io_uring: simplify io_resubmit_prep()

If not for async_data NULL check, io_resubmit_prep() is already an rw
specific version of io_req_prep_async(), but slower because 1) it always
goes through io_import_iovec() even if following io_setup_async_rw() the
result 2) instead of initialising iovec/iter in-place it does it
on-stack and then copies with io_setup_async_rw().
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -1032,14 +1032,10 @@ static struct file *io_file_get(struct io_submit_state *state,
 static void __io_queue_sqe(struct io_kiocb *req);
 static void io_rsrc_put_work(struct work_struct *work);
 
-static int io_import_iovec(int rw, struct io_kiocb *req, struct iovec **iovec,
-			   struct iov_iter *iter, bool needs_lock);
-static int io_setup_async_rw(struct io_kiocb *req, const struct iovec *iovec,
-			     const struct iovec *fast_iov,
-			     struct iov_iter *iter, bool force);
 static void io_req_task_queue(struct io_kiocb *req);
 static void io_submit_flush_completions(struct io_comp_state *cs,
 					struct io_ring_ctx *ctx);
+static int io_req_prep_async(struct io_kiocb *req);
 
 static struct kmem_cache *req_cachep;
 
@@ -2429,35 +2425,8 @@ static void kiocb_end_write(struct io_kiocb *req)
 #ifdef CONFIG_BLOCK
 static bool io_resubmit_prep(struct io_kiocb *req)
 {
-	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
-	int rw, ret;
-	struct iov_iter iter;
-
-	/* already prepared */
-	if (req->async_data)
-		return true;
-
-	switch (req->opcode) {
-	case IORING_OP_READV:
-	case IORING_OP_READ_FIXED:
-	case IORING_OP_READ:
-		rw = READ;
-		break;
-	case IORING_OP_WRITEV:
-	case IORING_OP_WRITE_FIXED:
-	case IORING_OP_WRITE:
-		rw = WRITE;
-		break;
-	default:
-		printk_once(KERN_WARNING "io_uring: bad opcode in resubmit %d\n",
-				req->opcode);
-		return false;
-	}
-
-	ret = io_import_iovec(rw, req, &iovec, &iter, false);
-	if (ret < 0)
-		return false;
-	return !io_setup_async_rw(req, iovec, inline_vecs, &iter, false);
+	/* either already prepared or successfully done */
+	return req->async_data || !io_req_prep_async(req);
 }
 
 static bool io_rw_should_reissue(struct io_kiocb *req)