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| -rw-r--r-- | docs/qapi-code-gen.txt | 429 | ||||
| -rw-r--r-- | docs/qmp/qmp-spec.txt | 107 |
2 files changed, 414 insertions, 122 deletions
diff --git a/docs/qapi-code-gen.txt b/docs/qapi-code-gen.txt index e8bbaf8a07..6404a2d734 100644 --- a/docs/qapi-code-gen.txt +++ b/docs/qapi-code-gen.txt @@ -9,61 +9,179 @@ 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/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. +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. -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 are used. +To map QMP and QGA 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 == -This file defines the types, commands, and events used by QMP. It should -fully describe the interface used by QMP. - -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. - -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. - -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, QMP 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 + ## + { 'type': '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 QMP that satisfies the +schema. A type name should not be defined more than once. + +There are six top-level expressions recognized by the parser: +'include', 'command', 'type', 'enum', 'union', and 'event'. There are +several built-in types, such as 'int' and 'str'; additionally, the +top-level expressions can define complex types, enumeration types, and +several flavors of union 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. 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. 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. + +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':COMPLEX-TYPE-NAME +means that an expression has an optional key 'base', which if present +must have a value that forms a complex type name. + + +=== 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 === Includes === +Usage: { 'include': STRING } + 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 -file using the directive. Multiple includes of the same file are safe. +file using the directive. Multiple includes of the same file are +safe. 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. === Complex types === -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: +Usage: { 'type': STRING, 'data': DICT, '*base': COMPLEX-TYPE-NAME } + +A complex type 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 +complex type is: { 'type': 'MyType', '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 QMP usage. The default initialization value of an optional argument should not be changed between versions of QEMU unless the new default maintains backward @@ -108,22 +226,52 @@ both fields like this: { "file": "/some/place/my-image", "backing": "/some/place/my-backing-file" } + === 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 } + +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 enumeration values are passed as strings over the QMP 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 QMP clients; +however, removing enum values would break compatibility. For any +complex type 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 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': COMPLEX-TYPE-NAME, + 'discriminator': ENUM-MEMBER-OF-BASE } +or: { 'union': STRING, 'data': DICT, 'discriminator': {} } +Union types are used to let the user choose between several different +variants for an object. There are three flavors: simple (no +discriminator or base), flat (both base and discriminator are +strings), and anonymous (discriminator is an empty dictionary). 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', @@ -133,36 +281,34 @@ like in this example: '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 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, as in these examples: + { "type": "file", "data" : { "filename": "/some/place/my-image" } } { "type": "qcow2", "data" : { "backing-file": "/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 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' } } - { 'union': 'BlockdevOptions', - 'base': 'BlockdevCommonOptions', - 'data': { 'raw': 'RawOptions', - 'qcow2': 'Qcow2Options' } } - -And it looks like this on the wire: +A flat union definition specifies a complex type 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 type. - { "type": "qcow2", - "readonly": false, - "data" : { "backing-file": "/some/place/my-image", - "lazy-refcounts": true } } - - -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: +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': [ 'raw', 'qcow2' ] } { 'type': 'BlockdevCommonOptions', @@ -170,28 +316,47 @@ The above example can then be modified as follows: { 'union': 'BlockdevOptions', 'base': 'BlockdevCommonOptions', 'discriminator': 'driver', - 'data': { 'raw': 'RawOptions', + 'data': { 'file': 'FileOptions', 'qcow2': 'Qcow2Options' } } -Resulting in this JSON object: +Resulting in these JSON objects: + + { "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. + +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 complex type with a single member named 'data'. That is, - { "driver": "qcow2", - "readonly": false, - "backing-file": "/some/place/my-image", - "lazy-refcounts": true } + { 'union': 'Simple', 'data': { 'one': 'str', 'two': 'int' } } +is identical on the wire to: -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. + { 'enum': 'Enum', 'data': ['one', 'two'] } + { 'type': 'Base', 'data': { 'type': 'Enum' } } + { 'type': 'Branch1', 'data': { 'data': 'str' } } + { 'type': 'Branch2', 'data': { 'data': 'int' } } + { 'union': 'Flat': 'base': 'Base', 'discriminator': 'type', + 'data': { 'one': 'Branch1', 'two': 'Branch2' } } -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. + +The final flavor of unions is an anonymous union. While the other two +union types are always passed as a JSON object in the wire format, an +anonymous union instead allows the direct use of different types in +its place. 