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authorLuiz Capitulino <lcapitulino@redhat.com>2013-09-10 17:00:45 -0400
committerLuiz Capitulino <lcapitulino@redhat.com>2013-09-18 08:57:02 -0400
commit7537fe0487c3f7991584ca1c4bf9b6c58cd33968 (patch)
tree118664e8db755f95683b4e141724e802a2c818b0 /QMP/qmp-spec.txt
parentd076a2adddece29ad33afcce01e441bfc1c6923d (diff)
QMP: QMP/ -> docs/qmp/
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com>
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- QEMU Monitor Protocol Specification - Version 0.1
-
-1. Introduction
-===============
-
-This document specifies the QEMU Monitor Protocol (QMP), a JSON-based protocol
-which is available for applications to control QEMU at the machine-level.
-
-To enable QMP support, QEMU has to be run in "control mode". This is done by
-starting QEMU with the appropriate command-line options. Please, refer to the
-QEMU manual page for more information.
-
-2. Protocol Specification
-=========================
-
-This section details the protocol format. For the purpose of this document
-"Client" is any application which is communicating with QEMU in control mode,
-and "Server" is QEMU itself.
-
-JSON data structures, when mentioned in this document, are always in the
-following format:
-
- json-DATA-STRUCTURE-NAME
-
-Where DATA-STRUCTURE-NAME is any valid JSON data structure, as defined by
-the JSON standard:
-
-http://www.ietf.org/rfc/rfc4627.txt
-
-For convenience, json-object members and json-array elements mentioned in
-this document will be in a certain order. However, in real protocol usage
-they can be in ANY order, thus no particular order should be assumed.
-
-2.1 General Definitions
------------------------
-
-2.1.1 All interactions transmitted by the Server are json-objects, always
- terminating with CRLF
-
-2.1.2 All json-objects members are mandatory when not specified otherwise
-
-2.2 Server Greeting
--------------------
-
-Right when connected the Server will issue a greeting message, which signals
-that the connection has been successfully established and that the Server is
-ready for capabilities negotiation (for more information refer to section
-'4. Capabilities Negotiation').
-
-The format is:
-
-{ "QMP": { "version": json-object, "capabilities": json-array } }
-
- Where,
-
-- The "version" member contains the Server's version information (the format
- is the same of the 'query-version' command)
-- The "capabilities" member specify the availability of features beyond the
- baseline specification
-
-2.3 Issuing Commands
---------------------
-
-The format for command execution is:
-
-{ "execute": json-string, "arguments": json-object, "id": json-value }
-
- Where,
-
-- The "execute" member identifies the command to be executed by the Server
-- The "arguments" member is used to pass any arguments required for the
- execution of the command, it is optional when no arguments are required
-- The "id" member is a transaction identification associated with the
- command execution, it is optional and will be part of the response if
- provided
-
-2.4 Commands Responses
-----------------------
-
-There are two possible responses which the Server will issue as the result
-of a command execution: success or error.
-
-2.4.1 success
--------------
-
-The success response is issued when the command execution has finished
-without errors.
-
-The format is:
-
-{ "return": json-object, "id": json-value }
-
- Where,
-
-- The "return" member contains the command returned data, which is defined
- in a per-command basis or an empty json-object if the command does not
- return data
-- The "id" member contains the transaction identification associated
- with the command execution (if issued by the Client)
-
-2.4.2 error
------------
-
-The error response is issued when the command execution could not be
-completed because of an error condition.
-
-The format is:
-
-{ "error": { "class": json-string, "desc": json-string }, "id": json-value }
-
- Where,
-
-- The "class" member contains the error class name (eg. "GenericError")
-- The "desc" member is a human-readable error message. Clients should
- not attempt to parse this message.
-- The "id" member contains the transaction identification associated with
- the command execution (if issued by the Client)
-
-NOTE: Some errors can occur before the Server is able to read the "id" member,
-in these cases the "id" member will not be part of the error response, even
-if provided by the client.
-
-2.5 Asynchronous events
------------------------
-
-As a result of state changes, the Server may send messages unilaterally
-to the Client at any time. They are called 'asynchronous events'.
