ext4: fix off-by-one fsmap error on 1k block filesystems

For 1k-block filesystems, the filesystem starts at block 1, not block 0.
This fact is recorded in s_first_data_block, so use that to bump up the
start_fsb before we start querying the filesystem for its space map.
Without this, ext4/026 fails on 1k block ext4 because various functions
(notably ext4_get_group_no_and_offset) don't know what to do with an
fsblock that is "before" the start of the filesystem and return garbage
results (blockgroup 2^32-1, etc.) that confuse fsmap.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/fsmap.c b/fs/ext4/fsmap.c
index b194360988371638272871cdd95ab650e58d295c..7ec340898598081e4322b190dce3372d6b14095d 100644 (file)
--- a/fs/ext4/fsmap.c
+++ b/fs/ext4/fsmap.c
@@ -480,6 +480,7 @@ static int ext4_getfsmap_datadev(struct super_block *sb,
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        ext4_fsblk_t start_fsb;
        ext4_fsblk_t end_fsb;
+       ext4_fsblk_t bofs;
        ext4_fsblk_t eofs;
        ext4_group_t start_ag;
        ext4_group_t end_ag;
@@ -487,9 +488,12 @@ static int ext4_getfsmap_datadev(struct super_block *sb,
        ext4_grpblk_t last_cluster;
        int error = 0;
 
+       bofs = le32_to_cpu(sbi->s_es->s_first_data_block);
        eofs = ext4_blocks_count(sbi->s_es);
        if (keys[0].fmr_physical >= eofs)
                return 0;
+       else if (keys[0].fmr_physical < bofs)
+               keys[0].fmr_physical = bofs;
        if (keys[1].fmr_physical >= eofs)
                keys[1].fmr_physical = eofs - 1;
        start_fsb = keys[0].fmr_physical;