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docs: convert qapi-code-gen.txt to ReST 

This is a very rudimentary conversion from .txt to .rst changing as
little as possible, but getting it to render somewhat nicely; without
using any Sphinx directives. (It is 'native' ReST.)

Further patches will add cross-references and Sphinx-specific extensions
to make it sparkle.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20210720235619.2048797-2-jsnow@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
This commit is contained in:
John Snow 2021-07-20 19:56:17 -04:00 committed by Markus Armbruster
parent e0366f9f2b
commit f7aa076dbd
2 changed files with 312 additions and 248 deletions
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1
docs/devel/index.rst
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@ -42,3 +42,4 @@ modifying QEMU's source code.
multi-process multi-process
ebpf_rss ebpf_rss
vfio-migration vfio-migration
qapi-code-gen

331
docs/devel/qapi-code-gen.txt → docs/devel/qapi-code-gen.rst
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@ -1,12 +1,17 @@
= How to use the QAPI code generator = ==================================
How to use the QAPI code generator
==================================
..
Copyright IBM Corp. 2011 Copyright IBM Corp. 2011
Copyright (C) 2012-2016 Red Hat, Inc. Copyright (C) 2012-2016 Red Hat, Inc.
This work is licensed under the terms of the GNU GPL, version 2 or This work is licensed under the terms of the GNU GPL, version 2 or
later. See the COPYING file in the top-level directory. later. See the COPYING file in the top-level directory.
== Introduction ==
Introduction
============
QAPI is a native C API within QEMU which provides management-level QAPI is a native C API within QEMU which provides management-level
functionality to internal and external users. For external functionality to internal and external users. For external
@ -23,7 +28,8 @@ Protocol and to C. It additionally provides guidance on maintaining
Client JSON Protocol compatibility. Client JSON Protocol compatibility.
== The QAPI schema language == The QAPI schema language
========================
The QAPI schema defines the Client JSON Protocol's commands and The QAPI schema defines the Client JSON Protocol's commands and
events, as well as types used by them. Forward references are events, as well as types used by them. Forward references are
@ -39,9 +45,10 @@ complex types (structs and two flavors of unions), and alternate types
(a choice between other types). (a choice between other types).
=== Schema syntax === Schema syntax
-------------
Syntax is loosely based on JSON (http://www.ietf.org/rfc/rfc8259.txt). Syntax is loosely based on `JSON <http://www.ietf.org/rfc/rfc8259.txt>`_.
Differences: Differences:
* Comments: start with a hash character (#) that is not part of a * Comments: start with a hash character (#) that is not part of a
@ -79,7 +86,7 @@ syntax in an EBNF-like notation:
The order of members within JSON objects does not matter unless The order of members within JSON objects does not matter unless
explicitly noted. explicitly noted.
A QAPI schema consists of a series of top-level expressions: A QAPI schema consists of a series of top-level expressions::
SCHEMA = TOP-LEVEL-EXPR... SCHEMA = TOP-LEVEL-EXPR...
@ -87,11 +94,11 @@ The top-level expressions are all JSON objects. Code and
documentation is generated in schema definition order. Code order documentation is generated in schema definition order. Code order
should not matter. should not matter.
A top-level expressions is either a directive or a definition: A top-level expressions is either a directive or a definition::
TOP-LEVEL-EXPR = DIRECTIVE | DEFINITION TOP-LEVEL-EXPR = DIRECTIVE | DEFINITION
There are two kinds of directives and six kinds of definitions: There are two kinds of directives and six kinds of definitions::
DIRECTIVE = INCLUDE | PRAGMA DIRECTIVE = INCLUDE | PRAGMA
DEFINITION = ENUM | STRUCT | UNION | ALTERNATE | COMMAND | EVENT DEFINITION = ENUM | STRUCT | UNION | ALTERNATE | COMMAND | EVENT
@ -99,9 +106,10 @@ There are two kinds of directives and six kinds of definitions:
These are discussed in detail below. These are discussed in detail below.
=== Built-in Types === Built-in Types
--------------
The following types are predefined, and map to C as follows: The following types are predefined, and map to C as follows::
Schema C JSON Schema C JSON
str char * any JSON string, UTF-8 str char * any JSON string, UTF-8
@ -124,12 +132,14 @@ The following types are predefined, and map to C as follows:
QType QType JSON string matching enum QType values QType QType JSON string matching enum QType values
=== Include directives === Include directives
------------------
Syntax::
Syntax:
INCLUDE = { 'include': STRING } INCLUDE = { 'include': STRING }
The QAPI schema definitions can be modularized using the 'include' directive: The QAPI schema definitions can be modularized using the 'include' directive::
{ 'include': 'path/to/file.json' } { 'include': 'path/to/file.json' }
@ -144,9 +154,11 @@ an outer file. The parser may be made stricter in the future to
prevent incomplete include files. prevent incomplete include files.
=== Pragma directives === Pragma directives
-----------------
Syntax::
Syntax:
PRAGMA = { 'pragma': { PRAGMA = { 'pragma': {
'*doc-required': BOOL, '*doc-required': BOOL,
'*command-name-exceptions': [ STRING, ... ], '*command-name-exceptions': [ STRING, ... ],
@ -172,9 +184,11 @@ names may contain uppercase letters, and '_' instead of '-'. Default
is none. is none.
