diff --git a/Makefile b/Makefile
index 0188ca8..3c2fe53 100644
--- a/Makefile
+++ b/Makefile
@@ -1,8 +1,8 @@
 all: realloc-inodes e2patch
 realloc-inodes: realloc-inodes.c bmove.c bmove.h check_uninit.c check_uninit.h Makefile patch_io.c patch_io.h patch.c patch.h
-	gcc -g -Wsign-compare -Wall -o realloc-inodes -lcom_err -lext2fs realloc-inodes.c bmove.c patch_io.c patch.c check_uninit.c
+	gcc -D_FILE_OFFSET_BITS=64 -g -Wsign-compare -Wall -o realloc-inodes -lcom_err -lext2fs realloc-inodes.c bmove.c patch_io.c patch.c check_uninit.c
 e2patch: e2patch.c patch.c patch.h
-	gcc -g -Wsign-compare -Wall -o e2patch -lcom_err -lext2fs e2patch.c patch.c
+	gcc -D_FILE_OFFSET_BITS=64 -g -Wsign-compare -Wall -o e2patch -lcom_err -lext2fs e2patch.c patch.c
 test-ext2.img:
 	sudo sh test-mkimages.sh
 	sudo chown $(shell id -u) *.img
diff --git a/e2patch.c b/e2patch.c
index bc4db5f..a3bde5d 100644
--- a/e2patch.c
+++ b/e2patch.c
@@ -45,7 +45,7 @@ errcode_t make_backup_patch(char *device, char *io_options, char *patch_file, ch
     blk64_t blk, start, buf_blocks;
     int eq;
     void *buf = NULL;
-    struct ext2fs_patch_file patch, backup;
+    struct ext2fs_patch_file patch = { 0 }, backup = { 0 };
     retval = mgr->open(device, IO_FLAG_EXCLUSIVE, &io);
     if (retval) goto out;
     if (io_options &&
@@ -93,7 +93,7 @@ errcode_t apply_patch(char *device, char *io_options, char *patch_file)
     blk64_t blk, start, buf_blocks;
     int eq;
     void *buf = NULL;
-    struct ext2fs_patch_file patch;
+    struct ext2fs_patch_file patch = { 0 };
     retval = mgr->open(device, IO_FLAG_EXCLUSIVE|IO_FLAG_RW, &io);
     if (retval) goto out;
     if (io_options &&
@@ -111,7 +111,7 @@ errcode_t apply_patch(char *device, char *io_options, char *patch_file)
         {
             if (start != blk)
             {
-                retval = retry_read_at(patch.patch_fd, start*patch.block_size, (blk-start)*patch.block_size, buf);
+                retval = retry_read_at(patch.patch_fd, patch.offset + start*patch.block_size, (blk-start)*patch.block_size, buf);
                 if (retval) goto out;
                 retval = io_channel_write_blk64(io, start, blk-start, buf);
                 if (retval) goto out;
diff --git a/patch.c b/patch.c
index 159dbcb..4725d97 100644
--- a/patch.c
+++ b/patch.c
@@ -32,7 +32,7 @@ errcode_t retry_read(int fd, ssize_t size, void *buf)
 	while (done < size)
 	{
 		r = read(fd, buf+done, size-done);
-		if (r < 0 && errno != EAGAIN)
+		if (!r || (r < 0 && errno != EAGAIN))
 			break;
 		done += r;
 	}
@@ -47,7 +47,7 @@ errcode_t retry_write(int fd, ssize_t size, const void *buf)
 	while (done < size)
 	{
 		r = write(fd, buf+done, size-done);
-		if (r < 0 && errno != EAGAIN)
+		if (r <= 0 && errno != EAGAIN)
 			break;
 		done += r;
 	}
@@ -78,7 +78,7 @@ errcode_t ext2fs_patch_read_bmap(struct ext2fs_patch_file *data)
 	void *buf = malloc(bufsize);
 	if (!buf)
 		return ENOMEM;
-	ext2fs_llseek(data->patch_fd, data->size*data->block_size, SEEK_SET);
+	ext2fs_llseek(data->patch_fd, data->block_size, SEEK_SET);
 	for (i = 0; i < data->size/8; )
 	{
 		r = bufsize;
@@ -100,10 +100,11 @@ errcode_t ext2fs_patch_write_bmap(struct ext2fs_patch_file *data)
 	errcode_t retval = 0;
 	int bufsize = 65536;
 	blk64_t i, r;
+	struct patchbd_super s;
 	void *buf = malloc(bufsize);
 	if (!buf)
 		return ENOMEM;
-	ext2fs_llseek(data->patch_fd, data->size*data->block_size, SEEK_SET);
+	ext2fs_llseek(data->patch_fd, data->block_size, SEEK_SET);
 	for (i = 0; i < data->size/8; )
 	{
 		r = bufsize;
@@ -115,8 +116,11 @@ errcode_t ext2fs_patch_write_bmap(struct ext2fs_patch_file *data)
 			goto out;
 		i += r;
 	}
-	write(data->patch_fd, &data->block_size, sizeof(__u32));
-	write(data->patch_fd, &data->size, sizeof(blk64_t));
+	ext2fs_llseek(data->patch_fd, 0, SEEK_SET);
+	s.magic = PATCHBD_MAGIC;
+	s.patch_block = data->block_size;
+	s.patch_size = data->size;
+	write(data->patch_fd, &s, sizeof(struct patchbd_super));
 out:
 	free(buf);
 	return 0;
