dm thin: correct comments

Remove documentation for unimplemented 'trim' message.

I'd planned a 'trim' target message for shrinking thin devices, but
this is better handled via the discard ioctl.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

Documentation/device-mapper/thin-provisioning.txt

@@ -237,16 +237,6 @@ iii) Messages
 
 	Deletes a thin device.  Irreversible.
 
-    trim <dev id> <new size in sectors>
-
-	Delete mappings from the end of a thin device.  Irreversible.
-	You might want to use this if you're reducing the size of
-	your thinly-provisioned device.  In many cases, due to the
-	sharing of blocks between devices, it is not possible to
-	determine in advance how much space 'trim' will release.  (In
-	future a userspace tool might be able to perform this
-	calculation.)
-
     set_transaction_id <current id> <new id>
 
 	Userland volume managers, such as LVM, need a way to

drivers/md/dm-thin.c

@@ -72,7 +72,7 @@
  * missed out if the io covers the block. (schedule_copy).
  *
  * iv) insert the new mapping into the origin's btree
- * (process_prepared_mappings).  This act of inserting breaks some
+ * (process_prepared_mapping).  This act of inserting breaks some
  * sharing of btree nodes between the two devices.  Breaking sharing only
  * effects the btree of that specific device.  Btrees for the other
  * devices that share the block never change.  The btree for the origin