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1 | = How to use the QAPI code generator = |
2 | ||
6fb55451 | 3 | Copyright IBM Corp. 2011 |
9ee86b85 | 4 | Copyright (C) 2012-2016 Red Hat, Inc. |
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5 | |
6 | This work is licensed under the terms of the GNU GPL, version 2 or | |
7 | later. See the COPYING file in the top-level directory. | |
8 | ||
9 | == Introduction == | |
10 | ||
b84da831 | 11 | QAPI is a native C API within QEMU which provides management-level |
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12 | functionality to internal and external users. For external |
13 | users/processes, this interface is made available by a JSON-based wire | |
14 | format for the QEMU Monitor Protocol (QMP) for controlling qemu, as | |
15 | well as the QEMU Guest Agent (QGA) for communicating with the guest. | |
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16 | The remainder of this document uses "Client JSON Protocol" when |
17 | referring to the wire contents of a QMP or QGA connection. | |
b84da831 | 18 | |
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19 | To map Client JSON Protocol interfaces to the native C QAPI |
20 | implementations, a JSON-based schema is used to define types and | |
21 | function signatures, and a set of scripts is used to generate types, | |
22 | signatures, and marshaling/dispatch code. This document will describe | |
23 | how the schemas, scripts, and resulting code are used. | |
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24 | |
25 | ||
26 | == QMP/Guest agent schema == | |
27 | ||
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28 | A QAPI schema file is designed to be loosely based on JSON |
29 | (http://www.ietf.org/rfc/rfc7159.txt) with changes for quoting style | |
30 | and the use of comments; a QAPI schema file is then parsed by a python | |
31 | code generation program. A valid QAPI schema consists of a series of | |
32 | top-level expressions, with no commas between them. Where | |
33 | dictionaries (JSON objects) are used, they are parsed as python | |
34 | OrderedDicts so that ordering is preserved (for predictable layout of | |
35 | generated C structs and parameter lists). Ordering doesn't matter | |
36 | between top-level expressions or the keys within an expression, but | |
37 | does matter within dictionary values for 'data' and 'returns' members | |
38 | of a single expression. QAPI schema input is written using 'single | |
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39 | quotes' instead of JSON's "double quotes" (in contrast, Client JSON |
40 | Protocol uses no comments, and while input accepts 'single quotes' as | |
41 | an extension, output is strict JSON using only "double quotes"). As | |
42 | in JSON, trailing commas are not permitted in arrays or dictionaries. | |
43 | Input must be ASCII (although QMP supports full Unicode strings, the | |
44 | QAPI parser does not). At present, there is no place where a QAPI | |
45 | schema requires the use of JSON numbers or null. | |
e790e666 | 46 | |
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47 | |
48 | === Comments === | |
49 | ||
e790e666 | 50 | Comments are allowed; anything between an unquoted # and the following |
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51 | newline is ignored. |
52 | ||
53 | A multi-line comment that starts and ends with a '##' line is a | |
54 | documentation comment. These are parsed by the documentation | |
55 | generator, which recognizes certain markup detailed below. | |
56 | ||
57 | ||
58 | ==== Documentation markup ==== | |
59 | ||
60 | Comment text starting with '=' is a section title: | |
61 | ||
62 | # = Section title | |
63 | ||
64 | Double the '=' for a subsection title: | |
65 | ||
66 | # == Subection title | |
67 | ||
68 | '|' denotes examples: | |
69 | ||
70 | # | Text of the example, may span | |
71 | # | multiple lines | |
72 | ||
73 | '*' starts an itemized list: | |
74 | ||
75 | # * First item, may span | |
76 | # multiple lines | |
77 | # * Second item | |
78 | ||
79 | You can also use '-' instead of '*'. | |
80 | ||
81 | A decimal number followed by '.' starts a numbered list: | |
82 | ||
83 | # 1. First item, may span | |
84 | # multiple lines | |
85 | # 2. Second item | |
86 | ||
87 | The actual number doesn't matter. You could even use '*' instead of | |
88 | '2.' for the second item. | |
89 | ||
90 | Lists can't be nested. Blank lines are currently not supported within | |
91 | lists. | |
92 | ||
93 | Additional whitespace between the initial '#' and the comment text is | |
94 | permitted. | |
95 | ||
96 | *foo* and _foo_ are for strong and emphasis styles respectively (they | |
97 | do not work over multiple lines). @foo is used to reference a name in | |
98 | the schema. | |
99 | ||
100 | Example: | |
101 | ||
102 | ## | |
103 | # = Section | |
104 | # == Subsection | |
105 | # | |
106 | # Some text foo with *strong* and _emphasis_ | |
107 | # 1. with a list | |
108 | # 2. like that | |
109 | # | |
110 | # And some code: | |
111 | # | $ echo foo | |
112 | # | -> do this | |
113 | # | <- get that | |
114 | # | |
115 | ## | |
116 | ||
117 | ||
118 | ==== Expression documentation ==== | |
119 | ||
120 | Each expression that isn't an include directive must be preceded by a | |
121 | documentation block. Such blocks are called expression documentation | |
122 | blocks. | |
123 | ||
124 | The documentation block consists of a first line naming the | |
125 | expression, an optional overview, a description of each argument (for | |
126 | commands and events) or member (for structs, unions and alternates), | |
127 | and optional tagged sections. | |
128 | ||
129 | FIXME: the parser accepts these things in almost any order. | |
130 | ||
131 | Optional arguments / members are tagged with the phrase '#optional', | |
