C++ EXT2_DESC_PER_BLOCK函数代码示例

struct ext2_group_desc *
get_group_desc(struct mount *mp, unsigned int block_group,
	       struct buf **bh)
{
	struct ext2_sb_info *sb = VFSTOEXT2(mp)->um_e2fs;
	unsigned long group_desc;
	unsigned long desc;
	struct ext2_group_desc *gdp;

	if (block_group >= sb->s_groups_count)
		panic ("get_group_desc: "
			    "block_group >= groups_count - "
			    "block_group = %d, groups_count = %lu",
			    block_group, sb->s_groups_count);

	group_desc = block_group / EXT2_DESC_PER_BLOCK(sb);
	desc = block_group % EXT2_DESC_PER_BLOCK(sb);
	if (!sb->s_group_desc[group_desc])
		panic ( "get_group_desc:"
			    "Group descriptor not loaded - "
			    "block_group = %d, group_desc = %lu, desc = %lu",
			     block_group, group_desc, desc);
	gdp = (struct ext2_group_desc *)
		sb->s_group_desc[group_desc]->b_data;
	if (bh)
		*bh = sb->s_group_desc[group_desc];
	return gdp + desc;
}

static struct ext2_group_desc * get_group_desc (struct super_block * sb,
						unsigned int block_group,
						struct buffer_head ** bh)
{
	unsigned long group_desc;
	unsigned long desc;
	struct ext2_group_desc * gdp;

	if (block_group >= sb->u.ext2_sb.s_groups_count)
		ext2_panic (sb, "get_group_desc",
			    "block_group >= groups_count - "
			    "block_group = %d, groups_count = %lu",
			    block_group, sb->u.ext2_sb.s_groups_count);

	group_desc = block_group / EXT2_DESC_PER_BLOCK(sb);
	desc = block_group % EXT2_DESC_PER_BLOCK(sb);
	if (!sb->u.ext2_sb.s_group_desc[group_desc])
		ext2_panic (sb, "get_group_desc",
			    "Group descriptor not loaded - "
			    "block_group = %d, group_desc = %lu, desc = %lu",
			     block_group, group_desc, desc);
	gdp = (struct ext2_group_desc *) 
		sb->u.ext2_sb.s_group_desc[group_desc]->b_data;
	if (bh)
		*bh = sb->u.ext2_sb.s_group_desc[group_desc];
	return gdp + desc;
}

int op_statfs (const char *path, struct statvfs *buf)
{
	unsigned long long i;
	unsigned long long s_gdb_count = 0;
	unsigned long long s_groups_count = 0;
	unsigned long long s_itb_per_group = 0;
	unsigned long long s_overhead_last = 0;
	unsigned long long s_inodes_per_block = 0;

	ext2_filsys e2fs;
	FUSE_EXT2_LOCK;
	e2fs	= current_ext2fs();

	debugf("enter");

	memset(buf, 0, sizeof(struct statvfs));

