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authorRajithaY <rajithax.yerrumsetty@intel.com>2017-04-25 03:31:15 -0700
committerRajitha Yerrumchetty <rajithax.yerrumsetty@intel.com>2017-05-22 06:48:08 +0000
commitbb756eebdac6fd24e8919e2c43f7d2c8c4091f59 (patch)
treeca11e03542edf2d8f631efeca5e1626d211107e3 /qemu/docs/qapi-code-gen.txt
parenta14b48d18a9ed03ec191cf16b162206998a895ce (diff)
Adding qemu as a submodule of KVMFORNFV
This Patch includes the changes to add qemu as a submodule to kvmfornfv repo and make use of the updated latest qemu for the execution of all testcase Change-Id: I1280af507a857675c7f81d30c95255635667bdd7 Signed-off-by:RajithaY<rajithax.yerrumsetty@intel.com>
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-= How to use the QAPI code generator =
-
-Copyright IBM Corp. 2011
-Copyright (C) 2012-2016 Red Hat, Inc.
-
-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 ==
-
-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.
-
-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.
-
-
-== QMP/Guest agent schema ==
-
-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 members 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 member 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. Member
-names cannot start with 'has-' or 'has_', as this is reserved for
-tracking optional members.
-
-Any name (command, event, type, member, or enum value) beginning with
-"x-" is marked experimental, and may be withdrawn or changed
-incompatibly in a future release. All names must begin with a letter,
-and contain only ASCII letters, digits, dash, and underscore. There
-are two exceptions: enum values may start with a digit, and any
-extensions added by downstream vendors should start 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). Names beginning with 'q_' are reserved
-for the generator: QMP names that resemble C keywords or other
-problematic strings will be munged in C to use this prefix. For
-example, a member named "default" in qapi becomes "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
- QType QType JSON string matching enum QType values
-
-
-=== Includes ===
-
-Usage: { 'include': STRING }
-
-The QAPI schema definitions can be modularized using the 'include' directive:
-
- { 'include': 'path/to/file.json' }
-
-The directive is evaluated recursively, and include paths are relative to the
-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 ===
-
-Usage: { 'struct': STRING, 'data': DICT, '*base': STRUCT-NAME }
-
-A struct is a dictionary containing a single 'data' key whose value is
-a dictionary; the dictionary may be empty. 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:
-
- { 'struct': 'MyType',
- 'data': { 'member1': 'str', 'member2': 'int', '*member3': 'str' } }
-
-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
-compatibility to the user-visible behavior of the old default.
-
-With proper documentation, this policy still allows some flexibility; for
-example, documenting that a default of 0 picks an optimal buffer size allows
-one release to declare the optimal size at 512 while another release declares
-the optimal size at 4096 - the user-visible behavior is not the bytes used by
-the buffer, but the fact that the buffer was optimal size.
-
-On input structures (only mentioned in the 'data' side of a command), changing
-from mandatory to optional is safe (older clients will supply the option, and
-newer clients can benefit from the default); changing from optional to
-mandatory is backwards incompatible (older clients may be omitting the option,
-and must continue to work).
-
-On output structures (only mentioned in the 'returns' side of a command),
-changing from mandatory to optional is in general unsafe (older clients may be
-expecting the member, and could crash if it is missing), although it
-can be done if the only way that the optional argument will be omitted
-is when it is triggered by the presence of a new input flag to the
-command that older clients don't know to send. Changing from optional
-to mandatory is safe.
-
-A structure that is used in both input and output of various commands
-must consider the backwards compatibility constraints of both directions
-of use.
-
-A struct definition can specify another struct as its base.
-In this case, the members of the base type are included as top-level members
-of the new struct's dictionary in the Client JSON Protocol wire
-format. An example definition is:
-
- { 'struct': 'BlockdevOptionsGenericFormat', 'data': { 'file': 'str' } }
- { 'struct': 'BlockdevOptionsGenericCOWFormat',
- 'base': 'BlockdevOptionsGenericFormat',
- 'data': { '*backing': 'str' } }
-
-An example BlockdevOptionsGenericCOWFormat object on the wire could use
-both members like this:
-
- { "file": "/some/place/my-image",
- "backing": "/some/place/my-backing-file" }
-
-
-=== Enumeration types ===
-
-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' ] }
-
-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' member
-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 member that will only contain
-a finite set of string values, using an enum type for that member is
-better than open-coding the member to be type 'str'.
