ext4: Use helper function to access group descriptor and its fields

The descriptor size is variable, thus array indices are not generically
applicable. The larger group descriptors also contain e.g. high parts
of block numbers, which have to be read and written.

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c
index b745d8d..90e7602 100644
--- a/fs/ext4/ext4_common.c
+++ b/fs/ext4/ext4_common.c
@@ -393,7 +393,7 @@
 	uint16_t crc = 0;
 	__le32 le32_i = cpu_to_le32(i);
 
-	desc = (struct ext2_block_group *)&fs->bgd[i];
+	desc = ext4fs_get_group_descriptor(fs, i);
 	if (le32_to_cpu(fs->sb->feature_ro_compat) & EXT4_FEATURE_RO_COMPAT_GDT_CSUM) {
 		int offset = offsetof(struct ext2_block_group, bg_checksum);
 
@@ -933,39 +933,41 @@
 	char *zero_buffer = zalloc(fs->blksz);
 	if (!journal_buffer || !zero_buffer)
 		goto fail;
-	struct ext2_block_group *bgd = (struct ext2_block_group *)fs->gdtable;
 
 	if (fs->first_pass_bbmap == 0) {
 		for (i = 0; i < fs->no_blkgrp; i++) {
-			if (le16_to_cpu(bgd[i].free_blocks)) {
-				if (le16_to_cpu(bgd[i].bg_flags) & EXT4_BG_BLOCK_UNINIT) {
-					uint16_t new_flags;
-					put_ext4((uint64_t)le32_to_cpu(bgd[i].block_id) * fs->blksz,
-						 zero_buffer, fs->blksz);
-					new_flags = le16_to_cpu(bgd[i].bg_flags) & ~EXT4_BG_BLOCK_UNINIT;
-					bgd[i].bg_flags = cpu_to_le16(new_flags);
+			struct ext2_block_group *bgd = NULL;
+			bgd = ext4fs_get_group_descriptor(fs, i);
+			if (ext4fs_bg_get_free_blocks(bgd, fs)) {
+				uint16_t bg_flags = ext4fs_bg_get_flags(bgd);
+				uint64_t b_bitmap_blk =
+					ext4fs_bg_get_block_id(bgd, fs);
+				if (bg_flags & EXT4_BG_BLOCK_UNINIT) {
 					memcpy(fs->blk_bmaps[i], zero_buffer,
 					       fs->blksz);
+					put_ext4(b_bitmap_blk * fs->blksz,
+						 fs->blk_bmaps[i], fs->blksz);
+					bg_flags &= ~EXT4_BG_BLOCK_UNINIT;
+					ext4fs_bg_set_flags(bgd, bg_flags);
 				}
 				fs->curr_blkno =
 				    _get_new_blk_no(fs->blk_bmaps[i]);
 				if (fs->curr_blkno == -1)
-					/* if block bitmap is completely fill */
+					/* block bitmap is completely filled */
 					continue;
 				fs->curr_blkno = fs->curr_blkno +
 						(i * fs->blksz * 8);
 				fs->first_pass_bbmap++;
-				ext4fs_bg_free_blocks_dec(&bgd[i]);
+				ext4fs_bg_free_blocks_dec(bgd);
 				ext4fs_sb_free_blocks_dec(fs->sb);
-				status = ext4fs_devread(
-							(lbaint_t)le32_to_cpu(bgd[i].block_id) *
-							fs->sect_perblk, 0,
-							fs->blksz,
+				status = ext4fs_devread(b_bitmap_blk *
+							fs->sect_perblk,
+							0, fs->blksz,
 							journal_buffer);
 				if (status == 0)
 					goto fail;
 				if (ext4fs_log_journal(journal_buffer,
-							le32_to_cpu(bgd[i].block_id)))
+						       b_bitmap_blk))
 					goto fail;
 				goto success;
 			} else {
@@ -992,7 +994,9 @@
 		if (bg_idx >= fs->no_blkgrp)
 			goto fail;
 
-		if (bgd[bg_idx].free_blocks == 0) {
+		struct ext2_block_group *bgd = NULL;
+		bgd = ext4fs_get_group_descriptor(fs, bg_idx);
+		if (ext4fs_bg_get_free_blocks(bgd, fs) == 0) {
 			debug("block group %u is full. Skipping\n", bg_idx);
 			fs->curr_blkno = (bg_idx + 1) * blk_per_grp;
 			if (fs->blksz == 1024)
@@ -1000,13 +1004,14 @@
 			goto restart;
 		}
 
