PR#57856 shows when using blkdiscard on eg, /dev/ld0 it asserts because
'0' is not between 'a' and 'p'. switch this to using DISKPART() on the
returned st_rdev, so it works on 'ld0c' or 'ld0' (rawpart=2.)
that matches the linux-util version.
comes in two forms: blkdiscard equivalent, and the (almost)
original interface i used (the "-s" option is conflicting and
i've switched to only the not yet implemented secure erase
option.) the only real difference is that "fdiscard" mode
requires the -R flag to do something, vs blkdiscard needs the
-n flag to not do anything.
not yet hooked into the build or sets. would like more testing
on it to be performed before doing that (but soon.)
andvar