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Signed-off-by: Markus Armbruster <armbru@redhat.com> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> Message-Id: <20221104160712.3005652-3-armbru@redhat.com>
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1956 lines
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ReStructuredText
==================================
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How to use the QAPI code generator
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==================================
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..
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Copyright IBM Corp. 2011
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Copyright (C) 2012-2016 Red Hat, Inc.
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This work is licensed under the terms of the GNU GPL, version 2 or
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later. See the COPYING file in the top-level directory.
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Introduction
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============
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QAPI is a native C API within QEMU which provides management-level
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functionality to internal and external users. For external
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users/processes, this interface is made available by a JSON-based wire
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format for the QEMU Monitor Protocol (QMP) for controlling qemu, as
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well as the QEMU Guest Agent (QGA) for communicating with the guest.
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The remainder of this document uses "Client JSON Protocol" when
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referring to the wire contents of a QMP or QGA connection.
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To map between Client JSON Protocol interfaces and the native C API,
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we generate C code from a QAPI schema. This document describes the
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QAPI schema language, and how it gets mapped to the Client JSON
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Protocol and to C. It additionally provides guidance on maintaining
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Client JSON Protocol compatibility.
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The QAPI schema language
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========================
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The QAPI schema defines the Client JSON Protocol's commands and
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events, as well as types used by them. Forward references are
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allowed.
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It is permissible for the schema to contain additional types not used
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by any commands or events, for the side effect of generated C code
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used internally.
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There are several kinds of types: simple types (a number of built-in
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types, such as ``int`` and ``str``; as well as enumerations), arrays,
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complex types (structs and unions), and alternate types (a choice
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between other types).
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Schema syntax
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-------------
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Syntax is loosely based on `JSON <http://www.ietf.org/rfc/rfc8259.txt>`_.
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Differences:
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* Comments: start with a hash character (``#``) that is not part of a
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string, and extend to the end of the line.
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* Strings are enclosed in ``'single quotes'``, not ``"double quotes"``.
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* Strings are restricted to printable ASCII, and escape sequences to
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just ``\\``.
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* Numbers and ``null`` are not supported.
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A second layer of syntax defines the sequences of JSON texts that are
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a correctly structured QAPI schema. We provide a grammar for this
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syntax in an EBNF-like notation:
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* Production rules look like ``non-terminal = expression``
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* Concatenation: expression ``A B`` matches expression ``A``, then ``B``
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* Alternation: expression ``A | B`` matches expression ``A`` or ``B``
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* Repetition: expression ``A...`` matches zero or more occurrences of
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expression ``A``
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* Repetition: expression ``A, ...`` matches zero or more occurrences of
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expression ``A`` separated by ``,``
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* Grouping: expression ``( A )`` matches expression ``A``
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* JSON's structural characters are terminals: ``{ } [ ] : ,``
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* JSON's literal names are terminals: ``false true``
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* String literals enclosed in ``'single quotes'`` are terminal, and match
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this JSON string, with a leading ``*`` stripped off
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* When JSON object member's name starts with ``*``, the member is
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optional.
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* The symbol ``STRING`` is a terminal, and matches any JSON string
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* The symbol ``BOOL`` is a terminal, and matches JSON ``false`` or ``true``
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* ALL-CAPS words other than ``STRING`` are non-terminals
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The order of members within JSON objects does not matter unless
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explicitly noted.
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A QAPI schema consists of a series of top-level expressions::
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SCHEMA = TOP-LEVEL-EXPR...
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The top-level expressions are all JSON objects. Code and
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documentation is generated in schema definition order. Code order
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should not matter.
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A top-level expressions is either a directive or a definition::
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TOP-LEVEL-EXPR = DIRECTIVE | DEFINITION
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There are two kinds of directives and six kinds of definitions::
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DIRECTIVE = INCLUDE | PRAGMA
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DEFINITION = ENUM | STRUCT | UNION | ALTERNATE | COMMAND | EVENT
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These are discussed in detail below.
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Built-in Types
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--------------
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The following types are predefined, and map to C as follows:
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============= ============== ============================================
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Schema C JSON
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============= ============== ============================================
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``str`` ``char *`` any JSON string, UTF-8
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``number`` ``double`` any JSON number
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``int`` ``int64_t`` a JSON number without fractional part
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that fits into the C integer type
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``int8`` ``int8_t`` likewise
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``int16`` ``int16_t`` likewise
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``int32`` ``int32_t`` likewise
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``int64`` ``int64_t`` likewise
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``uint8`` ``uint8_t`` likewise
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``uint16`` ``uint16_t`` likewise
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``uint32`` ``uint32_t`` likewise
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``uint64`` ``uint64_t`` likewise
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``size`` ``uint64_t`` like ``uint64_t``, except
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``StringInputVisitor`` accepts size suffixes
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``bool`` ``bool`` JSON ``true`` or ``false``
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``null`` ``QNull *`` JSON ``null``
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``any`` ``QObject *`` any JSON value
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``QType`` ``QType`` JSON string matching enum ``QType`` values
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============= ============== ============================================
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Include directives
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------------------
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Syntax::
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INCLUDE = { 'include': STRING }
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The QAPI schema definitions can be modularized using the 'include' directive::
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{ 'include': 'path/to/file.json' }
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The directive is evaluated recursively, and include paths are relative
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to the file using the directive. Multiple includes of the same file
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are idempotent.
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As a matter of style, it is a good idea to have all files be
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self-contained, but at the moment, nothing prevents an included file
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from making a forward reference to a type that is only introduced by
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an outer file. The parser may be made stricter in the future to
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prevent incomplete include files.
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.. _pragma:
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Pragma directives
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-----------------
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Syntax::
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PRAGMA = { 'pragma': {
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'*doc-required': BOOL,
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'*command-name-exceptions': [ STRING, ... ],
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'*command-returns-exceptions': [ STRING, ... ],
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'*member-name-exceptions': [ STRING, ... ] } }
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The pragma directive lets you control optional generator behavior.
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Pragma's scope is currently the complete schema. Setting the same
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pragma to different values in parts of the schema doesn't work.
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Pragma 'doc-required' takes a boolean value. If true, documentation
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is required. Default is false.
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Pragma 'command-name-exceptions' takes a list of commands whose names
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may contain ``"_"`` instead of ``"-"``. Default is none.
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Pragma 'command-returns-exceptions' takes a list of commands that may
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violate the rules on permitted return types. Default is none.
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Pragma 'member-name-exceptions' takes a list of types whose member
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names may contain uppercase letters, and ``"_"`` instead of ``"-"``.
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Default is none.
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.. _ENUM-VALUE:
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Enumeration types
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-----------------
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Syntax::
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ENUM = { 'enum': STRING,
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'data': [ ENUM-VALUE, ... ],
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'*prefix': STRING,
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'*if': COND,
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'*features': FEATURES }
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ENUM-VALUE = STRING
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| { 'name': STRING,
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'*if': COND,
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'*features': FEATURES }
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Member 'enum' names the enum type.
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Each member of the 'data' array defines a value of the enumeration
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type. The form STRING is shorthand for :code:`{ 'name': STRING }`. The
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'name' values must be be distinct.
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Example::
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{ 'enum': 'MyEnum', 'data': [ 'value1', 'value2', 'value3' ] }
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Nothing prevents an empty enumeration, although it is probably not
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useful.
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On the wire, an enumeration type's value is represented by its
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(string) name. In C, it's represented by an enumeration constant.
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These are of the form PREFIX_NAME, where PREFIX is derived from the
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enumeration type's name, and NAME from the value's name. For the
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example above, the generator maps 'MyEnum' to MY_ENUM and 'value1' to
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VALUE1, resulting in the enumeration constant MY_ENUM_VALUE1. The
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optional 'prefix' member overrides PREFIX.
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The generated C enumeration constants have values 0, 1, ..., N-1 (in
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QAPI schema order), where N is the number of values. There is an
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additional enumeration constant PREFIX__MAX with value N.
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Do not use string or an integer type when an enumeration type can do
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the job satisfactorily.
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The optional 'if' member specifies a conditional. See `Configuring the
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schema`_ below for more on this.
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The optional 'features' member specifies features. See Features_
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below for more on this.
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.. _TYPE-REF:
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Type references and array types
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-------------------------------
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Syntax::
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TYPE-REF = STRING | ARRAY-TYPE
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ARRAY-TYPE = [ STRING ]
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A string denotes the type named by the string.
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A one-element array containing a string denotes an array of the type
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named by the string. Example: ``['int']`` denotes an array of ``int``.
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Struct types
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------------
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Syntax::
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STRUCT = { 'struct': STRING,
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'data': MEMBERS,
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'*base': STRING,
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'*if': COND,
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'*features': FEATURES }
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MEMBERS = { MEMBER, ... }
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MEMBER = STRING : TYPE-REF
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| STRING : { 'type': TYPE-REF,
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'*if': COND,
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'*features': FEATURES }
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Member 'struct' names the struct type.
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Each MEMBER of the 'data' object defines a member of the struct type.
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.. _MEMBERS:
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The MEMBER's STRING name consists of an optional ``*`` prefix and the
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struct member name. If ``*`` is present, the member is optional.
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The MEMBER's value defines its properties, in particular its type.
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The form TYPE-REF_ is shorthand for :code:`{ 'type': TYPE-REF }`.
