qapi: Reserve '*List' type names for list types

[qemu.git] / docs / qapi-code-gen.txt

diff --git a/docs/qapi-code-gen.txt b/docs/qapi-code-gen.txt
index a6197a9133f2c5ceae4c3bef3ebb8b4f2c52740d..c4264a819b5620233c2d18b10dfe4c088b5814d0 100644 (file)
--- a/docs/qapi-code-gen.txt
+++ b/docs/qapi-code-gen.txt
@@ -1,66 +1,199 @@
 = How to use the QAPI code generator =
 
 = How to use the QAPI code generator =
 

-* Note: as of this writing, QMP does not use QAPI. Eventually QMP
-commands will be converted to use QAPI internally. The following
-information describes QMP/QAPI as it will exist after the
-conversion.
+Copyright IBM Corp. 2011
+Copyright (C) 2012-2015 Red Hat, Inc.

 
 

-QAPI is a native C API within QEMU which provides management-level
-functionality to internal/external users. For external
-users/processes, this interface is made available by a JSON-based
-QEMU Monitor protocol that is provided by the QMP server.
-
-To map QMP-defined interfaces to the native C QAPI implementations,
-a JSON-based schema is used to define types and function
-signatures, and a set of scripts is used to generate types/signatures,
-and marshaling/dispatch code. The QEMU Guest Agent also uses these
-scripts, paired with a separate schema, to generate
-marshaling/dispatch code for the guest agent server running in the
-guest.
-
-This document will describe how the schemas, scripts, and resulting
-code is used.
+This work is licensed under the terms of the GNU GPL, version 2 or
+later. See the COPYING file in the top-level directory.

 
 

+== Introduction ==

 
 

-== QMP/Guest agent schema ==
-
-This file defines the types, commands, and events used by QMP.  It should
-fully describe the interface used by QMP.
+QAPI is a native C API within QEMU which provides management-level
+functionality to internal and external users. For external
+users/processes, this interface is made available by a JSON-based wire
+format for the QEMU Monitor Protocol (QMP) for controlling qemu, as
+well as the QEMU Guest Agent (QGA) for communicating with the guest.
+The remainder of this document uses "Client JSON Protocol" when
+referring to the wire contents of a QMP or QGA connection.

 
 

-This file is designed to be loosely based on JSON although it's technically
-executable Python.  While dictionaries are used, they are parsed as
-OrderedDicts so that ordering is preserved.
+To map Client JSON Protocol interfaces to the native C QAPI
+implementations, a JSON-based schema is used to define types and
+function signatures, and a set of scripts is used to generate types,
+signatures, and marshaling/dispatch code. This document will describe
+how the schemas, scripts, and resulting code are used.

 
 

-There are two basic syntaxes used, type definitions and command definitions.

 
 

-The first syntax defines a type and is represented by a dictionary.  There are
-three kinds of user-defined types that are supported: complex types,
-enumeration types and union types.
+== QMP/Guest agent schema ==

 
 

-Generally speaking, types definitions should always use CamelCase for the type
-names. Command names should be all lower case with words separated by a hyphen.
+A QAPI schema file is designed to be loosely based on JSON
+(http://www.ietf.org/rfc/rfc7159.txt) with changes for quoting style
+and the use of comments; a QAPI schema file is then parsed by a python
+code generation program.  A valid QAPI schema consists of a series of
+top-level expressions, with no commas between them.  Where
+dictionaries (JSON objects) are used, they are parsed as python
+OrderedDicts so that ordering is preserved (for predictable layout of
+generated C structs and parameter lists).  Ordering doesn't matter
+between top-level expressions or the keys within an expression, but
+does matter within dictionary values for 'data' and 'returns' members
+of a single expression.  QAPI schema input is written using 'single
+quotes' instead of JSON's "double quotes" (in contrast, Client JSON
+Protocol uses no comments, and while input accepts 'single quotes' as
+an extension, output is strict JSON using only "double quotes").  As
+in JSON, trailing commas are not permitted in arrays or dictionaries.
+Input must be ASCII (although QMP supports full Unicode strings, the
+QAPI parser does not).  At present, there is no place where a QAPI
+schema requires the use of JSON numbers or null.
+
+Comments are allowed; anything between an unquoted # and the following
+newline is ignored.  Although there is not yet a documentation
+generator, a form of stylized comments has developed for consistently
+documenting details about an expression and when it was added to the
+schema.  The documentation is delimited between two lines of ##, then
+the first line names the expression, an optional overview is provided,
+then individual documentation about each member of 'data' is provided,
+and finally, a 'Since: x.y.z' tag lists the release that introduced
+the expression.  Optional fields are tagged with the phrase
+'#optional', often with their default value; and extensions added
+after the expression was first released are also given a '(since
+x.y.z)' comment.  For example:
+
+    ##
+    # @BlockStats:
+    #
+    # Statistics of a virtual block device or a block backing device.
+    #
+    # @device: #optional If the stats are for a virtual block device, the name
+    #          corresponding to the virtual block device.
+    #
+    # @stats:  A @BlockDeviceStats for the device.
+    #
+    # @parent: #optional This describes the file block device if it has one.
+    #
+    # @backing: #optional This describes the backing block device if it has one.
+    #           (Since 2.0)
+    #
+    # Since: 0.14.0
+    ##
+    { 'struct': 'BlockStats',
+      'data': {'*device': 'str', 'stats': 'BlockDeviceStats',
+               '*parent': 'BlockStats',
+               '*backing': 'BlockStats'} }
+
+The schema sets up a series of types, as well as commands and events
+that will use those types.  Forward references are allowed: the parser
+scans in two passes, where the first pass learns all type names, and
+the second validates the schema and generates the code.  This allows
+the definition of complex structs that can have mutually recursive
+types, and allows for indefinite nesting of Client JSON Protocol that
+satisfies the schema.  A type name should not be defined more than
+once.  It is permissible for the schema to contain additional types
+not used by any commands or events in the Client JSON Protocol, for
+the side effect of generated C code used internally.
+
+There are seven top-level expressions recognized by the parser:
+'include', 'command', 'struct', 'enum', 'union', 'alternate', and
+'event'.  There are several groups of types: simple types (a number of
+built-in types, such as 'int' and 'str'; as well as enumerations),
+complex types (structs and two flavors of unions), and alternate types
+(a choice between other types).  The 'command' and 'event' expressions
+can refer to existing types by name, or list an anonymous type as a
+dictionary. Listing a type name inside an array refers to a
+single-dimension array of that type; multi-dimension arrays are not
+directly supported (although an array of a complex struct that
+contains an array member is possible).
+
+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
+definitions should not end in 'Kind', as this namespace is used for
+creating implicit C enums for visiting union types, or in 'List', as
+this namespace is used for creating array types.  Command names,
+and field names within a type, should be all lower case with words
+separated by a hyphen.  However, some existing older commands and
+complex types use underscore; when extending such expressions,
+consistency is preferred over blindly avoiding underscore.  Event
+names should be ALL_CAPS with words separated by underscore.
+
+Any name (command, event, type, field, or enum value) beginning with
+"x-" is marked experimental, and may be withdrawn or changed
+incompatibly in a future release.  Downstream vendors may add
+extensions; such extensions should begin with a prefix matching
+"__RFQDN_" (for the reverse-fully-qualified-domain-name of the
+vendor), even if the rest of the name uses dash (example:
+__com.redhat_drive-mirror).  Other than downstream extensions (with
+leading underscore and the use of dots), all names should begin with a
+letter, and contain only ASCII letters, digits, dash, and underscore.
+It is okay to reuse names that match C keywords; the generator will
+rename a field named "default" in the QAPI to "q_default" in the
+generated C code.
+
+In the rest of this document, usage lines are given for each
+expression type, with literal strings written in lower case and
+placeholders written in capitals.  If a literal string includes a
+prefix of '*', that key/value pair can be omitted from the expression.
+For example, a usage statement that includes '*base':STRUCT-NAME
+means that an expression has an optional key 'base', which if present
+must have a value that forms a struct name.
+
+
+=== Built-in Types ===
+
+The following types are predefined, and map to C as follows:
+
+  Schema    C          JSON
+  str       char *     any JSON string, UTF-8
+  number    double     any JSON number
+  int       int64_t    a JSON number without fractional part
+                       that fits into the C integer type
+  int8      int8_t     likewise
+  int16     int16_t    likewise
+  int32     int32_t    likewise
+  int64     int64_t    likewise
+  uint8     uint8_t    likewise
+  uint16    uint16_t   likewise
+  uint32    uint32_t   likewise
+  uint64    uint64_t   likewise
+  size      uint64_t   like uint64_t, except StringInputVisitor
+                       accepts size suffixes
+  bool      bool       JSON true or false
+  any       QObject *  any JSON value

