FltSendMessage中的timeout怎么理解的?

Timeout
A pointer to a timeout value that specifies the total absolute or relative length of time, in units of 100 nanoseconds, for which the caller can be put into a wait state until the message is received by the user-mode application and until it receives a reply (if one is expected). Set to NULL if the caller can be put into a wait state indefinitely.

不是很懂，如果超时的话，完成端口是否还有数据等待读取？

Otherwise, the message is not delivered, and FltSendMessage returns STATUS_TIMEOUT.
msdn上有这一句话，是不是说明发送消息失败了

这个函数是一个同步操作。如果客户端没有用filterrelymessage返回信息，超时后会自动返回，有错误信息。