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Example::
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{ 'struct': 'MyType',
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'data': { 'member1': 'str', 'member2': ['int'], '*member3': 'str' } }
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A struct type corresponds to a struct in C, and an object in JSON.
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The C struct's members are generated in QAPI schema order.
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The optional 'base' member names a struct type whose members are to be
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included in this type. They go first in the C struct.
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Example::
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{ 'struct': 'BlockdevOptionsGenericFormat',
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'data': { 'file': 'str' } }
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{ 'struct': 'BlockdevOptionsGenericCOWFormat',
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'base': 'BlockdevOptionsGenericFormat',
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'data': { '*backing': 'str' } }
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An example BlockdevOptionsGenericCOWFormat object on the wire could use
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both members like this::
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{ "file": "/some/place/my-image",
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"backing": "/some/place/my-backing-file" }
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The optional 'if' member specifies a conditional. See `Configuring
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the schema`_ below for more on this.
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The optional 'features' member specifies features. See Features_
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below for more on this.
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Union types
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-----------
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Syntax::
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UNION = { 'union': STRING,
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'base': ( MEMBERS | STRING ),
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'discriminator': STRING,
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'data': BRANCHES,
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'*if': COND,
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'*features': FEATURES }
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BRANCHES = { BRANCH, ... }
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BRANCH = STRING : TYPE-REF
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| STRING : { 'type': TYPE-REF, '*if': COND }
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Member 'union' names the union type.
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The 'base' member defines the common members. If it is a MEMBERS_
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object, it defines common members just like a struct type's 'data'
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member defines struct type members. If it is a STRING, it names a
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struct type whose members are the common members.
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Member 'discriminator' must name a non-optional enum-typed member of
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the base struct. That member's value selects a branch by its name.
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If no such branch exists, an empty branch is assumed.
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Each BRANCH of the 'data' object defines a branch of the union. A
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union must have at least one branch.
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The BRANCH's STRING name is the branch name. It must be a value of
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the discriminator enum type.
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The BRANCH's value defines the branch's properties, in particular its
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type. The type must a struct type. The form TYPE-REF_ is shorthand
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for :code:`{ 'type': TYPE-REF }`.
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In the Client JSON Protocol, a union is represented by an object with
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the common members (from the base type) and the selected branch's
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members. The two sets of member names must be disjoint.
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Example::
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{ 'enum': 'BlockdevDriver', 'data': [ 'file', 'qcow2' ] }
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{ 'union': 'BlockdevOptions',
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'base': { 'driver': 'BlockdevDriver', '*read-only': 'bool' },
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'discriminator': 'driver',
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'data': { 'file': 'BlockdevOptionsFile',
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'qcow2': 'BlockdevOptionsQcow2' } }
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Resulting in these JSON objects::
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{ "driver": "file", "read-only": true,
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"filename": "/some/place/my-image" }
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{ "driver": "qcow2", "read-only": false,
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"backing": "/some/place/my-image", "lazy-refcounts": true }
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The order of branches need not match the order of the enum values.
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The branches need not cover all possible enum values. In the
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resulting generated C data types, a union is represented as a struct
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with the base members in QAPI schema order, and then a union of
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structures for each branch of the struct.
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The optional 'if' member specifies a conditional. See `Configuring
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the schema`_ below for more on this.
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The optional 'features' member specifies features. See Features_
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below for more on this.
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Alternate types
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---------------
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Syntax::
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ALTERNATE = { 'alternate': STRING,
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'data': ALTERNATIVES,
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'*if': COND,
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'*features': FEATURES }
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ALTERNATIVES = { ALTERNATIVE, ... }
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ALTERNATIVE = STRING : STRING
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| STRING : { 'type': STRING, '*if': COND }
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Member 'alternate' names the alternate type.
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Each ALTERNATIVE of the 'data' object defines a branch of the
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alternate. An alternate must have at least one branch.
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The ALTERNATIVE's STRING name is the branch name.
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The ALTERNATIVE's value defines the branch's properties, in particular
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its type. The form STRING is shorthand for :code:`{ 'type': STRING }`.
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Example::
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{ 'alternate': 'BlockdevRef',
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'data': { 'definition': 'BlockdevOptions',
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'reference': 'str' } }
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An alternate type is like a union type, except there is no
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discriminator on the wire. Instead, the branch to use is inferred
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from the value. An alternate can only express a choice between types
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represented differently on the wire.
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If a branch is typed as the 'bool' built-in, the alternate accepts
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true and false; if it is typed as any of the various numeric
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built-ins, it accepts a JSON number; if it is typed as a 'str'
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built-in or named enum type, it accepts a JSON string; if it is typed
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as the 'null' built-in, it accepts JSON null; and if it is typed as a
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complex type (struct or union), it accepts a JSON object.
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The example alternate declaration above allows using both of the
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following example objects::
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{ "file": "my_existing_block_device_id" }
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{ "file": { "driver": "file",
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"read-only": false,
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"filename": "/tmp/mydisk.qcow2" } }
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The optional 'if' member specifies a conditional. See `Configuring
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the schema`_ below for more on this.
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The optional 'features' member specifies features. See Features_
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below for more on this.
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Commands
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--------
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Syntax::
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COMMAND = { 'command': STRING,
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(
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'*data': ( MEMBERS | STRING ),
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'data': STRING,
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'boxed': true,
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)
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'*returns': TYPE-REF,
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'*success-response': false,
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'*gen': false,
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'*allow-oob': true,
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'*allow-preconfig': true,
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'*coroutine': true,
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'*if': COND,
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'*features': FEATURES }
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Member 'command' names the command.
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Member 'data' defines the arguments. It defaults to an empty MEMBERS_
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object.
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If 'data' is a MEMBERS_ object, then MEMBERS defines arguments just
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like a struct type's 'data' defines struct type members.
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If 'data' is a STRING, then STRING names a complex type whose members
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are the arguments. A union type requires ``'boxed': true``.
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Member 'returns' defines the command's return type. It defaults to an
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empty struct type. It must normally be a complex type or an array of
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a complex type. To return anything else, the command must be listed
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in pragma 'commands-returns-exceptions'. If you do this, extending
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the command to return additional information will be harder. Use of
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the pragma for new commands is strongly discouraged.
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A command's error responses are not specified in the QAPI schema.
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Error conditions should be documented in comments.
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In the Client JSON Protocol, the value of the "execute" or "exec-oob"
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member is the command name. The value of the "arguments" member then
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has to conform to the arguments, and the value of the success
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response's "return" member will conform to the return type.
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Some example commands::
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{ 'command': 'my-first-command',
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'data': { 'arg1': 'str', '*arg2': 'str' } }
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{ 'struct': 'MyType', 'data': { '*value': 'str' } }
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{ 'command': 'my-second-command',
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'returns': [ 'MyType' ] }
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which would validate this Client JSON Protocol transaction::
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=> { "execute": "my-first-command",
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"arguments": { "arg1": "hello" } }
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<= { "return": { } }
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=> { "execute": "my-second-command" }
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<= { "return": [ { "value": "one" }, { } ] }
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The generator emits a prototype for the C function implementing the
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command. The function itself needs to be written by hand. See
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section `Code generated for commands`_ for examples.
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The function returns the return type. When member 'boxed' is absent,
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it takes the command arguments as arguments one by one, in QAPI schema
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order. Else it takes them wrapped in the C struct generated for the
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complex argument type. It takes an additional ``Error **`` argument in
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either case.
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The generator also emits a marshalling function that extracts
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arguments for the user's function out of an input QDict, calls the
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user's function, and if it succeeded, builds an output QObject from
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its return value. This is for use by the QMP monitor core.
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In rare cases, QAPI cannot express a type-safe representation of a
|
|
corresponding Client JSON Protocol command. You then have to suppress
|
|
generation of a marshalling function by including a member 'gen' with
|
|
boolean value false, and instead write your own function. For
|
|
example::
|
|
|
|
{ 'command': 'netdev_add',
|
|
'data': {'type': 'str', 'id': 'str'},
|
|
'gen': false }
|
|
|
|
Please try to avoid adding new commands that rely on this, and instead
|
|
use type-safe unions.
|
|
|
|
Normally, the QAPI schema is used to describe synchronous exchanges,
|
|
where a response is expected. But in some cases, the action of a
|
|
command is expected to change state in a way that a successful
|
|
response is not possible (although the command will still return an
|
|
error object on failure). When a successful reply is not possible,
|
|
the command definition includes the optional member 'success-response'
|
|
with boolean value false. So far, only QGA makes use of this member.
|
|
|
|
Member 'allow-oob' declares whether the command supports out-of-band
|
|
(OOB) execution. It defaults to false. For example::
|
|
|
|
{ 'command': 'migrate_recover',
|
|
'data': { 'uri': 'str' }, 'allow-oob': true }
|
|
|
|
See qmp-spec.txt for out-of-band execution syntax and semantics.
|
|
|
|
Commands supporting out-of-band execution can still be executed
|
|
in-band.
|
|
|
|
When a command is executed in-band, its handler runs in the main
|
|
thread with the BQL held.
|
|
|
|
When a command is executed out-of-band, its handler runs in a
|
|
dedicated monitor I/O thread with the BQL *not* held.