132 | often with their default value; and extensions added after the | |
133 | expression was first released are also given a '(since x.y.z)' | |
134 | comment. | |
135 | ||
136 | A tagged section starts with one of the following words: | |
137 | "Note:"/"Notes:", "Since:", "Example"/"Examples", "Returns:", "TODO:". | |
138 | The section ends with the start of a new section. | |
139 | ||
140 | A 'Since: x.y.z' tagged section lists the release that introduced the | |
141 | expression. | |
142 | ||
143 | For example: | |
144 | ||
145 | ## | |
146 | # @BlockStats: | |
147 | # | |
148 | # Statistics of a virtual block device or a block backing device. | |
149 | # | |
150 | # @device: #optional If the stats are for a virtual block device, the name | |
151 | # corresponding to the virtual block device. | |
152 | # | |
153 | # @node-name: #optional The node name of the device. (since 2.3) | |
154 | # | |
155 | # ... more members ... | |
156 | # | |
157 | # Since: 0.14.0 | |
158 | ## | |
159 | { 'struct': 'BlockStats', | |
160 | 'data': {'*device': 'str', '*node-name': 'str', | |
161 | ... more members ... } } | |
162 | ||
163 | ## | |
164 | # @query-blockstats: | |
165 | # | |
166 | # Query the @BlockStats for all virtual block devices. | |
167 | # | |
168 | # @query-nodes: #optional If true, the command will query all the | |
169 | # block nodes ... explain, explain ... (since 2.3) | |
170 | # | |
171 | # Returns: A list of @BlockStats for each virtual block devices. | |
172 | # | |
173 | # Since: 0.14.0 | |
174 | # | |
175 | # Example: | |
176 | # | |
177 | # -> { "execute": "query-blockstats" } | |
178 | # <- { | |
179 | # ... lots of output ... | |
180 | # } | |
181 | # | |
182 | ## | |
183 | { 'command': 'query-blockstats', | |
184 | 'data': { '*query-nodes': 'bool' }, | |
185 | 'returns': ['BlockStats'] } | |
186 | ||
187 | ==== Free-form documentation ==== | |
188 | ||
189 | A documentation block that isn't an expression documentation block is | |
190 | a free-form documentation block. These may be used to provide | |
191 | additional text and structuring content. | |
192 | ||
193 | ||
194 | === Schema overview === | |
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195 | |
196 | The schema sets up a series of types, as well as commands and events | |
197 | that will use those types. Forward references are allowed: the parser | |
198 | scans in two passes, where the first pass learns all type names, and | |
199 | the second validates the schema and generates the code. This allows | |
200 | the definition of complex structs that can have mutually recursive | |
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201 | types, and allows for indefinite nesting of Client JSON Protocol that |
202 | satisfies the schema. A type name should not be defined more than | |
203 | once. It is permissible for the schema to contain additional types | |
204 | not used by any commands or events in the Client JSON Protocol, for | |
205 | the side effect of generated C code used internally. | |
e790e666 | 206 | |
7b1b98c4 | 207 | There are seven top-level expressions recognized by the parser: |
3b2a8b85 | 208 | 'include', 'command', 'struct', 'enum', 'union', 'alternate', and |
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209 | 'event'. There are several groups of types: simple types (a number of |
210 | built-in types, such as 'int' and 'str'; as well as enumerations), | |
211 | complex types (structs and two flavors of unions), and alternate types | |
212 | (a choice between other types). The 'command' and 'event' expressions | |
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213 | can refer to existing types by name, or list an anonymous type as a |
214 | dictionary. Listing a type name inside an array refers to a | |
215 | single-dimension array of that type; multi-dimension arrays are not | |
216 | directly supported (although an array of a complex struct that | |
217 | contains an array member is possible). | |
218 | ||
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219 | All names must begin with a letter, and contain only ASCII letters, |
220 | digits, hyphen, and underscore. There are two exceptions: enum values | |
221 | may start with a digit, and names that are downstream extensions (see | |
222 | section Downstream extensions) start with underscore. | |
223 | ||
224 | Names beginning with 'q_' are reserved for the generator, which uses | |
225 | them for munging QMP names that resemble C keywords or other | |
226 | problematic strings. For example, a member named "default" in qapi | |
227 | becomes "q_default" in the generated C code. | |
228 | ||
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229 | Types, commands, and events share a common namespace. Therefore, |
230 | generally speaking, type definitions should always use CamelCase for | |
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231 | user-defined type names, while built-in types are lowercase. |
232 | ||
233 | Type names ending with 'Kind' or 'List' are reserved for the | |
234 | generator, which uses them for implicit union enums and array types, | |
235 | respectively. | |
236 | ||
237 | Command names, and member names within a type, should be all lower | |
238 | case with words separated by a hyphen. However, some existing older | |
239 | commands and complex types use underscore; when extending such | |
240 | expressions, consistency is preferred over blindly avoiding | |
241 | underscore. | |
242 | ||
243 | Event names should be ALL_CAPS with words separated by underscore. | |
244 | ||
245 | Member names starting with 'has-' or 'has_' are reserved for the | |
246 | generator, which uses them for tracking optional members. | |
e790e666 | 247 | |
9ee86b85 | 248 | Any name (command, event, type, member, or enum value) beginning with |
e790e666 | 249 | "x-" is marked experimental, and may be withdrawn or changed |