-
-
-=== Union types ===
-
-Usage: { 'union': STRING, 'data': DICT }
-or: { 'union': STRING, 'data': DICT, 'base': STRUCT-NAME-OR-DICT,
- '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), and flat (both discriminator and base). A union
-type is defined using a data dictionary as explained in the following
-paragraphs. The data dictionary for either type of union must not
-be empty.
-
-A simple union type defines a mapping from automatic discriminator
-values to data types like in this example:
-
- { 'struct': 'BlockdevOptionsFile', 'data': { 'filename': 'str' } }
- { 'struct': 'BlockdevOptionsQcow2',
- 'data': { 'backing': 'str', '*lazy-refcounts': 'bool' } }
-
- { 'union': 'BlockdevOptionsSimple',
- 'data': { 'file': 'BlockdevOptionsFile',
- 'qcow2': 'BlockdevOptionsQcow2' } }
-
-In the Client JSON Protocol, a simple union is represented by a
-dictionary that contains the 'type' member as a discriminator, and a
-'data' member 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": "/some/place/my-image",
- "lazy-refcounts": true } }
-
-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 avoids nesting on the wire, and specifies a
-set of common members that occur in all variants of the union. The
-'base' key must specifiy either a type name (the type must be a
-struct, not a union), or a dictionary representing an anonymous type.
-All branches of the union must be complex types, and the top-level
-members of the union dictionary on the wire will be combination of
-members from both the base type and the appropriate branch type (when
-merging two dictionaries, there must be no keys in common). The
-'discriminator' member must be the name of a non-optional enum-typed
-member of the base struct.
-
-The following example enhances the above simple union example by
-adding an optional common member 'read-only', renaming the
-discriminator to something more applicable than the simple union's
-default of 'type', and reducing the number of {} required on the wire:
-
- { 'enum': 'BlockdevDriver', 'data': [ 'file', 'qcow2' ] }
- { 'union': 'BlockdevOptions',
- 'base': { 'driver': 'BlockdevDriver', '*read-only': 'bool' },
- 'discriminator': 'driver',
- 'data': { 'file': 'BlockdevOptionsFile',
- 'qcow2': 'BlockdevOptionsQcow2' } }
-
-Resulting in these JSON objects:
-
- { "driver": "file", "read-only": true,
- "filename": "/some/place/my-image" }
- { "driver": "qcow2", "read-only": false,
- "backing": "/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 members included directly, and
-then a union of structures for each branch of the struct.
-
-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,
-
- { 'union': 'Simple', 'data': { 'one': 'str', 'two': 'int' } }
-
-is identical on the wire to:
-
- { 'enum': 'Enum', 'data': ['one', 'two'] }
- { 'struct': 'Branch1', 'data': { 'data': 'str' } }
- { 'struct': 'Branch2', 'data': { 'data': 'int' } }
- { 'union': 'Flat': 'base': { 'type': 'Enum' }, 'discriminator': 'type',
- 'data': { 'one': 'Branch1', 'two': 'Branch2' } }
-
-
-=== Alternate types ===
-
-Usage: { 'alternate': STRING, 'data': DICT }
-
-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:
-
- { 'alternate': 'BlockdevRef',
- 'data': { 'definition': 'BlockdevOptions',
- 'reference': 'str' } }
-
-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",
- "read-only": false,
- "filename": "/tmp/mydisk.qcow2" } }
-
-
-=== Commands ===
-
-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" member
-of a Client JSON Protocol reply on successful completion of a command.
-The member is optional from the command declaration; if absent, the
-"return" member 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 member 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 member.
-
-
-=== Events ===
-
-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:
-
-{ 'event': 'EVENT_C',
- 'data': { '*a': 'int', 'b': 'str' } }
-
-Resulting in this JSON object:
-
-{ "event": "EVENT_C",
- "data": { "b": "test string" },
- "timestamp": { "seconds": 1267020223, "microseconds": 435656 } }
-
-
-== Client JSON Protocol introspection ==
-
-Clients of a Client JSON Protocol commonly need to figure out what
-exactly the server (QEMU) supports.
