[$] Support for atomic block writes in 6.13

Atomic block writes, which have been discussed here a
few times in the past, are block operations that either complete fully or
do not occur at all, ensuring data consistency and preventing partial (or
'torn') writes. This means the disk will, at all times, contain either the
complete new data from the atomic write operation or the complete old data
from a previous write. It will never have a mix of both the old and the new
data, even if a power failure occurs during an ongoing atomic write
operation. Atomic writes have been of interest to many Linux users,
particularly database developers, as this feature can provide significant
performance improvements.