79f75981 | 250 | incompatibly in a future release. |
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251 | |
252 | In the rest of this document, usage lines are given for each | |
253 | expression type, with literal strings written in lower case and | |
254 | placeholders written in capitals. If a literal string includes a | |
255 | prefix of '*', that key/value pair can be omitted from the expression. | |
3b2a8b85 | 256 | For example, a usage statement that includes '*base':STRUCT-NAME |
e790e666 | 257 | means that an expression has an optional key 'base', which if present |
3b2a8b85 | 258 | must have a value that forms a struct name. |
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259 | |
260 | ||
261 | === Built-in Types === | |
262 | ||
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263 | The following types are predefined, and map to C as follows: |
264 | ||
265 | Schema C JSON | |
266 | str char * any JSON string, UTF-8 | |
267 | number double any JSON number | |
268 | int int64_t a JSON number without fractional part | |
269 | that fits into the C integer type | |
270 | int8 int8_t likewise | |
271 | int16 int16_t likewise | |
272 | int32 int32_t likewise | |
273 | int64 int64_t likewise | |
274 | uint8 uint8_t likewise | |
275 | uint16 uint16_t likewise | |
276 | uint32 uint32_t likewise | |
277 | uint64 uint64_t likewise | |
278 | size uint64_t like uint64_t, except StringInputVisitor | |
279 | accepts size suffixes | |
280 | bool bool JSON true or false | |
28770e05 | 281 | any QObject * any JSON value |
7264f5c5 | 282 | QType QType JSON string matching enum QType values |
51631493 | 283 | |
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284 | |
285 | === Includes === | |
286 | ||
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287 | Usage: { 'include': STRING } |
288 | ||
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289 | The QAPI schema definitions can be modularized using the 'include' directive: |
290 | ||
e790e666 | 291 | { 'include': 'path/to/file.json' } |
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292 | |
293 | The directive is evaluated recursively, and include paths are relative to the | |
e790e666 | 294 | file using the directive. Multiple includes of the same file are |
4247f839 | 295 | idempotent. No other keys should appear in the expression, and the include |
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296 | value should be a string. |
297 | ||
298 | As a matter of style, it is a good idea to have all files be | |
299 | self-contained, but at the moment, nothing prevents an included file | |
300 | from making a forward reference to a type that is only introduced by | |
301 | an outer file. The parser may be made stricter in the future to | |
302 | prevent incomplete include files. | |
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303 | |
304 | ||
3b2a8b85 | 305 | === Struct types === |
51631493 | 306 | |
3b2a8b85 | 307 | Usage: { 'struct': STRING, 'data': DICT, '*base': STRUCT-NAME } |
e790e666 | 308 | |
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309 | A struct is a dictionary containing a single 'data' key whose value is |
310 | a dictionary; the dictionary may be empty. This corresponds to a | |
311 | struct in C or an Object in JSON. Each value of the 'data' dictionary | |
312 | must be the name of a type, or a one-element array containing a type | |
313 | name. An example of a struct is: | |
b84da831 | 314 | |
3b2a8b85 | 315 | { 'struct': 'MyType', |
acf8394e | 316 | 'data': { 'member1': 'str', 'member2': 'int', '*member3': 'str' } } |
b84da831 | 317 | |
e790e666 | 318 | The use of '*' as a prefix to the name means the member is optional in |
363b4262 | 319 | the corresponding JSON protocol usage. |
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320 | |
321 | The default initialization value of an optional argument should not be changed | |
322 | between versions of QEMU unless the new default maintains backward | |
323 | compatibility to the user-visible behavior of the old default. | |
324 | ||
325 | With proper documentation, this policy still allows some flexibility; for | |
326 | example, documenting that a default of 0 picks an optimal buffer size allows | |
327 | one release to declare the optimal size at 512 while another release declares | |
328 | the optimal size at 4096 - the user-visible behavior is not the bytes used by | |
329 | the buffer, but the fact that the buffer was optimal size. | |
330 | ||
331 | On input structures (only mentioned in the 'data' side of a command), changing | |
332 | from mandatory to optional is safe (older clients will supply the option, and | |
333 | newer clients can benefit from the default); changing from optional to | |
334 | mandatory is backwards incompatible (older clients may be omitting the option, | |
335 | and must continue to work). | |
336 | ||
337 | On output structures (only mentioned in the 'returns' side of a command), | |
338 | changing from mandatory to optional is in general unsafe (older clients may be | |
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339 | expecting the member, and could crash if it is missing), although it |
340 | can be done if the only way that the optional argument will be omitted | |
341 | is when it is triggered by the presence of a new input flag to the | |
342 | command that older clients don't know to send. Changing from optional | |
343 | to mandatory is safe. | |
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344 | |
345 | A structure that is used in both input and output of various commands | |
346 | must consider the backwards compatibility constraints of both directions | |
347 | of use. | |
622f557f | 348 | |
3b2a8b85 | 349 | A struct definition can specify another struct as its base. |
