CFT: TRIM Consolodation on UFS/FFS filesystems

[Mark Millard]

Just an FYI.

I figured out a hack that allows the e.MMC on a microsd card
adapter to be used to boot and operate the Pine64+ 2GB, in
DDR52 mode at that. (And so shows what was missing in the
FreeBSD operation even if the code change is not the
proper form of an official fix.)

But in the process I discovered that FreeBSD is using
(for e.MMC in this tested context):

mmc0: REQUEST: CMD38 arg 0x1 flags 0x1d

That "0x1" means: TRIM that forces reads of zeros: the true
Data Removal command for mmc protocol, a form of erase. 0x3
would be DISCARD, the "performance command" that does not
guarantee what would be read afterwards: no erase required.

TRIM is older (added in e/MCC 4.4). DISCARD is newer (added
in e.MMC 4.5). Each is mandatory when the version has the
function at all.

Does FreeBSD have a policy of preferring erasure when
there is also the option to not require it?


===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)