On Fri, May 01, 2009 at 04:46:13AM -0400, Nick Dokos wrote:
> Running e2fsck -n -f <device> on a brand-new, never-mounted 32Tib fs
> was producing checksum errors on half the groups (the lower half)
> before it got to pass1 and block or inode bitmap conflicts on some
> groups in the upper half. The checksum errors were actually caused by
> the conflicts: e2fsck does a sanity check on block allocations, finds
> a conflict, and uses the backup superblock at 32768. But when it does
> that, it assumes the worst: it clears the UNINIT FLAGS and zeroes the
> free inode count for each group, assuming that it will fix them up
> during the run. That triggers the checksum errors (although it's not
> clear to me why only the lower half of the groups get checksum
> errors.)
>
> dumpe2fs showed that the conflicts were not artifacts of e2fsck
> processing: they existed on disk. In fact, the block bitmap of a group
> conflicted with the inode bitmap of the group fifteen steps further
> along. That smelled like flex_bg, so I remade the fs with flex_bg
> off and then *every* group in the upper half (more precisely, with
> blocks above the 32-bit boundary) had a conflict with itself: the
> block bitmap and inode bitmap were allocated on top of each other.
> That led to ext2fs_get_free_blocks2() which was truncating 64-bit block
> numbers by casting them to blk_t.
>
> This patch eliminates the casts. The resulting file system is free of
> the conflicts (with or without flex_bg.) However, it does not fsck
> cleanly yet: there are block bitmap differences in the very last group.
>
> Signed-off-by: Nick Dokos <nicholas.dokos@xxxxxx>
> ---
> lib/ext2fs/alloc.c | 3 +--
> 1 files changed, 1 insertions(+), 2 deletions(-)
>
> diff --git a/lib/ext2fs/alloc.c b/lib/ext2fs/alloc.c
> index b1d1f9c..9f11673 100644
> --- a/lib/ext2fs/alloc.c
> +++ b/lib/ext2fs/alloc.c
> @@ -272,8 +272,7 @@ errcode_t ext2fs_get_free_blocks2(ext2_filsys fs, blk64_t start, blk64_t finish,
> do {
> if (b+num-1 > ext2fs_blocks_count(fs->super))
> b = fs->super->s_first_data_block;
> - if (ext2fs_fast_test_block_bitmap_range2(map, (blk_t) b,
> - (blk_t) num)) {
> + if (ext2fs_fast_test_block_bitmap_range2(map, b, num)) {
> *ret = b;
> return 0;
> }
> --
> 1.6.0.6
Signed-off-by: Valerie Aurora (Henson) <vaurora@xxxxxxxxxx>
-VAL
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