libnvdimm: enable iostat

This is disabled by default as the overhead is prohibitive, but if the
user takes the action to turn it on we'll oblige.

Reviewed-by: Vishal Verma <vishal.l.verma@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c
index 18a2463..c02065a 100644
--- a/drivers/nvdimm/btt.c
+++ b/drivers/nvdimm/btt.c
@@ -1177,8 +1177,10 @@
 	struct bio_integrity_payload *bip = bio_integrity(bio);
 	struct btt *btt = q->queuedata;
 	struct bvec_iter iter;
+	unsigned long start;
 	struct bio_vec bvec;
 	int err = 0, rw;
+	bool do_acct;
 
 	/*
 	 * bio_integrity_enabled also checks if the bio already has an
@@ -1191,6 +1193,7 @@
 		goto out;
 	}
 
+	do_acct = nd_iostat_start(bio, &start);
 	rw = bio_data_dir(bio);
 	bio_for_each_segment(bvec, bio, iter) {
 		unsigned int len = bvec.bv_len;
@@ -1208,9 +1211,11 @@
 					"io error in %s sector %lld, len %d,\n",
 					(rw == READ) ? "READ" : "WRITE",
 					(unsigned long long) iter.bi_sector, len);
-			goto out;
+			break;
 		}
 	}
+	if (do_acct)
+		nd_iostat_end(bio, start);
 
 out:
 	bio_endio(bio, err);