ext4: add a new function which adds a flex group to a fs

This patch adds a new function named ext4_flex_group_add() which adds a
flex group to a fs.  The function is used by 64bit-resize interface.
Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/resize.c

@@ -1348,6 +1348,88 @@ static void ext4_update_super(struct super_block *sb,
 		       blocks_count, free_blocks, reserved_blocks);
 }
 
+/* Add a flex group to an fs. Ensure we handle all possible error conditions
+ * _before_ we start modifying the filesystem, because we cannot abort the
+ * transaction and not have it write the data to disk.
+ */
+static int ext4_flex_group_add(struct super_block *sb,
+			       struct inode *resize_inode,
+			       struct ext4_new_flex_group_data *flex_gd)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct ext4_super_block *es = sbi->s_es;
+	ext4_fsblk_t o_blocks_count;
+	ext4_grpblk_t last;
+	ext4_group_t group;
+	handle_t *handle;
+	unsigned reserved_gdb;
+	int err = 0, err2 = 0, credit;
+
+	BUG_ON(!flex_gd->count || !flex_gd->groups || !flex_gd->bg_flags);
+
+	reserved_gdb = le16_to_cpu(es->s_reserved_gdt_blocks);
+	o_blocks_count = ext4_blocks_count(es);
+	ext4_get_group_no_and_offset(sb, o_blocks_count, &group, &last);
+	BUG_ON(last);
+
+	err = setup_new_flex_group_blocks(sb, flex_gd);
+	if (err)
+		goto exit;
+	/*
+	 * We will always be modifying at least the superblock and  GDT
+	 * block.  If we are adding a group past the last current GDT block,
+	 * we will also modify the inode and the dindirect block.  If we
+	 * are adding a group with superblock/GDT backups  we will also
+	 * modify each of the reserved GDT dindirect blocks.
+	 */
+	credit = flex_gd->count * 4 + reserved_gdb;
+	handle = ext4_journal_start_sb(sb, credit);
+	if (IS_ERR(handle)) {
+		err = PTR_ERR(handle);
+		goto exit;
+	}
+
+	err = ext4_journal_get_write_access(handle, sbi->s_sbh);
+	if (err)
+		goto exit_journal;
+
+	group = flex_gd->groups[0].group;
+	BUG_ON(group != EXT4_SB(sb)->s_groups_count);
+	err = ext4_add_new_descs(handle, sb, group,
+				resize_inode, flex_gd->count);
+	if (err)
+		goto exit_journal;
+
+	err = ext4_setup_new_descs(handle, sb, flex_gd);
+	if (err)
+		goto exit_journal;
+
+	ext4_update_super(sb, flex_gd);
+
+	err = ext4_handle_dirty_super(handle, sb);
+
+exit_journal:
+	err2 = ext4_journal_stop(handle);
+	if (!err)
+		err = err2;
+
+	if (!err) {
+		int i;
+		update_backups(sb, sbi->s_sbh->b_blocknr, (char *)es,
+			       sizeof(struct ext4_super_block));
+		for (i = 0; i < flex_gd->count; i++, group++) {
+			struct buffer_head *gdb_bh;
+			int gdb_num;
+			gdb_num = group / EXT4_BLOCKS_PER_GROUP(sb);
+			gdb_bh = sbi->s_group_desc[gdb_num];
+			update_backups(sb, gdb_bh->b_blocknr, gdb_bh->b_data,
+				       gdb_bh->b_size);
+		}
+	}
+exit:
+	return err;
+}
+
 /* Add group descriptor data to an existing or new group descriptor block.
  * Ensure we handle all possible error conditions _before_ we start modifying
  * the filesystem, because we cannot abort the transaction and not have it