diff --git a/tools/firmware-utils/src/wrt400n.c b/tools/firmware-utils/src/wrt400n.c
index 1cf1deb..70d4c32 100644
--- a/tools/firmware-utils/src/wrt400n.c
+++ b/tools/firmware-utils/src/wrt400n.c
@@ -6,110 +6,34 @@
  * from a kernel image file and root fs file
  *
  *	Author: Sandeep Mistry
+ *	Author: Yousong Zhou
+ *		- remove size limit on kernel and rootfs part
  */
 #include <arpa/inet.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <stdint.h>
+#include <stdbool.h>
 #include <string.h>
+#include <errno.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
 
 #include "cyg_crc.h"
 
-// https://dev.openwrt.org/browser/trunk/target/linux/rdc-2.6/files/drivers/mtd/maps/rdc3210.c
-static uint32_t crctab[257] =
-{
-	0x00000000, 0x77073096, 0xee0e612c, 0x990951ba,
-	0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3,
-	0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
-	0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91,
-	0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
-	0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
-	0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,
-	0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5,
-	0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
-	0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
-	0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940,
-	0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
-	0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116,
-	0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,
-	0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
-	0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,
-	0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a,
-	0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
-	0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818,
-	0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
-	0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
-	0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457,
-	0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c,
-	0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
-	0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
-	0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb,
-	0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
-	0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,
-	0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086,
-	0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
-	0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4,
-	0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad,
-	0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
-	0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683,
-	0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
-	0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
-	0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe,
-	0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7,
-	0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
-	0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
-	0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252,
-	0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
-	0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60,
-	0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79,
-	0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
-	0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f,
-	0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04,
-	0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
-	0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a,
-	0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
-	0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
-	0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21,
-	0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e,
-	0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
-	0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
-	0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,
-	0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
-	0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db,
-	0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0,
-	0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
-	0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6,
-	0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf,
-	0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
-	0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d,
-	0
-};
-
-static uint32_t crc32(uint8_t* buf, uint32_t len)
-{
-	register int i;
-	uint32_t sum;
-	register uint32_t s0;
-	s0 = ~0;
-	for (i = 0; i < len; i++)
-	{
-		s0 = (s0 >> 8) ^ crctab[(uint8_t) (s0 & 0xFF) ^ buf[i]];
-	}
-	sum = ~s0;
-	return sum;
-}
-
-#define HEADERSIZE	60
-#define MAGIC		"GMTKRT400N"
-
-// global variables
-uint8_t kernelbuf[0x100000];	// kernel - lzma - uImage
-uint8_t rootfsbuf[0x2FFFC4];	// root - squashfs
-
-uint8_t buf[0x400000];		// buffer for image
+// Prelimiary test shows that the OEM upgrade program only checks checksum of
+// the whole firmware image, ignoring specific checksums of kernel and rootfs
+// part.  But we are computing crc32 sums of fixed length of data here in lieu
+// of read_fw utility found in OEM SDK
+#define CRC_SZ_KERNEL 0x100000
+#define CRC_SZ_ROOTFS 0x2fffc4
+// OEM firmware has size limit on "linux" and "rootfs" partition.  That's also
+// the limit for factory firmware images as fwupgrade utility in the OEM system
+// needs to write kernel and rootfs to those two partitions (/dev/mtd2 and
+// /dev/mtd3 to be exact)
+#define SZ_MAX_KERNEL (0x180000 - 0x40000)
+#define SZ_MAX_ROOTFS (0x7b0000 - 0x18000)
 