|
|
|
|
An OOB-capable command handler must satisfy the following conditions:
|
|
|
|
- It terminates quickly.
|
|
- It does not invoke system calls that may block.
|
|
- It does not access guest RAM that may block when userfaultfd is
|
|
enabled for postcopy live migration.
|
|
- It takes only "fast" locks, i.e. all critical sections protected by
|
|
any lock it takes also satisfy the conditions for OOB command
|
|
handler code.
|
|
|
|
The restrictions on locking limit access to shared state. Such access
|
|
requires synchronization, but OOB commands can't take the BQL or any
|
|
other "slow" lock.
|
|
|
|
When in doubt, do not implement OOB execution support.
|
|
|
|
Member 'allow-preconfig' declares whether the command is available
|
|
before the machine is built. It defaults to false. For example::
|
|
|
|
{ 'enum': 'QMPCapability',
|
|
'data': [ 'oob' ] }
|
|
{ 'command': 'qmp_capabilities',
|
|
'data': { '*enable': [ 'QMPCapability' ] },
|
|
'allow-preconfig': true }
|
|
|
|
QMP is available before the machine is built only when QEMU was
|
|
started with --preconfig.
|
|
|
|
Member 'coroutine' tells the QMP dispatcher whether the command handler
|
|
is safe to be run in a coroutine. It defaults to false. If it is true,
|
|
the command handler is called from coroutine context and may yield while
|
|
waiting for an external event (such as I/O completion) in order to avoid
|
|
blocking the guest and other background operations.
|
|
|
|
Coroutine safety can be hard to prove, similar to thread safety. Common
|
|
pitfalls are:
|
|
|
|
- The global mutex isn't held across ``qemu_coroutine_yield()``, so
|
|
operations that used to assume that they execute atomically may have
|
|
to be more careful to protect against changes in the global state.
|
|
|
|
- Nested event loops (``AIO_WAIT_WHILE()`` etc.) are problematic in
|
|
coroutine context and can easily lead to deadlocks. They should be
|
|
replaced by yielding and reentering the coroutine when the condition
|
|
becomes false.
|
|
|
|
Since the command handler may assume coroutine context, any callers
|
|
other than the QMP dispatcher must also call it in coroutine context.
|
|
In particular, HMP commands calling such a QMP command handler must be
|
|
marked ``.coroutine = true`` in hmp-commands.hx.
|
|
|
|
It is an error to specify both ``'coroutine': true`` and ``'allow-oob': true``
|
|
for a command. We don't currently have a use case for both together and
|
|
without a use case, it's not entirely clear what the semantics should
|
|
be.
|
|
|
|
The optional 'if' member specifies a conditional. See `Configuring
|
|
the schema`_ below for more on this.
|
|
|
|
The optional 'features' member specifies features. See Features_
|
|
below for more on this.
|
|
|
|
|
|
Events
|
|
------
|
|
|
|
Syntax::
|
|
|
|
EVENT = { 'event': STRING,
|
|
(
|
|
'*data': ( MEMBERS | STRING ),
|
|
|
|
|
'data': STRING,
|
|
'boxed': true,
|
|
)
|
|
'*if': COND,
|
|
'*features': FEATURES }
|
|
|
|
Member 'event' names the event. This is the event name used in the
|
|
Client JSON Protocol.
|
|
|
|
Member 'data' defines the event-specific data. It defaults to an
|
|
empty MEMBERS object.
|
|
|
|
If 'data' is a MEMBERS object, then MEMBERS defines event-specific
|
|
data just like a struct type's 'data' defines struct type members.
|
|
|
|
If 'data' is a STRING, then STRING names a complex type whose members
|
|
are the event-specific data. A union type requires ``'boxed': true``.
|
|
|
|
An example event is::
|
|
|
|
{ 'event': 'EVENT_C',
|
|
'data': { '*a': 'int', 'b': 'str' } }
|
|
|
|
Resulting in this JSON object::
|
|
|
|
{ "event": "EVENT_C",
|
|
"data": { "b": "test string" },
|
|
"timestamp": { "seconds": 1267020223, "microseconds": 435656 } }
|
|
|
|
The generator emits a function to send the event. When member 'boxed'
|
|
is absent, it takes event-specific data one by one, in QAPI schema
|
|
order. Else it takes them wrapped in the C struct generated for the
|
|
complex type. See section `Code generated for events`_ for examples.
|
|
|
|
The optional 'if' member specifies a conditional. See `Configuring
|
|
the schema`_ below for more on this.
|
|
|
|
The optional 'features' member specifies features. See Features_
|
|
below for more on this.
|
|
|
|
|
|
.. _FEATURE:
|
|
|
|
Features
|
|
--------
|
|
|
|
Syntax::
|
|
|
|
FEATURES = [ FEATURE, ... ]
|
|
FEATURE = STRING
|
|
| { 'name': STRING, '*if': COND }
|
|
|
|
Sometimes, the behaviour of QEMU changes compatibly, but without a
|
|
change in the QMP syntax (usually by allowing values or operations
|
|
that previously resulted in an error). QMP clients may still need to
|
|
know whether the extension is available.
|
|
|
|
For this purpose, a list of features can be specified for a command or
|
|
struct type. Each list member can either be ``{ 'name': STRING, '*if':
|
|
COND }``, or STRING, which is shorthand for ``{ 'name': STRING }``.
|
|
|
|
The optional 'if' member specifies a conditional. See `Configuring
|
|
the schema`_ below for more on this.
|
|
|
|
Example::
|
|
|
|
{ 'struct': 'TestType',
|
|
'data': { 'number': 'int' },
|
|
'features': [ 'allow-negative-numbers' ] }
|
|
|
|
The feature strings are exposed to clients in introspection, as
|
|
explained in section `Client JSON Protocol introspection`_.
|
|
|
|
Intended use is to have each feature string signal that this build of
|
|
QEMU shows a certain behaviour.
|
|
|
|
|
|
Special features
|
|
~~~~~~~~~~~~~~~~
|
|
|
|
Feature "deprecated" marks a command, event, enum value, or struct
|
|
member as deprecated. It is not supported elsewhere so far.
|
|
Interfaces so marked may be withdrawn in future releases in accordance
|
|
with QEMU's deprecation policy.
|
|
|
|
Feature "unstable" marks a command, event, enum value, or struct
|
|
member as unstable. It is not supported elsewhere so far. Interfaces
|
|
so marked may be withdrawn or changed incompatibly in future releases.
|
|
|
|
|
|
Naming rules and reserved names
|
|
-------------------------------
|
|
|
|
All names must begin with a letter, and contain only ASCII letters,
|
|
digits, hyphen, and underscore. There are two exceptions: enum values
|
|
may start with a digit, and names that are downstream extensions (see
|
|
section `Downstream extensions`_) start with underscore.
|
|
|
|
Names beginning with ``q_`` are reserved for the generator, which uses
|
|
them for munging QMP names that resemble C keywords or other
|
|
problematic strings. For example, a member named ``default`` in qapi
|
|
becomes ``q_default`` in the generated C code.
|
|
|
|
Types, commands, and events share a common namespace. Therefore,
|
|
generally speaking, type definitions should always use CamelCase for
|
|
user-defined type names, while built-in types are lowercase.
|
|
|
|
Type names ending with ``Kind`` or ``List`` are reserved for the
|
|
generator, which uses them for implicit union enums and array types,
|
|
respectively.
|
|
|
|
Command names, member names within a type, and feature names should be
|
|
all lower case with words separated by a hyphen. However, some
|
|
existing older commands and complex types use underscore; when
|
|
extending them, consistency is preferred over blindly avoiding
|
|
underscore.
|
|
|
|
Event names should be ALL_CAPS with words separated by underscore.
|
|
|
|
Member name ``u`` and names starting with ``has-`` or ``has_`` are reserved
|
|
for the generator, which uses them for unions and for tracking
|
|
optional members.
|
|
|
|
Names beginning with ``x-`` used to signify "experimental". This
|
|
convention has been replaced by special feature "unstable".
|
|
|
|
Pragmas ``command-name-exceptions`` and ``member-name-exceptions`` let
|
|
you violate naming rules. Use for new code is strongly discouraged. See
|
|
`Pragma directives`_ for details.
|
|
|
|
|
|
Downstream extensions
|
|
---------------------
|
|
|
|
QAPI schema names that are externally visible, say in the Client JSON
|
|
Protocol, need to be managed with care. Names starting with a
|
|
downstream prefix of the form __RFQDN_ are reserved for the downstream
|
|
who controls the valid, reverse fully qualified domain name RFQDN.
|
|
RFQDN may only contain ASCII letters, digits, hyphen and period.
|
|
|
|
Example: Red Hat, Inc. controls redhat.com, and may therefore add a
|
|
downstream command ``__com.redhat_drive-mirror``.
|
|
|
|
|
|
Configuring the schema
|
|
----------------------
|
|
|
|
Syntax::
|
|
|
|
COND = STRING
|
|
| { 'all: [ COND, ... ] }
|
|
| { 'any: [ COND, ... ] }
|
|
| { 'not': COND }
|
|
|
|
All definitions take an optional 'if' member. Its value must be a
|
|
string, or an object with a single member 'all', 'any' or 'not'.
