+/* Initializes an uninitialized block bitmap if given, and returns the
+ * number of blocks free in the group. */
+unsigned ext4_init_block_bitmap(struct super_block *sb, struct buffer_head *bh,
+ int block_group, struct ext4_group_desc *gdp)
+{
+ unsigned long start;
+ int bit, bit_max;
+ unsigned free_blocks, group_blocks;
+ struct ext4_sb_info *sbi = EXT4_SB(sb);
+
+ if (bh) {
+ J_ASSERT_BH(bh, buffer_locked(bh));
+
+ /* If checksum is bad mark all blocks used to prevent allocation
+ * essentially implementing a per-group read-only flag. */
+ if (!ext4_group_desc_csum_verify(sbi, block_group, gdp)) {
+ ext4_error(sb, __FUNCTION__,
+ "Checksum bad for group %u\n", block_group);
+ gdp->bg_free_blocks_count = 0;
+ gdp->bg_free_inodes_count = 0;
+ gdp->bg_itable_unused = 0;
+ memset(bh->b_data, 0xff, sb->s_blocksize);
+ return 0;
+ }
+ memset(bh->b_data, 0, sb->s_blocksize);
+ }
+
+ /* Check for superblock and gdt backups in this group */
+ bit_max = ext4_bg_has_super(sb, block_group);
+
+ if (!EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_META_BG) ||
+ block_group < le32_to_cpu(sbi->s_es->s_first_meta_bg) *
+ sbi->s_desc_per_block) {
+ if (bit_max) {
+ bit_max += ext4_bg_num_gdb(sb, block_group);
+ bit_max +=
+ le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks);
+ }
+ } else { /* For META_BG_BLOCK_GROUPS */
+ int group_rel = (block_group -
+ le32_to_cpu(sbi->s_es->s_first_meta_bg)) %
+ EXT4_DESC_PER_BLOCK(sb);
+ if (group_rel == 0 || group_rel == 1 ||
+ (group_rel == EXT4_DESC_PER_BLOCK(sb) - 1))
+ bit_max += 1;
+ }
+
+ if (block_group == sbi->s_groups_count - 1) {
+ /*
+ * Even though mke2fs always initialize first and last group
+ * if some other tool enabled the EXT4_BG_BLOCK_UNINIT we need
+ * to make sure we calculate the right free blocks
+ */
+ group_blocks = ext4_blocks_count(sbi->s_es) -
+ le32_to_cpu(sbi->s_es->s_first_data_block) -
+ (EXT4_BLOCKS_PER_GROUP(sb) * (sbi->s_groups_count -1));
+ } else {
+ group_blocks = EXT4_BLOCKS_PER_GROUP(sb);
+ }
+
+ free_blocks = group_blocks - bit_max;
+
+ if (bh) {
+ for (bit = 0; bit < bit_max; bit++)
+ ext4_set_bit(bit, bh->b_data);
+
+ start = block_group * EXT4_BLOCKS_PER_GROUP(sb) +
+ le32_to_cpu(sbi->s_es->s_first_data_block);
+
+ /* Set bits for block and inode bitmaps, and inode table */
+ ext4_set_bit(ext4_block_bitmap(sb, gdp) - start, bh->b_data);
+ ext4_set_bit(ext4_inode_bitmap(sb, gdp) - start, bh->b_data);
+ for (bit = (ext4_inode_table(sb, gdp) - start),
+ bit_max = bit + sbi->s_itb_per_group; bit < bit_max; bit++)
+ ext4_set_bit(bit, bh->b_data);
+
+ /*
+ * Also if the number of blocks within the group is
+ * less than the blocksize * 8 ( which is the size
+ * of bitmap ), set rest of the block bitmap to 1
+ */
+ mark_bitmap_end(group_blocks, sb->s_blocksize * 8, bh->b_data);
+ }
+
+ return free_blocks - sbi->s_itb_per_group - 2;
+}
+
+