libext2fs: Improve flex_bg inode table placement algorithm

When trying to find the best place for the inode table in the last
flex block group, use the true size for the flex_bg's portion of the
inode table instead of the worst case required size of the inode table
fragment if the file system is resized.  This fixes a corner case
where if the size of the filesystem is just big enough that there is
only room for a single block group in the last flex_bg, and that
partial block group is too small for the full portion of the inode
table, the inode table is placed in the very first block group:

Group 64: (Blocks 2097152-2099199) [INODE_UNINIT, ITABLE_ZEROED]
  Checksum 0xd305, unused inodes 8080
  Block bitmap at 2097152 (+0), Inode bitmap at 2097168 (+16)
  Inode table at 8626-9130 (+4292878770)
                 ^^^^^^^^^

Thanks to Vyacheslav Dubeyko for pointing this out.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/lib/ext2fs/alloc_tables.c b/lib/ext2fs/alloc_tables.c
index 8547ad6..55e6174 100644 (file)
--- a/lib/ext2fs/alloc_tables.c
+++ b/lib/ext2fs/alloc_tables.c
@@ -181,6 +181,8 @@ errcode_t ext2fs_allocate_group_table(ext2_filsys fs, dgrp_t group,
                blk_t prev_block = 0;
                if (group && fs->group_desc[group-1].bg_inode_table)
                        prev_block = fs->group_desc[group-1].bg_inode_table;
+               if (last_grp == fs->group_desc_count)
+                       rem_grps = last_grp - group;
                group_blk = flexbg_offset(fs, group, prev_block, bmap,
                                                 flexbg_size * 2,
                                                 fs->inode_blocks_per_group *