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FLUSH(5)							      FLUSH(5)

NAME
       flush - abort a message

SYNOPSIS
       size[4] Tflush tag[2] oldtag[2]
       size[4] Rflush tag[2]

DESCRIPTION
       When the response to a request is no longer needed, such as when a user
       interrupts a process doing a read(2), a Tflush request is sent  to  the
       server  to  purge  the  pending response.  The message being flushed is
       identified by oldtag.  The  semantics  of  flush	 depends  on  messages
       arriving in order.

       The  server  should answer the flush message immediately.  If it recog‐
       nizes 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  mes‐
       sage.  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	 Tflushes be received for a pending request, they must
       be answered in order.  A	 Rflush	 for  any  of  the  multiple  Tflushes
       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 correspond‐
       ing 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 canceled, and should be  treated
       as though it had never been sent.

       Several exceptional conditions are handled correctly by the above spec‐
       ification: sending multiple flushes for a single tag, flushing after  a
       transaction  is	completed,  flushing a Tflush, and flushing an invalid
       tag.

								      FLUSH(5)
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