 
 
 === Includes ===
 
 
 
 === Includes ===
 

+Usage: { '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' }

 
 The directive is evaluated recursively, and include paths are relative to the
 
 The directive is evaluated recursively, and include paths are relative to the

-file using the directive. Multiple includes of the same file are safe.
+file using the directive. Multiple includes of the same file are
+idempotent.  No other keys should appear in the expression, and the include
+value should be a string.
+
+As a matter of style, it is a good idea to have all files be
+self-contained, but at the moment, nothing prevents an included file
+from making a forward reference to a type that is only introduced by
+an outer file.  The parser may be made stricter in the future to
+prevent incomplete include files.
+

 
 

+=== Struct types ===

 
 

-=== Complex types ===
+Usage: { 'struct': STRING, 'data': DICT, '*base': STRUCT-NAME }

 
 

-A complex type is a dictionary containing a single key whose value is a
-dictionary.  This corresponds to a struct in C or an Object in JSON.  An
-example of a complex type is:
+A struct is a dictionary containing a single 'data' key whose
+value is a dictionary.  This corresponds to a struct in C or an Object
+in JSON. Each value of the 'data' dictionary must be the name of a
+type, or a one-element array containing a type name.  An example of a
+struct is:

 
 

- { 'type': 'MyType',
+ { 'struct': 'MyType',

    'data': { 'member1': 'str', 'member2': 'int', '*member3': 'str' } }
 
    'data': { 'member1': 'str', 'member2': 'int', '*member3': 'str' } }
 

-The use of '*' as a prefix to the name means the member is optional.
+The use of '*' as a prefix to the name means the member is optional in
+the corresponding JSON protocol usage.

 
 The default initialization value of an optional argument should not be changed
 between versions of QEMU unless the new default maintains backward
 
 The default initialization value of an optional argument should not be changed
 between versions of QEMU unless the new default maintains backward


@@ -89,13 +222,13 @@ A structure that is used in both input and output of various commands
 must consider the backwards compatibility constraints of both directions
 of use.
 
 must consider the backwards compatibility constraints of both directions
 of use.
 

-A complex type definition can specify another complex type as its base.
+A struct definition can specify another struct as its base.

 In this case, the fields of the base type are included as top-level fields
 In this case, the fields of the base type are included as top-level fields

-of the new complex type's dictionary in the QMP wire format. An example
-definition is:
+of the new struct's dictionary in the Client JSON Protocol wire
+format. An example definition is:

 
 

- { 'type': 'BlockdevOptionsGenericFormat', 'data': { 'file': 'str' } }
- { 'type': 'BlockdevOptionsGenericCOWFormat',
+ { 'struct': 'BlockdevOptionsGenericFormat', 'data': { 'file': 'str' } }
+ { 'struct': 'BlockdevOptionsGenericCOWFormat',

    'base': 'BlockdevOptionsGenericFormat',
    'data': { '*backing': 'str' } }
 
    'base': 'BlockdevOptionsGenericFormat',
    'data': { '*backing': 'str' } }
 


@@ -105,97 +238,165 @@ both fields like this:
  { "file": "/some/place/my-image",
    "backing": "/some/place/my-backing-file" }
 
  { "file": "/some/place/my-image",
    "backing": "/some/place/my-backing-file" }
 

+

 === Enumeration types ===
 
 === Enumeration types ===
 

-An enumeration type is a dictionary containing a single key whose value is a
-list of strings.  An example enumeration is:
+Usage: { 'enum': STRING, 'data': ARRAY-OF-STRING }
+       { 'enum': STRING, '*prefix': STRING, 'data': ARRAY-OF-STRING }
+
+An enumeration type is a dictionary containing a single 'data' key
+whose value is a list of strings.  An example enumeration is:

 
  { 'enum': 'MyEnum', 'data': [ 'value1', 'value2', 'value3' ] }
 
 
  { 'enum': 'MyEnum', 'data': [ 'value1', 'value2', 'value3' ] }
 

+Nothing prevents an empty enumeration, although it is probably not
+useful.  The list of strings should be lower case; if an enum name
+represents multiple words, use '-' between words.  The string 'max' is
+not allowed as an enum value, and values should not be repeated.
+
+The enum constants will be named by using a heuristic to turn the
+type name into a set of underscore separated words. For the example
+above, 'MyEnum' will turn into 'MY_ENUM' giving a constant name
+of 'MY_ENUM_VALUE1' for the first value. If the default heuristic
+does not result in a desirable name, the optional 'prefix' field
+can be used when defining the enum.
+
+The enumeration values are passed as strings over the Client JSON
+Protocol, but are encoded as C enum integral values in generated code.
+While the C code starts numbering at 0, it is better to use explicit
+comparisons to enum values than implicit comparisons to 0; the C code
+will also include a generated enum member ending in _MAX for tracking
+the size of the enum, useful when using common functions for
+converting between strings and enum values.  Since the wire format
+always passes by name, it is acceptable to reorder or add new
+enumeration members in any location without breaking clients of Client
+JSON Protocol; however, removing enum values would break
+compatibility.  For any struct that has a field that will only contain
+a finite set of string values, using an enum type for that field is
+better than open-coding the field to be type 'str'.
+
+

 === Union types ===
 
 === Union types ===
 

-Union types are used to let the user choose between several different data
-types.  A union type is defined using a dictionary as explained in the
-following paragraphs.
+Usage: { 'union': STRING, 'data': DICT }
+or:    { 'union': STRING, 'data': DICT, 'base': STRUCT-NAME,
+         'discriminator': ENUM-MEMBER-OF-BASE }

 
 

+Union types are used to let the user choose between several different
+variants for an object.  There are two flavors: simple (no
+discriminator or base), flat (both discriminator and base).  A union
+type is defined using a data dictionary as explained in the following
+paragraphs.

 
 

-A simple union type defines a mapping from discriminator values to data types
-like in this example:
+A simple union type defines a mapping from automatic discriminator
+values to data types like in this example:

 
 

- { 'type': 'FileOptions', 'data': { 'filename': 'str' } }
- { 'type': 'Qcow2Options',
+ { 'struct': 'FileOptions', 'data': { 'filename': 'str' } }
+ { 'struct': 'Qcow2Options',

    'data': { 'backing-file': 'str', 'lazy-refcounts': 'bool' } }
 
  { 'union': 'BlockdevOptions',
    'data': { 'file': 'FileOptions',
              'qcow2': 'Qcow2Options' } }
 
    'data': { 'backing-file': 'str', 'lazy-refcounts': 'bool' } }
 
  { 'union': 'BlockdevOptions',
    'data': { 'file': 'FileOptions',
              'qcow2': 'Qcow2Options' } }
 

-In the QMP wire format, a simple union is represented by a dictionary that
-contains the 'type' field as a discriminator, and a 'data' field that is of the
-specified data type corresponding to the discriminator value:
+In the Client JSON Protocol, a simple union is represented by a
+dictionary that contains the 'type' field as a discriminator, and a
+'data' field that is of the specified data type corresponding to the
+discriminator value, as in these examples:

 
 

+ { "type": "file", "data" : { "filename": "/some/place/my-image" } }

  { "type": "qcow2", "data" : { "backing-file": "/some/place/my-image",
                                "lazy-refcounts": true } }
 
  { "type": "qcow2", "data" : { "backing-file": "/some/place/my-image",
                                "lazy-refcounts": true } }
 

-
-A union definition can specify a complex type as its base. In this case, the
-fields of the complex type are included as top-level fields of the union
-dictionary in the QMP wire format. An example definition is:
-
- { 'type': 'BlockdevCommonOptions', 'data': { 'readonly': 'bool' } }
+The generated C code uses a struct containing a union. Additionally,
+an implicit C enum 'NameKind' is created, corresponding to the union
+'Name', for accessing the various branches of the union.  No branch of
+the union can be named 'max', as this would collide with the implicit
+enum.  The value for each branch can be of any type.
+
+A flat union definition specifies a struct as its base, and
+avoids nesting on the wire.  All branches of the union must be
+complex types, and the top-level fields of the union dictionary on
+the wire will be combination of fields from both the base type and the
+appropriate branch type (when merging two dictionaries, there must be
+no keys in common).  The 'discriminator' field must be the name of an
+enum-typed member of the base struct.
+
+The following example enhances the above simple union example by
+adding a common field 'readonly', renaming the discriminator to
+something more applicable, and reducing the number of {} required on
+the wire:
+
+ { 'enum': 'BlockdevDriver', 'data': [ 'file', 'qcow2' ] }
+ { 'struct': 'BlockdevCommonOptions',
+   'data': { 'driver': 'BlockdevDriver', 'readonly': 'bool' } }

  { 'union': 'BlockdevOptions',
    'base': 'BlockdevCommonOptions',
  { 'union': 'BlockdevOptions',
    'base': 'BlockdevCommonOptions',

-   'data': { 'raw': 'RawOptions',
+   'discriminator': 'driver',
+   'data': { 'file': 'FileOptions',

              'qcow2': 'Qcow2Options' } }
 
              'qcow2': 'Qcow2Options' } }
 

-And it looks like this on the wire:
+Resulting in these JSON objects:

 
 

- { "type": "qcow2",
-   "readonly": false,
-   "data" : { "backing-file": "/some/place/my-image",
-              "lazy-refcounts": true } }
+ { "driver": "file", "readonly": true,
+   "filename": "/some/place/my-image" }
+ { "driver": "qcow2", "readonly": false,
+   "backing-file": "/some/place/my-image", "lazy-refcounts": true }

 
 

+Notice that in a flat union, the discriminator name is controlled by
+the user, but because it must map to a base member with enum type, the
+code generator can ensure that branches exist for all values of the
+enum (although the order of the keys need not match the declaration of
+the enum).  In the resulting generated C data types, a flat union is
+represented as a struct with the base member fields included directly,
+and then a union of structures for each branch of the struct.