9ee86b85 | 350 | In this case, the members of the base type are included as top-level members |
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351 | of the new struct's dictionary in the Client JSON Protocol wire |
352 | format. An example definition is: | |
622f557f | 353 | |
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354 | { 'struct': 'BlockdevOptionsGenericFormat', 'data': { 'file': 'str' } } |
355 | { 'struct': 'BlockdevOptionsGenericCOWFormat', | |
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356 | 'base': 'BlockdevOptionsGenericFormat', |
357 | 'data': { '*backing': 'str' } } | |
358 | ||
359 | An example BlockdevOptionsGenericCOWFormat object on the wire could use | |
9ee86b85 | 360 | both members like this: |
622f557f KW |
361 | |
362 | { "file": "/some/place/my-image", | |
363 | "backing": "/some/place/my-backing-file" } | |
364 | ||
e790e666 | 365 | |
51631493 KW |
366 | === Enumeration types === |
367 | ||
e790e666 | 368 | Usage: { 'enum': STRING, 'data': ARRAY-OF-STRING } |
351d36e4 | 369 | { 'enum': STRING, '*prefix': STRING, 'data': ARRAY-OF-STRING } |
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370 | |
371 | An enumeration type is a dictionary containing a single 'data' key | |
372 | whose value is a list of strings. An example enumeration is: | |
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373 | |
374 | { 'enum': 'MyEnum', 'data': [ 'value1', 'value2', 'value3' ] } | |
375 | ||
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376 | Nothing prevents an empty enumeration, although it is probably not |
377 | useful. The list of strings should be lower case; if an enum name | |
378 | represents multiple words, use '-' between words. The string 'max' is | |
379 | not allowed as an enum value, and values should not be repeated. | |
380 | ||
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381 | The enum constants will be named by using a heuristic to turn the |
382 | type name into a set of underscore separated words. For the example | |
383 | above, 'MyEnum' will turn into 'MY_ENUM' giving a constant name | |
384 | of 'MY_ENUM_VALUE1' for the first value. If the default heuristic | |
9ee86b85 | 385 | does not result in a desirable name, the optional 'prefix' member |
351d36e4 DB |
386 | can be used when defining the enum. |
387 | ||
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388 | The enumeration values are passed as strings over the Client JSON |
389 | Protocol, but are encoded as C enum integral values in generated code. | |
390 | While the C code starts numbering at 0, it is better to use explicit | |
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391 | comparisons to enum values than implicit comparisons to 0; the C code |
392 | will also include a generated enum member ending in _MAX for tracking | |
393 | the size of the enum, useful when using common functions for | |
394 | converting between strings and enum values. Since the wire format | |
395 | always passes by name, it is acceptable to reorder or add new | |
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396 | enumeration members in any location without breaking clients of Client |
397 | JSON Protocol; however, removing enum values would break | |
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398 | compatibility. For any struct that has a member that will only contain |
399 | a finite set of string values, using an enum type for that member is | |
400 | better than open-coding the member to be type 'str'. | |
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401 | |
402 | ||
51631493 KW |
403 | === Union types === |
404 | ||
e790e666 | 405 | Usage: { 'union': STRING, 'data': DICT } |
ac4338f8 | 406 | or: { 'union': STRING, 'data': DICT, 'base': STRUCT-NAME-OR-DICT, |
e790e666 | 407 | 'discriminator': ENUM-MEMBER-OF-BASE } |
51631493 | 408 | |
e790e666 | 409 | Union types are used to let the user choose between several different |
7b1b98c4 | 410 | variants for an object. There are two flavors: simple (no |
02a57ae3 | 411 | discriminator or base), and flat (both discriminator and base). A union |
7b1b98c4 | 412 | type is defined using a data dictionary as explained in the following |
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413 | paragraphs. The data dictionary for either type of union must not |
414 | be empty. | |
51631493 | 415 | |
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416 | A simple union type defines a mapping from automatic discriminator |
417 | values to data types like in this example: | |
51631493 | 418 | |
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419 | { 'struct': 'BlockdevOptionsFile', 'data': { 'filename': 'str' } } |
420 | { 'struct': 'BlockdevOptionsQcow2', | |
421 | 'data': { 'backing': 'str', '*lazy-refcounts': 'bool' } } | |
51631493 | 422 | |
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423 | { 'union': 'BlockdevOptionsSimple', |
424 | 'data': { 'file': 'BlockdevOptionsFile', | |
425 | 'qcow2': 'BlockdevOptionsQcow2' } } | |
51631493 | 426 | |
363b4262 | 427 | In the Client JSON Protocol, a simple union is represented by a |
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428 | dictionary that contains the 'type' member as a discriminator, and a |
429 | 'data' member that is of the specified data type corresponding to the | |
363b4262 | 430 | discriminator value, as in these examples: |
51631493 | 431 | |
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432 | { "type": "file", "data": { "filename": "/some/place/my-image" } } |
433 | { "type": "qcow2", "data": { "backing": "/some/place/my-image", | |
434 | "lazy-refcounts": true } } | |
51631493 | 435 | |
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436 | The generated C code uses a struct containing a union. Additionally, |
437 | an implicit C enum 'NameKind' is created, corresponding to the union | |