-
-For this purpose, QMP provides introspection via command
-query-qmp-schema. QGA currently doesn't support introspection.
-
-While Client JSON Protocol wire compatibility should be maintained
-between qemu versions, we cannot make the same guarantees for
-introspection stability. For example, one version of qemu may provide
-a non-variant optional member of a struct, and a later version rework
-the member to instead be non-optional and associated with a variant.
-Likewise, one version of qemu may list a member with open-ended type
-'str', and a later version could convert it to a finite set of strings
-via an enum type; or a member may be converted from a specific type to
-an alternate that represents a choice between the original type and
-something else.
-
-query-qmp-schema returns a JSON array of SchemaInfo objects. These
-objects together describe the wire ABI, as defined in the QAPI schema.
-There is no specified order to the SchemaInfo objects returned; a
-client must search for a particular name throughout the entire array
-to learn more about that name, but is at least guaranteed that there
-will be no collisions between type, command, and event names.
-
-However, the SchemaInfo can't reflect all the rules and restrictions
-that apply to QMP. It's interface introspection (figuring out what's
-there), not interface specification. The specification is in the QAPI
-schema. To understand how QMP is to be used, you need to study the
-QAPI schema.
-
-Like any other command, query-qmp-schema is itself defined in the QAPI
-schema, along with the SchemaInfo type. This text attempts to give an
-overview how things work. For details you need to consult the QAPI
-schema.
-
-SchemaInfo objects have common members "name" 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": "q_empty", "ret-type": "SchemaInfoList" }
-
- Type "q_empty" is an automatic object type without members, and type
- "SchemaInfoList" is the array of SchemaInfo type.
-
-The SchemaInfo for an event has meta-type "event", and variant member
-"arg-type". On the wire, a "data" member that the server passes in an
-event conforms to the object type named by "arg-type".
-
-If the event carries no additional information, "arg-type" names an
-object type without members. The event may not have a data member on
-the wire then.
-
-Each command or event defined with 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": "q_obj-EVENT_C-arg" }
-
- Type "q_obj-EVENT_C-arg" is an implicitly defined object type with
- the two members from the event's definition.
-
-The SchemaInfo for struct and union types has meta-type "object".
-
-The SchemaInfo for a struct type has variant member "members".
-
-The SchemaInfo for a union type additionally has variant members "tag"
-and "variants".
-
-"members" is a JSON array describing the object's common members, if
-any. Each element is a JSON object with members "name" (the member's
-name), "type" (the name of its type), 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. The "members" array is in no particular order; clients
-must search the entire object when learning whether a particular
-member is supported.
-
-Example: the SchemaInfo for MyType from section Struct types
-
- { "name": "MyType", "meta-type": "object",
- "members": [
- { "name": "member1", "type": "str" },
- { "name": "member2", "type": "int" },
- { "name": "member3", "type": "str", "default": null } ] }
-
-"tag" is the name of the common member serving as type tag.
-"variants" is a JSON array describing the object's variant members.
-Each element is a JSON object with members "case" (the value of type
-tag this element applies to) and "type" (the name of an object type
-that provides the variant members for this type tag value). The
-"variants" array is in no particular order, and is not guaranteed to
-list cases in the same order as the corresponding "tag" enum type.
-
-Example: the SchemaInfo for flat union BlockdevOptions from section
-Union types
-
- { "name": "BlockdevOptions", "meta-type": "object",
- "members": [
- { "name": "driver", "type": "BlockdevDriver" },
- { "name": "read-only", "type": "bool", "default": null } ],
- "tag": "driver",
- "variants": [
- { "case": "file", "type": "BlockdevOptionsFile" },
- { "case": "qcow2", "type": "BlockdevOptionsQcow2" } ] }
-
-Note that base types are "flattened": its members are included in the
-"members" array.
