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[PATCH 2/2] libxfs: fix crc field handling in xfs_sb_to/from_disk

To: xfs@xxxxxxxxxxx
Subject: [PATCH 2/2] libxfs: fix crc field handling in xfs_sb_to/from_disk
From: Eric Sandeen <sandeen@xxxxxxxxxx>
Date: Mon, 16 Jun 2014 18:14:21 -0500
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1402960461-27881-1-git-send-email-sandeen@xxxxxxxxxx>
References: <1402960461-27881-1-git-send-email-sandeen@xxxxxxxxxx>
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>
---
 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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