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VERSION(9P)							   VERSION(9P)

       version - negotiate protocol version

       size[4] Tversion	tag[2] msize[4]	version[s]
       size[4] Rversion	tag[2] msize[4]	version[s]

       The version request negotiates the protocol version and message size to
       be used on the connection  and  initializes  the	 connection  for  I/O.
       Tversion	 must  be the first message sent on the	9P connection, and the
       client cannot issue any further requests	 until	it  has	 received  the
       Rversion	 reply.	 The tag should	be NOTAG (value	(ushort)~0) for	a ver-
       sion message.

       The client suggests a maximum message size, msize, that is the  maximum
       length,	in bytes, it will ever generate	or expect to receive in	a sin-
       gle 9P message.	This count includes all	 9P  protocol  data,  starting
       from the	size field and extending through the message, but excludes en-
       veloping	transport protocols.  The server responds with its  own	 maxi-
       mum,  msize,  which  must  be less than or equal	to the client's	value.
       Thenceforth, both sides of the connection must honor this limit.

       The version string identifies the level of the  protocol.   The	string
       must  always  begin with	the two	characters ``9P''.  If the server does
       not understand the client's version string, it should respond  with  an
       Rversion	 message (not Rerror) with the version string the 7 characters

       The server may respond with the client's	version	string,	or  a  version
       string identifying an earlier defined protocol version.	Currently, the
       only defined version is the 6 characters	``9P2000''.   Version  strings
       are defined such	that, if the client string contains one	or more	period
       characters, the initial substring up to but not	including  any	single
       period  in the version string defines a version of the protocol.	 After
       stripping any such period-separated suffix, the server  is  allowed  to
       respond	with  a	 string	of the form 9Pnnnn, where nnnn is less than or
       equal to	the digits sent	by the client.

       The client and server will use the  protocol  version  defined  by  the
       server's	response for all subsequent communication on the connection.

       A successful version request initializes	the connection.	 All outstand-
       ing I/O on the  connection  is  aborted;	 all  active  fids  are	 freed
       (`clunked')  automatically.   The  set  of messages between version re-
       quests is called	a session.

       Fsversion (see generates	version	messages; it is	 called	 automatically
       by fsmount.



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