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. { 'union': 'BlockRef', 'discriminator': {}, @@ -208,23 +373,95 @@ This example allows using both of the following example objects: === 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-OR-DICT, + '*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 QMP +command exchange. + +The 'data' argument maps to the "arguments" dictionary passed in as +part of a QMP 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 'type' expression, with one exception noted below when +'gen' is used. + +The 'returns' member describes what will appear in the "return" field +of a QMP 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, or a dictionary +that declares an anonymous type with the same semantics as a 'type' +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. + +All commands 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' } } + { 'type': 'MyType', 'data': { '*value': 'str' } } + { 'command': 'my-second-command', + 'returns': [ 'MyType' ] } + +which would validate this QMP 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 QMP 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: + + { 'command': 'netdev_add', + 'data': {'type': 'str', 'id': 'str', '*props': '**'}, + '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 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 'type' 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: @@ -319,7 +556,7 @@ Example: #ifndef EXAMPLE_QAPI_TYPES_H #define EXAMPLE_QAPI_TYPES_H -[Builtin types omitted...] +[Built-in types omitted...] typedef struct UserDefOne UserDefOne; @@ -332,7 +569,7 @@ Example: struct UserDefOneList *next; } UserDefOneList; -[Functions on builtin types omitted...] +[Functions on built-in types omitted...] struct UserDefOne { @@ -431,7 +668,7 @@ Example: #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); diff --git a/docs/qmp/qmp-spec.txt b/docs/qmp/qmp-spec.txt index cb1600a983..4c28cd9438 100644 --- a/docs/qmp/qmp-spec.txt +++ b/docs/qmp/qmp-spec.txt @@ -11,8 +11,11 @@ later. See the COPYING file in the top-level directory. 1. Introduction =============== -This document specifies the QEMU Machine Protocol (QMP), a JSON-based protocol -which is available for applications to operate QEMU at the machine-level. +This document specifies the QEMU Machine Protocol (QMP), a JSON-based +protocol which is available for applications to operate QEMU at the +machine-level. It is also in use by the QEMU Guest Agent (QGA), which +is available for host applications to interact with the guest +operating system. 2. Protocol Specification ========================= @@ -26,14 +29,27 @@ following format: json-DATA-STRUCTURE-NAME -Where DATA-STRUCTURE-NAME is any valid JSON data structure, as defined by -the JSON standard: +Where DATA-STRUCTURE-NAME is any valid JSON data structure, as defined +by the JSON standard: -http://www.ietf.org/rfc/rfc4627.txt +http://www.ietf.org/rfc/rfc7159.txt -For convenience, json-object members and json-array elements mentioned in -this document will be in a certain order. However, in real protocol usage -they can be in ANY order, thus no particular order should be assumed. +The protocol is always encoded in UTF-8 except for synchronization +bytes (documented below); although thanks to json-string escape +sequences, the server will reply using only the strict ASCII subset. + +For convenience, json-object members mentioned in this document will +be in a certain order. However, in real protocol usage they can be in +ANY order, thus no particular order should be assumed. On the other +hand, use of json-array elements presumes that preserving order is +important unless specifically documented otherwise. Repeating a key +within a json-object gives unpredictable results. + +Also for convenience, the server will accept an extension of +'single-quoted' strings in place of the usual "double-quoted" +json-string, and both input forms of strings understand an additional +escape sequence of "\'" for a single quote. The server will only use +double quoting on output. 