io_uring: rename prev to head

to #26323588

commit 9d76377f7e13c19441fdd066033345289f89b5fe upstream.

Calling "prev" a head of a link is a bit misleading. Rename it
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

fs/io_uring.c

@@ -4070,10 +4070,10 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	 * conditions are true (normal request), then just queue it.
 	 */
 	if (*link) {
-		struct io_kiocb *prev = *link;
+		struct io_kiocb *head = *link;
 
 		if (sqe->flags & IOSQE_IO_DRAIN)
-			(*link)->flags |= REQ_F_DRAIN_LINK | REQ_F_IO_DRAIN;
+			head->flags |= REQ_F_DRAIN_LINK | REQ_F_IO_DRAIN;
 
 		if (sqe->flags & IOSQE_IO_HARDLINK)
 			req->flags |= REQ_F_HARDLINK;
@@ -4086,11 +4086,11 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		ret = io_req_defer_prep(req, sqe);
 		if (ret) {
 			/* fail even hard links since we don't submit */
-			prev->flags |= REQ_F_FAIL_LINK;
+			head->flags |= REQ_F_FAIL_LINK;
 			goto err_req;
 		}
-		trace_io_uring_link(ctx, req, prev);
-		list_add_tail(&req->link_list, &prev->link_list);
+		trace_io_uring_link(ctx, req, head);
+		list_add_tail(&req->link_list, &head->link_list);
 	} else if (sqe->flags & (IOSQE_IO_LINK|IOSQE_IO_HARDLINK)) {
 		req->flags |= REQ_F_LINK;
 		if (sqe->flags & IOSQE_IO_HARDLINK)