=== Enumeration types === Enumeration types
-----------------
Syntax::
Syntax:
ENUM = { 'enum': STRING, ENUM = { 'enum': STRING,
'data': [ ENUM-VALUE, ... ], 'data': [ ENUM-VALUE, ... ],
'*prefix': STRING, '*prefix': STRING,
@ -189,7 +203,7 @@ Each member of the 'data' array defines a value of the enumeration
type. The form STRING is shorthand for { 'name': STRING }. The type. The form STRING is shorthand for { 'name': STRING }. The
'name' values must be be distinct. 'name' values must be be distinct.
Example: Example::
{ 'enum': 'MyEnum', 'data': [ 'value1', 'value2', 'value3' ] } { 'enum': 'MyEnum', 'data': [ 'value1', 'value2', 'value3' ] }
@ -218,9 +232,11 @@ The optional 'features' member specifies features. See "Features"
below for more on this. below for more on this.
=== Type references and array types === Type references and array types
-------------------------------
Syntax::
Syntax:
TYPE-REF = STRING | ARRAY-TYPE TYPE-REF = STRING | ARRAY-TYPE
ARRAY-TYPE = [ STRING ] ARRAY-TYPE = [ STRING ]
@ -230,9 +246,11 @@ A one-element array containing a string denotes an array of the type
named by the string. Example: ['int'] denotes an array of 'int'. named by the string. Example: ['int'] denotes an array of 'int'.
=== Struct types === Struct types
------------
Syntax::
Syntax:
STRUCT = { 'struct': STRING, STRUCT = { 'struct': STRING,
'data': MEMBERS, 'data': MEMBERS,
'*base': STRING, '*base': STRING,
@ -254,7 +272,7 @@ struct member name. If '*' is present, the member is optional.
The MEMBER's value defines its properties, in particular its type. The MEMBER's value defines its properties, in particular its type.
The form TYPE-REF is shorthand for { 'type': TYPE-REF }. The form TYPE-REF is shorthand for { 'type': TYPE-REF }.
Example: Example::
{ 'struct': 'MyType', { 'struct': 'MyType',
'data': { 'member1': 'str', 'member2': ['int'], '*member3': 'str' } } 'data': { 'member1': 'str', 'member2': ['int'], '*member3': 'str' } }
@ -265,7 +283,7 @@ The C struct's members are generated in QAPI schema order.
The optional 'base' member names a struct type whose members are to be The optional 'base' member names a struct type whose members are to be
included in this type. They go first in the C struct. included in this type. They go first in the C struct.
Example: Example::
{ 'struct': 'BlockdevOptionsGenericFormat', { 'struct': 'BlockdevOptionsGenericFormat',
'data': { 'file': 'str' } } 'data': { 'file': 'str' } }
@ -274,7 +292,7 @@ Example:
'data': { '*backing': 'str' } } 'data': { '*backing': 'str' } }
An example BlockdevOptionsGenericCOWFormat object on the wire could use An example BlockdevOptionsGenericCOWFormat object on the wire could use
both members like this: both members like this::
{ "file": "/some/place/my-image", { "file": "/some/place/my-image",
"backing": "/some/place/my-backing-file" } "backing": "/some/place/my-backing-file" }
@ -286,9 +304,11 @@ The optional 'features' member specifies features. See "Features"
below for more on this. below for more on this.
=== Union types === Union types
-----------
Syntax::
Syntax:
UNION = { 'union': STRING, UNION = { 'union': STRING,
'data': BRANCHES, 'data': BRANCHES,
'*if': COND, '*if': COND,
@ -317,7 +337,7 @@ The BRANCH's value defines the branch's properties, in particular its
type. The form TYPE-REF is shorthand for { 'type': TYPE-REF }. type. The form TYPE-REF is shorthand for { 'type': TYPE-REF }.
A simple union type defines a mapping from automatic discriminator A simple union type defines a mapping from automatic discriminator
values to data types like in this example: values to data types like in this example::
{ 'struct': 'BlockdevOptionsFile', 'data': { 'filename': 'str' } } { 'struct': 'BlockdevOptionsFile', 'data': { 'filename': 'str' } }
{ 'struct': 'BlockdevOptionsQcow2', { 'struct': 'BlockdevOptionsQcow2',
@ -330,7 +350,7 @@ values to data types like in this example:
In the Client JSON Protocol, a simple union is represented by an In the Client JSON Protocol, a simple union is represented by an
object that contains the 'type' member as a discriminator, and a object that contains the 'type' member as a discriminator, and a
'data' member that is of the specified data type corresponding to the 'data' member that is of the specified data type corresponding to the
discriminator value, as in these examples: discriminator value, as in these examples::
{ "type": "file", "data": { "filename": "/some/place/my-image" } } { "type": "file", "data": { "filename": "/some/place/my-image" } }
{ "type": "qcow2", "data": { "backing": "/some/place/my-image", { "type": "qcow2", "data": { "backing": "/some/place/my-image",
@ -361,7 +381,7 @@ struct.