 
 // Header format:
@@ -117,27 +41,6 @@ uint8_t buf[0x400000];		// buffer for image
 //		GPL Tarball: http://downloads.linksysbycisco.com/downloads/WRT400N_1.0.01.19_US.tar,0.gz
 //		File: WRT400N_1.0.01.19_US/FW_WRT400N_1.0.01.19_US_20081229/GTK/user/include/fw_upgrade.h
 //
-//
-//		Struct:
-//			typedef struct
-//			{
-//				UINT32		checksum;		/* CRC32 */
-//				UINT8			magic[11];		/* The value of GTIMG_MAGIC */
-//				UINT32		kernel_length;		/* The length of the kernel image */
-//				//UINT32		kernel_entry_point;	/* Kernel's entry point for RedBoot's information */
-//				UINT32		kernel_upgrade_flag;	/* Set to 1 if we need to upgrade the kernel parition of the Flash */
-//				UINT32		rootfs_length;		/* The length of the rootfs image */
-//				//UINT32		rootfs_entry_point;	/* Not in use */
-//				UINT32		rootfs_upgrade_flag;	/* Set to 1 if we need to upgrade the rootfs parition of the Flash */
-//
-//				// Add 3 items by Vic Yu, 2006-05/10
-//				UINT32		kernel_checksum;
-//				UINT32		rootfs_checksum;
-//				UINT32		fw_totalsize;
-//				UINT32		reserved[4];
-//			}imghdr_t , *pLinuxFWHeader_T;
-//
-//
 //		Description
 //			- checksum: 			CRC32 of kernel and root fs, back to back
 //			- magic:				GMTKRT400N
@@ -151,186 +54,214 @@ uint8_t buf[0x400000];		// buffer for image
 //									set to 0xFF upto 0x2FFFC4 bytes	(total length)
 //			- fw_totalsize:			total firmware image file length (header length + kernel length + root fs length)
 //			- reserved[4]:			reserved ??? - set to all 0xFF
+struct imghdr_t
+{
+	uint32_t		checksum;		/* CRC32 */
+	uint8_t			magic[12];		/* The value of GTIMG_MAGIC */
+	uint32_t		kernel_length;		/* The length of the kernel image */
+	//uint32_t		kernel_entry_point;	/* Kernel's entry point for RedBoot's information */
+	uint32_t		kernel_upgrade_flag;	/* Set to 1 if we need to upgrade the kernel parition of the Flash */
+	uint32_t		rootfs_length;		/* The length of the rootfs image */
+	//uint32_t		rootfs_entry_point;	/* Not in use */
+	uint32_t		rootfs_upgrade_flag;	/* Set to 1 if we need to upgrade the rootfs parition of the Flash */
+
+	// Add 3 items by Vic Yu, 2006-05/10
+	uint32_t		kernel_checksum;
+	uint32_t		rootfs_checksum;
+	uint32_t		fw_totalsize;
+	uint32_t		reserved[4];
+};
 
+struct file_info {
+	char		*filename;
+	int			filesize;
+	int			fd;
+	uint32_t	crc32sum;
+	int			crc_sz;
+};
 
-
-int main(int argc, char *argv[])
+int get_file_info(struct file_info *fi, uint32_t *crc32_acc)
 {
-	// file descriptors ...
-	int 		kernelfd		= -1;
-	int 		rootfsfd			= -1;
-	int			outfd			= -1;
+	int fd;
+	int filesize = 0;
+	uint32_t crc32sum = 0;
+	uint32_t _crc32_acc;
+	int crc_rem = fi->crc_sz;
+	int sz;
+	char buf[1024];
+
+	if (crc32_acc)
+		_crc32_acc = *crc32_acc;
+	else
+		_crc32_acc = 0;
+
+	fd = open(fi->filename, O_RDONLY);
+	if(fd < 0) {
+		fprintf(stderr, "error: opening '%s'\n", fi->filename);
+		return -1;
+	}
+	while (true) {
+		sz = read(fd, buf, sizeof(buf));
+		if (sz > 0) {
+			if (crc32_acc)
+				_crc32_acc = cyg_crc32_accumulate(_crc32_acc, buf, sz);
+			if (crc_rem > 0) {
+				if (crc_rem < sz) {
+					crc32sum = cyg_crc32_accumulate(crc32sum, buf, crc_rem);
+					crc_rem = 0;
+				} else {
+					crc32sum = cyg_crc32_accumulate(crc32sum, buf, sz);
+					crc_rem -= sz;
+				}
+			}
+			filesize += sz;
+		} else if (sz == 0) {
+			break;
+		} else {
+			fprintf(stderr, "error read '%s'", strerror(errno));
+			return -1;
+		}
+	}
 