-		if (le16_to_cpu(bgd[bg_idx].bg_flags) & EXT4_BG_BLOCK_UNINIT) {
-			uint16_t new_flags;
-			put_ext4((uint64_t)le32_to_cpu(bgd[bg_idx].block_id) * fs->blksz,
-				 zero_buffer, fs->blksz);
+		uint16_t bg_flags = ext4fs_bg_get_flags(bgd);
+		uint64_t b_bitmap_blk = ext4fs_bg_get_block_id(bgd, fs);
+		if (bg_flags & EXT4_BG_BLOCK_UNINIT) {
 			memcpy(fs->blk_bmaps[bg_idx], zero_buffer, fs->blksz);
-			new_flags = le16_to_cpu(bgd[bg_idx].bg_flags) & ~EXT4_BG_BLOCK_UNINIT;
-			bgd[bg_idx].bg_flags = cpu_to_le16(new_flags);
+			put_ext4(b_bitmap_blk * fs->blksz,
+				 zero_buffer, fs->blksz);
+			bg_flags &= ~EXT4_BG_BLOCK_UNINIT;
+			ext4fs_bg_set_flags(bgd, bg_flags);
 		}
 
 		if (ext4fs_set_block_bmap(fs->curr_blkno, fs->blk_bmaps[bg_idx],
@@ -1019,19 +1024,16 @@
 
 		/* journal backup */
 		if (prev_bg_bitmap_index != bg_idx) {
-			status = ext4fs_devread(
-						(lbaint_t)le32_to_cpu(bgd[bg_idx].block_id)
-						* fs->sect_perblk,
+			status = ext4fs_devread(b_bitmap_blk * fs->sect_perblk,
 						0, fs->blksz, journal_buffer);
 			if (status == 0)
 				goto fail;
-			if (ext4fs_log_journal(journal_buffer,
-						le32_to_cpu(bgd[bg_idx].block_id)))
+			if (ext4fs_log_journal(journal_buffer, b_bitmap_blk))
 				goto fail;
 
 			prev_bg_bitmap_index = bg_idx;
 		}
-		ext4fs_bg_free_blocks_dec(&bgd[bg_idx]);
+		ext4fs_bg_free_blocks_dec(bgd);
 		ext4fs_sb_free_blocks_dec(fs->sb);
 		goto success;
 	}
@@ -1059,46 +1061,49 @@
 	char *zero_buffer = zalloc(fs->blksz);
 	if (!journal_buffer || !zero_buffer)
 		goto fail;
-	struct ext2_block_group *bgd = (struct ext2_block_group *)fs->gdtable;
 	int has_gdt_chksum = le32_to_cpu(fs->sb->feature_ro_compat) &
 		EXT4_FEATURE_RO_COMPAT_GDT_CSUM ? 1 : 0;
 