The following example enhances the above simple union example by The following example enhances the above simple union example by
adding an optional common member 'read-only', renaming the adding an optional common member 'read-only', renaming the
discriminator to something more applicable than the simple union's discriminator to something more applicable than the simple union's
default of 'type', and reducing the number of {} required on the wire: default of 'type', and reducing the number of {} required on the wire::
{ 'enum': 'BlockdevDriver', 'data': [ 'file', 'qcow2' ] } { 'enum': 'BlockdevDriver', 'data': [ 'file', 'qcow2' ] }
{ 'union': 'BlockdevOptions', { 'union': 'BlockdevOptions',
@ -370,7 +390,7 @@ default of 'type', and reducing the number of {} required on the wire:
'data': { 'file': 'BlockdevOptionsFile', 'data': { 'file': 'BlockdevOptionsFile',
'qcow2': 'BlockdevOptionsQcow2' } } 'qcow2': 'BlockdevOptionsQcow2' } }
Resulting in these JSON objects: Resulting in these JSON objects::
{ "driver": "file", "read-only": true, { "driver": "file", "read-only": true,
"filename": "/some/place/my-image" } "filename": "/some/place/my-image" }
@ -390,11 +410,11 @@ struct.
A simple union can always be re-written as a flat union where the base A simple union can always be re-written as a flat union where the base
class has a single member named 'type', and where each branch of the class has a single member named 'type', and where each branch of the
union has a struct with a single member named 'data'. That is, union has a struct with a single member named 'data'. That is, ::
{ 'union': 'Simple', 'data': { 'one': 'str', 'two': 'int' } } { 'union': 'Simple', 'data': { 'one': 'str', 'two': 'int' } }
is identical on the wire to: is identical on the wire to::
{ 'enum': 'Enum', 'data': ['one', 'two'] } { 'enum': 'Enum', 'data': ['one', 'two'] }
{ 'struct': 'Branch1', 'data': { 'data': 'str' } } { 'struct': 'Branch1', 'data': { 'data': 'str' } }
@ -409,9 +429,11 @@ The optional 'features' member specifies features. See "Features"
below for more on this. below for more on this.
=== Alternate types === Alternate types
---------------
Syntax::
Syntax:
ALTERNATE = { 'alternate': STRING, ALTERNATE = { 'alternate': STRING,
'data': ALTERNATIVES, 'data': ALTERNATIVES,
'*if': COND, '*if': COND,
@ -430,7 +452,7 @@ The ALTERNATIVE's STRING name is the branch name.
The ALTERNATIVE's value defines the branch's properties, in particular The ALTERNATIVE's value defines the branch's properties, in particular
its type. The form STRING is shorthand for { 'type': STRING }. its type. The form STRING is shorthand for { 'type': STRING }.
Example: Example::
{ 'alternate': 'BlockdevRef', { 'alternate': 'BlockdevRef',
'data': { 'definition': 'BlockdevOptions', 'data': { 'definition': 'BlockdevOptions',
@ -449,7 +471,7 @@ as the 'null' built-in, it accepts JSON null; and if it is typed as a
complex type (struct or union), it accepts a JSON object. complex type (struct or union), it accepts a JSON object.
The example alternate declaration above allows using both of the The example alternate declaration above allows using both of the
following example objects: following example objects::
{ "file": "my_existing_block_device_id" } { "file": "my_existing_block_device_id" }
{ "file": { "driver": "file", { "file": { "driver": "file",
@ -463,9 +485,11 @@ The optional 'features' member specifies features. See "Features"
below for more on this. below for more on this.
=== Commands === Commands
--------
Syntax::
Syntax:
COMMAND = { 'command': STRING, COMMAND = { 'command': STRING,
( (
'*data': ( MEMBERS | STRING ), '*data': ( MEMBERS | STRING ),
@ -508,7 +532,7 @@ member is the command name. The value of the "arguments" member then
has to conform to the arguments, and the value of the success has to conform to the arguments, and the value of the success
response's "return" member will conform to the return type. response's "return" member will conform to the return type.
Some example commands: Some example commands::
{ 'command': 'my-first-command', { 'command': 'my-first-command',
'data': { 'arg1': 'str', '*arg2': 'str' } } 'data': { 'arg1': 'str', '*arg2': 'str' } }
@ -516,7 +540,7 @@ Some example commands:
{ 'command': 'my-second-command', { 'command': 'my-second-command',
'returns': [ 'MyType' ] } 'returns': [ 'MyType' ] }
which would validate this Client JSON Protocol transaction: which would validate this Client JSON Protocol transaction::
=> { "execute": "my-first-command", => { "execute": "my-first-command",
"arguments": { "arg1": "hello" } } "arguments": { "arg1": "hello" } }
@ -543,7 +567,7 @@ In rare cases, QAPI cannot express a type-safe representation of a
corresponding Client JSON Protocol command. You then have to suppress corresponding Client JSON Protocol command. You then have to suppress
generation of a marshalling function by including a member 'gen' with generation of a marshalling function by including a member 'gen' with
boolean value false, and instead write your own function. For boolean value false, and instead write your own function. For
example: example::
{ 'command': 'netdev_add', { 'command': 'netdev_add',
'data': {'type': 'str', 'id': 'str'}, 'data': {'type': 'str', 'id': 'str'},
@ -561,7 +585,7 @@ the command definition includes the optional member 'success-response'
with boolean value false. So far, only QGA makes use of this member. with boolean value false. So far, only QGA makes use of this member.
Member 'allow-oob' declares whether the command supports out-of-band Member 'allow-oob' declares whether the command supports out-of-band
(OOB) execution. It defaults to false. For example: (OOB) execution. It defaults to false. For example::
{ 'command': 'migrate_recover', { 'command': 'migrate_recover',
'data': { 'uri': 'str' }, 'allow-oob': true } 'data': { 'uri': 'str' }, 'allow-oob': true }
@ -594,7 +618,7 @@ other "slow" lock.
