--- linux/fs/pipe.c	2018/04/24 18:03:41	1.1.1.4
+++ linux/fs/pipe.c	2018/04/24 18:05:54	1.1.1.5
@@ -41,7 +41,7 @@ int pipe_read(struct inode * inode, stru
 			put_fs_byte(((char *)inode->i_size)[size++],buf++);
 	}
 	wake_up(& PIPE_WRITE_WAIT(*inode));
-	return read;
+	return read?read:-EAGAIN;
 }
 	
 int pipe_write(struct inode * inode, struct file * filp, char * buf, int count)