-
-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 BlockdevOptionsSimple from section
-Union types
-
- { "name": "BlockdevOptionsSimple", "meta-type": "object",
- "members": [
- { "name": "type", "type": "BlockdevOptionsSimpleKind" } ],
- "tag": "type",
- "variants": [
- { "case": "file", "type": "q_obj-BlockdevOptionsFile-wrapper" },
- { "case": "qcow2", "type": "q_obj-BlockdevOptionsQcow2-wrapper" } ] }
-
- Enumeration type "BlockdevOptionsSimpleKind" and the object types
- "q_obj-BlockdevOptionsFile-wrapper", "q_obj-BlockdevOptionsQcow2-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. There is
-no guarantee on the order in which "members" will be listed.
-
-Example: the SchemaInfo for BlockdevRef from section Alternate types
-
- { "name": "BlockdevRef", "meta-type": "alternate",
- "members": [
- { "type": "BlockdevOptions" },
- { "type": "str" } ] }
-
-The SchemaInfo for an array type has meta-type "array", and variant
-member "element-type", which names the array's element type. Array
-types are implicitly defined. For convenience, the array's name may
-resemble the element type; however, clients should examine member
-"element-type" instead of making assumptions based on parsing member
-"name".
-
-Example: the SchemaInfo for ['str']
-
- { "name": "[str]", "meta-type": "array",
- "element-type": "str" }
-
-The SchemaInfo for an enumeration type has meta-type "enum" and
-variant member "values". The values are listed in no particular
-order; clients must search the entire enum when learning whether a
-particular value is supported.
-
-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 ==
-
-Schemas are fed into five 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, map the response back to a Client JSON Protocol response
-to be returned to the user, and introspect the commands.
-
-As an example, we'll use the following schema, which describes a
-single complex user-defined type, along with command which takes a
-list of that type as a parameter, and returns a single element of that
-type. The user is responsible for writing the implementation of
-qmp_my_command(); everything else is produced by the generator.
-
- $ cat example-schema.json
- { 'struct': 'UserDefOne',
- 'data': { 'integer': 'int', '*string': 'str' } }
-
- { 'command': 'my-command',
- 'data': { 'arg1': ['UserDefOne'] },
- 'returns': 'UserDefOne' }
-
- { 'event': 'MY_EVENT' }
-
-For a more thorough look at generated code, the testsuite includes
-tests/qapi-schema/qapi-schema-tests.json that covers more examples of
-what the generator will accept, and compiles the resulting C code as
-part of 'make check-unit'.
-
-=== scripts/qapi-types.py ===
-
-Used to generate the C types defined by a schema, along with
-supporting code. The following files are created:
-
-$(prefix)qapi-types.h - C types corresponding to types defined in
- the schema you pass in
-$(prefix)qapi-types.c - Cleanup functions for the above C types
-
-The $(prefix) is an optional parameter used as a namespace to keep the
-generated code from one schema/code-generation separated from others so code
-can be generated/used from multiple schemas without clobbering previously
-created code.
-
-Example:
-
- $ python scripts/qapi-types.py --output-dir="qapi-generated" \
- --prefix="example-" example-schema.json
- $ cat qapi-generated/example-qapi-types.h
-[Uninteresting stuff omitted...]
-
- #ifndef EXAMPLE_QAPI_TYPES_H
- #define EXAMPLE_QAPI_TYPES_H
-
-[Built-in types omitted...]
-
- typedef struct UserDefOne UserDefOne;
-
- typedef struct UserDefOneList UserDefOneList;
-
- struct UserDefOne {
- int64_t integer;
- bool has_string;
- char *string;
- };
-
- void qapi_free_UserDefOne(UserDefOne *obj);
-
- struct UserDefOneList {
- UserDefOneList *next;
- UserDefOne *value;
- };
-
- void qapi_free_UserDefOneList(UserDefOneList *obj);
-
- #endif
- $ cat qapi-generated/example-qapi-types.c
-[Uninteresting stuff omitted...]
