On Mon, Jun 16, 2014 at 06:14:21PM -0500, Eric Sandeen wrote:
> If we xfs_mdrestore an image from a non-crc filesystem, lo
> and behold the restored image has gained a CRC:
>
> # db/xfs_metadump.sh -o /dev/sdc1 - | xfs_mdrestore - test.img
> # xfs_db -c "sb 0" -c "p crc" /dev/sdc1
> crc = 0 (correct)
> # xfs_db -c "sb 0" -c "p crc" test.img
> crc = 0xb6f8d6a0 (correct)
>
> This is because xfs_sb_from_disk doesn't fill in sb_crc,
> but xfs_sb_to_disk(XFS_SB_ALL_BITS) does write the in-memory
> CRC to disk - so we get uninitialized memory on disk.
>
> Fix this by always initializing sb_crc to 0 when we read
> the superblock, and masking out the CRC bit from ALL_BITS
> when we write it.
>
> This same fix has already been sent for kernelspace.
>
> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> ---
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
> libxfs/xfs_sb.c | 5 +++++
> 1 files changed, 5 insertions(+), 0 deletions(-)
>
> diff --git a/libxfs/xfs_sb.c b/libxfs/xfs_sb.c
> index 7ee4612..ea89367 100644
> --- a/libxfs/xfs_sb.c
> +++ b/libxfs/xfs_sb.c
> @@ -408,6 +408,8 @@ xfs_sb_from_disk(
> to->sb_features_incompat = be32_to_cpu(from->sb_features_incompat);
> to->sb_features_log_incompat =
> be32_to_cpu(from->sb_features_log_incompat);
> + /* crc is only used on disk, not in memory; just init to 0 here. */
> + to->sb_crc = 0;
> to->sb_pad = 0;
> to->sb_pquotino = be64_to_cpu(from->sb_pquotino);
> to->sb_lsn = be64_to_cpu(from->sb_lsn);
> @@ -485,6 +487,9 @@ xfs_sb_to_disk(
> if (!fields)
> return;
>
> + /* We should never write the crc here, it's updated in the IO path */
> + fields &= ~XFS_SB_CRC;
> +
> xfs_sb_quota_to_disk(to, from, &fields);
> while (fields) {
> f = (xfs_sb_field_t)xfs_lowbit64((__uint64_t)fields);
> --
> 1.7.1
>
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