	if (e2fs->super->s_default_mount_opts & EXT2_MOUNT_MINIX_DF) {
		s_overhead_last = 0;
	} else {
		s_overhead_last = e2fs->super->s_first_data_block;
		s_groups_count = ((EXT2_BLOCKS_COUNT(e2fs->super) - e2fs->super->s_first_data_block - 1) / e2fs->super->s_blocks_per_group) + 1;
		s_gdb_count = (s_groups_count + EXT2_DESC_PER_BLOCK(e2fs->super) - 1) / EXT2_DESC_PER_BLOCK(e2fs->super);
		for (i = 0; i < s_groups_count; i++) {
			s_overhead_last += ext2_bg_has_super(e2fs, i) + ((ext2_bg_num_gdb(e2fs, i) == 0) ? 0 : s_gdb_count);
		}
		s_inodes_per_block = EXT2_BLOCK_SIZE(e2fs->super) / EXT2_INODE_SIZE(e2fs->super);
		s_itb_per_group = e2fs->super->s_inodes_per_group / s_inodes_per_block;
		s_overhead_last += (s_groups_count * (2 +  s_itb_per_group));
	}
	buf->f_bsize = EXT2_BLOCK_SIZE(e2fs->super);
	buf->f_frsize = /*EXT2_FRAG_SIZE(e2fs->super);*/ buf->f_bsize;
	buf->f_blocks = EXT2_BLOCKS_COUNT(e2fs->super) - s_overhead_last;
	buf->f_bfree = EXT2_FBLOCKS_COUNT(e2fs->super);
	if (EXT2_FBLOCKS_COUNT(e2fs->super) < EXT2_RBLOCKS_COUNT(e2fs->super)) {
		buf->f_bavail = 0;
	} else {
		buf->f_bavail = EXT2_FBLOCKS_COUNT(e2fs->super) - EXT2_RBLOCKS_COUNT(e2fs->super);
	}
	buf->f_files = e2fs->super->s_inodes_count;
	buf->f_ffree = e2fs->super->s_free_inodes_count;
	buf->f_favail = e2fs->super->s_free_inodes_count;
	buf->f_namemax = EXT2_NAME_LEN;

	debugf("leave");
	FUSE_EXT2_UNLOCK;
	return 0;
}

/*
 * ext2fs_super_and_bgd_loc2()
 * @fs:			ext2 fs pointer
 * @group		given block group
 * @ret_super_blk:	if !NULL, returns super block location
 * @ret_old_desc_blk:	if !NULL, returns location of the old block
 *			group descriptor
 * @ret_new_desc_blk:	if !NULL, returns location of meta_bg block
 *			group descriptor
 * @ret_used_blks:	if !NULL, returns number of blocks used by
 *			super block and group_descriptors.
 *
 * Returns errcode_t of 0
 */
errcode_t ext2fs_super_and_bgd_loc2(ext2_filsys fs,
					   dgrp_t group,
					   blk64_t *ret_super_blk,
					   blk64_t *ret_old_desc_blk,
					   blk64_t *ret_new_desc_blk,
					   blk_t *ret_used_blks)
{
	blk64_t	group_block, super_blk = 0, old_desc_blk = 0, new_desc_blk = 0;
	unsigned int meta_bg, meta_bg_size;
	blk_t	numblocks = 0;
	blk64_t old_desc_blocks;
	int	has_super;

	group_block = ext2fs_group_first_block2(fs, group);
	if (group_block == 0 && fs->blocksize == 1024)
		group_block = 1; /* Deal with 1024 blocksize && bigalloc */

	if (ext2fs_has_feature_meta_bg(fs->super))
		old_desc_blocks = fs->super->s_first_meta_bg;
	else
		old_desc_blocks =
			fs->desc_blocks + fs->super->s_reserved_gdt_blocks;

	has_super = ext2fs_bg_has_super(fs, group);

	if (has_super) {
		super_blk = group_block;
		numblocks++;
	}
	meta_bg_size = EXT2_DESC_PER_BLOCK(fs->super);
	meta_bg = group / meta_bg_size;

	if (!ext2fs_has_feature_meta_bg(fs->super) ||
	    (meta_bg < fs->super->s_first_meta_bg)) {
		if (has_super) {
			old_desc_blk = group_block + 1;
			numblocks += old_desc_blocks;
		}
	} else {
		if (((group % meta_bg_size) == 0) ||
		    ((group % meta_bg_size) == 1) ||
		    ((group % meta_bg_size) == (meta_bg_size-1))) {
			if (has_super)
				has_super = 1;
			new_desc_blk = group_block + has_super;
			numblocks++;
		}
	}

	if (ret_super_blk)
		*ret_super_blk = super_blk;
	if (ret_old_desc_blk)
		*ret_old_desc_blk = old_desc_blk;
	if (ret_new_desc_blk)
		*ret_new_desc_blk = new_desc_blk;
	if (ret_used_blks)
		*ret_used_blks = numblocks;

	return 0;
}

/*
 * Calculate the number of GDT blocks to reserve for online filesystem growth.
 * The absolute maximum number of GDT blocks we can reserve is determined by
 * the number of block pointers that can fit into a single block.
 */
static unsigned int calc_reserved_gdt_blocks(ext2_filsys fs)
{
	struct ext2_super_block *sb = fs->super;
	unsigned long bpg = sb->s_blocks_per_group;
	unsigned int gdpb = EXT2_DESC_PER_BLOCK(sb);
	unsigned long max_blocks = 0xffffffff;
	unsigned long rsv_groups;
	unsigned int rsv_gdb;

