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QMP: spec: Capability negotiation updates 

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Luiz Capitulino 2010-02-04 18:10:07 -02:00 committed by Anthony Liguori
parent 09069b19f4
commit 5307d7d35e
1 changed files with 29 additions and 17 deletions
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46
QMP/qmp-spec.txt
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@ -44,7 +44,8 @@ they can be in ANY order, thus no particular order should be assumed.
Right when connected the Server will issue a greeting message, which signals Right when connected the Server will issue a greeting message, which signals
that the connection has been successfully established and that the Server is that the connection has been successfully established and that the Server is
waiting for commands. ready for capabilities negotiation (for more information refer to section
'4. Capabilities Negotiation').
The format is: The format is:
@ -181,25 +182,36 @@ S: {"error": {"class": "JSONParsing", "desc": "Invalid JSON syntax", "data":
S: {"timestamp": {"seconds": 1258551470, "microseconds": 802384}, "event": S: {"timestamp": {"seconds": 1258551470, "microseconds": 802384}, "event":
"POWERDOWN"} "POWERDOWN"}
4. Compatibility Considerations 4. Capabilities Negotiation
-------------------------------- ----------------------------
In order to achieve maximum compatibility between versions, Clients must not When a Client successfully establishes a connection, the Server is in
assume any particular: Capabilities Negotiation mode.
In this mode only the 'qmp_capabilities' command is allowed to run, all
other commands will return the CommandNotFound error. Asynchronous messages
are not delivered either.
Clients should use the 'qmp_capabilities' command to enable capabilities
advertised in the Server's greeting (section '2.2 Server Greeting') they
support.
When the 'qmp_capabilities' command is issued, and if it does not return an
error, the Server enters in Command mode where capabilities changes take
effect, all commands (except 'qmp_capabilities') are allowed and asynchronous
messages are delivered.
5 Compatibility Considerations
------------------------------
All protocol changes or new features which modify the protocol format in an
incompatible way are disabled by default and will be advertised by the
capabilities array (section '2.2 Server Greeting'). Thus, Clients can check
that array and enable the capabilities they support.
Additionally, Clients must not assume any particular:
- Size of json-objects or length of json-arrays - Size of json-objects or length of json-arrays
- Order of json-object members or json-array elements - Order of json-object members or json-array elements
- Amount of errors generated by a command, that is, new errors can be added - Amount of errors generated by a command, that is, new errors can be added
to any existing command in newer versions of the Server to any existing command in newer versions of the Server
Additionally, Clients should always:
- Check the capabilities json-array at connection time
- Check the availability of commands with 'query-commands' before issuing them
5. Recommendations to Client implementors
-----------------------------------------
5.1 The Server should be always started in pause mode, thus the Client is
able to perform any setup procedure without the risk of race conditions
and related problems