When in doubt, do not implement OOB execution support. When in doubt, do not implement OOB execution support.
Member 'allow-preconfig' declares whether the command is available Member 'allow-preconfig' declares whether the command is available
before the machine is built. It defaults to false. For example: before the machine is built. It defaults to false. For example::
{ 'enum': 'QMPCapability', { 'enum': 'QMPCapability',
'data': [ 'oob' ] } 'data': [ 'oob' ] }
@ -640,9 +664,11 @@ The optional 'features' member specifies features. See "Features"
below for more on this. below for more on this.
=== Events === Events
------
Syntax::
Syntax:
EVENT = { 'event': STRING, EVENT = { 'event': STRING,
( (
'*data': ( MEMBERS | STRING ), '*data': ( MEMBERS | STRING ),
@ -665,12 +691,12 @@ 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 If 'data' is a STRING, then STRING names a complex type whose members
are the event-specific data. A union type requires 'boxed': true. are the event-specific data. A union type requires 'boxed': true.
An example event is: An example event is::
{ 'event': 'EVENT_C', { 'event': 'EVENT_C',
'data': { '*a': 'int', 'b': 'str' } } 'data': { '*a': 'int', 'b': 'str' } }
Resulting in this JSON object: Resulting in this JSON object::
{ "event": "EVENT_C", { "event": "EVENT_C",
"data": { "b": "test string" }, "data": { "b": "test string" },
@ -688,9 +714,11 @@ The optional 'features' member specifies features. See "Features"
below for more on this. below for more on this.
=== Features === Features
--------
Syntax::
Syntax:
FEATURES = [ FEATURE, ... ] FEATURES = [ FEATURE, ... ]
FEATURE = STRING FEATURE = STRING
| { 'name': STRING, '*if': COND } | { 'name': STRING, '*if': COND }
@ -701,13 +729,13 @@ that previously resulted in an error). QMP clients may still need to
know whether the extension is available. know whether the extension is available.
For this purpose, a list of features can be specified for a command or 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': struct type. Each list member can either be ``{ 'name': STRING, '*if':
COND }, or STRING, which is shorthand for { 'name': STRING }. COND }``, or STRING, which is shorthand for ``{ 'name': STRING }``.
The optional 'if' member specifies a conditional. See "Configuring The optional 'if' member specifies a conditional. See "Configuring
the schema" below for more on this. the schema" below for more on this.
Example: Example::
{ 'struct': 'TestType', { 'struct': 'TestType',
'data': { 'number': 'int' }, 'data': { 'number': 'int' },
@ -720,20 +748,22 @@ Intended use is to have each feature string signal that this build of
QEMU shows a certain behaviour. QEMU shows a certain behaviour.
==== Special features ==== Special features
~~~~~~~~~~~~~~~~
Feature "deprecated" marks a command, event, or struct member as Feature "deprecated" marks a command, event, or struct member as
deprecated. It is not supported elsewhere so far. deprecated. It is not supported elsewhere so far.
=== Naming rules and reserved names === Naming rules and reserved names
-------------------------------
All names must begin with a letter, and contain only ASCII letters, All names must begin with a letter, and contain only ASCII letters,
digits, hyphen, and underscore. There are two exceptions: enum values digits, hyphen, and underscore. There are two exceptions: enum values
may start with a digit, and names that are downstream extensions (see may start with a digit, and names that are downstream extensions (see
section Downstream extensions) start with underscore. section Downstream extensions) start with underscore.
Names beginning with 'q_' are reserved for the generator, which uses Names beginning with 'q\_' are reserved for the generator, which uses
them for munging QMP names that resemble C keywords or other them for munging QMP names that resemble C keywords or other
problematic strings. For example, a member named "default" in qapi problematic strings. For example, a member named "default" in qapi
becomes "q_default" in the generated C code. becomes "q_default" in the generated C code.
@ -753,7 +783,7 @@ consistency is preferred over blindly avoiding underscore.
Event names should be ALL_CAPS with words separated by underscore. Event names should be ALL_CAPS with words separated by underscore.
Member name 'u' and names starting with 'has-' or 'has_' are reserved Member name 'u' and names starting with 'has-' or 'has\_' are reserved
for the generator, which uses them for unions and for tracking for the generator, which uses them for unions and for tracking
optional members. optional members.
@ -765,7 +795,8 @@ Pragmas 'command-name-exceptions' and 'member-name-exceptions' let you
violate naming rules. Use for new code is strongly discouraged. violate naming rules. Use for new code is strongly discouraged.
=== Downstream extensions === Downstream extensions
---------------------
QAPI schema names that are externally visible, say in the Client JSON QAPI schema names that are externally visible, say in the Client JSON
Protocol, need to be managed with care. Names starting with a Protocol, need to be managed with care. Names starting with a
@ -777,9 +808,11 @@ Example: Red Hat, Inc. controls redhat.com, and may therefore add a
downstream command __com.redhat_drive-mirror. downstream command __com.redhat_drive-mirror.
=== Configuring the schema === Configuring the schema
----------------------
Syntax::
Syntax:
COND = STRING COND = STRING
| [ STRING, ... ] | [ STRING, ... ]
@ -788,12 +821,12 @@ string or a list of strings. A string is shorthand for a list
containing just that string. The code generated for the definition containing just that string. The code generated for the definition
will then be guarded by #if STRING for each STRING in the COND list. will then be guarded by #if STRING for each STRING in the COND list.
