alloc_sb.c revision 4efbac6fed75c29d3d5f1b676b932754653a2ac5 
1/*
2 * alloc_sb.c --- Allocate the superblock and block group descriptors for a
3 * newly initialized filesystem.  Used by mke2fs when initializing a filesystem
4 *
5 * Copyright (C) 1994, 1995, 1996, 2003 Theodore Ts'o.
6 *
7 * %Begin-Header%
8 * This file may be redistributed under the terms of the GNU Public
9 * License.
10 * %End-Header%
11 */
12
13#include <stdio.h>
14#include <string.h>
15#if HAVE_UNISTD_H
16#include <unistd.h>
17#endif
18#include <fcntl.h>
19#include <time.h>
20#if HAVE_SYS_STAT_H
21#include <sys/stat.h>
22#endif
23#if HAVE_SYS_TYPES_H
24#include <sys/types.h>
25#endif
26
27#include "ext2_fs.h"
28#include "ext2fs.h"
29
30/*
31 * This function reserves the superblock and block group descriptors
32 * for a given block group.  It currently returns the number of free
33 * blocks assuming that inode table and allocation bitmaps will be in
34 * the group.  This is not necessarily the case when the flex_bg
35 * feature is enabled, so callers should take care!  It was only
36 * really intended for use by mke2fs, and even there it's not that
37 * useful.  In the future, when we redo this function for 64-bit block
38 * numbers, we should probably return the number of blocks used by the
39 * super block and group descriptors instead.
40 *
41 * See also the comment for ext2fs_super_and_bgd_loc()
42 */
43int ext2fs_reserve_super_and_bgd(ext2_filsys fs,
44				 dgrp_t group,
45				 ext2fs_block_bitmap bmap)
46{
47	blk64_t	super_blk, old_desc_blk, new_desc_blk;
48	blk_t	used_blks;
49	int	j, old_desc_blocks, num_blocks;
50
51	ext2fs_super_and_bgd_loc2(fs, group, &super_blk,
52				  &old_desc_blk, &new_desc_blk, &used_blks);
53
54	if (fs->super->s_feature_incompat & EXT2_FEATURE_INCOMPAT_META_BG)
55		old_desc_blocks = fs->super->s_first_meta_bg;
56	else
57		old_desc_blocks =
58			fs->desc_blocks + fs->super->s_reserved_gdt_blocks;
59
60	if (super_blk || (group == 0))
61		ext2fs_mark_block_bitmap2(bmap, super_blk);
62
63	if (old_desc_blk) {
64		if (fs->super->s_reserved_gdt_blocks && fs->block_map == bmap)
65			ext2fs_bg_flag_clear(fs, group, EXT2_BG_BLOCK_UNINIT);
66		for (j=0; j < old_desc_blocks; j++)
67			if (old_desc_blk + j < ext2fs_blocks_count(fs->super))
68				ext2fs_mark_block_bitmap2(bmap,
69							 old_desc_blk + j);
70	}
71	if (new_desc_blk)
72		ext2fs_mark_block_bitmap2(bmap, new_desc_blk);
73
74	if (group == fs->group_desc_count-1) {
75		num_blocks = (ext2fs_blocks_count(fs->super) -
76			     fs->super->s_first_data_block) %
77			fs->super->s_blocks_per_group;
78		if (!num_blocks)
79			num_blocks = fs->super->s_blocks_per_group;
80	} else
81		num_blocks = fs->super->s_blocks_per_group;
82
83	num_blocks -= 2 + fs->inode_blocks_per_group + used_blks;
84
85	return num_blocks  ;
86}
87