	/* We set it at 1024x the current filesystem size, or
	 * the upper block count limit (2^32), whichever is lower.
	 */
	if (ext2fs_blocks_count(sb) < max_blocks / 1024)
		max_blocks = ext2fs_blocks_count(sb) * 1024;
	/*
	 * ext2fs_div64_ceil() is unnecessary because max_blocks is
	 * max _GDT_ blocks, which is limited to 32 bits.
	 */
	rsv_groups = ext2fs_div_ceil(max_blocks - sb->s_first_data_block, bpg);
	rsv_gdb = ext2fs_div_ceil(rsv_groups, gdpb) - fs->desc_blocks;
	if (rsv_gdb > EXT2_ADDR_PER_BLOCK(sb))
		rsv_gdb = EXT2_ADDR_PER_BLOCK(sb);
#ifdef RES_GDT_DEBUG
	printf("max_blocks %lu, rsv_groups = %lu, rsv_gdb = %u\n",
	       max_blocks, rsv_groups, rsv_gdb);
#endif

	return rsv_gdb;
}

struct ext2_group_desc * ext2_get_group_desc(struct super_block * sb,
					     unsigned int block_group,
					     struct buffer_head ** bh)
{
	unsigned long group_desc;
	unsigned long offset;
	struct ext2_group_desc * desc;
	struct ext2_sb_info *sbi = EXT2_SB(sb);

	if (block_group >= sbi->s_groups_count) {
		ext2_error (sb, "ext2_get_group_desc",
			    "block_group >= groups_count - "
			    "block_group = %d, groups_count = %lu",
			    block_group, sbi->s_groups_count);

		return NULL;
	}

	group_desc = block_group >> EXT2_DESC_PER_BLOCK_BITS(sb);
	offset = block_group & (EXT2_DESC_PER_BLOCK(sb) - 1);
	if (!sbi->s_group_desc[group_desc]) {
		ext2_error (sb, "ext2_get_group_desc",
			    "Group descriptor not loaded - "
			    "block_group = %d, group_desc = %lu, desc = %lu",
			     block_group, group_desc, offset);
		return NULL;
	}

	desc = (struct ext2_group_desc *) sbi->s_group_desc[group_desc]->b_data;
	if (bh)
		*bh = sbi->s_group_desc[group_desc];
	return desc + offset;
}

/*
 * ext2fs_super_and_bgd_loc2()
 * @fs:			ext2 fs pointer
 * @group		given block group
 * @ret_super_blk:	if !NULL, returns super block location
 * @ret_old_desc_blk:	if !NULL, returns location of the old block
 *			group descriptor
 * @ret_new_desc_blk:	if !NULL, returns location of meta_bg block
 *			group descriptor
 * @ret_used_blks:	if !NULL, returns number of blocks used by
 *			super block and group_descriptors.
 *
 * Returns errcode_t of 0
 */
errcode_t ext2fs_super_and_bgd_loc2(ext2_filsys fs,
					   dgrp_t group,
					   blk64_t *ret_super_blk,
					   blk64_t *ret_old_desc_blk,
					   blk64_t *ret_new_desc_blk,
					   blk_t *ret_used_blks)
{
	blk64_t	group_block, super_blk = 0, old_desc_blk = 0, new_desc_blk = 0;
	unsigned int meta_bg, meta_bg_size;
	blk_t	numblocks = 0;
	blk64_t old_desc_blocks;
	int	has_super;

	group_block = ext2fs_group_first_block2(fs, group);