Example: a conditional struct Example: a conditional struct ::
{ 'struct': 'IfStruct', 'data': { 'foo': 'int' }, { 'struct': 'IfStruct', 'data': { 'foo': 'int' },
'if': ['defined(CONFIG_FOO)', 'defined(HAVE_BAR)'] } 'if': ['defined(CONFIG_FOO)', 'defined(HAVE_BAR)'] }
gets its generated code guarded like this: gets its generated code guarded like this::
#if defined(CONFIG_FOO) #if defined(CONFIG_FOO)
#if defined(HAVE_BAR) #if defined(HAVE_BAR)
@ -806,7 +839,7 @@ event-specific data can also be made conditional. This requires the
longhand form of MEMBER. longhand form of MEMBER.
Example: a struct type with unconditional member 'foo' and conditional Example: a struct type with unconditional member 'foo' and conditional
member 'bar' member 'bar' ::
{ 'struct': 'IfStruct', 'data': { 'struct': 'IfStruct', 'data':
{ 'foo': 'int', { 'foo': 'int',
@ -818,7 +851,7 @@ Likewise, individual enumeration values be conditional. This requires
the longhand form of ENUM-VALUE. the longhand form of ENUM-VALUE.
Example: an enum type with unconditional value 'foo' and conditional Example: an enum type with unconditional value 'foo' and conditional
value 'bar' value 'bar' ::
{ 'enum': 'IfEnum', 'data': { 'enum': 'IfEnum', 'data':
[ 'foo', [ 'foo',
@ -827,7 +860,7 @@ value 'bar'
Likewise, features can be conditional. This requires the longhand Likewise, features can be conditional. This requires the longhand
form of FEATURE. form of FEATURE.
Example: a struct with conditional feature 'allow-negative-numbers' Example: a struct with conditional feature 'allow-negative-numbers' ::
{ 'struct': 'TestType', { 'struct': 'TestType',
'data': { 'number': 'int' }, 'data': { 'number': 'int' },
@ -843,12 +876,13 @@ shows a conditional entity only when the condition is satisfied in
this particular build. this particular build.
=== Documentation comments === Documentation comments
----------------------
A multi-line comment that starts and ends with a '##' line is a A multi-line comment that starts and ends with a '##' line is a
documentation comment. documentation comment.
If the documentation comment starts like If the documentation comment starts like ::
## ##
# @SYMBOL: # @SYMBOL:
@ -861,10 +895,12 @@ See below for more on definition documentation.
Free-form documentation may be used to provide additional text and Free-form documentation may be used to provide additional text and
structuring content. structuring content.
==== Headings and subheadings ====
Headings and subheadings
~~~~~~~~~~~~~~~~~~~~~~~~
A free-form documentation comment containing a line which starts with A free-form documentation comment containing a line which starts with
some '=' symbols and then a space defines a section heading: some '=' symbols and then a space defines a section heading::
## ##
# = This is a top level heading # = This is a top level heading
@ -883,17 +919,19 @@ comment block.
Section headings must always be correctly nested, so you can only Section headings must always be correctly nested, so you can only
define a third-level heading inside a second-level heading, and so on. define a third-level heading inside a second-level heading, and so on.
==== Documentation markup ====
Documentation markup
~~~~~~~~~~~~~~~~~~~~
Documentation comments can use most rST markup. In particular, Documentation comments can use most rST markup. In particular,
a '::' literal block can be used for examples: a '::' literal block can be used for examples::
# :: # ::
# #
# Text of the example, may span # Text of the example, may span
# multiple lines # multiple lines
'*' starts an itemized list: '*' starts an itemized list::
# * First item, may span # * First item, may span
# multiple lines # multiple lines
@ -901,7 +939,7 @@ a '::' literal block can be used for examples:
You can also use '-' instead of '*'. You can also use '-' instead of '*'.
A decimal number followed by '.' starts a numbered list: A decimal number followed by '.' starts a numbered list::
# 1. First item, may span # 1. First item, may span
# multiple lines # multiple lines
@ -920,7 +958,7 @@ 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 can also use '@foo' to reference a name in the schema; this is
rendered the same way as '``foo``'. rendered the same way as '``foo``'.
Example: Example::
## ##
# Some text foo with **bold** and *emphasis* # Some text foo with **bold** and *emphasis*
@ -937,7 +975,8 @@ Example:
## ##
==== Definition documentation ==== Definition documentation
~~~~~~~~~~~~~~~~~~~~~~~~
Definition documentation, if present, must immediately precede the Definition documentation, if present, must immediately precede the
definition it documents. definition it documents.
@ -956,7 +995,7 @@ text can start on the line following the '@argname:', in which case it
must not be indented at all. It can also start on the same line as must not be indented at all. It can also start on the same line as
the '@argname:'. In this case if it spans multiple lines then second the '@argname:'. In this case if it spans multiple lines then second
and subsequent lines must be indented to line up with the first and subsequent lines must be indented to line up with the first
character of the first line of the description: character of the first line of the description::
# @argone: # @argone:
# This is a two line description # This is a two line description
@ -997,7 +1036,7 @@ An 'Example' or 'Examples' section is automatically rendered
entirely as literal fixed-width text. In other sections, entirely as literal fixed-width text. In other sections,
the text is formatted, and rST markup can be used. the text is formatted, and rST markup can be used.