 	if (fs->first_pass_ibmap == 0) {
 		for (i = 0; i < fs->no_blkgrp; i++) {
-			if (bgd[i].free_inodes) {
+			uint32_t free_inodes;
+			struct ext2_block_group *bgd = NULL;
+			bgd = ext4fs_get_group_descriptor(fs, i);
+			free_inodes = ext4fs_bg_get_free_inodes(bgd, fs);
+			if (free_inodes) {
+				uint16_t bg_flags = ext4fs_bg_get_flags(bgd);
+				uint64_t i_bitmap_blk =
+					ext4fs_bg_get_inode_id(bgd, fs);
 				if (has_gdt_chksum)
-					bgd[i].bg_itable_unused =
-						bgd[i].free_inodes;
-				if (le16_to_cpu(bgd[i].bg_flags) & EXT4_BG_INODE_UNINIT) {
-					int new_flags;
-					put_ext4((uint64_t)le32_to_cpu(bgd[i].inode_id) * fs->blksz,
+					bgd->bg_itable_unused = free_inodes;
+				if (bg_flags & EXT4_BG_INODE_UNINIT) {
+					put_ext4(i_bitmap_blk * fs->blksz,
 						 zero_buffer, fs->blksz);
-					new_flags = le16_to_cpu(bgd[i].bg_flags) & ~EXT4_BG_INODE_UNINIT;
-					bgd[i].bg_flags = cpu_to_le16(new_flags);
+					bg_flags &= ~EXT4_BG_INODE_UNINIT;
+					ext4fs_bg_set_flags(bgd, bg_flags);
 					memcpy(fs->inode_bmaps[i],
 					       zero_buffer, fs->blksz);
 				}
 				fs->curr_inode_no =
 				    _get_new_inode_no(fs->inode_bmaps[i]);
 				if (fs->curr_inode_no == -1)
-					/* if block bitmap is completely fill */
+					/* inode bitmap is completely filled */
 					continue;
 				fs->curr_inode_no = fs->curr_inode_no +
 							(i * inodes_per_grp);
 				fs->first_pass_ibmap++;
-				ext4fs_bg_free_inodes_dec(&bgd[i]);
+				ext4fs_bg_free_inodes_dec(bgd);
 				if (has_gdt_chksum)
-					ext4fs_bg_itable_unused_dec(&bgd[i]);
+					ext4fs_bg_itable_unused_dec(bgd);
 				ext4fs_sb_free_inodes_dec(fs->sb);
-				status = ext4fs_devread(
-							(lbaint_t)le32_to_cpu(bgd[i].inode_id) *
-							fs->sect_perblk, 0,
-							fs->blksz,
+				status = ext4fs_devread(i_bitmap_blk *
+							fs->sect_perblk,
+							0, fs->blksz,
 							journal_buffer);
 				if (status == 0)
 					goto fail;
 				if (ext4fs_log_journal(journal_buffer,
-							le32_to_cpu(bgd[i].inode_id)))
+						       i_bitmap_blk))
 					goto fail;
 				goto success;
 			} else
@@ -1110,12 +1115,16 @@
 		fs->curr_inode_no++;
 		/* get the blockbitmap index respective to blockno */
 		ibmap_idx = fs->curr_inode_no / inodes_per_grp;
-		if (le16_to_cpu(bgd[ibmap_idx].bg_flags) & EXT4_BG_INODE_UNINIT) {
-			int new_flags;
-			put_ext4((uint64_t)le32_to_cpu(bgd[ibmap_idx].inode_id) * fs->blksz,
+		struct ext2_block_group *bgd =
+			ext4fs_get_group_descriptor(fs, ibmap_idx);
+		uint16_t bg_flags = ext4fs_bg_get_flags(bgd);
+		uint64_t i_bitmap_blk = ext4fs_bg_get_inode_id(bgd, fs);
+
+		if (bg_flags & EXT4_BG_INODE_UNINIT) {
+			put_ext4(i_bitmap_blk * fs->blksz,
 				 zero_buffer, fs->blksz);
-			new_flags = le16_to_cpu(bgd[ibmap_idx].bg_flags) & ~EXT4_BG_INODE_UNINIT;
-			bgd[ibmap_idx].bg_flags = cpu_to_le16(new_flags);
+			bg_flags &= ~EXT4_BG_INODE_UNINIT;
+			ext4fs_bg_set_flags(bgd, bg_flags);
 			memcpy(fs->inode_bmaps[ibmap_idx], zero_buffer,
 				fs->blksz);
 		}
@@ -1130,22 +1139,18 @@
 
 		/* journal backup */
 		if (prev_inode_bitmap_index != ibmap_idx) {
-			memset(journal_buffer, '\0', fs->blksz);
-			status = ext4fs_devread(
-						(lbaint_t)le32_to_cpu(bgd[ibmap_idx].inode_id)
-						* fs->sect_perblk,
+			status = ext4fs_devread(i_bitmap_blk * fs->sect_perblk,
 						0, fs->blksz, journal_buffer);
 			if (status == 0)
 				goto fail;
 			if (ext4fs_log_journal(journal_buffer,
-						le32_to_cpu(bgd[ibmap_idx].inode_id)))
+						le32_to_cpu(bgd->inode_id)))
 				goto fail;
 			prev_inode_bitmap_index = ibmap_idx;
 		}
-		ext4fs_bg_free_inodes_dec(&bgd[ibmap_idx]);
+		ext4fs_bg_free_inodes_dec(bgd);
 		if (has_gdt_chksum)
-			bgd[ibmap_idx].bg_itable_unused =
-					bgd[ibmap_idx].free_inodes;
+			bgd->bg_itable_unused = bgd->free_inodes;
 		ext4fs_sb_free_inodes_dec(fs->sb);
 		goto success;
 	}
@@ -1561,7 +1566,7 @@
 		return 0;
 