438 | 'Name', for accessing the various branches of the union. No branch of | |
439 | the union can be named 'max', as this would collide with the implicit | |
440 | enum. The value for each branch can be of any type. | |
51631493 | 441 | |
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442 | A flat union definition avoids nesting on the wire, and specifies a |
443 | set of common members that occur in all variants of the union. The | |
d33c8a7d | 444 | 'base' key must specify either a type name (the type must be a |
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445 | struct, not a union), or a dictionary representing an anonymous type. |
446 | All branches of the union must be complex types, and the top-level | |
447 | members of the union dictionary on the wire will be combination of | |
448 | members from both the base type and the appropriate branch type (when | |
449 | merging two dictionaries, there must be no keys in common). The | |
450 | 'discriminator' member must be the name of a non-optional enum-typed | |
451 | member of the base struct. | |
51631493 | 452 | |
e790e666 | 453 | The following example enhances the above simple union example by |
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454 | adding an optional common member 'read-only', renaming the |
455 | discriminator to something more applicable than the simple union's | |
456 | default of 'type', and reducing the number of {} required on the wire: | |
50f2bdc7 | 457 | |
94a3f0af | 458 | { 'enum': 'BlockdevDriver', 'data': [ 'file', 'qcow2' ] } |
50f2bdc7 | 459 | { 'union': 'BlockdevOptions', |
ac4338f8 | 460 | 'base': { 'driver': 'BlockdevDriver', '*read-only': 'bool' }, |
50f2bdc7 | 461 | 'discriminator': 'driver', |
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462 | 'data': { 'file': 'BlockdevOptionsFile', |
463 | 'qcow2': 'BlockdevOptionsQcow2' } } | |
50f2bdc7 | 464 | |
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465 | Resulting in these JSON objects: |
466 | ||
bd59adce | 467 | { "driver": "file", "read-only": true, |
e790e666 | 468 | "filename": "/some/place/my-image" } |
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469 | { "driver": "qcow2", "read-only": false, |
470 | "backing": "/some/place/my-image", "lazy-refcounts": true } | |
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471 | |
472 | Notice that in a flat union, the discriminator name is controlled by | |
473 | the user, but because it must map to a base member with enum type, the | |
474 | code generator can ensure that branches exist for all values of the | |
475 | enum (although the order of the keys need not match the declaration of | |
476 | the enum). In the resulting generated C data types, a flat union is | |
9ee86b85 EB |
477 | represented as a struct with the base members included directly, and |
478 | then a union of structures for each branch of the struct. | |
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479 | |
480 | A simple union can always be re-written as a flat union where the base | |
481 | class has a single member named 'type', and where each branch of the | |
3b2a8b85 | 482 | union has a struct with a single member named 'data'. That is, |
50f2bdc7 | 483 | |
e790e666 | 484 | { 'union': 'Simple', 'data': { 'one': 'str', 'two': 'int' } } |
50f2bdc7 | 485 | |
e790e666 | 486 | is identical on the wire to: |
50f2bdc7 | 487 | |
e790e666 | 488 | { 'enum': 'Enum', 'data': ['one', 'two'] } |
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489 | { 'struct': 'Branch1', 'data': { 'data': 'str' } } |
490 | { 'struct': 'Branch2', 'data': { 'data': 'int' } } | |
ac4338f8 | 491 | { 'union': 'Flat': 'base': { 'type': 'Enum' }, 'discriminator': 'type', |
e790e666 | 492 | 'data': { 'one': 'Branch1', 'two': 'Branch2' } } |
69dd62df | 493 | |
e790e666 | 494 | |
7b1b98c4 | 495 | === Alternate types === |
69dd62df | 496 | |
7b1b98c4 EB |
497 | Usage: { 'alternate': STRING, 'data': DICT } |
498 | ||
499 | An alternate type is one that allows a choice between two or more JSON | |
500 | data types (string, integer, number, or object, but currently not | |
501 | array) on the wire. The definition is similar to a simple union type, | |
502 | where each branch of the union names a QAPI type. For example: | |
503 | ||
bd59adce | 504 | { 'alternate': 'BlockdevRef', |
69dd62df KW |
505 | 'data': { 'definition': 'BlockdevOptions', |
506 | 'reference': 'str' } } | |
507 | ||
7b1b98c4 | 508 | Unlike a union, the discriminator string is never passed on the wire |
363b4262 EB |
509 | for the Client JSON Protocol. Instead, the value's JSON type serves |
510 | as an implicit discriminator, which in turn means that an alternate | |
511 | can only express a choice between types represented differently in | |
512 | JSON. If a branch is typed as the 'bool' built-in, the alternate | |
513 | accepts true and false; if it is typed as any of the various numeric | |
514 | built-ins, it accepts a JSON number; if it is typed as a 'str' | |
515 | built-in or named enum type, it accepts a JSON string; and if it is | |
516 | typed as a complex type (struct or union), it accepts a JSON object. | |
517 | Two different complex types, for instance, aren't permitted, because | |
518 | both are represented as a JSON object. | |
7b1b98c4 EB |
519 | |
520 | The example alternate declaration above allows using both of the | |
521 | following example objects: | |
69dd62df KW |
522 | |
523 | { "file": "my_existing_block_device_id" } | |
524 | { "file": { "driver": "file", | |
bd59adce | 525 | "read-only": false, |
63922c64 | 526 | "filename": "/tmp/mydisk.qcow2" } } |
69dd62df KW |
527 | |
528 | ||
51631493 | 529 | === Commands === |
b84da831 | 530 | |
e790e666 | 531 | Usage: { 'command': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT, |
c818408e | 532 | '*returns': TYPE-NAME, '*boxed': true, |
e790e666 EB |
533 | '*gen': false, '*success-response': false } |
