dm bio prison: introduce support for locking ranges of blocks

Ranges will be placed in the same cell if they overlap.

Range locking is a prerequisite for more efficient multi-block discard
support in both the cache and thin-provisioning targets.

Signed-off-by: Joe Thornber <[e-mail]>
Signed-off-by: Mike Snitzer <[e-mail]>

drivers/md/dm-bio-prison.c

···
 	if (lhs->dev > rhs->dev)
 		return 1;
 
-	if (lhs->block < rhs->block)
+	if (lhs->block_end <= rhs->block_begin)
 		return -1;
 
-	if (lhs->block > rhs->block)
+	if (lhs->block_begin >= rhs->block_end)
 		return 1;
 
 	return 0;

drivers/md/dm-bio-prison.h

···
  */
 struct dm_bio_prison;
 
-/* FIXME: this needs to be more abstract */
+/*
+ * Keys define a range of blocks within either a virtual or physical
+ * device.
+ */
 struct dm_cell_key {
 	int virtual;
 	dm_thin_id dev;
-	dm_block_t block;
+	dm_block_t block_begin, block_end;
 };
 
 /*
···
 			     struct dm_bio_prison_cell *cell);
 
 /*
- * Creates, or retrieves a cell for the given key.
+ * Creates, or retrieves a cell that overlaps the given key.
  *
  * Returns 1 if pre-existing cell returned, zero if new cell created using
  * @cell_prealloc.
···
 		struct dm_bio_prison_cell **cell_result);
 
 /*
- * An atomic op that combines retrieving a cell, and adding a bio to it.
+ * An atomic op that combines retrieving or creating a cell, and adding a
+ * bio to it.
  *
  * Returns 1 if the cell was already held, 0 if @inmate is the new holder.
  */

drivers/md/dm-cache-target.c

···
 {
 	key->virtual = 0;
 	key->dev = 0;
-	key->block = from_oblock(oblock);
+	key->block_begin = from_oblock(oblock);
+	key->block_end = key->block_begin + 1ULL;
 }
 
 /*

drivers/md/dm-thin.c

···
 {
 	key->virtual = 0;
 	key->dev = dm_thin_dev_id(td);
-	key->block = b;
+	key->block_begin = b;
+	key->block_end = b + 1ULL;
 }
 
 static void build_virtual_key(struct dm_thin_device *td, dm_block_t b,
···
 {
 	key->virtual = 1;
 	key->dev = dm_thin_dev_id(td);
-	key->block = b;
+	key->block_begin = b;
+	key->block_end = b + 1ULL;
 }
 
 /*----------------------------------------------------------------*/