	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;

	has_super = ext2fs_bg_has_super(fs, group);

	if (has_super) {
		super_blk = group_block;
		numblocks++;
	}
	meta_bg_size = EXT2_DESC_PER_BLOCK(fs->super);
	meta_bg = group / meta_bg_size;

	if (!(fs->super->s_feature_incompat & EXT2_FEATURE_INCOMPAT_META_BG) ||
	    (meta_bg < fs->super->s_first_meta_bg)) {
		if (has_super) {
			old_desc_blk = group_block + 1;
			numblocks += old_desc_blocks;
		}
	} else {
		if (((group % meta_bg_size) == 0) ||
		    ((group % meta_bg_size) == 1) ||
		    ((group % meta_bg_size) == (meta_bg_size-1))) {
			if (has_super)
				has_super = 1;
			new_desc_blk = group_block + has_super;
			numblocks++;
		}
	}

	if (ret_super_blk)
		*ret_super_blk = super_blk;
	if (ret_old_desc_blk)
		*ret_old_desc_blk = old_desc_blk;
	if (ret_new_desc_blk)
		*ret_new_desc_blk = new_desc_blk;
	if (ret_used_blks)
		*ret_used_blks = numblocks;

	return 0;
}

static int ext2_check_descriptors (struct super_block * sb)
{
	int i;
	int desc_block = 0;
	struct ext2_sb_info *sbi = EXT2_SB(sb);
	struct ext2_group_desc * gdp = NULL;

	ext2_debug ("Checking group descriptors");

	for (i = 0; i < sbi->s_groups_count; i++)
	{
		ext2_fsblk_t first_block = ext2_group_first_block_no(sb, i);
		ext2_fsblk_t last_block;

		if (i == sbi->s_groups_count - 1)
			last_block = le32_to_cpu(sbi->s_es->s_blocks_count) - 1;
		else
			last_block = first_block +
				(EXT2_BLOCKS_PER_GROUP(sb) - 1);

		if ((i % EXT2_DESC_PER_BLOCK(sb)) == 0)
			gdp = (struct ext2_group_desc *) sbi->s_group_desc[desc_block++]->b_data;
		if (le32_to_cpu(gdp->bg_block_bitmap) < first_block ||
		    le32_to_cpu(gdp->bg_block_bitmap) > last_block)
		{
			ext2_error (sb, "ext2_check_descriptors",
				    "Block bitmap for group %d"
				    " not in group (block %lu)!",
				    i, (unsigned long) le32_to_cpu(gdp->bg_block_bitmap));
			return 0;
		}
		if (le32_to_cpu(gdp->bg_inode_bitmap) < first_block ||
		    le32_to_cpu(gdp->bg_inode_bitmap) > last_block)
		{
			ext2_error (sb, "ext2_check_descriptors",
				    "Inode bitmap for group %d"
				    " not in group (block %lu)!",
				    i, (unsigned long) le32_to_cpu(gdp->bg_inode_bitmap));
			return 0;
		}
		if (le32_to_cpu(gdp->bg_inode_table) < first_block ||
		    le32_to_cpu(gdp->bg_inode_table) + sbi->s_itb_per_group - 1 >
		    last_block)
		{
			ext2_error (sb, "ext2_check_descriptors",
				    "Inode table for group %d"
				    " not in group (block %lu)!",
				    i, (unsigned long) le32_to_cpu(gdp->bg_inode_table));
			return 0;
		}
		gdp++;
	}
	return 1;
}

void ext2_get_group_desc(ext2_VOLUME* volume,
		   int group_id, struct ext2_group_desc *gdp)
{
	unsigned int block, offset;
	struct ext2_group_desc *le_gdp;

	block = 1 + volume->super->s_first_data_block;
	block += group_id / EXT2_DESC_PER_BLOCK(volume->super);
	ext2_read_block(volume,  block);

	offset = group_id % EXT2_DESC_PER_BLOCK(volume->super);
	offset *= sizeof(*gdp);