|
|
|
|
The C code generated for the definition will then be guarded by an #if
|
|
preprocessing directive with an operand generated from that condition:
|
|
|
|
* STRING will generate defined(STRING)
|
|
* { 'all': [COND, ...] } will generate (COND && ...)
|
|
* { 'any': [COND, ...] } will generate (COND || ...)
|
|
* { 'not': COND } will generate !COND
|
|
|
|
Example: a conditional struct ::
|
|
|
|
{ 'struct': 'IfStruct', 'data': { 'foo': 'int' },
|
|
'if': { 'all': [ 'CONFIG_FOO', 'HAVE_BAR' ] } }
|
|
|
|
gets its generated code guarded like this::
|
|
|
|
#if defined(CONFIG_FOO) && defined(HAVE_BAR)
|
|
... generated code ...
|
|
#endif /* defined(HAVE_BAR) && defined(CONFIG_FOO) */
|
|
|
|
Individual members of complex types, commands arguments, and
|
|
event-specific data can also be made conditional. This requires the
|
|
longhand form of MEMBER.
|
|
|
|
Example: a struct type with unconditional member 'foo' and conditional
|
|
member 'bar' ::
|
|
|
|
{ 'struct': 'IfStruct',
|
|
'data': { 'foo': 'int',
|
|
'bar': { 'type': 'int', 'if': 'IFCOND'} } }
|
|
|
|
A union's discriminator may not be conditional.
|
|
|
|
Likewise, individual enumeration values be conditional. This requires
|
|
the longhand form of ENUM-VALUE_.
|
|
|
|
Example: an enum type with unconditional value 'foo' and conditional
|
|
value 'bar' ::
|
|
|
|
{ 'enum': 'IfEnum',
|
|
'data': [ 'foo',
|
|
{ 'name' : 'bar', 'if': 'IFCOND' } ] }
|
|
|
|
Likewise, features can be conditional. This requires the longhand
|
|
form of FEATURE_.
|
|
|
|
Example: a struct with conditional feature 'allow-negative-numbers' ::
|
|
|
|
{ 'struct': 'TestType',
|
|
'data': { 'number': 'int' },
|
|
'features': [ { 'name': 'allow-negative-numbers',
|
|
'if': 'IFCOND' } ] }
|
|
|
|
Please note that you are responsible to ensure that the C code will
|
|
compile with an arbitrary combination of conditions, since the
|
|
generator is unable to check it at this point.
|
|
|
|
The conditions apply to introspection as well, i.e. introspection
|
|
shows a conditional entity only when the condition is satisfied in
|
|
this particular build.
|
|
|
|
|
|
Documentation comments
|
|
----------------------
|
|
|
|
A multi-line comment that starts and ends with a ``##`` line is a
|
|
documentation comment.
|
|
|
|
If the documentation comment starts like ::
|
|
|
|
##
|
|
# @SYMBOL:
|
|
|
|
it documents the definition of SYMBOL, else it's free-form
|
|
documentation.
|
|
|
|
See below for more on `Definition documentation`_.
|
|
|
|
Free-form documentation may be used to provide additional text and
|
|
structuring content.
|
|
|
|
|
|
Headings and subheadings
|
|
~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
A free-form documentation comment containing a line which starts with
|
|
some ``=`` symbols and then a space defines a section heading::
|
|
|
|
##
|
|
# = This is a top level heading
|
|
#
|
|
# This is a free-form comment which will go under the
|
|
# top level heading.
|
|
##
|
|
|
|
##
|
|
# == This is a second level heading
|
|
##
|
|
|
|
A heading line must be the first line of the documentation
|
|
comment block.
|
|
|
|
Section headings must always be correctly nested, so you can only
|
|
define a third-level heading inside a second-level heading, and so on.
|
|
|
|
|
|
Documentation markup
|
|
~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Documentation comments can use most rST markup. In particular,
|
|
a ``::`` literal block can be used for examples::
|
|
|
|
# ::
|
|
#
|
|
# Text of the example, may span
|
|
# multiple lines
|
|
|
|
``*`` starts an itemized list::
|
|
|
|
# * First item, may span
|
|
# multiple lines
|
|
# * Second item
|
|
|
|
You can also use ``-`` instead of ``*``.
|
|
|
|
A decimal number followed by ``.`` starts a numbered list::
|
|
|
|
# 1. First item, may span
|
|
# multiple lines
|
|
# 2. Second item
|
|
|
|
The actual number doesn't matter.
|
|
|
|
Lists of either kind must be preceded and followed by a blank line.
|
|
If a list item's text spans multiple lines, then the second and
|
|
subsequent lines must be correctly indented to line up with the
|
|
first character of the first line.
|
|
|
|
The usual ****strong****, *\*emphasized\** and ````literal```` markup
|
|
should be used. If you need a single literal ``*``, you will need to
|
|
backslash-escape it. As an extension beyond the usual rST syntax, you
|
|
can also use ``@foo`` to reference a name in the schema; this is rendered
|
|
the same way as ````foo````.
|
|
|
|
Example::
|
|
|
|
##
|
|
# Some text foo with **bold** and *emphasis*
|
|
# 1. with a list
|
|
# 2. like that
|
|
#
|
|
# And some code:
|
|
#
|
|
# ::
|
|
#
|
|
# $ echo foo
|
|
# -> do this
|
|
# <- get that
|
|
##
|
|
|
|
|
|
Definition documentation
|
|
~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Definition documentation, if present, must immediately precede the
|
|
definition it documents.
|
|
|
|
When documentation is required (see pragma_ 'doc-required'), every
|
|
definition must have documentation.
|
|
|
|
Definition documentation starts with a line naming the definition,
|
|
followed by an optional overview, a description of each argument (for
|
|
commands and events), member (for structs and unions), branch (for
|
|
alternates), or value (for enums), a description of each feature (if
|
|
any), and finally optional tagged sections.
|
|
|
|
The description of an argument or feature 'name' starts with
|
|
'\@name:'. The description text can start on the line following the
|
|
'\@name:', in which case it must not be indented at all. It can also
|
|
start on the same line as the '\@name:'. In this case if it spans
|
|
multiple lines then second and subsequent lines must be indented to
|
|
line up with the first character of the first line of the
|
|
description::
|
|
|
|
# @argone:
|
|
# This is a two line description
|
|
# in the first style.
|
|
#
|
|
# @argtwo: This is a two line description
|
|
# in the second style.
|
|
|
|
The number of spaces between the ':' and the text is not significant.
|
|
|
|
.. admonition:: FIXME
|
|
|
|
The parser accepts these things in almost any order.
|
|
|
|
.. admonition:: FIXME
|
|
|
|
union branches should be described, too.
|
|
|
|
Extensions added after the definition was first released carry a
|
|
'(since x.y.z)' comment.
|
|
|
|
The feature descriptions must be preceded by a line "Features:", like
|
|
this::
|
|
|
|
# Features:
|
|
# @feature: Description text
|
|
|
|
A tagged section starts with one of the following words:
|
|
"Note:"/"Notes:", "Since:", "Example"/"Examples", "Returns:", "TODO:".
|
|
The section ends with the start of a new section.
|
|
|
|
The text of a section can start on a new line, in
|
|
which case it must not be indented at all. It can also start
|
|
on the same line as the 'Note:', 'Returns:', etc tag. In this
|
|
case if it spans multiple lines then second and subsequent
|
|
lines must be indented to match the first, in the same way as
|
|
multiline argument descriptions.
|
|
|
|
A 'Since: x.y.z' tagged section lists the release that introduced the
|
|
definition.
|
|
|
|
An 'Example' or 'Examples' section is automatically rendered
|
|
entirely as literal fixed-width text. In other sections,
|
|
the text is formatted, and rST markup can be used.
|
|
|
|
For example::
|
|
|
|
##
|
|
# @BlockStats:
|
|
#
|
|
# Statistics of a virtual block device or a block backing device.
|
|
#
|
|
# @device: If the stats are for a virtual block device, the name
|
|
# corresponding to the virtual block device.
|
|
#
|
|
# @node-name: The node name of the device. (since 2.3)
|
|
#
|
|
# ... more members ...
|
|
#
|
|
# Since: 0.14.0
|
|
##
|
|
{ 'struct': 'BlockStats',
|
|
'data': {'*device': 'str', '*node-name': 'str',
|
|
... more members ... } }
|
|
|
|
##
|
|
# @query-blockstats:
|
|
#
|
|
# Query the @BlockStats for all virtual block devices.
|
|
#
|
|
# @query-nodes: If true, the command will query all the
|
|
# block nodes ... explain, explain ... (since 2.3)
|
|
#
|
|
# Returns: A list of @BlockStats for each virtual block devices.
|
|
#
|
|
# Since: 0.14.0
|
|
#
|
|
# Example:
|
|
#
|
|
# -> { "execute": "query-blockstats" }
|
|
# <- {
|
|
# ... lots of output ...
|
|
# }
|
|
#
|
|
##
|
|
{ 'command': 'query-blockstats',
|
|
'data': { '*query-nodes': 'bool' },
|
|
'returns': ['BlockStats'] }
|
|
|
|
|
|
Client JSON Protocol introspection
|
|
==================================
|
|
|
|
Clients of a Client JSON Protocol commonly need to figure out what
|
|
exactly the server (QEMU) supports.
