1 files changed, 70 insertions, 0 deletions
diff --git a/fs/ext4/format/alloc_sb.c b/fs/ext4/format/alloc_sb.c
new file mode 100755
index 0000000..3bbe43d
--- /dev/null
+++ b/fs/ext4/format/alloc_sb.c
@@ -0,0 +1,70 @@
+/*
+ * alloc_sb.c --- Allocate the superblock and block group descriptors for a
+ * newly initialized filesystem.  Used by mke2fs when initializing a filesystem
+ *
+ * Copyright (C) 1994, 1995, 1996, 2003 Theodore Ts'o.
+ *
+ * %Begin-Header%
+ * This file may be redistributed under the terms of the GNU Library
+ * General Public License, version 2.
+ * %End-Header%
+ */
+
+#include <common.h>
+//#include <ext_common.h>
+//#include <ext4fs.h>
+#include <malloc.h>
+#include <stddef.h>
+#include <linux/stat.h>
+#include <linux/time.h>
+
+
+#include "ext2_fs.h"
+#include "ext2fs.h"
+
+/*
+ * This function reserves the superblock and block group descriptors
+ * for a given block group.  It currently returns the number of free
+ * blocks assuming that inode table and allocation bitmaps will be in
+ * the group.  This is not necessarily the case when the flex_bg
+ * feature is enabled, so callers should take care!  It was only
+ * really intended for use by mke2fs, and even there it's not that
+ * useful.  In the future, when we redo this function for 64-bit block
+ * numbers, we should probably return the number of blocks used by the
+ * super block and group descriptors instead.
+ *
+ * See also the comment for ext2fs_super_and_bgd_loc()
+ */
+int ext2fs_reserve_super_and_bgd(ext2_filsys fs,
+				 dgrp_t group,
+				 ext2fs_block_bitmap bmap)
+{
+	blk_t	super_blk, old_desc_blk, new_desc_blk;
+	int	j, old_desc_blocks, num_blocks;
+
+	num_blocks = ext2fs_super_and_bgd_loc(fs, group, &super_blk,
+					      &old_desc_blk, &new_desc_blk, 0);//how many data blocks
+
+
+	if (fs->super->s_feature_incompat & EXT2_FEATURE_INCOMPAT_META_BG)
+		old_desc_blocks = fs->super->s_first_meta_bg;
+	else
+		old_desc_blocks =
+			fs->desc_blocks + fs->super->s_reserved_gdt_blocks;//how many block the group descriptions will take and reserve
+
+	if (super_blk || (group == 0))
+		ext2fs_mark_block_bitmap(bmap, super_blk);//mark the superblock in block bitmap
+
+	if (old_desc_blk) {
+		if (fs->super->s_reserved_gdt_blocks && fs->block_map == bmap)
+			fs->group_desc[group].bg_flags &= ~EXT2_BG_BLOCK_UNINIT;
+		for (j=0; j < old_desc_blocks; j++)
+			if (old_desc_blk + j < fs->super->s_blocks_count)
+				ext2fs_mark_block_bitmap(bmap,
+							 old_desc_blk + j);//mar the group descriptions in the block bitmap
+	}
+	if (new_desc_blk)
+		ext2fs_mark_block_bitmap(bmap, new_desc_blk);
+
+	return num_blocks;//how many data blocks
+}