= How to use the QAPI code generator =
Copyright IBM Corp. 2011
-Copyright (C) 2012-2015 Red Hat, Inc.
+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.
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
+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:
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. Command names,
-and field names within a type, should be all lower case with words
+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. The
-special string '**' appears for some commands that manually perform
-their own type checking rather than relying on the type-safe code
-produced by the qapi code generators.
+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, field, or enum value) beginning with
+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"x-" is marked experimental, and may be withdrawn or changed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. 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
+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
=== Built-in Types ===
-The following types are built-in to the parser:
- 'str' - arbitrary UTF-8 string
- 'int' - 64-bit signed integer (although the C code may place further
- restrictions on acceptable range)
- 'number' - floating point number
- 'bool' - JSON value of true or false
- 'int8', 'int16', 'int32', 'int64' - like 'int', but enforce maximum
- bit size
- 'uint8', 'uint16', 'uint32', 'uint64' - unsigned counterparts
- 'size' - like 'uint64', but allows scaled suffix from command line
- visitor
+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 ===
The directive is evaluated recursively, and include paths are relative to the
file using the directive. Multiple includes of the same file are
-safe. No other keys should appear in the expression, and the include
+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
Usage: { 'struct': STRING, 'data': DICT, '*base': STRUCT-NAME }
-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:
+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' } }
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 field, 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.
+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 fields of the base type are included as top-level fields
+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:
'data': { '*backing': 'str' } }
An example BlockdevOptionsGenericCOWFormat object on the wire could use
-both fields like this:
+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:
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
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'.
+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: { '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), flat (both discriminator and base). A union
+discriminator or base), and flat (both discriminator and base). A union
type is defined using a data dictionary as explained in the following
-paragraphs.
+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': 'FileOptions', 'data': { 'filename': 'str' } }
- { 'struct': 'Qcow2Options',
- 'data': { 'backing-file': 'str', 'lazy-refcounts': 'bool' } }
+ { 'struct': 'BlockdevOptionsFile', 'data': { 'filename': 'str' } }
+ { 'struct': 'BlockdevOptionsQcow2',
+ 'data': { 'backing': 'str', '*lazy-refcounts': 'bool' } }
- { 'union': 'BlockdevOptions',
- 'data': { 'file': 'FileOptions',
- 'qcow2': 'Qcow2Options' } }
+ { 'union': 'BlockdevOptionsSimple',
+ 'data': { 'file': 'BlockdevOptionsFile',
+ 'qcow2': 'BlockdevOptionsQcow2' } }
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
+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-file": "/some/place/my-image",
- "lazy-refcounts": true } }
+ { "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
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.
+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 a common field 'readonly', renaming the discriminator to
-something more applicable, and reducing the number of {} required on
-the wire:
+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': [ 'raw', 'qcow2' ] }
- { 'struct': 'BlockdevCommonOptions',
- 'data': { 'driver': 'BlockdevDriver', 'readonly': 'bool' } }
+ { 'enum': 'BlockdevDriver', 'data': [ 'file', 'qcow2' ] }
{ 'union': 'BlockdevOptions',
- 'base': 'BlockdevCommonOptions',
+ 'base': { 'driver': 'BlockdevDriver', '*read-only': 'bool' },
'discriminator': 'driver',
- 'data': { 'file': 'FileOptions',
- 'qcow2': 'Qcow2Options' } }
+ 'data': { 'file': 'BlockdevOptionsFile',
+ 'qcow2': 'BlockdevOptionsQcow2' } }
Resulting in these JSON objects:
- { "driver": "file", "readonly": true,
+ { "driver": "file", "read-only": true,
"filename": "/some/place/my-image" }
- { "driver": "qcow2", "readonly": false,
- "backing-file": "/some/place/my-image", "lazy-refcounts": true }
+ { "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 member fields included directly,
-and then a union of structures for each branch of the struct.