For example: For example::
## ##
# @BlockStats: # @BlockStats:
@ -1042,7 +1081,8 @@ For example:
'returns': ['BlockStats'] } 'returns': ['BlockStats'] }
== Client JSON Protocol introspection == Client JSON Protocol introspection
==================================
Clients of a Client JSON Protocol commonly need to figure out what Clients of a Client JSON Protocol commonly need to figure out what
exactly the server (QEMU) supports. exactly the server (QEMU) supports.
@ -1114,7 +1154,7 @@ If the command takes no arguments, "arg-type" names an object type
without members. Likewise, if the command returns nothing, "ret-type" without members. Likewise, if the command returns nothing, "ret-type"
names an object type without members. names an object type without members.
Example: the SchemaInfo for command query-qmp-schema Example: the SchemaInfo for command query-qmp-schema ::
{ "name": "query-qmp-schema", "meta-type": "command", { "name": "query-qmp-schema", "meta-type": "command",
"arg-type": "q_empty", "ret-type": "SchemaInfoList" } "arg-type": "q_empty", "ret-type": "SchemaInfoList" }
@ -1133,7 +1173,7 @@ the wire then.
Each command or event defined with 'data' as MEMBERS object in the Each command or event defined with 'data' as MEMBERS object in the
QAPI schema implicitly defines an object type. QAPI schema implicitly defines an object type.
Example: the SchemaInfo for EVENT_C from section Events Example: the SchemaInfo for EVENT_C from section Events ::
{ "name": "EVENT_C", "meta-type": "event", { "name": "EVENT_C", "meta-type": "event",
"arg-type": "q_obj-EVENT_C-arg" } "arg-type": "q_obj-EVENT_C-arg" }
@ -1157,7 +1197,7 @@ extensions. The "members" array is in no particular order; clients
must search the entire object when learning whether a particular must search the entire object when learning whether a particular
member is supported. member is supported.
Example: the SchemaInfo for MyType from section Struct types Example: the SchemaInfo for MyType from section Struct types ::
{ "name": "MyType", "meta-type": "object", { "name": "MyType", "meta-type": "object",
"members": [ "members": [
@ -1168,7 +1208,7 @@ Example: the SchemaInfo for MyType from section Struct types
"features" exposes the command's feature strings as a JSON array of "features" exposes the command's feature strings as a JSON array of
strings. strings.
Example: the SchemaInfo for TestType from section Features: Example: the SchemaInfo for TestType from section Features::
{ "name": "TestType", "meta-type": "object", { "name": "TestType", "meta-type": "object",
"members": [ "members": [
@ -1184,7 +1224,7 @@ that provides the variant members for this type tag value). The
list cases in the same order as the corresponding "tag" enum type. list cases in the same order as the corresponding "tag" enum type.
Example: the SchemaInfo for flat union BlockdevOptions from section Example: the SchemaInfo for flat union BlockdevOptions from section
Union types Union types ::
{ "name": "BlockdevOptions", "meta-type": "object", { "name": "BlockdevOptions", "meta-type": "object",
"members": [ "members": [
@ -1205,7 +1245,7 @@ A simple union implicitly defines an object type for each of its
variants. variants.
Example: the SchemaInfo for simple union BlockdevOptionsSimple from section Example: the SchemaInfo for simple union BlockdevOptionsSimple from section
Union types Union types ::
{ "name": "BlockdevOptionsSimple", "meta-type": "object", { "name": "BlockdevOptionsSimple", "meta-type": "object",
"members": [ "members": [
@ -1225,7 +1265,7 @@ 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 alternate type conform to exactly one of its member types. There is
no guarantee on the order in which "members" will be listed. no guarantee on the order in which "members" will be listed.
Example: the SchemaInfo for BlockdevRef from section Alternate types Example: the SchemaInfo for BlockdevRef from section Alternate types ::
{ "name": "BlockdevRef", "meta-type": "alternate", { "name": "BlockdevRef", "meta-type": "alternate",
"members": [ "members": [
@ -1239,7 +1279,7 @@ resemble the element type; however, clients should examine member
"element-type" instead of making assumptions based on parsing member "element-type" instead of making assumptions based on parsing member
"name". "name".
Example: the SchemaInfo for ['str'] Example: the SchemaInfo for ['str'] ::
{ "name": "[str]", "meta-type": "array", { "name": "[str]", "meta-type": "array",
"element-type": "str" } "element-type": "str" }
@ -1249,7 +1289,7 @@ variant member "values". The values are listed in no particular
order; clients must search the entire enum when learning whether a order; clients must search the entire enum when learning whether a
particular value is supported. particular value is supported.
Example: the SchemaInfo for MyEnum from section Enumeration types Example: the SchemaInfo for MyEnum from section Enumeration types ::
{ "name": "MyEnum", "meta-type": "enum", { "name": "MyEnum", "meta-type": "enum",
"values": [ "value1", "value2", "value3" ] } "values": [ "value1", "value2", "value3" ] }
@ -1259,7 +1299,7 @@ the QAPI schema (see section Built-in Types), with one exception
detailed below. It has variant member "json-type" that shows how detailed below. It has variant member "json-type" that shows how
values of this type are encoded on the wire. values of this type are encoded on the wire.