534 | ||
535 | Commands are defined by using a dictionary containing several members, | |
536 | where three members are most common. The 'command' member is a | |
363b4262 EB |
537 | mandatory string, and determines the "execute" value passed in a |
538 | Client JSON Protocol command exchange. | |
e790e666 EB |
539 | |
540 | The 'data' argument maps to the "arguments" dictionary passed in as | |
363b4262 EB |
541 | part of a Client JSON Protocol command. The 'data' member is optional |
542 | and defaults to {} (an empty dictionary). If present, it must be the | |
315932b5 MA |
543 | string name of a complex type, or a dictionary that declares an |
544 | anonymous type with the same semantics as a 'struct' expression, with | |
545 | one exception noted below when 'gen' is used. | |
e790e666 | 546 | |
9ee86b85 | 547 | The 'returns' member describes what will appear in the "return" member |
363b4262 EB |
548 | of a Client JSON Protocol reply on successful completion of a command. |
549 | The member is optional from the command declaration; if absent, the | |
9ee86b85 | 550 | "return" member will be an empty dictionary. If 'returns' is present, |
363b4262 EB |
551 | it must be the string name of a complex or built-in type, a |
552 | one-element array containing the name of a complex or built-in type, | |
9b090d42 MA |
553 | with one exception noted below when 'gen' is used. Although it is |
554 | permitted to have the 'returns' member name a built-in type or an | |
555 | array of built-in types, any command that does this cannot be extended | |
556 | to return additional information in the future; thus, new commands | |
557 | should strongly consider returning a dictionary-based type or an array | |
9ee86b85 | 558 | of dictionaries, even if the dictionary only contains one member at the |
9b090d42 | 559 | present. |
363b4262 EB |
560 | |
561 | All commands in Client JSON Protocol use a dictionary to report | |
562 | failure, with no way to specify that in QAPI. Where the error return | |
563 | is different than the usual GenericError class in order to help the | |
564 | client react differently to certain error conditions, it is worth | |
565 | documenting this in the comments before the command declaration. | |
e790e666 EB |
566 | |
567 | Some example commands: | |
568 | ||
569 | { 'command': 'my-first-command', | |
570 | 'data': { 'arg1': 'str', '*arg2': 'str' } } | |
3b2a8b85 | 571 | { 'struct': 'MyType', 'data': { '*value': 'str' } } |
e790e666 EB |
572 | { 'command': 'my-second-command', |
573 | 'returns': [ 'MyType' ] } | |
574 | ||
363b4262 | 575 | which would validate this Client JSON Protocol transaction: |
e790e666 EB |
576 | |
577 | => { "execute": "my-first-command", | |
578 | "arguments": { "arg1": "hello" } } | |
579 | <= { "return": { } } | |
580 | => { "execute": "my-second-command" } | |
581 | <= { "return": [ { "value": "one" }, { } ] } | |
582 | ||
c818408e EB |
583 | The generator emits a prototype for the user's function implementing |
584 | the command. Normally, 'data' is a dictionary for an anonymous type, | |
585 | or names a struct type (possibly empty, but not a union), and its | |
586 | members are passed as separate arguments to this function. If the | |
587 | command definition includes a key 'boxed' with the boolean value true, | |
588 | then 'data' is instead the name of any non-empty complex type | |
589 | (struct, union, or alternate), and a pointer to that QAPI type is | |
590 | passed as a single argument. | |
591 | ||
592 | The generator also emits a marshalling function that extracts | |
593 | arguments for the user's function out of an input QDict, calls the | |
594 | user's function, and if it succeeded, builds an output QObject from | |
595 | its return value. | |
596 | ||
e790e666 | 597 | In rare cases, QAPI cannot express a type-safe representation of a |
2d21291a MA |
598 | corresponding Client JSON Protocol command. You then have to suppress |
599 | generation of a marshalling function by including a key 'gen' with | |
600 | boolean value false, and instead write your own function. Please try | |
601 | to avoid adding new commands that rely on this, and instead use | |
602 | type-safe unions. For an example of this usage: | |
e790e666 EB |
603 | |
604 | { 'command': 'netdev_add', | |
b8a98326 | 605 | 'data': {'type': 'str', 'id': 'str'}, |
e790e666 EB |
606 | 'gen': false } |
607 | ||
608 | Normally, the QAPI schema is used to describe synchronous exchanges, | |
609 | where a response is expected. But in some cases, the action of a | |
610 | command is expected to change state in a way that a successful | |
611 | response is not possible (although the command will still return a | |
612 | normal dictionary error on failure). When a successful reply is not | |
613 | possible, the command expression should include the optional key | |
614 | 'success-response' with boolean value false. So far, only QGA makes | |
9ee86b85 | 615 | use of this member. |
b84da831 | 616 | |
b84da831 | 617 | |
21cd70df WX |
618 | === Events === |
619 | ||
c818408e EB |
620 | Usage: { 'event': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT, |
621 | '*boxed': true } | |
e790e666 EB |
622 | |
623 | Events are defined with the keyword 'event'. It is not allowed to | |
624 | name an event 'MAX', since the generator also produces a C enumeration | |
625 | of all event names with a generated _MAX value at the end. When | |
626 | 'data' is also specified, additional info will be included in the | |
3b2a8b85 | 627 | event, with similar semantics to a 'struct' expression. Finally there |
e790e666 EB |
628 | will be C API generated in qapi-event.h; when called by QEMU code, a |
629 | message with timestamp will be emitted on the wire. | |
21cd70df WX |
630 | |
631 | An example event is: | |
632 | ||
633 | { 'event': 'EVENT_C', | |