+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
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',
+ { 'union': 'Flat': 'base': { 'type': 'Enum' }, 'discriminator': 'type',
'data': { 'one': 'Branch1', 'two': 'Branch2' } }
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': 'BlockRef',
+ { 'alternate': 'BlockdevRef',
'data': { 'definition': 'BlockdevOptions',
'reference': 'str' } }
-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
{ "file": "my_existing_block_device_id" }
{ "file": { "driver": "file",
- "readonly": false,
+ "read-only": false,
"filename": "/tmp/mydisk.qcow2" } }
=== Commands ===
Usage: { 'command': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT,
- '*returns': TYPE-NAME-OR-DICT,
+ '*returns': TYPE-NAME,
'*gen': false, '*success-response': false }
Commands are defined by using a dictionary containing several members,
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, a one-element array containing the 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.
+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
+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" field will be an empty dictionary. If 'returns' is present,
+"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,
-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. 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.
+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
<= { "return": [ { "value": "one" }, { } ] }
In rare cases, QAPI cannot express a type-safe representation of a
-corresponding Client JSON Protocol command. In these cases, if the
-command expression includes the key 'gen' with boolean value false,
-then the 'data' or 'returns' member that intends to bypass generated
-type-safety and do its own manual validation should use an inline
-dictionary definition, with a value of '**' rather than a valid type
-name for the keys that the generated code will not validate. Please
-try to avoid adding new commands that rely on this, and instead use
-type-safe unions. For an example of bypass usage:
+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', '*props': '**'},
+ 'data': {'type': 'str', 'id': 'str'},
'gen': false }
Normally, the QAPI schema is used to describe synchronous exchanges,
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.
+use of this member.
=== Events ===
"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 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 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.
+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 (which will produce a C struct, along with a list
-node structure that can be used to chain together a list of such types in
-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:
+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' } }
+ 'data': { 'integer': 'int', '*string': 'str' } }
{ 'command': 'my-command',
- 'data': {'arg1': 'UserDefOne'},
+ '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. The following files are
-created:
+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
$ 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_UserDefOneList(UserDefOneList *obj)
+ void qapi_free_UserDefOne(UserDefOne *obj)
{
- QapiDeallocVisitor *md;
+ QapiDeallocVisitor *qdv;
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, NULL, &obj, 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;
}
- 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, NULL, &obj, 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
-
-[Built-in types omitted...]
-
- typedef struct UserDefOne UserDefOne;
-
- typedef struct UserDefOneList
- {
- union {
- UserDefOne *value;
- uint64_t padding;
- };
- struct UserDefOneList *next;
- } UserDefOneList;
-
-[Functions on built-in types omitted...]
-
- struct UserDefOne
- {
- int64_t integer;
- char *string;
- };
-
- void qapi_free_UserDefOneList(UserDefOneList *obj);
- void qapi_free_UserDefOne(UserDefOne *obj);
-
- #endif
-
=== scripts/qapi-visit.py ===
-Used to generate the visitor functions used to walk through and convert
-a QObject (as provided by QMP) to a native C data structure and
-vice-versa, as well as the visitor function used to dealloc a complex
-schema-defined C type.
+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:
$ 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...]