-
- void qapi_free_UserDefOne(UserDefOne *obj)
- {
- QapiDeallocVisitor *qdv;
- Visitor *v;
-
- if (!obj) {
- return;
- }
-
- qdv = qapi_dealloc_visitor_new();
- v = qapi_dealloc_get_visitor(qdv);
- visit_type_UserDefOne(v, NULL, &obj, NULL);
- qapi_dealloc_visitor_cleanup(qdv);
- }
-
- void qapi_free_UserDefOneList(UserDefOneList *obj)
- {
- QapiDeallocVisitor *qdv;
- Visitor *v;
-
- if (!obj) {
- return;
- }
-
- qdv = qapi_dealloc_visitor_new();
- v = qapi_dealloc_get_visitor(qdv);
- visit_type_UserDefOneList(v, NULL, &obj, NULL);
- qapi_dealloc_visitor_cleanup(qdv);
- }
-
-=== scripts/qapi-visit.py ===
-
-Used to generate the visitor functions used to walk through and
-convert between a native QAPI C data structure and some other format
-(such as QObject); the generated functions are named visit_type_FOO()
-and visit_type_FOO_members().
-
-The following files are generated:
-
-$(prefix)qapi-visit.c: visitor function for a particular C type, used
- to automagically convert QObjects into the
- corresponding C type and vice-versa, as well
- as for deallocating memory for an existing C
- type
-
-$(prefix)qapi-visit.h: declarations for previously mentioned visitor
- functions
-
-Example:
-
- $ python scripts/qapi-visit.py --output-dir="qapi-generated"
- --prefix="example-" example-schema.json
- $ cat qapi-generated/example-qapi-visit.h
-[Uninteresting stuff omitted...]
-
- #ifndef EXAMPLE_QAPI_VISIT_H
- #define EXAMPLE_QAPI_VISIT_H
-
-[Visitors for built-in types omitted...]
-
- void visit_type_UserDefOne_members(Visitor *v, UserDefOne *obj, Error **errp);
- void visit_type_UserDefOne(Visitor *v, const char *name, UserDefOne **obj, Error **errp);
- void visit_type_UserDefOneList(Visitor *v, const char *name, UserDefOneList **obj, Error **errp);
-
- #endif
- $ cat qapi-generated/example-qapi-visit.c
-[Uninteresting stuff omitted...]
-
- void visit_type_UserDefOne_members(Visitor *v, UserDefOne *obj, Error **errp)
- {
- Error *err = NULL;
-
- visit_type_int(v, "integer", &obj->integer, &err);
- if (err) {
- goto out;
- }
- if (visit_optional(v, "string", &obj->has_string)) {
- visit_type_str(v, "string", &obj->string, &err);
- if (err) {
- goto out;
- }
- }
-
- out:
- error_propagate(errp, err);
- }
-
- void visit_type_UserDefOne(Visitor *v, const char *name, UserDefOne **obj, Error **errp)
- {
- Error *err = NULL;
-
- visit_start_struct(v, name, (void **)obj, sizeof(UserDefOne), &err);
- if (err) {
- goto out;
- }
- if (!*obj) {
- goto out_obj;
- }
- visit_type_UserDefOne_members(v, *obj, &err);
- error_propagate(errp, err);
- err = NULL;
- out_obj:
- visit_end_struct(v, &err);
- out:
- error_propagate(errp, err);
- }
-
- void visit_type_UserDefOneList(Visitor *v, const char *name, UserDefOneList **obj, Error **errp)
- {
- Error *err = NULL;
- GenericList *i, **prev;
-
- visit_start_list(v, name, &err);
- if (err) {
- goto out;
- }
-
- for (prev = (GenericList **)obj;
- !err && (i = visit_next_list(v, prev, sizeof(**obj))) != NULL;
- prev = &i) {
- UserDefOneList *native_i = (UserDefOneList *)i;
- visit_type_UserDefOne(v, NULL, &native_i->value, &err);
- }
-
- visit_end_list(v);
- out:
- error_propagate(errp, err);
- }
-
-=== scripts/qapi-commands.py ===
-
-Used to generate the marshaling/dispatch functions for the commands
-defined in the schema. The generated code implements
-qmp_marshal_COMMAND() (mentioned in qmp-commands.hx, and registered
-automatically), and declares qmp_COMMAND() that the user must
-implement. The following files are generated:
-
-$(prefix)qmp-marshal.c: command marshal/dispatch functions for each
- QMP command defined in the schema. Functions
- generated by qapi-visit.py are used to
- convert QObjects received from the wire into
- function parameters, and uses the same
- visitor functions to convert native C return
- values to QObjects from transmission back
- over the wire.
