block_dev: support RFW_NOWAIT on block device nodes

All support is already there in the generic code, we just need to wire
it up.

Signed-off-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>

fs/block_dev.c

···
 	 */
 	filp->f_flags |= O_LARGEFILE;
 
+	filp->f_mode |= FMODE_NOWAIT;
+
 	if (filp->f_flags & O_NDELAY)
 		filp->f_mode |= FMODE_NDELAY;
 	if (filp->f_flags & O_EXCL)
···
 
 	if (iocb->ki_pos >= size)
 		return -ENOSPC;
+
+	if ((iocb->ki_flags & (IOCB_NOWAIT | IOCB_DIRECT)) == IOCB_NOWAIT)
+		return -EOPNOTSUPP;
 
 	iov_iter_truncate(from, size - iocb->ki_pos);