 	inodes_per_block = EXT2_BLOCK_SIZE(data) / fs->inodesz;
-	blkno = le32_to_cpu(blkgrp.inode_table_id) +
+	blkno = ext4fs_bg_get_inode_table_id(&blkgrp, fs) +
 	    (ino % le32_to_cpu(sblock->inodes_per_group)) / inodes_per_block;
 	blkoff = (ino % inodes_per_block) * fs->inodesz;
 	/* Read the inode. */
diff --git a/fs/ext4/ext4_write.c b/fs/ext4/ext4_write.c
index e4f0905..2c123e3 100644
--- a/fs/ext4/ext4_write.c
+++ b/fs/ext4/ext4_write.c
@@ -53,21 +53,26 @@
 	short i;
 	ext4fs_update_journal();
 	struct ext_filesystem *fs = get_fs();
+	struct ext2_block_group *bgd = NULL;
 
 	/* update  super block */
 	put_ext4((uint64_t)(SUPERBLOCK_SIZE),
 		 (struct ext2_sblock *)fs->sb, (uint32_t)SUPERBLOCK_SIZE);
 
-	/* update block groups */
+	/* update block bitmaps */
 	for (i = 0; i < fs->no_blkgrp; i++) {
-		fs->bgd[i].bg_checksum = cpu_to_le16(ext4fs_checksum_update(i));
-		put_ext4((uint64_t)le32_to_cpu(fs->bgd[i].block_id) * fs->blksz,
+		bgd = ext4fs_get_group_descriptor(fs, i);
+		bgd->bg_checksum = cpu_to_le16(ext4fs_checksum_update(i));
+		uint64_t b_bitmap_blk = ext4fs_bg_get_block_id(bgd, fs);
+		put_ext4(b_bitmap_blk * fs->blksz,
 			 fs->blk_bmaps[i], fs->blksz);
 	}
 
-	/* update inode table groups */
+	/* update inode bitmaps */
 	for (i = 0; i < fs->no_blkgrp; i++) {
-		put_ext4((uint64_t)le32_to_cpu(fs->bgd[i].inode_id) * fs->blksz,
+		bgd = ext4fs_get_group_descriptor(fs, i);
+		uint64_t i_bitmap_blk = ext4fs_bg_get_inode_id(bgd, fs);
+		put_ext4(i_bitmap_blk * fs->blksz,
 			 fs->inode_bmaps[i], fs->blksz);
 	}
 
@@ -85,15 +90,12 @@
 int ext4fs_get_bgdtable(void)
 {
 	int status;
-	int grp_desc_size;
 	struct ext_filesystem *fs = get_fs();
-	grp_desc_size = sizeof(struct ext2_block_group);
-	fs->no_blk_pergdt = (fs->no_blkgrp * grp_desc_size) / fs->blksz;
-	if ((fs->no_blkgrp * grp_desc_size) % fs->blksz)
-		fs->no_blk_pergdt++;
+	int gdsize_total = ROUND(fs->no_blkgrp * fs->gdsize, fs->blksz);
+	fs->no_blk_pergdt = gdsize_total / fs->blksz;
 
 	/* allocate memory for gdtable */
-	fs->gdtable = zalloc(fs->blksz * fs->no_blk_pergdt);
+	fs->gdtable = zalloc(gdsize_total);
 	if (!fs->gdtable)
 		return -ENOMEM;
 	/* read the group descriptor table */
@@ -130,8 +132,6 @@
 		printf("No memory\n");
 		return;
 	}
-	/* get  block group descriptor table */
-	bgd = (struct ext2_block_group *)fs->gdtable;
 
