tap: add support for IOCB_NOWAIT

The tap driver already supports passing in nonblocking state based
on O_NONBLOCK, add support for checking IOCB_NOWAIT as well. With that
done, we can flag it with FMODE_NOWAIT as well.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/8f859870-e6e2-09ca-9c0f-a2aa7c984fb2@kernel.dkSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/tap.c

@@ -555,6 +555,9 @@ static int tap_open(struct inode *inode, struct file *file)
 		goto err_put;
 	}
 
+	/* tap groks IOCB_NOWAIT just fine, mark it as such */
+	file->f_mode |= FMODE_NOWAIT;
+
 	dev_put(tap->dev);
 
 	rtnl_unlock();
@@ -771,8 +774,12 @@ static ssize_t tap_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct file *file = iocb->ki_filp;
 	struct tap_queue *q = file->private_data;
+	int noblock = 0;
+
+	if ((file->f_flags & O_NONBLOCK) || (iocb->ki_flags & IOCB_NOWAIT))
+		noblock = 1;
 
-	return tap_get_user(q, NULL, from, file->f_flags & O_NONBLOCK);
+	return tap_get_user(q, NULL, from, noblock);
 }
 
 /* Put packet to the user space buffer */
@@ -888,8 +895,12 @@ static ssize_t tap_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	struct file *file = iocb->ki_filp;
 	struct tap_queue *q = file->private_data;
 	ssize_t len = iov_iter_count(to), ret;
+	int noblock = 0;
+
+	if ((file->f_flags & O_NONBLOCK) || (iocb->ki_flags & IOCB_NOWAIT))
+		noblock = 1;
 
-	ret = tap_do_read(q, to, file->f_flags & O_NONBLOCK, NULL);
+	ret = tap_do_read(q, to, noblock, NULL);
 	ret = min_t(ssize_t, ret, len);
 	if (ret > 0)
 		iocb->ki_pos = ret;