 
 

-Flat union types avoid the nesting on the wire. They are used whenever a
-specific field of the base type is declared as the discriminator ('type' is
-then no longer generated). The discriminator must be of enumeration type.
-The above example can then be modified as follows:
+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
+union has a struct with a single member named 'data'.  That is,

 
 

- { 'enum': 'BlockdevDriver', 'data': [ 'raw', 'qcow2' ] }
- { 'type': 'BlockdevCommonOptions',
-   'data': { 'driver': 'BlockdevDriver', 'readonly': 'bool' } }
- { 'union': 'BlockdevOptions',
-   'base': 'BlockdevCommonOptions',
-   'discriminator': 'driver',
-   'data': { 'raw': 'RawOptions',
-             'qcow2': 'Qcow2Options' } }
+ { 'union': 'Simple', 'data': { 'one': 'str', 'two': 'int' } }

 
 

-Resulting in this JSON object:
+is identical on the wire to:
+
+ { 'enum': 'Enum', 'data': ['one', 'two'] }
+ { 'struct': 'Base', 'data': { 'type': 'Enum' } }
+ { 'struct': 'Branch1', 'data': { 'data': 'str' } }
+ { 'struct': 'Branch2', 'data': { 'data': 'int' } }
+ { 'union': 'Flat', 'base': 'Base', 'discriminator': 'type',
+   'data': { 'one': 'Branch1', 'two': 'Branch2' } }

 
 

- { "driver": "qcow2",
-   "readonly": false,
-   "backing-file": "/some/place/my-image",
-   "lazy-refcounts": true }

 
 

+=== Alternate types ===

 
 

-A special type of unions are anonymous unions. They don't form a dictionary in
-the wire format but allow the direct use of different types in their place. As
-they aren't structured, they don't have any explicit discriminator but use
-the (QObject) data type of their value as an implicit discriminator. This means
-that they are restricted to using only one discriminator value per QObject
-type. For example, you cannot have two different complex types in an anonymous
-union, or two different integer types.
+Usage: { 'alternate': STRING, 'data': DICT }

 
 

-Anonymous unions are declared using an empty dictionary as their discriminator.
-The discriminator values never appear on the wire, they are only used in the
-generated C code. Anonymous unions cannot have a base type.
+An alternate type is one that allows a choice between two or more JSON
+data types (string, integer, number, or object, but currently not
+array) on the wire.  The definition is similar to a simple union type,
+where each branch of the union names a QAPI type.  For example:

 
 

- { 'union': 'BlockRef',
-   'discriminator': {},
+ { 'alternate': 'BlockRef',

    'data': { 'definition': 'BlockdevOptions',
              'reference': 'str' } }
 
    'data': { 'definition': 'BlockdevOptions',
              'reference': 'str' } }
 

-This example allows using both of the following example objects:
+Just like for a simple union, an implicit C enum 'NameKind' is created
+to enumerate the branches for the alternate 'Name'.
+
+Unlike a union, the discriminator string is never passed on the wire
+for the Client JSON Protocol.  Instead, the value's JSON type serves
+as an implicit discriminator, which in turn means that an alternate
+can only express a choice between types represented differently in
+JSON.  If a branch is typed as the 'bool' built-in, the alternate
+accepts true and false; if it is typed as any of the various numeric
+built-ins, it accepts a JSON number; if it is typed as a 'str'
+built-in or named enum type, it accepts a JSON string; and if it is
+typed as a complex type (struct or union), it accepts a JSON object.
+Two different complex types, for instance, aren't permitted, because
+both are represented as a JSON object.
+
+The example alternate declaration above allows using both of the
+following example objects:

 
  { "file": "my_existing_block_device_id" }
  { "file": { "driver": "file",
 
  { "file": "my_existing_block_device_id" }
  { "file": { "driver": "file",


@@ -205,23 +406,90 @@ This example allows using both of the following example objects:
 
 === Commands ===
 
 
 === Commands ===
 

-Commands are defined by using a list containing three members.  The first
-member is the command name, the second member is a dictionary containing
-arguments, and the third member is the return type.
-
-An example command is:
+Usage: { 'command': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT,
+         '*returns': TYPE-NAME,
+         '*gen': false, '*success-response': false }
+
+Commands are defined by using a dictionary containing several members,
+where three members are most common.  The 'command' member is a
+mandatory string, and determines the "execute" value passed in a
+Client JSON Protocol command exchange.
+
+The 'data' argument maps to the "arguments" dictionary passed in as
+part of a Client JSON Protocol command.  The 'data' member is optional
+and defaults to {} (an empty dictionary).  If present, it must be the
+string name of a complex type, or a dictionary that declares an
+anonymous type with the same semantics as a 'struct' expression, with
+one exception noted below when 'gen' is used.
+
+The 'returns' member describes what will appear in the "return" field
+of a Client JSON Protocol reply on successful completion of a command.
+The member is optional from the command declaration; if absent, the
+"return" field will be an empty dictionary.  If 'returns' is present,
+it must be the string name of a complex or built-in type, a
+one-element array containing the name of a complex or built-in type,
+with one exception noted below when 'gen' is used.  Although it is
+permitted to have the 'returns' member name a built-in type or an
+array of built-in types, any command that does this cannot be extended
+to return additional information in the future; thus, new commands
+should strongly consider returning a dictionary-based type or an array
+of dictionaries, even if the dictionary only contains one field at the
+present.
+
+All commands in Client JSON Protocol use a dictionary to report
+failure, with no way to specify that in QAPI.  Where the error return
+is different than the usual GenericError class in order to help the
+client react differently to certain error conditions, it is worth
+documenting this in the comments before the command declaration.
+
+Some example commands:
+
+ { 'command': 'my-first-command',
+   'data': { 'arg1': 'str', '*arg2': 'str' } }
+ { 'struct': 'MyType', 'data': { '*value': 'str' } }
+ { 'command': 'my-second-command',
+   'returns': [ 'MyType' ] }
+
+which would validate this Client JSON Protocol transaction:
+
+ => { "execute": "my-first-command",
+      "arguments": { "arg1": "hello" } }
+ <= { "return": { } }
+ => { "execute": "my-second-command" }
+ <= { "return": [ { "value": "one" }, { } ] }
+
+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 key 'gen' with
+boolean value false, and instead write your own function.  Please try
+to avoid adding new commands that rely on this, and instead use
+type-safe unions.  For an example of this usage:
+
+ { 'command': 'netdev_add',
+   'data': {'type': 'str', 'id': 'str'},
+   'gen': false }
+
+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 a
+normal dictionary error on failure).  When a successful reply is not
+possible, the command expression should include the optional key
+'success-response' with boolean value false.  So far, only QGA makes
+use of this field.