-	char*		kernelfilename	= NULL;
-	char*		rootfsfilename	= NULL;
-	char*		outputfilename	= NULL;
+	if (crc_rem) {
+		memset(buf, 0xff, sizeof(buf));
+		while (crc_rem > 0) {
+			if (crc_rem > sizeof(buf)) {
+				crc32sum = cyg_crc32_accumulate(crc32sum, buf, sizeof(buf));
+				crc_rem -= sizeof(buf);
+			} else {
+				crc32sum = cyg_crc32_accumulate(crc32sum, buf, crc_rem);
+				crc_rem = 0;
+				break;
+			}
+		}
+	}
 
-	// file sizes
-	uint32_t 	kernelsize 		= 0;
-	uint32_t 	rootfssize 		= 0;
-	uint32_t 	totalsize 		= 0;
+	fi->fd = fd;
+	fi->filesize = filesize;
+	fi->crc32sum = crc32sum;
+	if (crc32_acc)
+		*crc32_acc = _crc32_acc;
+	return 0;
+}
 
-	// header flags
-	uint32_t 	kernelflag 		= 0;
-	uint32_t 	rootfsflag 		= 0;
+int copy_file(int fromfd, int tofd)
+{
+	int szr, szw;
+	int buf[4096];
 
-	// checksums
-	uint32_t 	kernelchecksum 	= 0;
-	uint32_t 	rootfschecksum 	= 0;
-	uint32_t	crc				= 0;
+	if (lseek(fromfd, SEEK_SET, 0) < 0) {
+		fprintf(stderr, "lseek: %s\n", strerror(errno));
+		return -1;
+	}
+	while (true) {
+		szr = read(fromfd, buf, sizeof(buf));
+		if (szr > 0) {
+			szw = write(tofd, buf, szr);
+			if (szw != szr) {
+				fprintf(stderr, "copy_file: error writing %d bytes: %s\n", szr, strerror(errno));
+				return -1;
+			}
+		} else if (szr == 0) {
+			break;
+		} else {
+			fprintf(stderr, "copy_file: error reading: %s\n", strerror(errno));
+			return -1;
+		}
+	}
+	return 0;
+}
 
-	if(argc != 4)
-	{
+int main(int argc, char *argv[])
+{
+	struct file_info kernel_fi;
+	struct file_info rootfs_fi;
+	struct file_info output_fi;
+	struct imghdr_t ih;
+	int fd, sz;
+	int ret = -1;
+
+	if(argc != 4) {
 		printf("Usage:\n\t%s <kernel file> <rootfs file> <output file>\n", argv[0]);
 		return 1;
 	}
 
-	kernelfilename = argv[1];
-	rootfsfilename = argv[2];
-	outputfilename = argv[3];
+	kernel_fi.crc_sz = CRC_SZ_KERNEL;
+	rootfs_fi.crc_sz = CRC_SZ_ROOTFS;
 
-	// Fill the kernel, rootfs, main buffer
-	memset(kernelbuf, 0xFF, sizeof(kernelbuf));
-	memset(rootfsbuf, 0xFF, sizeof(rootfsbuf));
-	memset(buf, 0xFF, sizeof(buf));
+	kernel_fi.fd = -1;
+	rootfs_fi.fd = -1;
+	output_fi.fd = -1;
 
-	// open the kernel ..
-	kernelfd = open(kernelfilename, O_RDONLY);
+	kernel_fi.filename = argv[1];
+	rootfs_fi.filename = argv[2];
+	output_fi.filename = argv[3];
 
