It's present (but undocumented) in the illumos gate and used exclusively
by rmformat(1) (which I recommend as a nice blast from the past),
and also the math assumes 512B sectors and is therefore wrong
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes#12191
d406a695c6