 
 

- { 'command': 'my-command',
-   'data': { 'arg1': 'str', '*arg2': 'str' },
-   'returns': 'str' }

 
 === Events ===
 
 
 === Events ===
 

-Events are defined with the keyword 'event'.  When 'data' is also specified,
-additional info will be included in the event.  Finally there will be C API
-generated in qapi-event.h; when called by QEMU code, a message with timestamp
-will be emitted on the wire.  If timestamp is -1, it means failure to retrieve
-host time.
+Usage: { 'event': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT }
+
+Events are defined with the keyword 'event'.  It is not allowed to
+name an event 'MAX', since the generator also produces a C enumeration
+of all event names with a generated _MAX value at the end.  When
+'data' is also specified, additional info will be included in the
+event, with similar semantics to a 'struct' expression.  Finally there
+will be C API generated in qapi-event.h; when called by QEMU code, a
+message with timestamp will be emitted on the wire.

 
 An example event is:
 
 
 An example event is:
 


@@ -234,13 +502,205 @@ Resulting in this JSON object:
   "data": { "b": "test string" },
   "timestamp": { "seconds": 1267020223, "microseconds": 435656 } }
 
   "data": { "b": "test string" },
   "timestamp": { "seconds": 1267020223, "microseconds": 435656 } }
 

+
+== 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.
+
+query-qmp-schema returns a JSON array of SchemaInfo objects.  These
+objects together describe the wire ABI, as defined in the QAPI schema.
+
+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" and "meta-type", 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.
+
+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" and "ret-type".  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".
+
+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": ":empty", "ret-type": "SchemaInfoList" }
+
+    Type ":empty" is an 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 dictionary-valued 'data' 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": ":obj-EVENT_C-arg" }
+
+    Type ":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), and optionally "default".  The
+member is optional if "default" is present.  Currently, "default" can
+only have value null.  Other values are reserved for future
+extensions.
+
+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 } ] }
+
+"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).
+
+Example: the SchemaInfo for flat union BlockdevOptions from section
+Union types
+
+    { "name": "BlockdevOptions", "meta-type": "object",
+      "members": [
+          { "name": "driver", "type": "BlockdevDriver" },
+          { "name": "readonly", "type": "bool"} ],
+      "tag": "driver",
+      "variants": [
+          { "case": "file", "type": "FileOptions" },
+          { "case": "qcow2", "type": "Qcow2Options" } ] }
+
+Note that base types are "flattened": its members are included in the
+"members" array.
+
+A simple union implicitly defines an enumeration type for its implicit
+discriminator (called "type" on the wire, see section Union types).
+
+A simple union implicitly defines an object type for each of its
+variants.
+
+Example: the SchemaInfo for simple union BlockdevOptions from section
+Union types
+
+    { "name": "BlockdevOptions", "meta-type": "object",
+      "members": [
+          { "name": "kind", "type": "BlockdevOptionsKind" } ],
+      "tag": "type",
+      "variants": [
+          { "case": "file", "type": ":obj-FileOptions-wrapper" },
+          { "case": "qcow2", "type": ":obj-Qcow2Options-wrapper" } ] }
+
+    Enumeration type "BlockdevOptionsKind" and the object types
+    ":obj-FileOptions-wrapper", ":obj-Qcow2Options-wrapper" are
+    implicitly defined.
+
+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.
+
+Example: the SchemaInfo for BlockRef from section Alternate types
+
+    { "name": "BlockRef", "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.
+
+Example: the SchemaInfo for ['str']
+
+    { "name": "strList", "meta-type": "array",
+      "element-type": "str" }
+
+The SchemaInfo for an enumeration type has meta-type "enum" and
+variant member "values".
+
+Example: the SchemaInfo for MyEnum from section Enumeration types
+
+    { "name": "MyEnum", "meta-type": "enum",
+      "values": [ "value1", "value2", "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.
+
+

 == Code generation ==
 
 == Code generation ==
 

-Schemas are fed into 3 scripts to generate all the code/files that, paired
-with the core QAPI libraries, comprise everything required to take JSON
-commands read in by a QMP/guest agent server, unmarshal the arguments into
-the underlying C types, call into the corresponding C function, and map the
-response back to a QMP/guest agent response to be returned to the user.
+Schemas are fed into four scripts to generate all the code/files that,
+paired with the core QAPI libraries, comprise 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, and map the response back to a Client JSON Protocol
+response to be returned to the user.

 
 As an example, we'll use the following schema, which describes a single
 complex user-defined type (which will produce a C struct, along with a list
 
 As an example, we'll use the following schema, which describes a single
 complex user-defined type (which will produce a C struct, along with a list


@@ -249,13 +709,15 @@ case we want to accept/return a list of this type with a command), and a
 command which takes that type as a parameter and returns the same type:
 
     $ cat example-schema.json
 command which takes that type as a parameter and returns the same type:
 
     $ cat example-schema.json

-    { 'type': 'UserDefOne',
+    { 'struct': 'UserDefOne',

       'data': { 'integer': 'int', 'string': 'str' } }
 
     { 'command': 'my-command',
       'data':    {'arg1': 'UserDefOne'},
       'returns': 'UserDefOne' }
 
       'data': { 'integer': 'int', 'string': 'str' } }
 
     { 'command': 'my-command',
       'data':    {'arg1': 'UserDefOne'},
       'returns': 'UserDefOne' }
 

+    { 'event': 'MY_EVENT' }
+

 === scripts/qapi-types.py ===
 
 Used to generate the C types defined by a schema. The following files are
 === scripts/qapi-types.py ===
 
 Used to generate the C types defined by a schema. The following files are


@@ -273,69 +735,67 @@ created code.
 Example:
 
     $ python scripts/qapi-types.py --output-dir="qapi-generated" \
 Example:
 
     $ python scripts/qapi-types.py --output-dir="qapi-generated" \

-    --prefix="example-" --input-file=example-schema.json
+    --prefix="example-" example-schema.json

     $ cat qapi-generated/example-qapi-types.c
 [Uninteresting stuff omitted...]
 