|
|
|
|
For this purpose, QMP provides introspection via command
|
|
query-qmp-schema. QGA currently doesn't support introspection.
|
|
|
|
While Client JSON Protocol wire compatibility should be maintained
|
|
between qemu versions, we cannot make the same guarantees for
|
|
introspection stability. For example, one version of qemu may provide
|
|
a non-variant optional member of a struct, and a later version rework
|
|
the member to instead be non-optional and associated with a variant.
|
|
Likewise, one version of qemu may list a member with open-ended type
|
|
'str', and a later version could convert it to a finite set of strings
|
|
via an enum type; or a member may be converted from a specific type to
|
|
an alternate that represents a choice between the original type and
|
|
something else.
|
|
|
|
query-qmp-schema returns a JSON array of SchemaInfo objects. These
|
|
objects together describe the wire ABI, as defined in the QAPI schema.
|
|
There is no specified order to the SchemaInfo objects returned; a
|
|
client must search for a particular name throughout the entire array
|
|
to learn more about that name, but is at least guaranteed that there
|
|
will be no collisions between type, command, and event names.
|
|
|
|
However, the SchemaInfo can't reflect all the rules and restrictions
|
|
that apply to QMP. It's interface introspection (figuring out what's
|
|
there), not interface specification. The specification is in the QAPI
|
|
schema. To understand how QMP is to be used, you need to study the
|
|
QAPI schema.
|
|
|
|
Like any other command, query-qmp-schema is itself defined in the QAPI
|
|
schema, along with the SchemaInfo type. This text attempts to give an
|
|
overview how things work. For details you need to consult the QAPI
|
|
schema.
|
|
|
|
SchemaInfo objects have common members "name", "meta-type",
|
|
"features", and additional variant members depending on the value of
|
|
meta-type.
|
|
|
|
Each SchemaInfo object describes a wire ABI entity of a certain
|
|
meta-type: a command, event or one of several kinds of type.
|
|
|
|
SchemaInfo for commands and events have the same name as in the QAPI
|
|
schema.
|
|
|
|
Command and event names are part of the wire ABI, but type names are
|
|
not. Therefore, the SchemaInfo for types have auto-generated
|
|
meaningless names. For readability, the examples in this section use
|
|
meaningful type names instead.
|
|
|
|
Optional member "features" exposes the entity's feature strings as a
|
|
JSON array of strings.
|
|
|
|
To examine a type, start with a command or event using it, then follow
|
|
references by name.
|
|
|
|
QAPI schema definitions not reachable that way are omitted.
|
|
|
|
The SchemaInfo for a command has meta-type "command", and variant
|
|
members "arg-type", "ret-type" and "allow-oob". On the wire, the
|
|
"arguments" member of a client's "execute" command must conform to the
|
|
object type named by "arg-type". The "return" member that the server
|
|
passes in a success response conforms to the type named by "ret-type".
|
|
When "allow-oob" is true, it means the command supports out-of-band
|
|
execution. It defaults to false.
|
|
|
|
If the command takes no arguments, "arg-type" names an object type
|
|
without members. Likewise, if the command returns nothing, "ret-type"
|
|
names an object type without members.
|
|
|
|
Example: the SchemaInfo for command query-qmp-schema ::
|
|
|
|
{ "name": "query-qmp-schema", "meta-type": "command",
|
|
"arg-type": "q_empty", "ret-type": "SchemaInfoList" }
|
|
|
|
Type "q_empty" is an automatic object type without members, and type
|
|
"SchemaInfoList" is the array of SchemaInfo type.
|
|
|
|
The SchemaInfo for an event has meta-type "event", and variant member
|
|
"arg-type". On the wire, a "data" member that the server passes in an
|
|
event conforms to the object type named by "arg-type".
|
|
|
|
If the event carries no additional information, "arg-type" names an
|
|
object type without members. The event may not have a data member on
|
|
the wire then.
|
|
|
|
Each command or event defined with 'data' as MEMBERS object in the
|
|
QAPI schema implicitly defines an object type.
|
|
|
|
Example: the SchemaInfo for EVENT_C from section Events_ ::
|
|
|
|
{ "name": "EVENT_C", "meta-type": "event",
|
|
"arg-type": "q_obj-EVENT_C-arg" }
|
|
|
|
Type "q_obj-EVENT_C-arg" is an implicitly defined object type with
|
|
the two members from the event's definition.
|
|
|
|
The SchemaInfo for struct and union types has meta-type "object".
|
|
|
|
The SchemaInfo for a struct type has variant member "members".
|
|
|
|
The SchemaInfo for a union type additionally has variant members "tag"
|
|
and "variants".
|
|
|
|
"members" is a JSON array describing the object's common members, if
|
|
any. Each element is a JSON object with members "name" (the member's
|
|
name), "type" (the name of its type), "features" (a JSON array of
|
|
feature strings), and "default". The latter two are optional. The
|
|
member is optional if "default" is present. Currently, "default" can
|
|
only have value null. Other values are reserved for future
|
|
extensions. The "members" array is in no particular order; clients
|
|
must search the entire object when learning whether a particular
|
|
member is supported.
|
|
|
|
Example: the SchemaInfo for MyType from section `Struct types`_ ::
|
|
|
|
{ "name": "MyType", "meta-type": "object",
|
|
"members": [
|
|
{ "name": "member1", "type": "str" },
|
|
{ "name": "member2", "type": "int" },
|
|
{ "name": "member3", "type": "str", "default": null } ] }
|
|
|
|
"features" exposes the command's feature strings as a JSON array of
|
|
strings.
|
|
|
|
Example: the SchemaInfo for TestType from section Features_::
|
|
|
|
{ "name": "TestType", "meta-type": "object",
|
|
"members": [
|
|
{ "name": "number", "type": "int" } ],
|
|
"features": ["allow-negative-numbers"] }
|
|
|
|
"tag" is the name of the common member serving as type tag.
|
|
"variants" is a JSON array describing the object's variant members.
|
|
Each element is a JSON object with members "case" (the value of type
|
|
tag this element applies to) and "type" (the name of an object type
|
|
that provides the variant members for this type tag value). The
|
|
"variants" array is in no particular order, and is not guaranteed to
|
|
list cases in the same order as the corresponding "tag" enum type.
|
|
|
|
Example: the SchemaInfo for union BlockdevOptions from section
|
|
`Union types`_ ::
|
|
|
|
{ "name": "BlockdevOptions", "meta-type": "object",
|
|
"members": [
|
|
{ "name": "driver", "type": "BlockdevDriver" },
|
|
{ "name": "read-only", "type": "bool", "default": null } ],
|
|
"tag": "driver",
|
|
"variants": [
|
|
{ "case": "file", "type": "BlockdevOptionsFile" },
|
|
{ "case": "qcow2", "type": "BlockdevOptionsQcow2" } ] }
|
|
|
|
Note that base types are "flattened": its members are included in the
|
|
"members" array.
|
|
|
|
The SchemaInfo for an alternate type has meta-type "alternate", and
|
|
variant member "members". "members" is a JSON array. Each element is
|
|
a JSON object with member "type", which names a type. Values of the
|
|
alternate type conform to exactly one of its member types. There is
|
|
no guarantee on the order in which "members" will be listed.
|
|
|
|
Example: the SchemaInfo for BlockdevRef from section `Alternate types`_ ::
|
|
|
|
{ "name": "BlockdevRef", "meta-type": "alternate",
|
|
"members": [
|
|
{ "type": "BlockdevOptions" },
|
|
{ "type": "str" } ] }
|
|
|
|
The SchemaInfo for an array type has meta-type "array", and variant
|
|
member "element-type", which names the array's element type. Array
|
|
types are implicitly defined. For convenience, the array's name may
|
|
resemble the element type; however, clients should examine member
|
|
"element-type" instead of making assumptions based on parsing member
|
|
"name".
|
|
|
|
Example: the SchemaInfo for ['str'] ::
|
|
|
|
{ "name": "[str]", "meta-type": "array",
|
|
"element-type": "str" }
|
|
|
|
The SchemaInfo for an enumeration type has meta-type "enum" and
|
|
variant member "members".
|
|
|
|
"members" is a JSON array describing the enumeration values. Each
|
|
element is a JSON object with member "name" (the member's name), and
|
|
optionally "features" (a JSON array of feature strings). The
|
|
"members" array is in no particular order; clients must search the
|
|
entire array when learning whether a particular value is supported.
|
|
|
|
Example: the SchemaInfo for MyEnum from section `Enumeration types`_ ::
|
|
|
|
{ "name": "MyEnum", "meta-type": "enum",
|
|
"members": [
|
|
{ "name": "value1" },
|
|
{ "name": "value2" },
|
|
{ "name": "value3" }
|
|
] }
|
|
|
|
The SchemaInfo for a built-in type has the same name as the type in
|
|
the QAPI schema (see section `Built-in Types`_), with one exception
|
|
detailed below. It has variant member "json-type" that shows how
|
|
values of this type are encoded on the wire.
|
|
|
|
Example: the SchemaInfo for str ::
|
|
|
|
{ "name": "str", "meta-type": "builtin", "json-type": "string" }
|
|
|
|
The QAPI schema supports a number of integer types that only differ in
|
|
how they map to C. They are identical as far as SchemaInfo is
|
|
concerned. Therefore, they get all mapped to a single type "int" in
|
|
SchemaInfo.
