io_uring: io_kiocb_update_pos() should not touch file for non -1 offset

-1 tells use to use the current position, but we check if the file is
a stream regardless of that. Fix up io_kiocb_update_pos() to only
dip into file if we need to. This is both more efficient and also drops
12 bytes of text on aarch64 and 64 bytes on x86-64.

Fixes: b4aec40 ("io_uring: do not recalculate ppos unnecessarily")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: axboe

fs/io_uring.c

@@ -3183,19 +3183,18 @@ static inline void io_rw_done(struct kiocb *kiocb, ssize_t ret)
 static inline loff_t *io_kiocb_update_pos(struct io_kiocb *req)
 {
 	struct kiocb *kiocb = &req->rw.kiocb;
-	bool is_stream = req->file->f_mode & FMODE_STREAM;
 
-	if (kiocb->ki_pos == -1) {
-		if (!is_stream) {
-			req->flags |= REQ_F_CUR_POS;
-			kiocb->ki_pos = req->file->f_pos;
-			return &kiocb->ki_pos;
-		} else {
-			kiocb->ki_pos = 0;
-			return NULL;
-		}
+	if (kiocb->ki_pos != -1)
+		return &kiocb->ki_pos;
+
+	if (!(req->file->f_mode & FMODE_STREAM)) {
+		req->flags |= REQ_F_CUR_POS;
+		kiocb->ki_pos = req->file->f_pos;
+		return &kiocb->ki_pos;
 	}
-	return is_stream ? NULL : &kiocb->ki_pos;
+
+	kiocb->ki_pos = 0;
+	return NULL;
 }
 
 static void kiocb_done(struct io_kiocb *req, ssize_t ret,