fix-off-by-one-fsmap-error-on-1k-block-filesystems

   1 ext4: fix off-by-one fsmap error on 1k block filesystems
   2
   3 From: "Darrick J. Wong" <darrick.wong@oracle.com>
   4
   5 For 1k-block filesystems, the filesystem starts at block 1, not block 0.
   6 This fact is recorded in s_first_data_block, so use that to bump up the
   7 start_fsb before we start querying the filesystem for its space map.
   8 Without this, ext4/026 fails on 1k block ext4 because various functions
   9 (notably ext4_get_group_no_and_offset) don't know what to do with an
  10 fsblock that is "before" the start of the filesystem and return garbage
  11 results (blockgroup 2^32-1, etc.) that confuse fsmap.
  12
  13 Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
  14 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  15 ---
  16  fs/ext4/fsmap.c |    4 ++++
  17  1 file changed, 4 insertions(+)
  18
  19 diff --git a/fs/ext4/fsmap.c b/fs/ext4/fsmap.c
  20 index b194360..7ec3408 100644
  21 --- a/fs/ext4/fsmap.c
  22 +++ b/fs/ext4/fsmap.c
  23 @@ -480,6 +480,7 @@ static int ext4_getfsmap_datadev(struct super_block *sb,
  24         struct ext4_sb_info *sbi = EXT4_SB(sb);
  25         ext4_fsblk_t start_fsb;
  26         ext4_fsblk_t end_fsb;
  27 +       ext4_fsblk_t bofs;
  28         ext4_fsblk_t eofs;
  29         ext4_group_t start_ag;
  30         ext4_group_t end_ag;
  31 @@ -487,9 +488,12 @@ static int ext4_getfsmap_datadev(struct super_block *sb,
  32         ext4_grpblk_t last_cluster;
  33         int error = 0;
  34
  35 +       bofs = le32_to_cpu(sbi->s_es->s_first_data_block);
  36         eofs = ext4_blocks_count(sbi->s_es);
  37         if (keys[0].fmr_physical >= eofs)
  38                 return 0;
  39 +       else if (keys[0].fmr_physical < bofs)
  40 +               keys[0].fmr_physical = bofs;
  41         if (keys[1].fmr_physical >= eofs)
  42                 keys[1].fmr_physical = eofs - 1;
  43         start_fsb = keys[0].fmr_physical;
  44