	le_gdp = (struct ext2_group_desc *)(volume->buffer + offset);

	gdp->bg_block_bitmap = __le32_to_cpu(le_gdp->bg_block_bitmap);
	gdp->bg_inode_bitmap = __le32_to_cpu(le_gdp->bg_inode_bitmap);
	gdp->bg_inode_table = __le32_to_cpu(le_gdp->bg_inode_table);
	gdp->bg_free_blocks_count = __le16_to_cpu(le_gdp->bg_free_blocks_count);
	gdp->bg_free_inodes_count = __le16_to_cpu(le_gdp->bg_free_inodes_count);
	gdp->bg_used_dirs_count = __le16_to_cpu(le_gdp->bg_used_dirs_count);
}

/*
 * Checks that the data in the descriptor blocks make sense.
 */
int
ext2_check_descriptors(struct ext2_sb_info *sb)
{
        int i;
        int desc_block = 0;
        unsigned long block = sb->s_es->s_first_data_block;
        struct ext2_group_desc *gdp = NULL;

        /* ext2_debug ("Checking group descriptors"); */

        for (i = 0; i < sb->s_groups_count; i++)
        {
		/* examine next descriptor block */
                if ((i % EXT2_DESC_PER_BLOCK(sb)) == 0)
                        gdp = (struct ext2_group_desc *)
				sb->s_group_desc[desc_block++]->b_data;
                if (gdp->bg_block_bitmap < block ||
                    gdp->bg_block_bitmap >= block + EXT2_BLOCKS_PER_GROUP(sb))
                {
                        kprintf ("ext2_check_descriptors: "
                                    "Block bitmap for group %d"
                                    " not in group (block %lu)!\n",
                                    i, (unsigned long) gdp->bg_block_bitmap);
                        return 0;
                }
                if (gdp->bg_inode_bitmap < block ||
                    gdp->bg_inode_bitmap >= block + EXT2_BLOCKS_PER_GROUP(sb))
                {
                        kprintf ("ext2_check_descriptors: "
                                    "Inode bitmap for group %d"
                                    " not in group (block %lu)!\n",
                                    i, (unsigned long) gdp->bg_inode_bitmap);
                        return 0;
                }
                if (gdp->bg_inode_table < block ||
                    gdp->bg_inode_table + sb->s_itb_per_group >=
                    block + EXT2_BLOCKS_PER_GROUP(sb))
                {
                        kprintf ("ext2_check_descriptors: "
                                    "Inode table for group %d"
                                    " not in group (block %lu)!\n",
                                    i, (unsigned long) gdp->bg_inode_table);
                        return 0;
                }
                block += EXT2_BLOCKS_PER_GROUP(sb);
                gdp++;
        }
        return 1;
}

blk64_t ext2fs_descriptor_block_loc2(ext2_filsys fs, blk64_t group_block,
				     dgrp_t i)
{
	int	bg;
	int	has_super = 0, group_zero_adjust = 0;
	blk64_t	ret_blk;

	/*
	 * On a bigalloc FS with 1K blocks, block 0 is reserved for non-ext4
	 * stuff, so adjust for that if we're being asked for group 0.
	 */
	if (i == 0 && fs->blocksize == 1024 && EXT2FS_CLUSTER_RATIO(fs) > 1)
		group_zero_adjust = 1;

	if (!ext2fs_has_feature_meta_bg(fs->super) ||
	    (i < fs->super->s_first_meta_bg))
		return group_block + i + 1 + group_zero_adjust;

	bg = EXT2_DESC_PER_BLOCK(fs->super) * i;
	if (ext2fs_bg_has_super(fs, bg))
		has_super = 1;
	ret_blk = ext2fs_group_first_block2(fs, bg);
	/*
	 * If group_block is not the normal value, we're trying to use
	 * the backup group descriptors and superblock --- so use the
	 * alternate location of the second block group in the
	 * metablock group.  Ideally we should be testing each bg
	 * descriptor block individually for correctness, but we don't
	 * have the infrastructure in place to do that.
	 */
	if (group_block != fs->super->s_first_data_block &&
	    ((ret_blk + has_super + fs->super->s_blocks_per_group) <
	     ext2fs_blocks_count(fs->super))) {
		ret_blk += fs->super->s_blocks_per_group;

