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| <tr><td width=20><td><b>VERSION(9P)</b><td align=right><b>VERSION(9P)</b> |
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| <p><font size=+1><b>NAME </b></font><br> |
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| version – negotiate protocol version<br> |
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| <p><font size=+1><b>SYNOPSIS </b></font><br> |
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| <i>size</i>[4] <tt><font size=+1>Tversion</font></tt> <i>tag</i>[2] <i>msize</i>[4] <i>version</i>[<i>s</i>]<br> |
| <i>size</i>[4] <tt><font size=+1>Rversion</font></tt> <i>tag</i>[2] <i>msize</i>[4] <i>version</i>[<i>s</i>]<br> |
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| <p><font size=+1><b>DESCRIPTION </b></font><br> |
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| The <tt><font size=+1>version</font></tt> request negotiates the protocol version and message |
| size to be used on the connection and initializes the connection |
| for I/O. <tt><font size=+1>Tversion</font></tt> must be the first message sent on the 9P connection, |
| and the client cannot issue any further requests until it has |
| received the <tt><font size=+1>Rversion</font></tt> reply. The <i>tag</i> should be |
| <tt><font size=+1>NOTAG</font></tt> (value <tt><font size=+1>(ushort)~0</font></tt>) for a <tt><font size=+1>version</font></tt> message. |
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| The client suggests a maximum message size, <tt><font size=+1>msize</font></tt>, that is the |
| maximum length, in bytes, it will ever generate or expect to receive |
| in a single 9P message. This count includes all 9P protocol data, |
| starting from the <tt><font size=+1>size</font></tt> field and extending through the message, |
| but excludes enveloping transport protocols. The |
| server responds with its own maximum, <tt><font size=+1>msize</font></tt>, which must be less |
| than or equal to the client’s value. Thenceforth, both sides of |
| the connection must honor this limit. |
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| The <tt><font size=+1>version</font></tt> string identifies the level of the protocol. The string |
| must always begin with the two characters “<tt><font size=+1>9P</font></tt>”. If the server |
| does not understand the client’s version string, it should respond |
| with an <tt><font size=+1>Rversion</font></tt> message (not <tt><font size=+1>Rerror</font></tt>) with the <tt><font size=+1>version</font></tt> string |
| the 7 characters “<tt><font size=+1>unknown</font></tt>”. |
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| 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 “<tt><font size=+1>9P2000</font></tt>”. |
| 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 <tt><font size=+1>9P</font></tt><i>nnnn</i>, where <i>nnnn</i> is less than or equal to the digits sent |
| by the client. |
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| The client and server will use the protocol version defined by |
| the server’s response for all subsequent communication on the |
| connection. |
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| A successful <tt><font size=+1>version</font></tt> request initializes the connection. All outstanding |
| I/O on the connection is aborted; all active fids are freed (‘clunked’) |
| automatically. The set of messages between <tt><font size=+1>version</font></tt> requests is |
| called a <i>session</i>.<br> |
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| </table> |
| <p><font size=+1><b>ENTRY POINTS </b></font><br> |
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| <i>Fsversion</i> (see <a href="../man3/9pclient.html"><i>9pclient</i>(3)</a>) generates <tt><font size=+1>version</font></tt> messages; it is |
| called automatically by <i>fsmount</i>.<br> |
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