block: cleanup bio_add_pc_page

REQ_PC is out of date, so replace it with passthrough IO.

Also remove the local variable of 'prev' since we can reuse
the top local variable of 'bvec'.

No function change.

Cc: Omar Sandoval <osandov@fb.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: NMing Lei <ming.lei@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

block/bio.c

@@ -648,7 +648,7 @@ struct bio *bio_clone_fast(struct bio *bio, gfp_t gfp_mask, struct bio_set *bs)
 EXPORT_SYMBOL(bio_clone_fast);
 
 /**
- *	bio_add_pc_page	-	attempt to add page to bio
+ *	bio_add_pc_page	-	attempt to add page to passthrough bio
  *	@q: the target queue
  *	@bio: destination bio
  *	@page: page to add
@@ -660,7 +660,7 @@ EXPORT_SYMBOL(bio_clone_fast);
  *	limitations. The target block device must allow bio's up to PAGE_SIZE,
  *	so it is always possible to add a single page to an empty bio.
  *
- *	This should only be used by REQ_PC bios.
+ *	This should only be used by passthrough bios.
  */
 int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page
 		    *page, unsigned int len, unsigned int offset)
@@ -683,11 +683,11 @@ int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page
 	 * a consecutive offset.  Optimize this special case.
 	 */
 	if (bio->bi_vcnt > 0) {
-		struct bio_vec *prev = &bio->bi_io_vec[bio->bi_vcnt - 1];
+		bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
 
-		if (page == prev->bv_page &&
-		    offset == prev->bv_offset + prev->bv_len) {
-			prev->bv_len += len;
+		if (page == bvec->bv_page &&
+		    offset == bvec->bv_offset + bvec->bv_len) {
+			bvec->bv_len += len;
 			bio->bi_iter.bi_size += len;
 			goto done;
 		}
@@ -696,7 +696,7 @@ int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page
 		 * If the queue doesn't support SG gaps and adding this
 		 * offset would create a gap, disallow it.
 		 */
-		if (bvec_gap_to_prev(q, prev, offset))
+		if (bvec_gap_to_prev(q, bvec, offset))
 			return 0;
 	}