@@ -126,8 +130,10 @@ errcode_t ext2fs_patch_open(struct ext2fs_patch_file *data, char *patch_file, in
 {
 	errcode_t retval = 0;
 	ext2_loff_t size;
+	struct patchbd_super s;
 	data->block_size = 0;
 	data->size = 0;
+	data->offset = 0;
 	data->bmap = NULL;
 	data->patch_file = strdup(patch_file);
 	data->patch_fd = open(data->patch_file, flags|O_RDWR, 0666);
@@ -138,9 +144,14 @@ errcode_t ext2fs_patch_open(struct ext2fs_patch_file *data, char *patch_file, in
 		return errno;
 	if (size > 0)
 	{
-		size = ext2fs_llseek(data->patch_fd, size-sizeof(__u32)-sizeof(blk64_t), SEEK_SET);
-		read(data->patch_fd, &data->block_size, sizeof(__u32));
-		read(data->patch_fd, &data->size, sizeof(blk64_t));
+		size = ext2fs_llseek(data->patch_fd, 0, SEEK_SET);
+		read(data->patch_fd, &s, sizeof(struct patchbd_super));
+		if (s.magic != PATCHBD_MAGIC)
+			return 0;
+		data->block_size = s.patch_block;
+//		if (data->block_size != 4096)
+//			return EINVAL;
+		data->size = s.patch_size;
 		retval = ext2fs_patch_init_bmap(data, NULL);
 		if (retval)
 			return retval;
@@ -181,7 +192,10 @@ errcode_t ext2fs_patch_init_bmap(struct ext2fs_patch_file *data, io_channel chan
 	{
 		if (channel)
 		{
+			// channel is optional parameter, if passed, means 'take size from channel'
 			data->block_size = channel->block_size;
+//			if (data->block_size != 4096)
+//				return EINVAL;
 			retval = ext2fs_get_device_size2(channel->name, data->block_size, &data->size);
 			if (retval)
 				return retval;
@@ -190,6 +204,7 @@ errcode_t ext2fs_patch_init_bmap(struct ext2fs_patch_file *data, io_channel chan
 			return EINVAL;
 		retval = ext2fs_make_generic_bitmap(EXT2_ET_MAGIC_BLOCK_BITMAP, NULL,
 			0, data->size, data->size, "overwritten blocks", 0, &data->bmap);
+		data->offset = data->block_size + ((((data->size+7)>>3)+(data->block_size-1))&~(data->block_size-1));
 	}
 	return retval;
 }
@@ -209,5 +224,5 @@ errcode_t ext2fs_patch_write_blk64(struct ext2fs_patch_file *data, unsigned long
 	else
 		size = count*data->block_size;
 	ext2fs_mark_block_bitmap_range2(data->bmap, block, count);
-	return retry_write_at(data->patch_fd, block*data->block_size, size, buf);
+	return retry_write_at(data->patch_fd, data->offset + block*data->block_size, size, buf);
 }
diff --git a/patch.h b/patch.h
index 9cf23f1..a75bd21 100644
--- a/patch.h
+++ b/patch.h
@@ -31,15 +31,25 @@
 #include <ext2fs/ext2_fs.h>
 #include <ext2fs/ext2fs.h>
 
+#define PATCHBD_MAGIC 0x44623950 // P9bD
+
 struct ext2fs_patch_file
 {
 	char *patch_file;
 	int patch_fd;
 	__u32 block_size;
 	blk64_t size;
+	ext2_loff_t offset;
 	ext2fs_generic_bitmap bmap;
 };
 
+struct patchbd_super
+{
+	__u32 magic;
+	__u32 patch_block;
+	__u64 patch_size;
+};
+
 errcode_t retry_read(int fd, ssize_t size, void *buf);
 errcode_t retry_write(int fd, ssize_t size, const void *buf);
 errcode_t retry_read_at(int fd, unsigned long long offset, ssize_t size, void *buf);
diff --git a/patch_io.c b/patch_io.c
index de8fab9..d273216 100644
--- a/patch_io.c
+++ b/patch_io.c
@@ -222,7 +222,7 @@ static errcode_t patch_read_blk64(io_channel channel, unsigned long long block,
 		if (-count <= channel->block_size)
 		{
 			if (data->patch.bmap && ext2fs_test_generic_bitmap(data->patch.bmap, block))
-				retval = retry_read_at(data->patch.patch_fd, block*channel->block_size, -count, buf);
+				retval = retry_read_at(data->patch.patch_fd, data->patch.offset + block*channel->block_size, -count, buf);
 			else
 				retval = io_channel_read_blk64(data->real, block, count, buf);
 			return retval;
@@ -235,7 +235,7 @@ static errcode_t patch_read_blk64(io_channel channel, unsigned long long block,
 		for (n = 0; (b+n < count) && data->patch.bmap && ext2fs_test_generic_bitmap(data->patch.bmap, block+b+n); n++) {}
 		if (n > 0)
 		{
-			retval = retry_read_at(data->patch.patch_fd, (block+b)*channel->block_size, n*channel->block_size, buf+b*channel->block_size);
+			retval = retry_read_at(data->patch.patch_fd, data->patch.offset + (block+b)*channel->block_size, n*channel->block_size, buf+b*channel->block_size);
 			if (retval)
 				break;
 			b += n;