 	/* deleting the single indirect block associated with inode */
 	if (inode->b.blocks.indir_block != 0) {
@@ -144,18 +144,19 @@
 				bg_idx--;
 		}
 		ext4fs_reset_block_bmap(blknr, fs->blk_bmaps[bg_idx], bg_idx);
-		ext4fs_bg_free_blocks_inc(&bgd[bg_idx]);
+		/* get  block group descriptor table */
+		bgd = ext4fs_get_group_descriptor(fs, bg_idx);
+		ext4fs_bg_free_blocks_inc(bgd);
 		ext4fs_sb_free_blocks_inc(fs->sb);
 		/* journal backup */
 		if (prev_bg_bmap_idx != bg_idx) {
+			uint64_t b_bitmap_blk = ext4fs_bg_get_block_id(bgd, fs);
 			status = ext4fs_devread(
-					   (lbaint_t)le32_to_cpu(bgd[bg_idx].block_id) *
-					   fs->sect_perblk, 0, fs->blksz,
-					   journal_buffer);
+					   b_bitmap_blk * fs->sect_perblk,
+					   0, fs->blksz, journal_buffer);
 			if (status == 0)
 				goto fail;
-			if (ext4fs_log_journal
-			    (journal_buffer, le32_to_cpu(bgd[bg_idx].block_id)))
+			if (ext4fs_log_journal(journal_buffer, b_bitmap_blk))
 				goto fail;
 			prev_bg_bmap_idx = bg_idx;
 		}
@@ -182,8 +183,6 @@
 		printf("No memory\n");
 		return;
 	}
-	/* get the block group descriptor table */
-	bgd = (struct ext2_block_group *)fs->gdtable;
 
 	if (inode->b.blocks.double_indir_block != 0) {
 		di_buffer = zalloc(fs->blksz);
@@ -206,15 +205,18 @@
 				if (!remainder)
 					bg_idx--;
 			}
+			/* get  block group descriptor table */
+			bgd = ext4fs_get_group_descriptor(fs, bg_idx);
 			ext4fs_reset_block_bmap(le32_to_cpu(*di_buffer),
 					fs->blk_bmaps[bg_idx], bg_idx);
 			di_buffer++;
-			ext4fs_bg_free_blocks_inc(&bgd[bg_idx]);
+			ext4fs_bg_free_blocks_inc(bgd);
 			ext4fs_sb_free_blocks_inc(fs->sb);
 			/* journal backup */
 			if (prev_bg_bmap_idx != bg_idx) {
-				status = ext4fs_devread(
-							(lbaint_t)le32_to_cpu(bgd[bg_idx].block_id)
+				uint64_t b_bitmap_blk =
+					ext4fs_bg_get_block_id(bgd, fs);
+				status = ext4fs_devread(b_bitmap_blk
 							* fs->sect_perblk, 0,
 							fs->blksz,
 							journal_buffer);
@@ -222,7 +224,7 @@
 					goto fail;
 
 				if (ext4fs_log_journal(journal_buffer,
-							le32_to_cpu(bgd[bg_idx].block_id)))
+						       b_bitmap_blk))
 					goto fail;
 				prev_bg_bmap_idx = bg_idx;
 			}
@@ -236,20 +238,20 @@
 			if (!remainder)
 				bg_idx--;
 		}
+		/* get  block group descriptor table */
+		bgd = ext4fs_get_group_descriptor(fs, bg_idx);
 		ext4fs_reset_block_bmap(blknr, fs->blk_bmaps[bg_idx], bg_idx);
-		ext4fs_bg_free_blocks_inc(&bgd[bg_idx]);
+		ext4fs_bg_free_blocks_inc(bgd);
 		ext4fs_sb_free_blocks_inc(fs->sb);
 		/* journal backup */
 		if (prev_bg_bmap_idx != bg_idx) {
-			memset(journal_buffer, '\0', fs->blksz);
-			status = ext4fs_devread((lbaint_t)le32_to_cpu(bgd[bg_idx].block_id) *
-						fs->sect_perblk, 0, fs->blksz,
-						journal_buffer);
+			uint64_t b_bitmap_blk = ext4fs_bg_get_block_id(bgd, fs);
+			status = ext4fs_devread(b_bitmap_blk * fs->sect_perblk,
+						0, fs->blksz, journal_buffer);
 			if (status == 0)
 				goto fail;
 