- static void visit_type_UserDefOne_fields(Visitor *m, UserDefOne **obj, Error **errp)
+ void visit_type_UserDefOne_members(Visitor *v, UserDefOne *obj, Error **errp)
{
Error *err = NULL;
- visit_type_int(m, &(*obj)->integer, "integer", &err);
+
+ visit_type_int(v, "integer", &obj->integer, &err);
if (err) {
goto out;
}
- visit_type_str(m, &(*obj)->string, "string", &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 *m, UserDefOne **obj, const char *name, Error **errp)
+ void visit_type_UserDefOne(Visitor *v, const char *name, UserDefOne **obj, Error **errp)
{
Error *err = NULL;
- visit_start_struct(m, (void **)obj, "UserDefOne", name, sizeof(UserDefOne), &err);
- if (!err) {
- if (*obj) {
- visit_type_UserDefOne_fields(m, obj, errp);
- }
- visit_end_struct(m, &err);
+ 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 *m, UserDefOneList **obj, const char *name, Error **errp)
+ void visit_type_UserDefOneList(Visitor *v, const char *name, UserDefOneList **obj, Error **errp)
{
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;
- !err && (i = visit_next_list(m, prev, &err)) != NULL;
+ !err && (i = visit_next_list(v, prev, sizeof(**obj))) != NULL;
prev = &i) {
UserDefOneList *native_i = (UserDefOneList *)i;
- visit_type_UserDefOne(m, &native_i->value, NULL, &err);
+ visit_type_UserDefOne(v, NULL, &native_i->value, &err);
}
- error_propagate(errp, err);
- err = NULL;
- visit_end_list(m, &err);
+ visit_end_list(v);
out:
error_propagate(errp, err);
}
- $ 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(Visitor *m, UserDefOne **obj, const char *name, Error **errp);
- void visit_type_UserDefOneList(Visitor *m, UserDefOneList **obj, const char *name, Error **errp);
-
- #endif
=== scripts/qapi-commands.py ===
-Used to generate the marshaling/dispatch functions for the commands defined
-in the schema. The following files are generated:
+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
$ 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_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;
- 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, "unused", &ret_in, &err);
+ if (err) {
goto out;
}
- *ret_out = qmp_output_get_qobject(mo);
+ *ret_out = qmp_output_get_qobject(qov);
out:
- error_propagate(errp, local_err);
- qmp_output_visitor_cleanup(mo);
- md = qapi_dealloc_visitor_new();
- v = qapi_dealloc_get_visitor(md);
- visit_type_UserDefOne(v, &ret_in, "unused", NULL);
- qapi_dealloc_visitor_cleanup(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, "unused", &ret_in, NULL);
+ 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;
- UserDefOne *arg1 = NULL;
+ UserDefOneList *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_UserDefOneList(v, "arg1", &arg1, &err);
+ if (err) {
goto out;
}
- retval = qmp_my_command(arg1, &local_err);
- if (local_err) {
+ retval = qmp_my_command(arg1, &err);
+ if (err) {
goto out;
}
- qmp_marshal_output_my_command(retval, ret, &local_err);
+ qmp_marshal_output_UserDefOne(retval, ret, &err);
out:
- error_propagate(errp, local_err);
- qmp_input_visitor_cleanup(mi);
- md = qapi_dealloc_visitor_new();
- v = qapi_dealloc_get_visitor(md);
- visit_type_UserDefOne(v, &arg1, "arg1", NULL);
- qapi_dealloc_visitor_cleanup(md);
- return;
+ 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_input_my_command, QCO_NO_OPTIONS);
+ qmp_register_command("my-command", qmp_marshal_my_command, QCO_NO_OPTIONS);
}
qapi_init(qmp_init_marshal);
- $ 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(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:
+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
$ 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 *local_err = NULL;
+ Error *err = NULL;
QMPEventFuncEmit emit;
emit = qmp_event_get_func_emit();
if (!emit) {
qmp = qmp_event_build_dict("MY_EVENT");
- emit(EXAMPLE_QAPI_EVENT_MY_EVENT, qmp, &local_err);
+ emit(EXAMPLE_QAPI_EVENT_MY_EVENT, qmp, &err);
- error_propagate(errp, local_err);
+ error_propagate(errp, err);
QDECREF(qmp);
}
- const char *EXAMPLE_QAPIEvent_lookup[] = {
- "MY_EVENT",
- NULL,
+ 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
+=== scripts/qapi-introspect.py ===
- #include "qapi/error.h"
- #include "qapi/qmp/qdict.h"
- #include "example-qapi-types.h"
+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.
- void qapi_event_send_my_event(Error **errp);
+Example:
- extern const char *EXAMPLE_QAPIEvent_lookup[];
- typedef enum EXAMPLE_QAPIEvent
- {
- EXAMPLE_QAPI_EVENT_MY_EVENT = 0,
- EXAMPLE_QAPI_EVENT_MAX = 1,
- } EXAMPLE_QAPIEvent;
+ $ 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\"}]";
Code Review / kvmfornfv.git / blobdiff