xfs_copy: check for dirty log on non-duplicate copies

xfs_copy: check for dirty log on non-duplicate copies

xfs_copy either copies the log as-is or formats the log of the target(s)
based on whether duplicate copy mode is enabled. The target log is
formatted when non-duplicate mode is enabled because copies gain a new
fs UUID and the new UUID must be stamped into the log.

When non-duplicate mode is enabled, however, xfs_copy does not check
whether the source filesystem log is actually clean. If the source log
is dirty, the target filesystem is silently created with a clean log and
thus ends up in a potentially corrupted state.

Update xfs_copy to check the source log state and fail the copy if in
non-duplicate mode and the log is dirty. Encourage the user to mount the
filesystem or run xfs_repair to clear the log. Note that the log is
scanned unconditionally as opposed to only in non-duplicate mode because
v5 superblock log format support requires the current cycle number to
format the log correctly.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>