-			if (ext4fs_log_journal(journal_buffer,
-						le32_to_cpu(bgd[bg_idx].block_id)))
+			if (ext4fs_log_journal(journal_buffer, b_bitmap_blk))
 				goto fail;
 			prev_bg_bmap_idx = bg_idx;
 		}
@@ -280,8 +282,6 @@
 		printf("No memory\n");
 		return;
 	}
-	/* get block group descriptor table */
-	bgd = (struct ext2_block_group *)fs->gdtable;
 
 	if (inode->b.blocks.triple_indir_block != 0) {
 		tigp_buffer = zalloc(fs->blksz);
@@ -320,13 +320,17 @@
 							bg_idx);
 
 				tip_buffer++;
-				ext4fs_bg_free_blocks_inc(&bgd[bg_idx]);
+				/* get  block group descriptor table */
+				bgd = ext4fs_get_group_descriptor(fs, bg_idx);
+				ext4fs_bg_free_blocks_inc(bgd);
 				ext4fs_sb_free_blocks_inc(fs->sb);
 				/* journal backup */
 				if (prev_bg_bmap_idx != bg_idx) {
+					uint64_t b_bitmap_blk =
+						ext4fs_bg_get_block_id(bgd, fs);
 					status =
 					    ext4fs_devread(
-							(lbaint_t)le32_to_cpu(bgd[bg_idx].block_id) *
+							b_bitmap_blk *
 							fs->sect_perblk, 0,
 							fs->blksz,
 							journal_buffer);
@@ -334,7 +338,7 @@
 						goto fail;
 
 					if (ext4fs_log_journal(journal_buffer,
-							       le32_to_cpu(bgd[bg_idx].block_id)))
+							       b_bitmap_blk))
 						goto fail;
 					prev_bg_bmap_idx = bg_idx;
 				}
@@ -356,21 +360,24 @@
 						fs->blk_bmaps[bg_idx], bg_idx);
 
 			tigp_buffer++;
-			ext4fs_bg_free_blocks_inc(&bgd[bg_idx]);
+			/* get  block group descriptor table */
+			bgd = ext4fs_get_group_descriptor(fs, bg_idx);
+			ext4fs_bg_free_blocks_inc(bgd);
 			ext4fs_sb_free_blocks_inc(fs->sb);
 			/* journal backup */
 			if (prev_bg_bmap_idx != bg_idx) {
+				uint64_t b_bitmap_blk =
+					ext4fs_bg_get_block_id(bgd, fs);
 				memset(journal_buffer, '\0', fs->blksz);
-				status =
-				    ext4fs_devread(
-						   (lbaint_t)le32_to_cpu(bgd[bg_idx].block_id) *
-						   fs->sect_perblk, 0,
-						   fs->blksz, journal_buffer);
+				status = ext4fs_devread(b_bitmap_blk *
+							fs->sect_perblk, 0,
+							fs->blksz,
+							journal_buffer);
 				if (status == 0)
 					goto fail;
 
 				if (ext4fs_log_journal(journal_buffer,
-							le32_to_cpu(bgd[bg_idx].block_id)))
+						       b_bitmap_blk))
 					goto fail;
 				prev_bg_bmap_idx = bg_idx;
 			}
@@ -385,20 +392,19 @@
 				bg_idx--;
 		}
 		ext4fs_reset_block_bmap(blknr, fs->blk_bmaps[bg_idx], bg_idx);
-		ext4fs_bg_free_blocks_inc(&bgd[bg_idx]);
+		/* get  block group descriptor table */
+		bgd = ext4fs_get_group_descriptor(fs, bg_idx);
+		ext4fs_bg_free_blocks_inc(bgd);
 		ext4fs_sb_free_blocks_inc(fs->sb);
 		/* journal backup */
 		if (prev_bg_bmap_idx != bg_idx) {
-			memset(journal_buffer, '\0', fs->blksz);
-			status = ext4fs_devread(
-						(lbaint_t)le32_to_cpu(bgd[bg_idx].block_id) *
-						fs->sect_perblk, 0, fs->blksz,
-						journal_buffer);
+			uint64_t b_bitmap_blk = ext4fs_bg_get_block_id(bgd, fs);
+			status = ext4fs_devread(b_bitmap_blk * fs->sect_perblk,
+						0, fs->blksz, journal_buffer);
 			if (status == 0)
 				goto fail;
 