		/*
		 * If we're going to jump forward a block group, make sure
		 * that we adjust has_super to account for the next group's
		 * backup superblock (or lack thereof).
		 */
		if (ext2fs_bg_has_super(fs, bg + 1))
			has_super = 1;
		else
			has_super = 0;
	}
	return ret_blk + has_super + group_zero_adjust;
}

static int ext2_check_descriptors (struct super_block * sb)
{
	int i;
	int desc_block = 0;
	unsigned long block = le32_to_cpu(sb->u.ext2_sb.s_es->s_first_data_block);
	struct ext2_group_desc * gdp = NULL;

	ext2_debug ("Checking group descriptors");

	for (i = 0; i < sb->u.ext2_sb.s_groups_count; i++)
	{
		if ((i % EXT2_DESC_PER_BLOCK(sb)) == 0)
			gdp = (struct ext2_group_desc *) sb->u.ext2_sb.s_group_desc[desc_block++]->b_data;
		if (le32_to_cpu(gdp->bg_block_bitmap) < block ||
		    le32_to_cpu(gdp->bg_block_bitmap) >= block + EXT2_BLOCKS_PER_GROUP(sb))
		{
			ext2_error (sb, "ext2_check_descriptors",
				    "Block bitmap for group %d"
				    " not in group (block %lu)!",
				    i, (unsigned long) le32_to_cpu(gdp->bg_block_bitmap));
			return 0;
		}
		if (le32_to_cpu(gdp->bg_inode_bitmap) < block ||
		    le32_to_cpu(gdp->bg_inode_bitmap) >= block + EXT2_BLOCKS_PER_GROUP(sb))
		{
			ext2_error (sb, "ext2_check_descriptors",
				    "Inode bitmap for group %d"
				    " not in group (block %lu)!",
				    i, (unsigned long) le32_to_cpu(gdp->bg_inode_bitmap));
			return 0;
		}
		if (le32_to_cpu(gdp->bg_inode_table) < block ||
		    le32_to_cpu(gdp->bg_inode_table) + sb->u.ext2_sb.s_itb_per_group >=
		    block + EXT2_BLOCKS_PER_GROUP(sb))
		{
			ext2_error (sb, "ext2_check_descriptors",
				    "Inode table for group %d"
				    " not in group (block %lu)!",
				    i, (unsigned long) le32_to_cpu(gdp->bg_inode_table));
			return 0;
		}
		block += EXT2_BLOCKS_PER_GROUP(sb);
		gdp++;
	}
	return 1;
}

/*
 * This function returns the location of the superblock, 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.
 *
 * The ext2fs_super_and_bgd_loc2() function is 64-bit block number
 * capable and returns the number of blocks used by super block and
 * group descriptors.
 */
int ext2fs_super_and_bgd_loc(ext2_filsys fs,
			     dgrp_t group,
			     blk_t *ret_super_blk,
			     blk_t *ret_old_desc_blk,
			     blk_t *ret_new_desc_blk,
			     int *ret_meta_bg)
{
	blk64_t ret_super_blk2;
	blk64_t ret_old_desc_blk2;
	blk64_t ret_new_desc_blk2;
	blk_t ret_used_blks;
	blk_t numblocks;
	unsigned int meta_bg_size;

	ext2fs_super_and_bgd_loc2(fs, group, &ret_super_blk2,
					&ret_old_desc_blk2,
					&ret_new_desc_blk2,
					&ret_used_blks);

	if (group == fs->group_desc_count-1) {
		numblocks = (fs->super->s_blocks_count -
			     fs->super->s_first_data_block) %
			fs->super->s_blocks_per_group;
		if (!numblocks)
			numblocks = fs->super->s_blocks_per_group;
	} else
		numblocks = fs->super->s_blocks_per_group;