634 | 'data': { '*a': 'int', 'b': 'str' } } | |
635 | ||
636 | Resulting in this JSON object: | |
637 | ||
638 | { "event": "EVENT_C", | |
639 | "data": { "b": "test string" }, | |
640 | "timestamp": { "seconds": 1267020223, "microseconds": 435656 } } | |
b84da831 | 641 | |
c818408e EB |
642 | The generator emits a function to send the event. Normally, 'data' is |
643 | a dictionary for an anonymous type, or names a struct type (possibly | |
644 | empty, but not a union), and its members are passed as separate | |
645 | arguments to this function. If the event definition includes a key | |
646 | 'boxed' with the boolean value true, then 'data' is instead the name of | |
647 | any non-empty complex type (struct, union, or alternate), and a | |
648 | pointer to that QAPI type is passed as a single argument. | |
649 | ||
59a2c4ce | 650 | |
79f75981 MA |
651 | === Downstream extensions === |
652 | ||
653 | QAPI schema names that are externally visible, say in the Client JSON | |
654 | Protocol, need to be managed with care. Names starting with a | |
655 | downstream prefix of the form __RFQDN_ are reserved for the downstream | |
656 | who controls the valid, reverse fully qualified domain name RFQDN. | |
657 | RFQDN may only contain ASCII letters, digits, hyphen and period. | |
658 | ||
659 | Example: Red Hat, Inc. controls redhat.com, and may therefore add a | |
660 | downstream command __com.redhat_drive-mirror. | |
661 | ||
662 | ||
39a18158 MA |
663 | == Client JSON Protocol introspection == |
664 | ||
665 | Clients of a Client JSON Protocol commonly need to figure out what | |
666 | exactly the server (QEMU) supports. | |
667 | ||
668 | For this purpose, QMP provides introspection via command | |
669 | query-qmp-schema. QGA currently doesn't support introspection. | |
670 | ||
39a65e2c EB |
671 | While Client JSON Protocol wire compatibility should be maintained |
672 | between qemu versions, we cannot make the same guarantees for | |
673 | introspection stability. For example, one version of qemu may provide | |
674 | a non-variant optional member of a struct, and a later version rework | |
675 | the member to instead be non-optional and associated with a variant. | |
676 | Likewise, one version of qemu may list a member with open-ended type | |
677 | 'str', and a later version could convert it to a finite set of strings | |
678 | via an enum type; or a member may be converted from a specific type to | |
679 | an alternate that represents a choice between the original type and | |
680 | something else. | |
681 | ||
39a18158 MA |
682 | query-qmp-schema returns a JSON array of SchemaInfo objects. These |
683 | objects together describe the wire ABI, as defined in the QAPI schema. | |
f5455044 EB |
684 | There is no specified order to the SchemaInfo objects returned; a |
685 | client must search for a particular name throughout the entire array | |
686 | to learn more about that name, but is at least guaranteed that there | |
687 | will be no collisions between type, command, and event names. | |
39a18158 MA |
688 | |
689 | However, the SchemaInfo can't reflect all the rules and restrictions | |
690 | that apply to QMP. It's interface introspection (figuring out what's | |
691 | there), not interface specification. The specification is in the QAPI | |
692 | schema. To understand how QMP is to be used, you need to study the | |
693 | QAPI schema. | |
694 | ||
695 | Like any other command, query-qmp-schema is itself defined in the QAPI | |
696 | schema, along with the SchemaInfo type. This text attempts to give an | |
697 | overview how things work. For details you need to consult the QAPI | |
698 | schema. | |
699 | ||
700 | SchemaInfo objects have common members "name" and "meta-type", and | |
701 | additional variant members depending on the value of meta-type. | |
702 | ||
703 | Each SchemaInfo object describes a wire ABI entity of a certain | |
704 | meta-type: a command, event or one of several kinds of type. | |
705 | ||
1a9a507b MA |
706 | SchemaInfo for commands and events have the same name as in the QAPI |
707 | schema. | |
39a18158 MA |
708 | |
709 | Command and event names are part of the wire ABI, but type names are | |
1a9a507b MA |
710 | not. Therefore, the SchemaInfo for types have auto-generated |
711 | meaningless names. For readability, the examples in this section use | |
712 | meaningful type names instead. | |
713 | ||
714 | To examine a type, start with a command or event using it, then follow | |
715 | references by name. | |
39a18158 MA |
716 | |
717 | QAPI schema definitions not reachable that way are omitted. | |
718 | ||
719 | The SchemaInfo for a command has meta-type "command", and variant | |
720 | members "arg-type" and "ret-type". On the wire, the "arguments" | |
721 | member of a client's "execute" command must conform to the object type | |
722 | named by "arg-type". The "return" member that the server passes in a | |
723 | success response conforms to the type named by "ret-type". | |
724 | ||
725 | If the command takes no arguments, "arg-type" names an object type | |
726 | without members. Likewise, if the command returns nothing, "ret-type" | |
727 | names an object type without members. | |
728 | ||
729 | Example: the SchemaInfo for command query-qmp-schema | |
730 | ||
731 | { "name": "query-qmp-schema", "meta-type": "command", | |
7599697c | 732 | "arg-type": "q_empty", "ret-type": "SchemaInfoList" } |
39a18158 | 733 | |
7599697c | 734 | Type "q_empty" is an automatic object type without members, and type |
39a18158 MA |
735 | "SchemaInfoList" is the array of SchemaInfo type. |
736 | ||
737 | The SchemaInfo for an event has meta-type "event", and variant member | |
738 | "arg-type". On the wire, a "data" member that the server passes in an | |
739 | event conforms to the object type named by "arg-type". | |
740 | ||