Example: the SchemaInfo for str Example: the SchemaInfo for str ::
{ "name": "str", "meta-type": "builtin", "json-type": "string" } { "name": "str", "meta-type": "builtin", "json-type": "string" }
@ -1273,7 +1313,8 @@ the names of built-in types. Clients should examine member
"json-type" instead of hard-coding names of built-in types. "json-type" instead of hard-coding names of built-in types.
== Compatibility considerations == Compatibility considerations
============================
Maintaining backward compatibility at the Client JSON Protocol level Maintaining backward compatibility at the Client JSON Protocol level
while evolving the schema requires some care. This section is about while evolving the schema requires some care. This section is about
@ -1333,7 +1374,8 @@ may be freely renamed. Even certain refactorings are invisible, such
as splitting members from one type into a common base type. as splitting members from one type into a common base type.
== Code generation == Code generation
===============
The QAPI code generator qapi-gen.py generates code and documentation The QAPI code generator qapi-gen.py generates code and documentation
from the schema. Together with the core QAPI libraries, this code from the schema. Together with the core QAPI libraries, this code
@ -1347,7 +1389,7 @@ As an example, we'll use the following schema, which describes a
single complex user-defined type, along with command which takes 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 list of that type as a parameter, and returns a single element of that
type. The user is responsible for writing the implementation of type. The user is responsible for writing the implementation of
qmp_my_command(); everything else is produced by the generator. qmp_my_command(); everything else is produced by the generator. ::
$ cat example-schema.json $ cat example-schema.json
{ 'struct': 'UserDefOne', { 'struct': 'UserDefOne',
@ -1359,7 +1401,7 @@ qmp_my_command(); everything else is produced by the generator.
{ 'event': 'MY_EVENT' } { 'event': 'MY_EVENT' }
We run qapi-gen.py like this: We run qapi-gen.py like this::
$ python scripts/qapi-gen.py --output-dir="qapi-generated" \ $ python scripts/qapi-gen.py --output-dir="qapi-generated" \
--prefix="example-" example-schema.json --prefix="example-" example-schema.json
@ -1369,21 +1411,24 @@ tests/qapi-schema/qapi-schema-tests.json that covers more examples of
what the generator will accept, and compiles the resulting C code as what the generator will accept, and compiles the resulting C code as
part of 'make check-unit'. part of 'make check-unit'.
=== Code generated for QAPI types ===
Code generated for QAPI types
-----------------------------
The following files are created: The following files are created:
$(prefix)qapi-types.h - C types corresponding to types defined in ``$(prefix)qapi-types.h``
the schema C types corresponding to types defined in the schema
$(prefix)qapi-types.c - Cleanup functions for the above C types ``$(prefix)qapi-types.c``
Cleanup functions for the above C types
The $(prefix) is an optional parameter used as a namespace to keep the 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 generated code from one schema/code-generation separated from others so code
can be generated/used from multiple schemas without clobbering previously can be generated/used from multiple schemas without clobbering previously
created code. created code.
Example: Example::
$ cat qapi-generated/example-qapi-types.h $ cat qapi-generated/example-qapi-types.h
[Uninteresting stuff omitted...] [Uninteresting stuff omitted...]
@ -1453,7 +1498,7 @@ Example:
[Uninteresting stuff omitted...] [Uninteresting stuff omitted...]
For a modular QAPI schema (see section Include directives), code for For a modular QAPI schema (see section Include directives), code for
each sub-module SUBDIR/SUBMODULE.json is actually generated into each sub-module SUBDIR/SUBMODULE.json is actually generated into ::
SUBDIR/$(prefix)qapi-types-SUBMODULE.h SUBDIR/$(prefix)qapi-types-SUBMODULE.h
SUBDIR/$(prefix)qapi-types-SUBMODULE.c SUBDIR/$(prefix)qapi-types-SUBMODULE.c
@ -1461,11 +1506,15 @@ SUBDIR/$(prefix)qapi-types-SUBMODULE.c
If qapi-gen.py is run with option --builtins, additional files are If qapi-gen.py is run with option --builtins, additional files are
created: created:
qapi-builtin-types.h - C types corresponding to built-in types ``qapi-builtin-types.h``
C types corresponding to built-in types
qapi-builtin-types.c - Cleanup functions for the above C types ``qapi-builtin-types.c``
Cleanup functions for the above C types
=== Code generated for visiting QAPI types ===
Code generated for visiting QAPI types
--------------------------------------
These are the visitor functions used to walk through and convert These are the visitor functions used to walk through and convert
between a native QAPI C data structure and some other format (such as between a native QAPI C data structure and some other format (such as
@ -1474,16 +1523,15 @@ visit_type_FOO_members().
The following files are generated: The following files are generated:
$(prefix)qapi-visit.c: Visitor function for a particular C type, used ``$(prefix)qapi-visit.c``
to automagically convert QObjects into the Visitor function for a particular C type, used to automagically
corresponding C type and vice-versa, as well convert QObjects into the corresponding C type and vice-versa, as
as for deallocating memory for an existing C well as for deallocating memory for an existing C type
type
$(prefix)qapi-visit.h: Declarations for previously mentioned visitor ``$(prefix)qapi-visit.h``
functions Declarations for previously mentioned visitor functions
Example: Example::
$ cat qapi-generated/example-qapi-visit.h $ cat qapi-generated/example-qapi-visit.h
[Uninteresting stuff omitted...] [Uninteresting stuff omitted...]