	if (ret_super_blk)
		*ret_super_blk = (blk_t)ret_super_blk2;
	if (ret_old_desc_blk)
		*ret_old_desc_blk = (blk_t)ret_old_desc_blk2;
	if (ret_new_desc_blk)
		*ret_new_desc_blk = (blk_t)ret_new_desc_blk2;
	if (ret_meta_bg) {
		meta_bg_size = EXT2_DESC_PER_BLOCK(fs->super);
		*ret_meta_bg = group / meta_bg_size;
	}

	numblocks -= 2 + fs->inode_blocks_per_group + ret_used_blks;

	return numblocks;
}

static errcode_t adjust_fs_size(ext2_filsys fs, long long *new_size)
{
    errcode_t	retval;
    int    overhead = 0;
    int    rem;

    fs->super->s_blocks_count = (unsigned int)(*new_size / fs->blocksize);

retry:
    fs->group_desc_count = ext2fs_div_ceil(fs->super->s_blocks_count -
			       fs->super->s_first_data_block, EXT2_BLOCKS_PER_GROUP(fs->super));
    if (fs->group_desc_count == 0)
        return EXT2_ET_TOOSMALL;
    fs->desc_blocks = ext2fs_div_ceil(fs->group_desc_count, EXT2_DESC_PER_BLOCK(fs->super));

    /*
    * Overhead is the number of bookkeeping blocks per group.  It
    * includes the superblock backup, the group descriptor
    * backups, the inode bitmap, the block bitmap, and the inode
    * table.
    */
    overhead = (int) (2 + fs->inode_blocks_per_group);

    if (ext2fs_bg_has_super(fs, fs->group_desc_count - 1))
        overhead += 1 + fs->desc_blocks + fs->super->s_reserved_gdt_blocks;

    /*
    * See if the last group is big enough to support the
    * necessary data structures.  If not, we need to get rid of
    * it.
    */
    rem = (fs->super->s_blocks_count - fs->super->s_first_data_block) % fs->super->s_blocks_per_group;
    if ((fs->group_desc_count == 1) && rem && (rem < overhead))
        return EXT2_ET_TOOSMALL;

    if (rem && (rem < overhead+50)) {
        fs->super->s_blocks_count -= rem;
        goto retry;
    }

    *new_size = ((long long)fs->super->s_blocks_count * (long long)fs->blocksize);
    return 0;
}

/*
 * This function returns the location of the superblock, 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.
 *
 * The ext2fs_super_and_bgd_loc2() function is 64-bit block number
 * capable and returns the number of blocks used by super block and
 * group descriptors.
 */
int ext2fs_super_and_bgd_loc(ext2_filsys fs,
			     dgrp_t group,
			     blk_t *ret_super_blk,
			     blk_t *ret_old_desc_blk,
			     blk_t *ret_new_desc_blk,
			     int *ret_meta_bg)
{
	blk64_t ret_super_blk2;
	blk64_t ret_old_desc_blk2;
	blk64_t ret_new_desc_blk2;
	blk_t ret_used_blks;
	blk_t numblocks;
	unsigned int meta_bg_size;

	ext2fs_super_and_bgd_loc2(fs, group, &ret_super_blk2,
					&ret_old_desc_blk2,
					&ret_new_desc_blk2,
					&ret_used_blks);

	numblocks = ext2fs_group_blocks_count(fs, group);

	if (ret_super_blk)
		*ret_super_blk = (blk_t)ret_super_blk2;
	if (ret_old_desc_blk)
		*ret_old_desc_blk = (blk_t)ret_old_desc_blk2;
	if (ret_new_desc_blk)
		*ret_new_desc_blk = (blk_t)ret_new_desc_blk2;
	if (ret_meta_bg) {
		meta_bg_size = EXT2_DESC_PER_BLOCK(fs->super);
		*ret_meta_bg = group / meta_bg_size;
	}

	numblocks -= 2 + fs->inode_blocks_per_group + ret_used_blks;

	return numblocks;
}