-
-$(prefix)qmp-commands.h: Function prototypes for the QMP commands
- specified in the schema.
-
-Example:
-
- $ python scripts/qapi-commands.py --output-dir="qapi-generated"
- --prefix="example-" example-schema.json
- $ cat qapi-generated/example-qmp-commands.h
-[Uninteresting stuff omitted...]
-
- #ifndef EXAMPLE_QMP_COMMANDS_H
- #define EXAMPLE_QMP_COMMANDS_H
-
- #include "example-qapi-types.h"
- #include "qapi/qmp/qdict.h"
- #include "qapi/error.h"
-
- UserDefOne *qmp_my_command(UserDefOneList *arg1, Error **errp);
-
- #endif
- $ cat qapi-generated/example-qmp-marshal.c
-[Uninteresting stuff omitted...]
-
- static void qmp_marshal_output_UserDefOne(UserDefOne *ret_in, QObject **ret_out, Error **errp)
- {
- Error *err = NULL;
- QmpOutputVisitor *qov = qmp_output_visitor_new();
- QapiDeallocVisitor *qdv;
- Visitor *v;
-
- v = qmp_output_get_visitor(qov);
- visit_type_UserDefOne(v, "unused", &ret_in, &err);
- if (err) {
- goto out;
- }
- *ret_out = qmp_output_get_qobject(qov);
-
- out:
- error_propagate(errp, err);
- qmp_output_visitor_cleanup(qov);
- qdv = qapi_dealloc_visitor_new();
- v = qapi_dealloc_get_visitor(qdv);
- visit_type_UserDefOne(v, "unused", &ret_in, NULL);
- qapi_dealloc_visitor_cleanup(qdv);
- }
-
- static void qmp_marshal_my_command(QDict *args, QObject **ret, Error **errp)
- {
- Error *err = NULL;
- UserDefOne *retval;
- QmpInputVisitor *qiv = qmp_input_visitor_new_strict(QOBJECT(args));
- QapiDeallocVisitor *qdv;
- Visitor *v;
- UserDefOneList *arg1 = NULL;
-
- v = qmp_input_get_visitor(qiv);
- visit_type_UserDefOneList(v, "arg1", &arg1, &err);
- if (err) {
- goto out;
- }
-
- retval = qmp_my_command(arg1, &err);
- if (err) {
- goto out;
- }
-
- qmp_marshal_output_UserDefOne(retval, ret, &err);
-
- out:
- error_propagate(errp, err);
- qmp_input_visitor_cleanup(qiv);
- qdv = qapi_dealloc_visitor_new();
- v = qapi_dealloc_get_visitor(qdv);
- visit_type_UserDefOneList(v, "arg1", &arg1, NULL);
- qapi_dealloc_visitor_cleanup(qdv);
- }
-
- static void qmp_init_marshal(void)
- {
- qmp_register_command("my-command", qmp_marshal_my_command, QCO_NO_OPTIONS);
- }
-
- qapi_init(qmp_init_marshal);
-
-=== scripts/qapi-event.py ===
-
-Used to generate the event-related C code defined by a schema, with
-implementations for qapi_event_send_FOO(). 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.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
- $ 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,
- };
-
-=== 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.h
-[Uninteresting stuff omitted...]
-
- #ifndef EXAMPLE_QMP_INTROSPECT_H
- #define EXAMPLE_QMP_INTROSPECT_H
-
- extern const char example_qmp_schema_json[];
-
- #endif
- $ 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\"}, {\"default\": null, \"name\": \"string\", \"type\": \"str\"}], \"meta-type\": \"object\", \"name\": \"2\"}, "
- "{\"element-type\": \"2\", \"meta-type\": \"array\", \"name\": \"[2]\"}, "
- "{\"json-type\": \"int\", \"meta-type\": \"builtin\", \"name\": \"int\"}, "
- "{\"json-type\": \"string\", \"meta-type\": \"builtin\", \"name\": \"str\"}]";