size [4] Rflush tag [2]
The server should answer the flush message immediately. If it recognizes oldtag as the tag of a pending transaction, it should abort any pending response and discard that tag. In either case, it should respond with an Rflush echoing the tag (not oldtag ) of the Tflush message. A Tflush can never be responded to by an Rerror message.
The server may respond to the pending request before responding to the Tflush . It is possible for a client to send multiple Tflush messages for a particular pending request. Each subsequent Tflush must contain as oldtag the tag of the pending request (not a previous Tflush ). Should multiple Tflush es be received for a pending request, they must be answered in order. An Rflush for any of the multiple Tflush es implies an answer for all previous ones. Therefore, should a server receive a request and then multiple flushes for that request, it need respond only to the last flush.
When the client sends a Tflush , it must wait to receive the corresponding Rflush before reusing oldtag for subsequent messages. If a response to the flushed request is received before the Rflush , the client must honor the response as if it had not been flushed, since the completed request may signify a state change in the server. For instance, Tcreate may have created a file and Twalk may have allocated a fid. If no response is received before the Rflush , the flushed transaction is considered to have been cancelled, and should be treated as though it had never been sent.
Several exceptional conditions are handled correctly by the above specification: sending multiple flushes for a single tag, flushing after a transaction is completed, flushing a Tflush , and flushing an invalid tag.