|
|
|
|
As explained above, type names are not part of the wire ABI. Not even
|
|
the names of built-in types. Clients should examine member
|
|
"json-type" instead of hard-coding names of built-in types.
|
|
|
|
|
|
Compatibility considerations
|
|
============================
|
|
|
|
Maintaining backward compatibility at the Client JSON Protocol level
|
|
while evolving the schema requires some care. This section is about
|
|
syntactic compatibility, which is necessary, but not sufficient, for
|
|
actual compatibility.
|
|
|
|
Clients send commands with argument data, and receive command
|
|
responses with return data and events with event data.
|
|
|
|
Adding opt-in functionality to the send direction is backwards
|
|
compatible: adding commands, optional arguments, enumeration values,
|
|
union and alternate branches; turning an argument type into an
|
|
alternate of that type; making mandatory arguments optional. Clients
|
|
oblivious of the new functionality continue to work.
|
|
|
|
Incompatible changes include removing commands, command arguments,
|
|
enumeration values, union and alternate branches, adding mandatory
|
|
command arguments, and making optional arguments mandatory.
|
|
|
|
The specified behavior of an absent optional argument should remain
|
|
the same. With proper documentation, this policy still allows some
|
|
flexibility; for example, when an optional 'buffer-size' argument is
|
|
specified to default to a sensible buffer size, the actual default
|
|
value can still be changed. The specified default behavior is not the
|
|
exact size of the buffer, only that the default size is sensible.
|
|
|
|
Adding functionality to the receive direction is generally backwards
|
|
compatible: adding events, adding return and event data members.
|
|
Clients are expected to ignore the ones they don't know.
|
|
|
|
Removing "unreachable" stuff like events that can't be triggered
|
|
anymore, optional return or event data members that can't be sent
|
|
anymore, and return or event data member (enumeration) values that
|
|
can't be sent anymore makes no difference to clients, except for
|
|
introspection. The latter can conceivably confuse clients, so tread
|
|
carefully.
|
|
|
|
Incompatible changes include removing return and event data members.
|
|
|
|
Any change to a command definition's 'data' or one of the types used
|
|
there (recursively) needs to consider send direction compatibility.
|
|
|
|
Any change to a command definition's 'return', an event definition's
|
|
'data', or one of the types used there (recursively) needs to consider
|
|
receive direction compatibility.
|
|
|
|
Any change to types used in both contexts need to consider both.
|
|
|
|
Enumeration type values and complex and alternate type members may be
|
|
reordered freely. For enumerations and alternate types, this doesn't
|
|
affect the wire encoding. For complex types, this might make the
|
|
implementation emit JSON object members in a different order, which
|
|
the Client JSON Protocol permits.
|
|
|
|
Since type names are not visible in the Client JSON Protocol, types
|
|
may be freely renamed. Even certain refactorings are invisible, such
|
|
as splitting members from one type into a common base type.
|
|
|
|
|
|
Code generation
|
|
===============
|
|
|
|
The QAPI code generator qapi-gen.py generates code and documentation
|
|
from the schema. Together with the core QAPI libraries, this code
|
|
provides everything required to take JSON commands read in by a Client
|
|
JSON Protocol server, unmarshal the arguments into the underlying C
|
|
types, call into the corresponding C function, map the response back
|
|
to a Client JSON Protocol response to be returned to the user, and
|
|
introspect the commands.
|
|
|
|
As an example, we'll use the following schema, which describes a
|
|
single complex user-defined type, along with command which takes a
|
|
list of that type as a parameter, and returns a single element of that
|
|
type. The user is responsible for writing the implementation of
|
|
qmp_my_command(); everything else is produced by the generator. ::
|
|
|
|
$ cat example-schema.json
|
|
{ 'struct': 'UserDefOne',
|
|
'data': { 'integer': 'int', '*string': 'str' } }
|
|
|
|
{ 'command': 'my-command',
|
|
'data': { 'arg1': ['UserDefOne'] },
|
|
'returns': 'UserDefOne' }
|
|
|
|
{ 'event': 'MY_EVENT' }
|
|
|
|
We run qapi-gen.py like this::
|
|
|
|
$ python scripts/qapi-gen.py --output-dir="qapi-generated" \
|
|
--prefix="example-" example-schema.json
|
|
|
|
For a more thorough look at generated code, the testsuite includes
|
|
tests/qapi-schema/qapi-schema-tests.json that covers more examples of
|
|
what the generator will accept, and compiles the resulting C code as
|
|
part of 'make check-unit'.
|
|
|
|
|
|
Code generated for QAPI types
|
|
-----------------------------
|
|
|
|
The following files are created:
|
|
|
|
``$(prefix)qapi-types.h``
|
|
C types corresponding to types defined in the schema
|
|
|
|
``$(prefix)qapi-types.c``
|
|
Cleanup functions for the above C types
|
|
|
|
The $(prefix) is an optional parameter used as a namespace to keep the
|
|
generated code from one schema/code-generation separated from others so code
|
|
can be generated/used from multiple schemas without clobbering previously
|
|
created code.
|
|
|
|
Example::
|
|
|
|
$ cat qapi-generated/example-qapi-types.h
|
|
[Uninteresting stuff omitted...]
|
|
|
|
#ifndef EXAMPLE_QAPI_TYPES_H
|
|
#define EXAMPLE_QAPI_TYPES_H
|
|
|
|
#include "qapi/qapi-builtin-types.h"
|
|
|
|
typedef struct UserDefOne UserDefOne;
|
|
|
|
typedef struct UserDefOneList UserDefOneList;
|
|
|
|
typedef struct q_obj_my_command_arg q_obj_my_command_arg;
|
|
|
|
struct UserDefOne {
|
|
int64_t integer;
|
|
bool has_string;
|
|
char *string;
|
|
};
|
|
|
|
void qapi_free_UserDefOne(UserDefOne *obj);
|
|
G_DEFINE_AUTOPTR_CLEANUP_FUNC(UserDefOne, qapi_free_UserDefOne)
|
|
|
|
struct UserDefOneList {
|
|
UserDefOneList *next;
|
|
UserDefOne *value;
|
|
};
|
|
|
|
void qapi_free_UserDefOneList(UserDefOneList *obj);
|
|
G_DEFINE_AUTOPTR_CLEANUP_FUNC(UserDefOneList, qapi_free_UserDefOneList)
|
|
|
|
struct q_obj_my_command_arg {
|
|
UserDefOneList *arg1;
|
|
};
|
|
|
|
#endif /* EXAMPLE_QAPI_TYPES_H */
|
|
$ cat qapi-generated/example-qapi-types.c
|
|
[Uninteresting stuff omitted...]
|
|
|
|
void qapi_free_UserDefOne(UserDefOne *obj)
|
|
{
|
|
Visitor *v;
|
|
|
|
if (!obj) {
|
|
return;
|
|
}
|
|
|
|
v = qapi_dealloc_visitor_new();
|
|
visit_type_UserDefOne(v, NULL, &obj, NULL);
|
|
visit_free(v);
|
|
}
|
|
|
|
void qapi_free_UserDefOneList(UserDefOneList *obj)
|
|
{
|
|
Visitor *v;
|
|
|
|
if (!obj) {
|
|
return;
|
|
}
|
|
|
|
v = qapi_dealloc_visitor_new();
|
|
visit_type_UserDefOneList(v, NULL, &obj, NULL);
|
|
visit_free(v);
|
|
}
|
|
|
|
[Uninteresting stuff omitted...]
|
|
|
|
For a modular QAPI schema (see section `Include directives`_), code for
|
|
each sub-module SUBDIR/SUBMODULE.json is actually generated into ::
|
|
|
|
SUBDIR/$(prefix)qapi-types-SUBMODULE.h
|
|
SUBDIR/$(prefix)qapi-types-SUBMODULE.c
|
|
|
|
If qapi-gen.py is run with option --builtins, additional files are
|
|
created:
|
|
|
|
``qapi-builtin-types.h``
|
|
C types corresponding to built-in types
|
|
|
|
``qapi-builtin-types.c``
|
|
Cleanup functions for the above C types
|
|
|
|
|
|
Code generated for visiting QAPI types
|
|
--------------------------------------
|
|
|
|
These are the visitor functions used to walk through and convert
|
|
between a native QAPI C data structure and some other format (such as
|
|
QObject); the generated functions are named visit_type_FOO() and
|
|
visit_type_FOO_members().
|
|
|
|
The following files are generated:
|
|
|
|
``$(prefix)qapi-visit.c``
|
|
Visitor function for a particular C type, used to automagically
|
|
convert QObjects into the corresponding C type and vice-versa, as
|
|
well as for deallocating memory for an existing C type
|
|
|
|
``$(prefix)qapi-visit.h``
|
|
Declarations for previously mentioned visitor functions
|
|
|
|
Example::
|
|
|
|
$ cat qapi-generated/example-qapi-visit.h
|
|
[Uninteresting stuff omitted...]
