The new way goes via /sys/dev/block/MAJOR:MINOR to map partitions to
devices and get discard parameters of the parent device. It also ensures
that the partition is aligned to the discard block size.
Contributed by Richard W.M. Jones
fstrim(8) discards unused blocks on a mounted filesystem. It is useful for
solid-state drives (SSDs) and thinly-provisioned storage.
Only trimming the full device (with no option) is supported.
Contributed by Richard W.M. Jones
Jean-Pierre André