     $ cat qapi-generated/example-qapi-types.c
 [Uninteresting stuff omitted...]
 

-    void qapi_free_UserDefOneList(UserDefOneList * obj)
+    void qapi_free_UserDefOne(UserDefOne *obj)

     {
     {

-        QapiDeallocVisitor *md;
+        QapiDeallocVisitor *qdv;

         Visitor *v;
 
         if (!obj) {
             return;
         }
 
         Visitor *v;
 
         if (!obj) {
             return;
         }
 

-        md = qapi_dealloc_visitor_new();
-        v = qapi_dealloc_get_visitor(md);
-        visit_type_UserDefOneList(v, &obj, NULL, NULL);
-        qapi_dealloc_visitor_cleanup(md);
+        qdv = qapi_dealloc_visitor_new();
+        v = qapi_dealloc_get_visitor(qdv);
+        visit_type_UserDefOne(v, &obj, NULL, NULL);
+        qapi_dealloc_visitor_cleanup(qdv);

     }
 
     }
 

-    void qapi_free_UserDefOne(UserDefOne * obj)
+    void qapi_free_UserDefOneList(UserDefOneList *obj)

     {
     {

-        QapiDeallocVisitor *md;
+        QapiDeallocVisitor *qdv;

         Visitor *v;
 
         if (!obj) {
             return;
         }
 
         Visitor *v;
 
         if (!obj) {
             return;
         }
 

-        md = qapi_dealloc_visitor_new();
-        v = qapi_dealloc_get_visitor(md);
-        visit_type_UserDefOne(v, &obj, NULL, NULL);
-        qapi_dealloc_visitor_cleanup(md);
+        qdv = qapi_dealloc_visitor_new();
+        v = qapi_dealloc_get_visitor(qdv);
+        visit_type_UserDefOneList(v, &obj, NULL, NULL);
+        qapi_dealloc_visitor_cleanup(qdv);

     }
     }

-

     $ cat qapi-generated/example-qapi-types.h
 [Uninteresting stuff omitted...]
 
     #ifndef EXAMPLE_QAPI_TYPES_H
     #define EXAMPLE_QAPI_TYPES_H
 
     $ cat qapi-generated/example-qapi-types.h
 [Uninteresting stuff omitted...]
 
     #ifndef EXAMPLE_QAPI_TYPES_H
     #define EXAMPLE_QAPI_TYPES_H
 

-[Builtin types omitted...]
+[Built-in types omitted...]

 
     typedef struct UserDefOne UserDefOne;
 
 
     typedef struct UserDefOne UserDefOne;
 

-    typedef struct UserDefOneList
-    {
+    typedef struct UserDefOneList UserDefOneList;
+
+    struct UserDefOne {
+        int64_t integer;
+        char *string;
+    };
+
+    void qapi_free_UserDefOne(UserDefOne *obj);
+
+    struct UserDefOneList {

         union {
             UserDefOne *value;
             uint64_t padding;
         };
         union {
             UserDefOne *value;
             uint64_t padding;
         };

-        struct UserDefOneList *next;
-    } UserDefOneList;
-
-[Functions on builtin types omitted...]
-
-    struct UserDefOne
-    {
-        int64_t integer;
-        char * string;
+        UserDefOneList *next;

     };
 
     };
 

-    void qapi_free_UserDefOneList(UserDefOneList * obj);
-    void qapi_free_UserDefOne(UserDefOne * obj);
+    void qapi_free_UserDefOneList(UserDefOneList *obj);

 
     #endif
 
 
     #endif
 


@@ -360,18 +820,19 @@ $(prefix)qapi-visit.h: declarations for previously mentioned visitor
 Example:
 
     $ python scripts/qapi-visit.py --output-dir="qapi-generated"
 Example:
 
     $ python scripts/qapi-visit.py --output-dir="qapi-generated"

-    --prefix="example-" --input-file=example-schema.json
+    --prefix="example-" example-schema.json

     $ cat qapi-generated/example-qapi-visit.c
 [Uninteresting stuff omitted...]
 
     $ cat qapi-generated/example-qapi-visit.c
 [Uninteresting stuff omitted...]
 

-    static void visit_type_UserDefOne_fields(Visitor *m, UserDefOne ** obj, Error **errp)
+    static void visit_type_UserDefOne_fields(Visitor *v, UserDefOne **obj, Error **errp)

     {
         Error *err = NULL;
     {
         Error *err = NULL;

-        visit_type_int(m, &(*obj)->integer, "integer", &err);
+
+        visit_type_int(v, &(*obj)->integer, "integer", &err);

         if (err) {
             goto out;
         }
         if (err) {
             goto out;
         }

-        visit_type_str(m, &(*obj)->string, "string", &err);
+        visit_type_str(v, &(*obj)->string, "string", &err);

         if (err) {
             goto out;
         }
         if (err) {
             goto out;
         }


@@ -380,55 +841,53 @@ Example:
         error_propagate(errp, err);
     }
 
         error_propagate(errp, err);
     }
 

-    void visit_type_UserDefOne(Visitor *m, UserDefOne ** obj, const char *name, Error **errp)
+    void visit_type_UserDefOne(Visitor *v, UserDefOne **obj, const char *name, Error **errp)

     {
         Error *err = NULL;
 
     {
         Error *err = NULL;
 

-        visit_start_struct(m, (void **)obj, "UserDefOne", name, sizeof(UserDefOne), &err);
+        visit_start_struct(v, (void **)obj, "UserDefOne", name, sizeof(UserDefOne), &err);

         if (!err) {
             if (*obj) {
         if (!err) {
             if (*obj) {