-			if (ext4fs_log_journal(journal_buffer,
-						le32_to_cpu(bgd[bg_idx].block_id)))
+			if (ext4fs_log_journal(journal_buffer, b_bitmap_blk))
 				goto fail;
 			prev_bg_bmap_idx = bg_idx;
 		}
@@ -435,8 +441,6 @@
 	char *journal_buffer = zalloc(fs->blksz);
 	if (!journal_buffer)
 		return -ENOMEM;
-	/* get the block group descriptor table */
-	bgd = (struct ext2_block_group *)fs->gdtable;
 	status = ext4fs_read_inode(ext4fs_root, inodeno, &inode);
 	if (status == 0)
 		goto fail;
@@ -475,18 +479,19 @@
 					bg_idx);
 		debug("EXT4 Block releasing %ld: %d\n", blknr, bg_idx);
 
-		ext4fs_bg_free_blocks_inc(&bgd[bg_idx]);
+		/* get  block group descriptor table */
+		bgd = ext4fs_get_group_descriptor(fs, bg_idx);
+		ext4fs_bg_free_blocks_inc(bgd);
 		ext4fs_sb_free_blocks_inc(fs->sb);
 		/* journal backup */
 		if (prev_bg_bmap_idx != bg_idx) {
-			uint32_t bgd_blknr = le32_to_cpu(bgd[bg_idx].block_id);
-			status = ext4fs_devread((lbaint_t)bgd_blknr *
-						fs->sect_perblk,
+			uint64_t b_bitmap_blk = ext4fs_bg_get_block_id(bgd, fs);
+			status = ext4fs_devread(b_bitmap_blk * fs->sect_perblk,
 						0, fs->blksz,
 						journal_buffer);
 			if (status == 0)
 				goto fail;
-			if (ext4fs_log_journal(journal_buffer, bgd_blknr))
+			if (ext4fs_log_journal(journal_buffer, b_bitmap_blk))
 				goto fail;
 			prev_bg_bmap_idx = bg_idx;
 		}
@@ -499,7 +504,9 @@
 
 	/* get the block no */
 	inodeno--;
-	blkno = le32_to_cpu(bgd[ibmap_idx].inode_table_id) +
+	/* get  block group descriptor table */
+	bgd = ext4fs_get_group_descriptor(fs, ibmap_idx);
+	blkno = ext4fs_bg_get_inode_table_id(bgd, fs) +
 		(inodeno % inode_per_grp) / inodes_per_block;
 
 	/* get the offset of the inode */
@@ -529,15 +536,15 @@
 	/* update the respective inode bitmaps */
 	inodeno++;
 	ext4fs_reset_inode_bmap(inodeno, fs->inode_bmaps[ibmap_idx], ibmap_idx);
-	ext4fs_bg_free_inodes_inc(&bgd[ibmap_idx]);
+	ext4fs_bg_free_inodes_inc(bgd);
 	ext4fs_sb_free_inodes_inc(fs->sb);
 	/* journal backup */
 	memset(journal_buffer, '\0', fs->blksz);
-	status = ext4fs_devread((lbaint_t)le32_to_cpu(bgd[ibmap_idx].inode_id) *
+	status = ext4fs_devread(ext4fs_bg_get_inode_id(bgd, fs) *
 				fs->sect_perblk, 0, fs->blksz, journal_buffer);
 	if (status == 0)
 		goto fail;
-	if (ext4fs_log_journal(journal_buffer, le32_to_cpu(bgd[ibmap_idx].inode_id)))
+	if (ext4fs_log_journal(journal_buffer, ext4fs_bg_get_inode_id(bgd, fs)))
 		goto fail;
 
 	ext4fs_update();
@@ -594,7 +601,6 @@
 		printf("Error in getting the block group descriptor table\n");
 		goto fail;
 	}
-	fs->bgd = (struct ext2_block_group *)fs->gdtable;
 
