 0;
+}
+
+/*
+ * Determine the entry value at index 'entry' in a FAT (16/32) table
+ */
+static __u32 determine_fatent(fsdata *mydata, __u32 entry)
+{
+	__u32 next_fat, next_entry = entry + 1;
+
+	while (1) {
+		next_fat = get_fatent_value(mydata, next_entry);
+		if (next_fat == 0) {
+			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)
+{
+	int idx = 0;
+	__u32 startsect;
+
+	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 (disk_write(startsect, size / mydata->sect_size, buffer) < 0) {
+		debug("Error writing data\n");
+		return -1;
+	}
+
+	if (size % mydata->sect_size) {
+		__u8 tmpbuf[mydata->sect_size];
+
+		idx = size / mydata->sect_size;
+		buffer += idx * mydata->sect_size;
+		memcpy(tmpbuf, buffer, size % mydata->sect_size);
+
+		if (disk_write(startsect + idx, 1, tmpbuf) < 0) {
+			debug("Error writing data\n");
+			return -1;
+		}
+
+		return 0;
+	}
+
+	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_value(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);
+
+	dir_curclust = dir_newclust;
+
+	if (flush_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 (1) {
+		fat_val = get_fatent_value(mydata, entry);
+		if (fat_val != 0)
+			set_fatent_value(mydata, entry, 0);
+		else
+			break;
+
+		if (fat_val == 0xfffffff || fat_val == 0xffff)
+			break;
+
+		entry = fat_val;
+	}
+
+	/* Flush fat buffer */
+	if (flush_fat_buffer(mydata) < 0)
+		return -1;
+
+	return 0;
+}
+
+/*
+ * Write at most 'maxsize' bytes from 'buffer' into
+ * the file associated with 'dentptr'
+ * Return the number of bytes read or -1 on fatal errors.
+ */
+static int
+set_contents(fsdata *mydata, dir_entry *dentptr, __u8 *buffer,
+	      unsigned long maxsize)
+{
+	unsigned long filesize = FAT2CPU32(dentptr->size), gotsize = 0;
+	unsigned int bytesperclust = mydata->clust_size * mydata->sect_size;
+	__u32 curclust = START(dentptr);
+	__u32 endclust = 0, newclust = 0;
+	unsigned long actsize;
+
+	debug("Filesize: %ld bytes\n", filesize);
+
+	if (maxsize > 0 && filesize > maxsize)
+		filesize = maxsize;
+
+	debug("%ld bytes\n", filesize);
+
+	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("curclust: 0x%x\n", newclust);
+				debug("Invalid FAT entry\n");
+				return gotsize;
+			}
+			endclust = newclust;
+			actsize += bytesperclust;
+		}
+		/* actsize >= file size */
+		actsize -= bytesperclust;
+		/* set remaining clusters */
+		if (set_cluster(mydata, curclust, buffer, (int)actsize) != 0) {
+			debug("error: writing cluster\n");
+			return -1;
+		}
+
+		/* set remaining bytes */
+		gotsize += (int)actsize;
+		filesize -= actsize;
+		buffer += actsize;
+		actsize = filesize;
+
+		if (set_cluster(mydata, endclust, buffer, (int)actsize) != 0) {
+			debug("error: writing cluster\n");
+			return -1;
+		}
+		gotsize += actsize;
+
+		/* Mark end of file in FAT */
+		if (mydata->fatsize == 16)
+			newclust = 0xffff;
+		else if (mydata->fatsize == 32)
+			newclust = 0xfffffff;
+		set_fatent_value(mydata, endclust, newclust);
+
+		return gotsize;
+getit:
+		if (set_cluster(mydata, curclust, buffer, (int)actsize) != 0) {
+			debug("error: writing cluster\n");
+			return -1;
+		}
+		gotsize += (int)actsize;
+		filesize -= actsize;
+		buffer += actsize;
+
+		if (CHECK_CLUST(curclust, mydata->fatsize)) {
+			debug("curclust: 0x%x\n", curclust);
+			debug("Invalid FAT entry\n");
+			return gotsize;
+		}
+		actsize = bytesperclust;
+		curclust = endclust = newclust;
+	} while (1);
+}
+
+/*
+ * Fill dir_entry
+ */
+static void fill_dentry(fsdata *mydata, dir_entry *dentptr,
+	const char *filename, __u32 start_cluster, __u32 size, __u8 attr)
+{
+	if (mydata->fatsize == 32)
+		dentptr->starthi =