@ -1588,7 +1636,7 @@ Example:
[Uninteresting stuff omitted...] [Uninteresting stuff omitted...]
For a modular QAPI schema (see section Include directives), code for For a modular QAPI schema (see section Include directives), code for
each sub-module SUBDIR/SUBMODULE.json is actually generated into each sub-module SUBDIR/SUBMODULE.json is actually generated into ::
SUBDIR/$(prefix)qapi-visit-SUBMODULE.h SUBDIR/$(prefix)qapi-visit-SUBMODULE.h
SUBDIR/$(prefix)qapi-visit-SUBMODULE.c SUBDIR/$(prefix)qapi-visit-SUBMODULE.c
@ -1596,11 +1644,15 @@ SUBDIR/$(prefix)qapi-visit-SUBMODULE.c
If qapi-gen.py is run with option --builtins, additional files are If qapi-gen.py is run with option --builtins, additional files are
created: created:
qapi-builtin-visit.h - Visitor functions for built-in types ``qapi-builtin-visit.h``
Visitor functions for built-in types
qapi-builtin-visit.c - Declarations for these visitor functions ``qapi-builtin-visit.c``
Declarations for these visitor functions
=== Code generated for commands ===
Code generated for commands
---------------------------
These are the marshaling/dispatch functions for the commands defined These are the marshaling/dispatch functions for the commands defined
in the schema. The generated code provides qmp_marshal_COMMAND(), and in the schema. The generated code provides qmp_marshal_COMMAND(), and
@ -1608,17 +1660,20 @@ declares qmp_COMMAND() that the user must implement.
The following files are generated: The following files are generated:
$(prefix)qapi-commands.c: Command marshal/dispatch functions for each ``$(prefix)qapi-commands.c``
QMP command defined in the schema Command marshal/dispatch functions for each QMP command defined in
the schema
$(prefix)qapi-commands.h: Function prototypes for the QMP commands ``$(prefix)qapi-commands.h``
specified in the schema Function prototypes for the QMP commands specified in the schema
$(prefix)qapi-init-commands.h - Command initialization prototype ``$(prefix)qapi-init-commands.h``
Command initialization prototype
$(prefix)qapi-init-commands.c - Command initialization code ``$(prefix)qapi-init-commands.c``
Command initialization code
Example: Example::
$ cat qapi-generated/example-qapi-commands.h $ cat qapi-generated/example-qapi-commands.h
[Uninteresting stuff omitted...] [Uninteresting stuff omitted...]
@ -1711,28 +1766,33 @@ Example:
[Uninteresting stuff omitted...] [Uninteresting stuff omitted...]
For a modular QAPI schema (see section Include directives), code for For a modular QAPI schema (see section Include directives), code for
each sub-module SUBDIR/SUBMODULE.json is actually generated into each sub-module SUBDIR/SUBMODULE.json is actually generated into::
SUBDIR/$(prefix)qapi-commands-SUBMODULE.h SUBDIR/$(prefix)qapi-commands-SUBMODULE.h
SUBDIR/$(prefix)qapi-commands-SUBMODULE.c SUBDIR/$(prefix)qapi-commands-SUBMODULE.c
=== Code generated for events ===
Code generated for events
-------------------------
This is the code related to events defined in the schema, providing This is the code related to events defined in the schema, providing
qapi_event_send_EVENT(). qapi_event_send_EVENT().
The following files are created: The following files are created:
$(prefix)qapi-events.h - Function prototypes for each event type ``$(prefix)qapi-events.h``
Function prototypes for each event type
$(prefix)qapi-events.c - Implementation of functions to send an event ``$(prefix)qapi-events.c``
Implementation of functions to send an event
$(prefix)qapi-emit-events.h - Enumeration of all event names, and ``$(prefix)qapi-emit-events.h``
common event code declarations Enumeration of all event names, and common event code declarations
$(prefix)qapi-emit-events.c - Common event code definitions ``$(prefix)qapi-emit-events.c``
Common event code definitions
Example: Example::
$ cat qapi-generated/example-qapi-events.h $ cat qapi-generated/example-qapi-events.h
[Uninteresting stuff omitted...] [Uninteresting stuff omitted...]
@ -1795,21 +1855,24 @@ Example:
[Uninteresting stuff omitted...] [Uninteresting stuff omitted...]
For a modular QAPI schema (see section Include directives), code for For a modular QAPI schema (see section Include directives), code for
each sub-module SUBDIR/SUBMODULE.json is actually generated into each sub-module SUBDIR/SUBMODULE.json is actually generated into ::
SUBDIR/$(prefix)qapi-events-SUBMODULE.h SUBDIR/$(prefix)qapi-events-SUBMODULE.h
SUBDIR/$(prefix)qapi-events-SUBMODULE.c SUBDIR/$(prefix)qapi-events-SUBMODULE.c
=== Code generated for introspection ===
Code generated for introspection
--------------------------------
The following files are created: The following files are created:
$(prefix)qapi-introspect.c - Defines a string holding a JSON ``$(prefix)qapi-introspect.c``
description of the schema Defines a string holding a JSON description of the schema
$(prefix)qapi-introspect.h - Declares the above string ``$(prefix)qapi-introspect.h``
Declares the above string
Example: Example::
$ cat qapi-generated/example-qapi-introspect.h $ cat qapi-generated/example-qapi-introspect.h
[Uninteresting stuff omitted...] [Uninteresting stuff omitted...]