1 058b0118 2005-01-03 devnull .TH FLUSH 9P
  2 058b0118 2005-01-03 devnull .SH NAME
  3 058b0118 2005-01-03 devnull flush \- abort a message
  4 058b0118 2005-01-03 devnull .SH SYNOPSIS
  5 058b0118 2005-01-03 devnull .ta \w'\fLTflush 'u
  6 058b0118 2005-01-03 devnull .IR size [4]
  7 058b0118 2005-01-03 devnull .B Tflush
  8 058b0118 2005-01-03 devnull .IR tag [2]
  9 058b0118 2005-01-03 devnull .IR oldtag [2]
 10 058b0118 2005-01-03 devnull .br
 11 058b0118 2005-01-03 devnull .IR size [4]
 12 058b0118 2005-01-03 devnull .B Rflush
 13 058b0118 2005-01-03 devnull .IR tag [2]
 14 058b0118 2005-01-03 devnull .SH DESCRIPTION
 15 058b0118 2005-01-03 devnull When the response to a request is no longer needed, such as when
 16 058b0118 2005-01-03 devnull a user interrupts a process doing a
 17 058b0118 2005-01-03 devnull .IR read (9p),
 18 058b0118 2005-01-03 devnull a
 19 058b0118 2005-01-03 devnull .B Tflush
 20 058b0118 2005-01-03 devnull request is sent to the server to purge the pending response.
 21 058b0118 2005-01-03 devnull The message being flushed is identified by
 22 058b0118 2005-01-03 devnull .IR oldtag .
 23 058b0118 2005-01-03 devnull The semantics of
 24 058b0118 2005-01-03 devnull .B flush
 25 058b0118 2005-01-03 devnull depends on messages arriving in order.
 26 058b0118 2005-01-03 devnull .PP
 27 058b0118 2005-01-03 devnull The server should answer the
 28 058b0118 2005-01-03 devnull .B flush
 29 058b0118 2005-01-03 devnull message immediately.
 30 058b0118 2005-01-03 devnull If it recognizes
 31 058b0118 2005-01-03 devnull .I oldtag
 32 058b0118 2005-01-03 devnull as the tag of a pending transaction, it should abort any pending response
 33 058b0118 2005-01-03 devnull and discard that tag.
 34 058b0118 2005-01-03 devnull In either case, it should respond with an
 35 058b0118 2005-01-03 devnull .B Rflush
 36 058b0118 2005-01-03 devnull echoing the
 37 058b0118 2005-01-03 devnull .I tag
 38 058b0118 2005-01-03 devnull (not
 39 058b0118 2005-01-03 devnull .IR oldtag )
 40 058b0118 2005-01-03 devnull of the
 41 058b0118 2005-01-03 devnull .B Tflush
 42 058b0118 2005-01-03 devnull message.
 43 058b0118 2005-01-03 devnull A
 44 058b0118 2005-01-03 devnull .B Tflush
 45 058b0118 2005-01-03 devnull can never be responded to by an
 46 058b0118 2005-01-03 devnull .B Rerror
 47 058b0118 2005-01-03 devnull message.
 48 058b0118 2005-01-03 devnull .PP
 49 058b0118 2005-01-03 devnull The server may respond to the pending request before
 50 058b0118 2005-01-03 devnull responding to the
 51 058b0118 2005-01-03 devnull .BR Tflush .
 52 058b0118 2005-01-03 devnull It is possible for a client to send multiple
 53 058b0118 2005-01-03 devnull .B Tflush
 54 058b0118 2005-01-03 devnull messages for a particular pending request.  Each
 55 058b0118 2005-01-03 devnull subsequent
 56 058b0118 2005-01-03 devnull .B Tflush
 57 058b0118 2005-01-03 devnull must contain as
 58 058b0118 2005-01-03 devnull .I oldtag
 59 058b0118 2005-01-03 devnull the tag of the pending request (not a previous
 60 058b0118 2005-01-03 devnull .BR Tflush ).
 61 058b0118 2005-01-03 devnull Should multiple
 62 058b0118 2005-01-03 devnull .BR Tflush es
 63 058b0118 2005-01-03 devnull be received for a pending request, they must be answered in
 64 058b0118 2005-01-03 devnull order.  A
 65 058b0118 2005-01-03 devnull .B Rflush
 66 058b0118 2005-01-03 devnull for any of the multiple
 67 058b0118 2005-01-03 devnull .BR Tflush es
 68 058b0118 2005-01-03 devnull implies an answer for all previous ones.  Therefore, should
 69 058b0118 2005-01-03 devnull a server receive a request and then multiple flushes for that
 70 058b0118 2005-01-03 devnull request, it need respond only to the last flush.
 71 058b0118 2005-01-03 devnull .PP
 72 058b0118 2005-01-03 devnull When the client sends a 
 73 058b0118 2005-01-03 devnull .BR Tflush ,
 74 058b0118 2005-01-03 devnull it must wait to receive the corresponding
 75 058b0118 2005-01-03 devnull .B Rflush
 76 058b0118 2005-01-03 devnull before reusing
 77 058b0118 2005-01-03 devnull .I oldtag
 78 058b0118 2005-01-03 devnull for subsequent messages.
 79 058b0118 2005-01-03 devnull If a response to the flushed request is received before the
 80 058b0118 2005-01-03 devnull .BR Rflush ,
 81 058b0118 2005-01-03 devnull the client must honor the response
 82 058b0118 2005-01-03 devnull as if it had not been flushed,
 83 058b0118 2005-01-03 devnull since the completed request may signify a state change in the server.
 84 058b0118 2005-01-03 devnull For instance,
 85 058b0118 2005-01-03 devnull .B Tcreate
 86 058b0118 2005-01-03 devnull may have created a file and
 87 058b0118 2005-01-03 devnull .B Twalk
 88 058b0118 2005-01-03 devnull may have allocated a fid.
 89 058b0118 2005-01-03 devnull If no response is received before the
 90 058b0118 2005-01-03 devnull .BR Rflush ,
 91 058b0118 2005-01-03 devnull the flushed transaction is considered to have been canceled,
 92 058b0118 2005-01-03 devnull and should be treated as though it had never been sent.
 93 058b0118 2005-01-03 devnull .PP
 94 058b0118 2005-01-03 devnull Several exceptional conditions are handled correctly by the above specification:
 95 058b0118 2005-01-03 devnull sending multiple flushes for a single tag,
 96 058b0118 2005-01-03 devnull flushing after a transaction is completed,
 97 058b0118 2005-01-03 devnull flushing a
 98 058b0118 2005-01-03 devnull .BR Tflush ,
 99 058b0118 2005-01-03 devnull and flushing an invalid tag.
100 058b0118 2005-01-03 devnull .SH ENTRY POINTS
101 058b0118 2005-01-03 devnull The
102 36cd4c58 2021-01-30 crossd .MR 9pclient (3)
103 058b0118 2005-01-03 devnull library does not generate
104 058b0118 2005-01-03 devnull .B flush
105 058b0118 2005-01-03 devnull transactions..
106 36cd4c58 2021-01-30 crossd .MR 9pserve (4)
107 058b0118 2005-01-03 devnull generates
108 058b0118 2005-01-03 devnull .B flush
109 058b0118 2005-01-03 devnull transactions to cancel transactions pending when a client hangs up.