|
|
|
|
#ifndef EXAMPLE_QAPI_VISIT_H
|
|
#define EXAMPLE_QAPI_VISIT_H
|
|
|
|
#include "qapi/qapi-builtin-visit.h"
|
|
#include "example-qapi-types.h"
|
|
|
|
|
|
bool visit_type_UserDefOne_members(Visitor *v, UserDefOne *obj, Error **errp);
|
|
|
|
bool visit_type_UserDefOne(Visitor *v, const char *name,
|
|
UserDefOne **obj, Error **errp);
|
|
|
|
bool visit_type_UserDefOneList(Visitor *v, const char *name,
|
|
UserDefOneList **obj, Error **errp);
|
|
|
|
bool visit_type_q_obj_my_command_arg_members(Visitor *v, q_obj_my_command_arg *obj, Error **errp);
|
|
|
|
#endif /* EXAMPLE_QAPI_VISIT_H */
|
|
$ cat qapi-generated/example-qapi-visit.c
|
|
[Uninteresting stuff omitted...]
|
|
|
|
bool visit_type_UserDefOne_members(Visitor *v, UserDefOne *obj, Error **errp)
|
|
{
|
|
if (!visit_type_int(v, "integer", &obj->integer, errp)) {
|
|
return false;
|
|
}
|
|
if (visit_optional(v, "string", &obj->has_string)) {
|
|
if (!visit_type_str(v, "string", &obj->string, errp)) {
|
|
return false;
|
|
}
|
|
}
|
|
return true;
|
|
}
|
|
|
|
bool visit_type_UserDefOne(Visitor *v, const char *name,
|
|
UserDefOne **obj, Error **errp)
|
|
{
|
|
bool ok = false;
|
|
|
|
if (!visit_start_struct(v, name, (void **)obj, sizeof(UserDefOne), errp)) {
|
|
return false;
|
|
}
|
|
if (!*obj) {
|
|
/* incomplete */
|
|
assert(visit_is_dealloc(v));
|
|
ok = true;
|
|
goto out_obj;
|
|
}
|
|
if (!visit_type_UserDefOne_members(v, *obj, errp)) {
|
|
goto out_obj;
|
|
}
|
|
ok = visit_check_struct(v, errp);
|
|
out_obj:
|
|
visit_end_struct(v, (void **)obj);
|
|
if (!ok && visit_is_input(v)) {
|
|
qapi_free_UserDefOne(*obj);
|
|
*obj = NULL;
|
|
}
|
|
return ok;
|
|
}
|
|
|
|
bool visit_type_UserDefOneList(Visitor *v, const char *name,
|
|
UserDefOneList **obj, Error **errp)
|
|
{
|
|
bool ok = false;
|
|
UserDefOneList *tail;
|
|
size_t size = sizeof(**obj);
|
|
|
|
if (!visit_start_list(v, name, (GenericList **)obj, size, errp)) {
|
|
return false;
|
|
}
|
|
|
|
for (tail = *obj; tail;
|
|
tail = (UserDefOneList *)visit_next_list(v, (GenericList *)tail, size)) {
|
|
if (!visit_type_UserDefOne(v, NULL, &tail->value, errp)) {
|
|
goto out_obj;
|
|
}
|
|
}
|
|
|
|
ok = visit_check_list(v, errp);
|
|
out_obj:
|
|
visit_end_list(v, (void **)obj);
|
|
if (!ok && visit_is_input(v)) {
|
|
qapi_free_UserDefOneList(*obj);
|
|
*obj = NULL;
|
|
}
|
|
return ok;
|
|
}
|
|
|
|
bool visit_type_q_obj_my_command_arg_members(Visitor *v, q_obj_my_command_arg *obj, Error **errp)
|
|
{
|
|
if (!visit_type_UserDefOneList(v, "arg1", &obj->arg1, errp)) {
|
|
return false;
|
|
}
|
|
return true;
|
|
}
|
|
|
|
[Uninteresting stuff omitted...]
|
|
|
|
For a modular QAPI schema (see section `Include directives`_), code for
|
|
each sub-module SUBDIR/SUBMODULE.json is actually generated into ::
|
|
|
|
SUBDIR/$(prefix)qapi-visit-SUBMODULE.h
|
|
SUBDIR/$(prefix)qapi-visit-SUBMODULE.c
|
|
|
|
If qapi-gen.py is run with option --builtins, additional files are
|
|
created:
|
|
|
|
``qapi-builtin-visit.h``
|
|
Visitor functions for built-in types
|
|
|
|
``qapi-builtin-visit.c``
|
|
Declarations for these visitor functions
|
|
|
|
|
|
Code generated for commands
|
|
---------------------------
|
|
|
|
These are the marshaling/dispatch functions for the commands defined
|
|
in the schema. The generated code provides qmp_marshal_COMMAND(), and
|
|
declares qmp_COMMAND() that the user must implement.
|
|
|
|
The following files are generated:
|
|
|
|
``$(prefix)qapi-commands.c``
|
|
Command marshal/dispatch functions for each QMP command defined in
|
|
the schema
|
|
|
|
``$(prefix)qapi-commands.h``
|
|
Function prototypes for the QMP commands specified in the schema
|
|
|
|
``$(prefix)qapi-commands.trace-events``
|
|
Trace event declarations, see :ref:`tracing`.
|
|
|
|
``$(prefix)qapi-init-commands.h``
|
|
Command initialization prototype
|
|
|
|
``$(prefix)qapi-init-commands.c``
|
|
Command initialization code
|
|
|
|
Example::
|
|
|
|
$ cat qapi-generated/example-qapi-commands.h
|
|
[Uninteresting stuff omitted...]
|
|
|
|
#ifndef EXAMPLE_QAPI_COMMANDS_H
|
|
#define EXAMPLE_QAPI_COMMANDS_H
|
|
|
|
#include "example-qapi-types.h"
|
|
|
|
UserDefOne *qmp_my_command(UserDefOneList *arg1, Error **errp);
|
|
void qmp_marshal_my_command(QDict *args, QObject **ret, Error **errp);
|
|
|
|
#endif /* EXAMPLE_QAPI_COMMANDS_H */
|
|
|
|
$ cat qapi-generated/example-qapi-commands.trace-events
|
|
# AUTOMATICALLY GENERATED, DO NOT MODIFY
|
|
|
|
qmp_enter_my_command(const char *json) "%s"
|
|
qmp_exit_my_command(const char *result, bool succeeded) "%s %d"
|
|
|
|
$ cat qapi-generated/example-qapi-commands.c
|
|
[Uninteresting stuff omitted...]
|
|
|
|
static void qmp_marshal_output_UserDefOne(UserDefOne *ret_in,
|
|
QObject **ret_out, Error **errp)
|
|
{
|
|
Visitor *v;
|
|
|
|
v = qobject_output_visitor_new_qmp(ret_out);
|
|
if (visit_type_UserDefOne(v, "unused", &ret_in, errp)) {
|
|
visit_complete(v, ret_out);
|
|
}
|
|
visit_free(v);
|
|
v = qapi_dealloc_visitor_new();
|
|
visit_type_UserDefOne(v, "unused", &ret_in, NULL);
|
|
visit_free(v);
|
|
}
|
|
|
|
void qmp_marshal_my_command(QDict *args, QObject **ret, Error **errp)
|
|
{
|
|
Error *err = NULL;
|
|
bool ok = false;
|
|
Visitor *v;
|
|
UserDefOne *retval;
|
|
q_obj_my_command_arg arg = {0};
|
|
|
|
v = qobject_input_visitor_new_qmp(QOBJECT(args));
|
|
if (!visit_start_struct(v, NULL, NULL, 0, errp)) {
|
|
goto out;
|
|
}
|
|
if (visit_type_q_obj_my_command_arg_members(v, &arg, errp)) {
|
|
ok = visit_check_struct(v, errp);
|
|
}
|
|
visit_end_struct(v, NULL);
|
|
if (!ok) {
|
|
goto out;
|
|
}
|
|
|
|
if (trace_event_get_state_backends(TRACE_QMP_ENTER_MY_COMMAND)) {
|
|
g_autoptr(GString) req_json = qobject_to_json(QOBJECT(args));
|
|
|
|
trace_qmp_enter_my_command(req_json->str);
|
|
}
|
|
|
|
retval = qmp_my_command(arg.arg1, &err);
|
|
if (err) {
|
|
trace_qmp_exit_my_command(error_get_pretty(err), false);
|
|
error_propagate(errp, err);
|
|
goto out;
|
|
}
|
|
|
|
qmp_marshal_output_UserDefOne(retval, ret, errp);
|
|
|
|
if (trace_event_get_state_backends(TRACE_QMP_EXIT_MY_COMMAND)) {
|
|
g_autoptr(GString) ret_json = qobject_to_json(*ret);
|
|
|
|
trace_qmp_exit_my_command(ret_json->str, true);
|
|
}
|
|
|
|
out:
|
|
visit_free(v);
|
|
v = qapi_dealloc_visitor_new();
|
|
visit_start_struct(v, NULL, NULL, 0, NULL);
|
|
visit_type_q_obj_my_command_arg_members(v, &arg, NULL);
|
|
visit_end_struct(v, NULL);
|
|
visit_free(v);
|
|
}
|
|
|
|
[Uninteresting stuff omitted...]
|
|
$ cat qapi-generated/example-qapi-init-commands.h
|
|
[Uninteresting stuff omitted...]