-	if(kernelfd == -1)
-	{
-		printf("Error: opening '%s'\n", kernelfilename);
-		goto done;
-	}
-
-	// read in the kernel ...
-	kernelsize = read(kernelfd, kernelbuf, sizeof(kernelbuf));
+	kernel_fi.crc32sum = 0;
+	rootfs_fi.crc32sum = 0;
+	output_fi.crc32sum = 0xffffffff;
 
-	if(kernelsize == -1)
-	{
-		printf("Error: reading '%s'\n", kernelfilename);
+	if (get_file_info(&kernel_fi, &output_fi.crc32sum) < 0)
 		goto done;
-	}
-
-	// calculate the kernel checksum ...
-	kernelchecksum = cyg_crc32_accumulate(0, kernelbuf, sizeof(kernelbuf));
+	if (get_file_info(&rootfs_fi, &output_fi.crc32sum) < 0)
+		goto done;
+	output_fi.crc32sum = ~output_fi.crc32sum;
 
 	// print out stats
-	printf("%s: size %d (0x%x), crc32 = 0x%x\n", kernelfilename, kernelsize, kernelsize, kernelchecksum);
-
-
-	// open the root fs ..
-	rootfsfd = open(rootfsfilename, O_RDONLY);
-
-	if(rootfsfd == -1)
-	{
-		printf("Error: opening '%s'\n", rootfsfilename);
+	fprintf(stderr, "%s: size %d (0x%x), crc32 = 0x%x\n",
+		kernel_fi.filename, kernel_fi.filesize, kernel_fi.filesize, kernel_fi.crc32sum);
+	fprintf(stderr, "%s: size %d (0x%x), crc32 = 0x%x\n",
+		rootfs_fi.filename, rootfs_fi.filesize, rootfs_fi.filesize, rootfs_fi.crc32sum);
+	if (kernel_fi.filesize > SZ_MAX_KERNEL) {
+		fprintf(stderr, "%s: filesize exceeds 0x%x limit\n", SZ_MAX_KERNEL);
 		goto done;
 	}
-
-	// read in the root fs ..
-	rootfssize = read(rootfsfd, rootfsbuf, sizeof(rootfsbuf));
-
-	if(rootfssize == -1)
-	{
-		printf("Error: reading '%s'\n", rootfsfilename);
+	if (rootfs_fi.filesize > SZ_MAX_ROOTFS) {
+		fprintf(stderr, "%s: filesize exceeds 0x%x limit\n", SZ_MAX_ROOTFS);
 		goto done;
 	}
 