2.1 General Definitions ----------------------- @@ -60,7 +76,16 @@ The greeting message format is: - The "version" member contains the Server's version information (the format is the same of the query-version command) - The "capabilities" member specify the availability of features beyond the - baseline specification + baseline specification; the order of elements in this array has no + particular significance, so a client must search the entire array + when looking for a particular capability + +2.2.1 Capabilities +------------------ + +As of the date this document was last revised, no server or client +capability strings have been defined. + 2.3 Issuing Commands -------------------- @@ -73,10 +98,14 @@ The format for command execution is: - The "execute" member identifies the command to be executed by the Server - The "arguments" member is used to pass any arguments required for the - execution of the command, it is optional when no arguments are required + execution of the command, it is optional when no arguments are + required. Each command documents what contents will be considered + valid when handling the json-argument - The "id" member is a transaction identification associated with the command execution, it is optional and will be part of the response if - provided + provided. The "id" member can be any json-value, although most + clients merely use a json-number incremented for each successive + command 2.4 Commands Responses ---------------------- @@ -89,13 +118,15 @@ of a command execution: success or error. The format of a success response is: -{ "return": json-object, "id": json-value } +{ "return": json-value, "id": json-value } Where, -- The "return" member contains the command returned data, which is defined - in a per-command basis or an empty json-object if the command does not - return data +- The "return" member contains the data returned by the command, which + is defined on a per-command basis (usually a json-object or + json-array of json-objects, but sometimes a json-number, json-string, + or json-array of json-strings); it is an empty json-object if the + command does not return data - The "id" member contains the transaction identification associated with the command execution if issued by the Client @@ -122,7 +153,8 @@ if provided by the client. ----------------------- As a result of state changes, the Server may send messages unilaterally -to the Client at any time. They are called "asynchronous events". +to the Client at any time, when not in the middle of any other +response. They are called "asynchronous events". The format of asynchronous events is: @@ -134,13 +166,27 @@ The format of asynchronous events is: - The "event" member contains the event's name - The "data" member contains event specific data, which is defined in a per-event basis, it is optional -- The "timestamp" member contains the exact time of when the event occurred - in the Server. It is a fixed json-object with time in seconds and - microseconds +- The "timestamp" member contains the exact time of when the event + occurred in the Server. It is a fixed json-object with time in + seconds and microseconds relative to the Unix Epoch (1 Jan 1970); if + there is a failure to retrieve host time, both members of the + timestamp will be set to -1. For a listing of supported asynchronous events, please, refer to the qmp-events.txt file. +2.5 QGA Synchronization +----------------------- + +When using QGA, an additional synchronization feature is built into +the protocol. If the Client sends a raw 0xFF sentinel byte (not valid +JSON), then the Server will reset its state and discard all pending +data prior to the sentinel. Conversely, if the Client makes use of +the 'guest-sync-delimited' command, the Server will send a raw 0xFF +sentinel byte prior to its response, to aid the Client in discarding +any data prior to the sentinel. + + 3. QMP Examples =============== @@ -153,32 +199,37 @@ This section provides some examples of real QMP usage, in all of them S: { "QMP": { "version": { "qemu": { "micro": 50, "minor": 6, "major": 1 }, "package": ""}, "capabilities": []}} -3.2 Simple 'stop' execution +3.2 Client QMP negotiation +-------------------------- +C: { "execute": "qmp_capabilities" } +S: { "return": {}} + +3.3 Simple 'stop' execution --------------------------- C: { "execute": "stop" } S: { "return": {} } -3.3 KVM information +3.4 KVM information ------------------- C: { "execute": "query-kvm", "id": "example" } S: { "return": { "enabled": true, "present": true }, "id": "example"} -3.4 Parsing error +3.5 Parsing error ------------------ C: { "execute": } S: { "error": { "class": "GenericError", "desc": "Invalid JSON syntax" } } -3.5 Powerdown event +3.6 Powerdown event ------------------- S: { "timestamp": { "seconds": 1258551470, "microseconds": 802384 }, "event": "POWERDOWN" } 4. Capabilities Negotiation ----------------------------- +=========================== When a Client successfully establishes a connection, the Server is in Capabilities Negotiation mode. @@ -197,7 +248,7 @@ effect, all commands (except qmp_capabilities) are allowed and asynchronous messages are delivered. 5 Compatibility Considerations ------------------------------- +============================== All protocol changes or new features which modify the protocol format in an incompatible way are disabled by default and will be advertised by the @@ -221,12 +272,16 @@ However, Clients must not assume any particular: - Amount of errors generated by a command, that is, new errors can be added to any existing command in newer versions of the Server +Any command or field name beginning with "x-" is deemed experimental, +and may be withdrawn or changed in an incompatible manner in a future +release. + Of course, the Server does guarantee to send valid JSON. But apart from this, a Client should be "conservative in what they send, and liberal in what they accept". 6. Downstream extension of QMP ------------------------------- +============================== We recommend that downstream consumers of QEMU do *not* modify QMP. Management tools should be able to support both upstream and downstream |