-                visit_type_UserDefOne_fields(m, obj, errp);
+                visit_type_UserDefOne_fields(v, obj, errp);

             }
             }

-            visit_end_struct(m, &err);
+            visit_end_struct(v, &err);

         }
         error_propagate(errp, err);
     }
 
         }
         error_propagate(errp, err);
     }
 

-    void visit_type_UserDefOneList(Visitor *m, UserDefOneList ** obj, const char *name, Error **errp)
+    void visit_type_UserDefOneList(Visitor *v, UserDefOneList **obj, const char *name, Error **errp)

     {
         Error *err = NULL;
         GenericList *i, **prev;
 
     {
         Error *err = NULL;
         GenericList *i, **prev;
 

-        visit_start_list(m, name, &err);
+        visit_start_list(v, name, &err);

         if (err) {
             goto out;
         }
 
         for (prev = (GenericList **)obj;
         if (err) {
             goto out;
         }
 
         for (prev = (GenericList **)obj;

-             !err && (i = visit_next_list(m, prev, &err)) != NULL;
+             !err && (i = visit_next_list(v, prev, &err)) != NULL;

              prev = &i) {
             UserDefOneList *native_i = (UserDefOneList *)i;
              prev = &i) {
             UserDefOneList *native_i = (UserDefOneList *)i;

-            visit_type_UserDefOne(m, &native_i->value, NULL, &err);
+            visit_type_UserDefOne(v, &native_i->value, NULL, &err);

         }
 
         error_propagate(errp, err);
         err = NULL;
         }
 
         error_propagate(errp, err);
         err = NULL;

-        visit_end_list(m, &err);
+        visit_end_list(v, &err);

     out:
         error_propagate(errp, err);
     }
     out:
         error_propagate(errp, err);
     }

-    $ python scripts/qapi-commands.py --output-dir="qapi-generated" \
-    --prefix="example-" --input-file=example-schema.json

     $ cat qapi-generated/example-qapi-visit.h
 [Uninteresting stuff omitted...]
 
     #ifndef EXAMPLE_QAPI_VISIT_H
     #define EXAMPLE_QAPI_VISIT_H
 
     $ cat qapi-generated/example-qapi-visit.h
 [Uninteresting stuff omitted...]
 
     #ifndef EXAMPLE_QAPI_VISIT_H
     #define EXAMPLE_QAPI_VISIT_H
 

-[Visitors for builtin types omitted...]
+[Visitors for built-in types omitted...]

 
 

-    void visit_type_UserDefOne(Visitor *m, UserDefOne ** obj, const char *name, Error **errp);
-    void visit_type_UserDefOneList(Visitor *m, UserDefOneList ** obj, const char *name, Error **errp);
+    void visit_type_UserDefOne(Visitor *v, UserDefOne **obj, const char *name, Error **errp);
+    void visit_type_UserDefOneList(Visitor *v, UserDefOneList **obj, const char *name, Error **errp);

 
     #endif
 
 
     #endif
 


@@ -451,67 +910,68 @@ $(prefix)qmp-commands.h: Function prototypes for the QMP commands
 
 Example:
 
 
 Example:
 

+    $ python scripts/qapi-commands.py --output-dir="qapi-generated"
+    --prefix="example-" example-schema.json

     $ cat qapi-generated/example-qmp-marshal.c
 [Uninteresting stuff omitted...]
 
     $ cat qapi-generated/example-qmp-marshal.c
 [Uninteresting stuff omitted...]
 

-    static void qmp_marshal_output_my_command(UserDefOne * ret_in, QObject **ret_out, Error **errp)
+    static void qmp_marshal_output_UserDefOne(UserDefOne *ret_in, QObject **ret_out, Error **errp)

     {
     {

-        Error *local_err = NULL;
-        QmpOutputVisitor *mo = qmp_output_visitor_new();
-        QapiDeallocVisitor *md;
+        Error *err = NULL;
+        QmpOutputVisitor *qov = qmp_output_visitor_new();
+        QapiDeallocVisitor *qdv;

         Visitor *v;
 
         Visitor *v;
 

-        v = qmp_output_get_visitor(mo);
-        visit_type_UserDefOne(v, &ret_in, "unused", &local_err);
-        if (local_err) {
+        v = qmp_output_get_visitor(qov);
+        visit_type_UserDefOne(v, &ret_in, "unused", &err);
+        if (err) {

             goto out;
         }
             goto out;
         }

-        *ret_out = qmp_output_get_qobject(mo);
+        *ret_out = qmp_output_get_qobject(qov);

 
     out:
 
     out:

-        error_propagate(errp, local_err);
-        qmp_output_visitor_cleanup(mo);
-        md = qapi_dealloc_visitor_new();
-        v = qapi_dealloc_get_visitor(md);
+        error_propagate(errp, err);
+        qmp_output_visitor_cleanup(qov);
+        qdv = qapi_dealloc_visitor_new();
+        v = qapi_dealloc_get_visitor(qdv);

         visit_type_UserDefOne(v, &ret_in, "unused", NULL);
         visit_type_UserDefOne(v, &ret_in, "unused", NULL);

-        qapi_dealloc_visitor_cleanup(md);
+        qapi_dealloc_visitor_cleanup(qdv);

     }
 
     }
 

-    static void qmp_marshal_input_my_command(QDict *args, QObject **ret, Error **errp)
+    static void qmp_marshal_my_command(QDict *args, QObject **ret, Error **errp)

     {
     {

-        Error *local_err = NULL;
-        UserDefOne * retval = NULL;
-        QmpInputVisitor *mi = qmp_input_visitor_new_strict(QOBJECT(args));
-        QapiDeallocVisitor *md;
+        Error *err = NULL;
+        UserDefOne *retval;
+        QmpInputVisitor *qiv = qmp_input_visitor_new_strict(QOBJECT(args));
+        QapiDeallocVisitor *qdv;

         Visitor *v;
         Visitor *v;

-        UserDefOne * arg1 = NULL;
+        UserDefOne *arg1 = NULL;

 
 