-
-The format is:
-
-{ "event": json-string, "data": json-object,
- "timestamp": { "seconds": json-number, "microseconds": json-number } }
-
- Where,
-
-- The "event" member contains the event's name
-- The "data" member contains event specific data, which is defined in a
- per-event basis, it is optional
-- The "timestamp" member contains the exact time of when the event occurred
- in the Server. It is a fixed json-object with time in seconds and
- microseconds
-
-For a listing of supported asynchronous events, please, refer to the
-qmp-events.txt file.
-
-3. QMP Examples
-===============
-
-This section provides some examples of real QMP usage, in all of them
-'C' stands for 'Client' and 'S' stands for 'Server'.
-
-3.1 Server greeting
--------------------
-
-S: {"QMP": {"version": {"qemu": "0.12.50", "package": ""}, "capabilities": []}}
-
-3.2 Simple 'stop' execution
----------------------------
-
-C: { "execute": "stop" }
-S: {"return": {}}
-
-3.3 KVM information
--------------------
-
-C: { "execute": "query-kvm", "id": "example" }
-S: {"return": {"enabled": true, "present": true}, "id": "example"}
-
-3.4 Parsing error
-------------------
-
-C: { "execute": }
-S: {"error": {"class": "GenericError", "desc": "Invalid JSON syntax" } }
-
-3.5 Powerdown event
--------------------
-
-S: {"timestamp": {"seconds": 1258551470, "microseconds": 802384}, "event":
-"POWERDOWN"}
-
-4. Capabilities Negotiation
-----------------------------
-
-When a Client successfully establishes a connection, the Server is in
-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.
-
-The QMP Server performs a type check on the arguments to a command. It
-generates an error if a value does not have the expected type for its
-key, or if it does not understand a key that the Client included. The
-strictness of the Server catches wrong assumptions of Clients about
-the Server's schema. Clients can assume that, when such validation
-errors occur, they will be reported before the command generated any
-side effect.
-
-However, Clients must not assume any particular:
-
-- Length of json-arrays
-- Size of json-objects; in particular, future versions of QEMU may add
- new keys and Clients should be able to ignore them.
-- Order of json-object members or json-array elements
-- Amount of errors generated by a command, that is, new errors can be added
- to any existing command in newer versions of the Server
-
-Of course, the Server does guarantee to send valid JSON. But apart from
-this, a Client should be "conservative in what they send, and liberal in
-what they accept".
-
-6. Downstream extension of QMP
-------------------------------
-
-We recommend that downstream consumers of QEMU do *not* modify QMP.
-Management tools should be able to support both upstream and downstream
-versions of QMP without special logic, and downstream extensions are
-inherently at odds with that.
-
-However, we recognize that it is sometimes impossible for downstreams to
-avoid modifying QMP. Both upstream and downstream need to take care to
-preserve long-term compatibility and interoperability.
-
-To help with that, QMP reserves JSON object member names beginning with
-'__' (double underscore) for downstream use ("downstream names"). This
-means upstream will never use any downstream names for its commands,
-arguments, errors, asynchronous events, and so forth.
-
-Any new names downstream wishes to add must begin with '__'. To
-ensure compatibility with other downstreams, it is strongly
-recommended that you prefix your downstram names with '__RFQDN_' where
-RFQDN is a valid, reverse fully qualified domain name which you
-control. For example, a qemu-kvm specific monitor command would be:
-
- (qemu) __org.linux-kvm_enable_irqchip
-
-Downstream must not change the server greeting (section 2.2) other than
-to offer additional capabilities. But see below for why even that is
-discouraged.
-
-Section '5 Compatibility Considerations' applies to downstream as well
-as to upstream, obviously. It follows that downstream must behave
-exactly like upstream for any input not containing members with
-downstream names ("downstream members"), except it may add members
-with downstream names to its output.
-
-Thus, a client should not be able to distinguish downstream from
-upstream as long as it doesn't send input with downstream members, and
-properly ignores any downstream members in the output it receives.
-
-Advice on downstream modifications:
-
-1. Introducing new commands is okay. If you want to extend an existing
- command, consider introducing a new one with the new behaviour
- instead.
-
-2. Introducing new asynchronous messages is okay. If you want to extend
- an existing message, consider adding a new one instead.
-
-3. Introducing new errors for use in new commands is okay. Adding new
- errors to existing commands counts as extension, so 1. applies.
-
-4. New capabilities are strongly discouraged. Capabilities are for
- evolving the basic protocol, and multiple diverging basic protocol
- dialects are most undesirable.