block: hide request sector and data_len

Block low level drivers for some reason have been pretty good at
abusing block layer API.  Especially struct request's fields tend to
get violated in all possible ways.  Make it clear that low level
drivers MUST NOT access or manipulate rq->sector and rq->data_len
directly by prefixing them with double underscores.

This change is also necessary to break build of out-of-tree codes
which assume the previous block API where internal fields can be
manipulated and rq->data_len carries residual count on completion.

[ Impact: hide internal fields, block API change ]

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/blk-core.c b/block/blk-core.c
index 3596ca7..6226a38 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -127,7 +127,7 @@
 	INIT_LIST_HEAD(&rq->timeout_list);
 	rq->cpu = -1;
 	rq->q = q;
-	rq->sector = (sector_t) -1;
+	rq->__sector = (sector_t) -1;
 	INIT_HLIST_NODE(&rq->hash);
 	RB_CLEAR_NODE(&rq->rb_node);
 	rq->cmd = rq->__cmd;
@@ -1095,7 +1095,7 @@
 		req->cmd_flags |= REQ_NOIDLE;
 
 	req->errors = 0;
-	req->sector = bio->bi_sector;
+	req->__sector = bio->bi_sector;
 	req->ioprio = bio_prio(bio);
 	blk_rq_bio_prep(req->q, req, bio);
 }
@@ -1143,7 +1143,7 @@
 
 		req->biotail->bi_next = bio;
 		req->biotail = bio;
-		req->data_len += bytes;
+		req->__data_len += bytes;
 		req->ioprio = ioprio_best(req->ioprio, prio);
 		if (!blk_rq_cpu_valid(req))
 			req->cpu = bio->bi_comp_cpu;
@@ -1169,8 +1169,8 @@
 		 * not touch req->buffer either...
 		 */
 		req->buffer = bio_data(bio);
-		req->sector = bio->bi_sector;
-		req->data_len += bytes;
+		req->__sector = bio->bi_sector;
+		req->__data_len += bytes;
 		req->ioprio = ioprio_best(req->ioprio, prio);
 		if (!blk_rq_cpu_valid(req))
 			req->cpu = bio->bi_comp_cpu;
@@ -1878,7 +1878,7 @@
 		 * can find how many bytes remain in the request
 		 * later.
 		 */
-		req->data_len = 0;
+		req->__data_len = 0;
 		return false;
 	}
 
@@ -1892,12 +1892,12 @@
 		bio_iovec(bio)->bv_len -= nr_bytes;
 	}
 
-	req->data_len -= total_bytes;
+	req->__data_len -= total_bytes;
 	req->buffer = bio_data(req->bio);
 
 	/* update sector only for requests with clear definition of sector */
 	if (blk_fs_request(req) || blk_discard_rq(req))
-		req->sector += total_bytes >> 9;
+		req->__sector += total_bytes >> 9;
 
 	/*
 	 * If total number of sectors is less than the first segment
@@ -1905,7 +1905,7 @@
 	 */
 	if (blk_rq_bytes(req) < blk_rq_cur_bytes(req)) {
 		printk(KERN_ERR "blk: request botched\n");
-		req->data_len = blk_rq_cur_bytes(req);
+		req->__data_len = blk_rq_cur_bytes(req);
 	}
 
 	/* recalculate the number of segments */
@@ -2032,7 +2032,7 @@
 		rq->nr_phys_segments = bio_phys_segments(q, bio);
 		rq->buffer = bio_data(bio);
 	}
-	rq->data_len = bio->bi_size;
+	rq->__data_len = bio->bi_size;
 	rq->bio = rq->biotail = bio;
 
 	if (bio->bi_bdev)