-        v = qmp_input_get_visitor(mi);
-        visit_type_UserDefOne(v, &arg1, "arg1", &local_err);
-        if (local_err) {
+        v = qmp_input_get_visitor(qiv);
+        visit_type_UserDefOne(v, &arg1, "arg1", &err);
+        if (err) {

             goto out;
         }
 
             goto out;
         }
 

-        retval = qmp_my_command(arg1, &local_err);
-        if (local_err) {
+        retval = qmp_my_command(arg1, &err);
+        if (err) {

             goto out;
         }
 
             goto out;
         }
 

-        qmp_marshal_output_my_command(retval, ret, &local_err);
+        qmp_marshal_output_UserDefOne(retval, ret, &err);

 
     out:
 
     out:

-        error_propagate(errp, local_err);
-        qmp_input_visitor_cleanup(mi);
-        md = qapi_dealloc_visitor_new();
-        v = qapi_dealloc_get_visitor(md);
+        error_propagate(errp, err);
+        qmp_input_visitor_cleanup(qiv);
+        qdv = qapi_dealloc_visitor_new();
+        v = qapi_dealloc_get_visitor(qdv);

         visit_type_UserDefOne(v, &arg1, "arg1", NULL);
         visit_type_UserDefOne(v, &arg1, "arg1", NULL);

-        qapi_dealloc_visitor_cleanup(md);
-        return;
+        qapi_dealloc_visitor_cleanup(qdv);

     }
 
     static void qmp_init_marshal(void)
     {
     }
 
     static void qmp_init_marshal(void)
     {

-        qmp_register_command("my-command", qmp_marshal_input_my_command, QCO_NO_OPTIONS);
+        qmp_register_command("my-command", qmp_marshal_my_command, QCO_NO_OPTIONS);

     }
 
     qapi_init(qmp_init_marshal);
     }
 
     qapi_init(qmp_init_marshal);


@@ -525,6 +985,100 @@ Example:
     #include "qapi/qmp/qdict.h"
     #include "qapi/error.h"
 
     #include "qapi/qmp/qdict.h"
     #include "qapi/error.h"
 

-    UserDefOne * qmp_my_command(UserDefOne * arg1, Error **errp);
+    UserDefOne *qmp_my_command(UserDefOne *arg1, Error **errp);
+
+    #endif
+
+=== scripts/qapi-event.py ===
+
+Used to generate the event-related C code defined by a schema. The
+following files are created:
+
+$(prefix)qapi-event.h - Function prototypes for each event type, plus an
+                        enumeration of all event names
+$(prefix)qapi-event.c - Implementation of functions to send an event
+
+Example:
+
+    $ python scripts/qapi-event.py --output-dir="qapi-generated"
+    --prefix="example-" example-schema.json
+    $ cat qapi-generated/example-qapi-event.c
+[Uninteresting stuff omitted...]
+
+    void qapi_event_send_my_event(Error **errp)
+    {
+        QDict *qmp;
+        Error *err = NULL;
+        QMPEventFuncEmit emit;
+        emit = qmp_event_get_func_emit();
+        if (!emit) {
+            return;
+        }
+
+        qmp = qmp_event_build_dict("MY_EVENT");
+
+        emit(EXAMPLE_QAPI_EVENT_MY_EVENT, qmp, &err);
+
+        error_propagate(errp, err);
+        QDECREF(qmp);
+    }
+
+    const char *const example_QAPIEvent_lookup[] = {
+        [EXAMPLE_QAPI_EVENT_MY_EVENT] = "MY_EVENT",
+        [EXAMPLE_QAPI_EVENT_MAX] = NULL,
+    };
+    $ cat qapi-generated/example-qapi-event.h
+[Uninteresting stuff omitted...]
+
+    #ifndef EXAMPLE_QAPI_EVENT_H
+    #define EXAMPLE_QAPI_EVENT_H
+
+    #include "qapi/error.h"
+    #include "qapi/qmp/qdict.h"
+    #include "example-qapi-types.h"
+
+
+    void qapi_event_send_my_event(Error **errp);
+
+    typedef enum example_QAPIEvent {
+        EXAMPLE_QAPI_EVENT_MY_EVENT = 0,
+        EXAMPLE_QAPI_EVENT_MAX = 1,
+    } example_QAPIEvent;
+
+    extern const char *const example_QAPIEvent_lookup[];
+
+    #endif
+
+=== scripts/qapi-introspect.py ===
+
+Used to generate the introspection C code for a schema. The following
+files are created:
+
+$(prefix)qmp-introspect.c - Defines a string holding a JSON
+                            description of the schema.
+$(prefix)qmp-introspect.h - Declares the above string.
+
+Example:
+
+    $ python scripts/qapi-introspect.py --output-dir="qapi-generated"
+    --prefix="example-" example-schema.json
+    $ cat qapi-generated/example-qmp-introspect.c
+[Uninteresting stuff omitted...]
+
+    const char example_qmp_schema_json[] = "["
+        "{\"arg-type\": \"0\", \"meta-type\": \"event\", \"name\": \"MY_EVENT\"}, "
+        "{\"arg-type\": \"1\", \"meta-type\": \"command\", \"name\": \"my-command\", \"ret-type\": \"2\"}, "
+        "{\"members\": [], \"meta-type\": \"object\", \"name\": \"0\"}, "
+        "{\"members\": [{\"name\": \"arg1\", \"type\": \"2\"}], \"meta-type\": \"object\", \"name\": \"1\"}, "
+        "{\"members\": [{\"name\": \"integer\", \"type\": \"int\"}, {\"name\": \"string\", \"type\": \"str\"}], \"meta-type\": \"object\", \"name\": \"2\"}, "
+        "{\"json-type\": \"int\", \"meta-type\": \"builtin\", \"name\": \"int\"}, "
+        "{\"json-type\": \"string\", \"meta-type\": \"builtin\", \"name\": \"str\"}]";
+    $ cat qapi-generated/example-qmp-introspect.h
+[Uninteresting stuff omitted...]
+
+    #ifndef EXAMPLE_QMP_INTROSPECT_H
+    #define EXAMPLE_QMP_INTROSPECT_H
+
+    extern const char example_qmp_schema_json[];

 
     #endif
 
     #endif