> On Jul 21, 2015, at 7:31 AM, Brian Foster <bfoster@xxxxxxxxxx> wrote:
>
>> On Thu, Jul 16, 2015 at 01:20:30PM -0500, Eric Sandeen wrote:
>> My prior commit, aaf90a2 xfs_copy: fix copy of hard 4k devices
>> causes xfs_copy to emit a CRC error warning when copying a
>> CRC filesystem.
>>
>> This is because we are now reading the maximum sector size,
>> and attempting to verify the CRC based on that (likely incorrect)
>> length.
>>
>> In xfs_db, we currently just don't verify this read, so it's
>> not a problem. In xfs_copy, we almost certainly want to verify.
>>
>> So, first do the maximal read with no verifier; once it's read,
>> drop that buffer, and re-read with the proper sector size and
>> verifier.
>>
>> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
>> ---
>>
>> diff --git a/copy/xfs_copy.c b/copy/xfs_copy.c
>> index 44a32e8..fd96e15 100644
>> --- a/copy/xfs_copy.c
>> +++ b/copy/xfs_copy.c
>> @@ -654,11 +654,17 @@ main(int argc, char **argv)
>>
>> memset(&mbuf, 0, sizeof(xfs_mount_t));
>> libxfs_buftarg_init(&mbuf, xargs.ddev, xargs.logdev, xargs.rtdev);
>> + /* We don't yet know the sector size, so read maximal size */
>> sbp = libxfs_readbuf(mbuf.m_ddev_targp, XFS_SB_DADDR,
>> - 1 << (XFS_MAX_SECTORSIZE_LOG - BBSHIFT),
>> - 0, &xfs_sb_buf_ops);
>> + 1 << (XFS_MAX_SECTORSIZE_LOG - BBSHIFT), 0, NULL);
>> sb = &mbuf.m_sb;
>> libxfs_sb_from_disk(sb, XFS_BUF_TO_SBP(sbp));
>> + /* Do it again, now with proper length and verifier */
>> + libxfs_putbuf(sbp);
>> + libxfs_purgebuf(sbp);
>
> Why the purge? On a quick look, it looks like the buffer cache code
> would handle this if the buffer size changes.
>
> Hmm, is it to ensure the verification occurs if the buffer size doesn't
> actually change? If so, I'd suggest to enhance the comment. :)
>
Without the purge, a re-read of a different size at the same offset seems to
cause cache mismatch problems.
Eric
> Brian
>
>> + sbp = libxfs_readbuf(mbuf.m_ddev_targp, XFS_SB_DADDR,
>> + 1 << (sb->sb_sectlog - BBSHIFT),
>> + 0, &xfs_sb_buf_ops);
>>
>> /*
>> * For now, V5 superblock filesystems are not supported without -d;
>>
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>
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