|
|
#ifndef EXAMPLE_QAPI_INIT_COMMANDS_H
|
|
#define EXAMPLE_QAPI_INIT_COMMANDS_H
|
|
|
|
#include "qapi/qmp/dispatch.h"
|
|
|
|
void example_qmp_init_marshal(QmpCommandList *cmds);
|
|
|
|
#endif /* EXAMPLE_QAPI_INIT_COMMANDS_H */
|
|
$ cat qapi-generated/example-qapi-init-commands.c
|
|
[Uninteresting stuff omitted...]
|
|
void example_qmp_init_marshal(QmpCommandList *cmds)
|
|
{
|
|
QTAILQ_INIT(cmds);
|
|
|
|
qmp_register_command(cmds, "my-command",
|
|
qmp_marshal_my_command, 0, 0);
|
|
}
|
|
[Uninteresting stuff omitted...]
|
|
|
|
For a modular QAPI schema (see section `Include directives`_), code for
|
|
each sub-module SUBDIR/SUBMODULE.json is actually generated into::
|
|
|
|
SUBDIR/$(prefix)qapi-commands-SUBMODULE.h
|
|
SUBDIR/$(prefix)qapi-commands-SUBMODULE.c
|
|
|
|
|
|
Code generated for events
|
|
-------------------------
|
|
|
|
This is the code related to events defined in the schema, providing
|
|
qapi_event_send_EVENT().
|
|
|
|
The following files are created:
|
|
|
|
``$(prefix)qapi-events.h``
|
|
Function prototypes for each event type
|
|
|
|
``$(prefix)qapi-events.c``
|
|
Implementation of functions to send an event
|
|
|
|
``$(prefix)qapi-emit-events.h``
|
|
Enumeration of all event names, and common event code declarations
|
|
|
|
``$(prefix)qapi-emit-events.c``
|
|
Common event code definitions
|
|
|
|
Example::
|
|
|
|
$ cat qapi-generated/example-qapi-events.h
|
|
[Uninteresting stuff omitted...]
|
|
|
|
#ifndef EXAMPLE_QAPI_EVENTS_H
|
|
#define EXAMPLE_QAPI_EVENTS_H
|
|
|
|
#include "qapi/util.h"
|
|
#include "example-qapi-types.h"
|
|
|
|
void qapi_event_send_my_event(void);
|
|
|
|
#endif /* EXAMPLE_QAPI_EVENTS_H */
|
|
$ cat qapi-generated/example-qapi-events.c
|
|
[Uninteresting stuff omitted...]
|
|
|
|
void qapi_event_send_my_event(void)
|
|
{
|
|
QDict *qmp;
|
|
|
|
qmp = qmp_event_build_dict("MY_EVENT");
|
|
|
|
example_qapi_event_emit(EXAMPLE_QAPI_EVENT_MY_EVENT, qmp);
|
|
|
|
qobject_unref(qmp);
|
|
}
|
|
|
|
[Uninteresting stuff omitted...]
|
|
$ cat qapi-generated/example-qapi-emit-events.h
|
|
[Uninteresting stuff omitted...]
|
|
|
|
#ifndef EXAMPLE_QAPI_EMIT_EVENTS_H
|
|
#define EXAMPLE_QAPI_EMIT_EVENTS_H
|
|
|
|
#include "qapi/util.h"
|
|
|
|
typedef enum example_QAPIEvent {
|
|
EXAMPLE_QAPI_EVENT_MY_EVENT,
|
|
EXAMPLE_QAPI_EVENT__MAX,
|
|
} example_QAPIEvent;
|
|
|
|
#define example_QAPIEvent_str(val) \
|
|
qapi_enum_lookup(&example_QAPIEvent_lookup, (val))
|
|
|
|
extern const QEnumLookup example_QAPIEvent_lookup;
|
|
|
|
void example_qapi_event_emit(example_QAPIEvent event, QDict *qdict);
|
|
|
|
#endif /* EXAMPLE_QAPI_EMIT_EVENTS_H */
|
|
$ cat qapi-generated/example-qapi-emit-events.c
|
|
[Uninteresting stuff omitted...]
|
|
|
|
const QEnumLookup example_QAPIEvent_lookup = {
|
|
.array = (const char *const[]) {
|
|
[EXAMPLE_QAPI_EVENT_MY_EVENT] = "MY_EVENT",
|
|
},
|
|
.size = EXAMPLE_QAPI_EVENT__MAX
|
|
};
|
|
|
|
[Uninteresting stuff omitted...]
|
|
|
|
For a modular QAPI schema (see section `Include directives`_), code for
|
|
each sub-module SUBDIR/SUBMODULE.json is actually generated into ::
|
|
|
|
SUBDIR/$(prefix)qapi-events-SUBMODULE.h
|
|
SUBDIR/$(prefix)qapi-events-SUBMODULE.c
|
|
|
|
|
|
Code generated for introspection
|
|
--------------------------------
|
|
|
|
The following files are created:
|
|
|
|
``$(prefix)qapi-introspect.c``
|
|
Defines a string holding a JSON description of the schema
|
|
|
|
``$(prefix)qapi-introspect.h``
|
|
Declares the above string
|
|
|
|
Example::
|
|
|
|
$ cat qapi-generated/example-qapi-introspect.h
|
|
[Uninteresting stuff omitted...]
|
|
|
|
#ifndef EXAMPLE_QAPI_INTROSPECT_H
|
|
#define EXAMPLE_QAPI_INTROSPECT_H
|
|
|
|
#include "qapi/qmp/qlit.h"
|
|
|
|
extern const QLitObject example_qmp_schema_qlit;
|
|
|
|
#endif /* EXAMPLE_QAPI_INTROSPECT_H */
|
|
$ cat qapi-generated/example-qapi-introspect.c
|
|
[Uninteresting stuff omitted...]
|
|
|
|
const QLitObject example_qmp_schema_qlit = QLIT_QLIST(((QLitObject[]) {
|
|
QLIT_QDICT(((QLitDictEntry[]) {
|
|
{ "arg-type", QLIT_QSTR("0"), },
|
|
{ "meta-type", QLIT_QSTR("command"), },
|
|
{ "name", QLIT_QSTR("my-command"), },
|
|
{ "ret-type", QLIT_QSTR("1"), },
|
|
{}
|
|
})),
|
|
QLIT_QDICT(((QLitDictEntry[]) {
|
|
{ "arg-type", QLIT_QSTR("2"), },
|
|
{ "meta-type", QLIT_QSTR("event"), },
|
|
{ "name", QLIT_QSTR("MY_EVENT"), },
|
|
{}
|
|
})),
|
|
/* "0" = q_obj_my-command-arg */
|
|
QLIT_QDICT(((QLitDictEntry[]) {
|
|
{ "members", QLIT_QLIST(((QLitObject[]) {
|
|
QLIT_QDICT(((QLitDictEntry[]) {
|
|
{ "name", QLIT_QSTR("arg1"), },
|
|
{ "type", QLIT_QSTR("[1]"), },
|
|
{}
|
|
})),
|
|
{}
|
|
})), },
|
|
{ "meta-type", QLIT_QSTR("object"), },
|
|
{ "name", QLIT_QSTR("0"), },
|
|
{}
|
|
})),
|
|
/* "1" = UserDefOne */
|
|
QLIT_QDICT(((QLitDictEntry[]) {
|
|
{ "members", QLIT_QLIST(((QLitObject[]) {
|
|
QLIT_QDICT(((QLitDictEntry[]) {
|
|
{ "name", QLIT_QSTR("integer"), },
|
|
{ "type", QLIT_QSTR("int"), },
|
|
{}
|
|
})),
|
|
QLIT_QDICT(((QLitDictEntry[]) {
|
|
{ "default", QLIT_QNULL, },
|
|
{ "name", QLIT_QSTR("string"), },
|
|
{ "type", QLIT_QSTR("str"), },
|
|
{}
|
|
})),
|
|
{}
|
|
})), },
|
|
{ "meta-type", QLIT_QSTR("object"), },
|
|
{ "name", QLIT_QSTR("1"), },
|
|
{}
|
|
})),
|
|
/* "2" = q_empty */
|
|
QLIT_QDICT(((QLitDictEntry[]) {
|
|
{ "members", QLIT_QLIST(((QLitObject[]) {
|
|
{}
|
|
})), },
|
|
{ "meta-type", QLIT_QSTR("object"), },
|
|
{ "name", QLIT_QSTR("2"), },
|
|
{}
|
|
})),
|
|
QLIT_QDICT(((QLitDictEntry[]) {
|
|
{ "element-type", QLIT_QSTR("1"), },
|
|
{ "meta-type", QLIT_QSTR("array"), },
|
|
{ "name", QLIT_QSTR("[1]"), },
|
|
{}
|
|
})),
|
|
QLIT_QDICT(((QLitDictEntry[]) {
|
|
{ "json-type", QLIT_QSTR("int"), },
|
|
{ "meta-type", QLIT_QSTR("builtin"), },
|
|
{ "name", QLIT_QSTR("int"), },
|
|
{}
|
|
})),
|
|
QLIT_QDICT(((QLitDictEntry[]) {
|
|
{ "json-type", QLIT_QSTR("string"), },
|
|
{ "meta-type", QLIT_QSTR("builtin"), },
|
|
{ "name", QLIT_QSTR("str"), },
|
|
{}
|
|
})),
|
|
{}
|
|
}));
|
|
|
|
[Uninteresting stuff omitted...]
|