+			cpu_to_le16((start_cluster & 0xffff0000) >> 16);
+	dentptr->start = cpu_to_le16(start_cluster & 0xffff);
+	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, unsigned long size)
+{
+	__u32 startsect, sect_num;
+
+	if (clustnum > 0) {
+		startsect = mydata->data_begin +
+				clustnum * mydata->clust_size;
+	} else {
+		startsect = mydata->rootdir_sect;
+	}
+
+	sect_num = size / mydata->sect_size;
+	if (size % mydata->sect_size)
+		sect_num++;
+
+	if (startsect + sect_num > 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)
+{
+	__u16 prevcksum = 0xffff;
+	__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)) {
+#ifdef CONFIG_SUPPORT_VFAT
+				if ((dentptr->attr & ATTR_VFAT) &&
+				    (dentptr->name[0] & LAST_LONG_ENTRY_MASK)) {
+					prevcksum =
+					((dir_slot *)dentptr)->alias_checksum;
+					get_long_file_name(mydata, curclust,
+						     get_dentfromdir_block,
+						     &dentptr, l_name);
+					debug("vfatname: |%s|\n", l_name);
+				} else
+#endif
+				{
+					/* 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;
+		}
+
+		curclust = get_fatent_value(mydata, dir_curclust);
+		if ((curclust >= 0xffffff8) || (curclust >= 0xfff8)) {
+			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,
+	unsigned long size)
+{
+	dir_entry *dentptr, *retdent;
+	dir_slot *slotptr;
+	__u32 startsect;
+	__u32 start_cluster;
+	boot_sector bs;
+	volume_info volinfo;
+	fsdata datablock;
+	fsdata *mydata = &datablock;
+	int cursect;
+	int root_cluster, ret = -1, name_len;
+	char l_filename[VFAT_MAXLEN_BYTES];
+
+	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 = part_size;
+
+	root_cluster = bs.root_cluster;
+
+	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;
+
+	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->fatbuf = malloc(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_block) < 0) {
+		debug("Error: reading rootdir block\n");
+		goto exit;
+	}
+	dentptr = (dir_entry *) do_fat_read_block;
+
+	name_len = strlen(filename);
+	memcpy(l_filename, filename, name_len);
+	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 = FAT2CPU16(retdent->start);
+		if (mydata->fatsize == 32)
+			start_cluster |=
+				(FAT2CPU16(retdent->starthi) << 16);
+
+		ret = check_overflow(mydata, start_cluster, size);
+		if (ret) {
+			printf("Error: %ld overflow\n", size);
+			goto exit;
+		}
+
+		ret = clear_fatent(mydata, start_cluster);
+		if (ret) {
+			printf("Error: clearing FAT entries\n");
+			goto exit;
+		}
+
+		ret = set_contents(mydata, retdent, buffer, size);
+		if (ret) {
+			printf("Error: writing contents\n");
+			goto exit;
+		}
+
+		/* Flush fat buffer */
+		ret = flush_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: wrinting directory entry\n");
+			goto exit;
+		}
+	} else {
+		slotptr = (dir_slot *)empty_dentptr;
+
+		/* Set short name to set alias checksum field in dir_slot */
+		set_name(empty_dentptr, filename);
+		fill_dir_slot(mydata, &empty_dentptr, filename);
+
+		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: %ld overflow\n", size);
+			goto exit;
+		}
+
+		/* Set attribute as archieve for regular file */
+		fill_dentry(mydata, empty_dentptr, filename,
+			start_cluster, size, 0x20);
+
+		ret = set_contents(mydata, empty_dentptr, buffer, size);
+		if (ret) {
+			printf("Error: writing contents\n");
+			goto exit;
+		}
+
+		/* Flush fat buffer */
+		ret = flush_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");
+			goto exit;
+		}
+	}
+
+exit:
+	free(mydata->fatbuf);
+	return ret;
+}
+
+int file_fat_write(const char *filename, void *buffer, unsigned long maxsize)
+{
+	printf("writing %s\n", filename);
+	return do_fat_write(filename, buffer, maxsize);
+}