-	// calculate the root fs checksum ...
-	rootfschecksum = cyg_crc32_accumulate(0, rootfsbuf, sizeof(rootfsbuf));
-
-	// print out stats
-	printf("%s: size %d (0x%x), crc32 = 0x%x\n", rootfsfilename, rootfssize, rootfssize, rootfschecksum);
-
-
 	// now for the header ...
-
-	totalsize = HEADERSIZE;
-
-	// copy over kernel
-	memcpy(buf + totalsize, kernelbuf, kernelsize);
-	totalsize += kernelsize;
-
-	// copy over root fs
-	memcpy(buf + totalsize, rootfsbuf, rootfssize);
-	totalsize += rootfssize;
-
-	// calculate crc
-	crc = crc32(buf + HEADERSIZE, totalsize - HEADERSIZE);
-
-	// print some stats out
-	printf("crc = 0x%x, total size = %d (0x%x)\n", crc, totalsize, totalsize);
-
-	// copy crc into header
-	crc = htonl(crc);
-	memcpy(buf, &crc, sizeof(crc));
-
-	// copy over magic
-	strcpy((char *)buf + 4, MAGIC);
-
-	// copy over kernel size
-	kernelsize = htonl(kernelsize);
-	memcpy(buf + 16, &kernelsize, sizeof(kernelsize));
-
-	// copy over kernal flag
-	kernelflag = htonl(0x1);
-	memcpy(buf + 20, &kernelflag, sizeof(kernelflag));
-
-	// copy over root fs size
-	rootfssize = htonl(rootfssize);
-	memcpy(buf + 24, &rootfssize, sizeof(rootfssize));
-
-	// copy over root fs flag
-	rootfsflag = htonl(0x1);
-	memcpy(buf + 28, &rootfsflag, sizeof(rootfsflag));
-
-	// copy over kernel check sum
-	kernelchecksum = htonl(kernelchecksum);
-	memcpy(buf + 32, &kernelchecksum, sizeof(kernelchecksum));
-
-	// copy over root fs checksum
-	rootfschecksum = htonl(rootfschecksum);
-	memcpy(buf + 36, &rootfschecksum, sizeof(rootfschecksum));
-
-	// copy over total size
-	totalsize = htonl(totalsize);
-	memcpy(buf + 40, &totalsize, sizeof(totalsize));
-
-	// undo the htonl (for write)
-	totalsize = htonl(totalsize);
-
-
-	// write out the file from the buffer
-	outfd = open(outputfilename, O_CREAT | O_WRONLY | O_TRUNC, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
-
-	if(outfd == -1)
-	{
-		printf("ERROR: opening '%s' for write\n", outputfilename);
-	}
-
-	write(outfd, buf, totalsize);
-
-done:
-	// close open fd's
-
-	if(kernelfd != -1)
-	{
-		close(kernelfd);
-		kernelfd = -1;
+	memset(&ih, 0xff, sizeof(ih));
+	strcpy(ih.magic, "GMTKRT400N");
+	ih.checksum = htonl(output_fi.crc32sum);
+	ih.kernel_length = htonl(kernel_fi.filesize);
+	ih.rootfs_length = htonl(rootfs_fi.filesize);
+	ih.kernel_upgrade_flag = htonl(0x1);
+	ih.rootfs_upgrade_flag = htonl(0x1);
+	ih.kernel_checksum = htonl(kernel_fi.crc32sum);
+	ih.rootfs_checksum = htonl(rootfs_fi.crc32sum);
+	ih.fw_totalsize = htonl(kernel_fi.filesize + rootfs_fi.filesize + sizeof(ih));
+
+	output_fi.fd = open(output_fi.filename, O_WRONLY | O_CREAT | O_TRUNC,
+			S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
+	sz = write(output_fi.fd, &ih, sizeof(ih));
+	if (sz != sizeof(ih)) {
+		fprintf(stderr, "error writing imghdr to output: %s\n", strerror(errno));
+		goto done;
 	}
-
-	if(rootfsfd != -1)
-	{
-		close(rootfsfd);
-		rootfsfd = -1;
+	if (copy_file(kernel_fi.fd, output_fi.fd)) {
+		fprintf(stderr, "error copying %s to %s\n", kernel_fi.filename, output_fi.filename);
+		goto done;
 	}
-
-	if(outfd != -1)
-	{
-		close(outfd);
-		outfd = -1;
+	if (copy_file(rootfs_fi.fd, output_fi.fd)) {
+		fprintf(stderr, "error copying %s to %s\n", rootfs_fi.filename, output_fi.filename);
+		goto done;
 	}
+	// print some stats out
+	fprintf(stderr, "crc = 0x%x, total size = %d (0x%x)\n",
+			output_fi.crc32sum, ntohl(ih.fw_totalsize), ntohl(ih.fw_totalsize));
+	ret = 0;
 
-	return 0;
+done:
+#define CLOSE_FI_FD(fi)	do {	\
+	if ((fi).fd >= 0) {			\
+		close((fi).fd);			\
+	}							\
+} while (0)
+
+	CLOSE_FI_FD(kernel_fi);
+	CLOSE_FI_FD(rootfs_fi);
+	CLOSE_FI_FD(output_fi);
+	return ret;
 }