 	/* load all the available bitmap block of the partition */
 	fs->blk_bmaps = zalloc(fs->no_blkgrp * sizeof(char *));
@@ -607,9 +613,9 @@
 	}
 
 	for (i = 0; i < fs->no_blkgrp; i++) {
-		status =
-		    ext4fs_devread(
-				   (lbaint_t)le32_to_cpu(fs->bgd[i].block_id) *
+		struct ext2_block_group *bgd =
+			ext4fs_get_group_descriptor(fs, i);
+		status = ext4fs_devread(ext4fs_bg_get_block_id(bgd, fs) *
 				   fs->sect_perblk, 0,
 				   fs->blksz, (char *)fs->blk_bmaps[i]);
 		if (status == 0)
@@ -627,8 +633,9 @@
 	}
 
 	for (i = 0; i < fs->no_blkgrp; i++) {
-		status = ext4fs_devread(
-					(lbaint_t)le32_to_cpu(fs->bgd[i].inode_id) *
+		struct ext2_block_group *bgd =
+			ext4fs_get_group_descriptor(fs, i);
+		status = ext4fs_devread(ext4fs_bg_get_inode_id(bgd, fs) *
 					fs->sect_perblk,
 					0, fs->blksz,
 					(char *)fs->inode_bmaps[i]);
@@ -642,10 +649,14 @@
 	 * with the  blockgroups freeblocks when improper
 	 * reboot of a linux kernel
 	 */
-	for (i = 0; i < fs->no_blkgrp; i++)
-		real_free_blocks = real_free_blocks + le16_to_cpu(fs->bgd[i].free_blocks);
-	if (real_free_blocks != le32_to_cpu(fs->sb->free_blocks))
-		fs->sb->free_blocks = cpu_to_le32(real_free_blocks);
+	for (i = 0; i < fs->no_blkgrp; i++) {
+		struct ext2_block_group *bgd =
+			ext4fs_get_group_descriptor(fs, i);
+		real_free_blocks = real_free_blocks +
+			ext4fs_bg_get_free_blocks(bgd, fs);
+	}
+	if (real_free_blocks != ext4fs_sb_get_free_blocks(fs->sb))
+		ext4fs_sb_set_free_blocks(fs->sb, real_free_blocks);
 
 	return 0;
 fail:
@@ -711,7 +722,6 @@
 
 	free(fs->gdtable);
 	fs->gdtable = NULL;
-	fs->bgd = NULL;
 	/*
 	 * reinitiliazed the global inode and
 	 * block bitmap first execution check variables
@@ -826,6 +836,7 @@
 	struct ext2_sblock *sblock = &(ext4fs_root->sblock);
 	unsigned int inodes_per_block;
 	unsigned int ibmap_idx;
+	struct ext2_block_group *bgd = NULL;
 	struct ext_filesystem *fs = get_fs();
 	ALLOC_CACHE_ALIGN_BUFFER(char, filename, 256);
 	memset(filename, 0x00, 256);
@@ -903,7 +914,8 @@
 		goto fail;
 	ibmap_idx = inodeno / le32_to_cpu(ext4fs_root->sblock.inodes_per_group);
 	inodeno--;
-	itable_blkno = le32_to_cpu(fs->bgd[ibmap_idx].inode_table_id) +
+	bgd = ext4fs_get_group_descriptor(fs, ibmap_idx);
+	itable_blkno = ext4fs_bg_get_inode_table_id(bgd, fs) +
 			(inodeno % le32_to_cpu(sblock->inodes_per_group)) /
 			inodes_per_block;
 	blkoff = (inodeno % inodes_per_block) * fs->inodesz;
@@ -923,7 +935,8 @@
 	}
 	ibmap_idx = parent_inodeno / le32_to_cpu(ext4fs_root->sblock.inodes_per_group);
 	parent_inodeno--;
-	parent_itable_blkno = le32_to_cpu(fs->bgd[ibmap_idx].inode_table_id) +
+	bgd = ext4fs_get_group_descriptor(fs, ibmap_idx);
+	parent_itable_blkno = ext4fs_bg_get_inode_table_id(bgd, fs) +
 	    (parent_inodeno %
 	     le32_to_cpu(sblock->inodes_per_group)) / inodes_per_block;
 	blkoff = (parent_inodeno % inodes_per_block) * fs->inodesz;
diff --git a/include/ext4fs.h b/include/ext4fs.h
index 7e1ee6c..965cd9e 100644
--- a/include/ext4fs.h
+++ b/include/ext4fs.h
@@ -98,7 +98,6 @@
 	/* Superblock */
 	struct ext2_sblock *sb;
 	/* Block group descritpor table */
-	struct ext2_block_group *bgd;
 	char *gdtable;
 
 	/* Block Bitmap Related */