lightnvm: reference rrpc lun in rrpc block

BugLink: http://bugs.launchpad.net/bugs/1531539

Currently, a rrpc block only points to its nvm_lun. If a user wants to
find the associated rrpc lun, it will have to calculate the index and
look it up manually. By referencing the rrpc lun directly, this step can
be omitted, at the cost of a larger memory footprint.

This is important for upcoming patches that implement write buffering in
rrpc.
Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit d7a64d27)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/lightnvm/rrpc.c

@@ -1150,6 +1150,7 @@ static int rrpc_luns_init(struct rrpc *rrpc, int lun_begin, int lun_end)
 			struct nvm_block *blk = &lun->blocks[j];
 
 			rblk->parent = blk;
+			rblk->rlun = rlun;
 			INIT_LIST_HEAD(&rblk->prio);
 			spin_lock_init(&rblk->lock);
 		}

drivers/lightnvm/rrpc.h

@@ -54,6 +54,7 @@ struct rrpc_rq {
 
 struct rrpc_block {
 	struct nvm_block *parent;
+	struct rrpc_lun *rlun;
 	struct list_head prio;
 
 #define MAX_INVALID_PAGES_STORAGE 8