741 | If the event carries no additional information, "arg-type" names an | |
742 | object type without members. The event may not have a data member on | |
743 | the wire then. | |
744 | ||
745 | Each command or event defined with dictionary-valued 'data' in the | |
1a9a507b | 746 | QAPI schema implicitly defines an object type. |
39a18158 MA |
747 | |
748 | Example: the SchemaInfo for EVENT_C from section Events | |
749 | ||
750 | { "name": "EVENT_C", "meta-type": "event", | |
7599697c | 751 | "arg-type": "q_obj-EVENT_C-arg" } |
39a18158 | 752 | |
7599697c | 753 | Type "q_obj-EVENT_C-arg" is an implicitly defined object type with |
39a18158 MA |
754 | the two members from the event's definition. |
755 | ||
756 | The SchemaInfo for struct and union types has meta-type "object". | |
757 | ||
758 | The SchemaInfo for a struct type has variant member "members". | |
759 | ||
760 | The SchemaInfo for a union type additionally has variant members "tag" | |
761 | and "variants". | |
762 | ||
763 | "members" is a JSON array describing the object's common members, if | |
764 | any. Each element is a JSON object with members "name" (the member's | |
765 | name), "type" (the name of its type), and optionally "default". The | |
766 | member is optional if "default" is present. Currently, "default" can | |
767 | only have value null. Other values are reserved for future | |
f5455044 EB |
768 | extensions. The "members" array is in no particular order; clients |
769 | must search the entire object when learning whether a particular | |
770 | member is supported. | |
39a18158 MA |
771 | |
772 | Example: the SchemaInfo for MyType from section Struct types | |
773 | ||
774 | { "name": "MyType", "meta-type": "object", | |
775 | "members": [ | |
776 | { "name": "member1", "type": "str" }, | |
777 | { "name": "member2", "type": "int" }, | |
778 | { "name": "member3", "type": "str", "default": null } ] } | |
779 | ||
780 | "tag" is the name of the common member serving as type tag. | |
781 | "variants" is a JSON array describing the object's variant members. | |
782 | Each element is a JSON object with members "case" (the value of type | |
783 | tag this element applies to) and "type" (the name of an object type | |
f5455044 EB |
784 | that provides the variant members for this type tag value). The |
785 | "variants" array is in no particular order, and is not guaranteed to | |
786 | list cases in the same order as the corresponding "tag" enum type. | |
39a18158 MA |
787 | |
788 | Example: the SchemaInfo for flat union BlockdevOptions from section | |
789 | Union types | |
790 | ||
791 | { "name": "BlockdevOptions", "meta-type": "object", | |
792 | "members": [ | |
793 | { "name": "driver", "type": "BlockdevDriver" }, | |
bd59adce | 794 | { "name": "read-only", "type": "bool", "default": null } ], |
39a18158 MA |
795 | "tag": "driver", |
796 | "variants": [ | |
bd59adce EB |
797 | { "case": "file", "type": "BlockdevOptionsFile" }, |
798 | { "case": "qcow2", "type": "BlockdevOptionsQcow2" } ] } | |
39a18158 MA |
799 | |
800 | Note that base types are "flattened": its members are included in the | |
801 | "members" array. | |
802 | ||
803 | A simple union implicitly defines an enumeration type for its implicit | |
804 | discriminator (called "type" on the wire, see section Union types). | |
39a18158 MA |
805 | |
806 | A simple union implicitly defines an object type for each of its | |
1a9a507b | 807 | variants. |
39a18158 | 808 | |
bd59adce | 809 | Example: the SchemaInfo for simple union BlockdevOptionsSimple from section |
39a18158 MA |
810 | Union types |
811 | ||
bd59adce | 812 | { "name": "BlockdevOptionsSimple", "meta-type": "object", |
39a18158 | 813 | "members": [ |
bd59adce | 814 | { "name": "type", "type": "BlockdevOptionsSimpleKind" } ], |
39a18158 MA |
815 | "tag": "type", |
816 | "variants": [ | |
bd59adce EB |
817 | { "case": "file", "type": "q_obj-BlockdevOptionsFile-wrapper" }, |
818 | { "case": "qcow2", "type": "q_obj-BlockdevOptionsQcow2-wrapper" } ] } | |
39a18158 | 819 | |
bd59adce EB |
820 | Enumeration type "BlockdevOptionsSimpleKind" and the object types |
821 | "q_obj-BlockdevOptionsFile-wrapper", "q_obj-BlockdevOptionsQcow2-wrapper" | |
822 | are implicitly defined. | |
39a18158 MA |
823 | |
824 | The SchemaInfo for an alternate type has meta-type "alternate", and | |
825 | variant member "members". "members" is a JSON array. Each element is | |
826 | a JSON object with member "type", which names a type. Values of the | |
f5455044 EB |
827 | alternate type conform to exactly one of its member types. There is |
828 | no guarantee on the order in which "members" will be listed. | |
39a18158 | 829 | |
bd59adce | 830 | Example: the SchemaInfo for BlockdevRef from section Alternate types |
39a18158 | 831 | |
bd59adce | 832 | { "name": "BlockdevRef", "meta-type": "alternate", |
39a18158 MA |
833 | "members": [ |
834 | { "type": "BlockdevOptions" }, | |
835 | { "type": "str" } ] } | |
836 | ||
837 | The SchemaInfo for an array type has meta-type "array", and variant | |
838 | member "element-type", which names the array's element type. Array | |
ce5fcb47 EB |
839 | types are implicitly defined. For convenience, the array's name may |
840 | resemble the element type; however, clients should examine member | |
841 | "element-type" instead of making assumptions based on parsing member | |
842 | "name". | |
39a18158 MA |
843 | |
844 | Example: the SchemaInfo for ['str'] | |
845 | ||
ce5fcb47 | 846 | { "name": "[str]", "meta-type": "array", |
39a18158 MA |
847 | "element-type": "str" } |
848 | ||
849 | The SchemaInfo for an enumeration type has meta-type "enum" and | |
f5455044 EB |
850 | variant member "values". The values are listed in no particular |
851 | order; clients must search the entire enum when learning whether a | |
852 | particular value is supported. | |
39a18158 MA |
853 | |
854 | Example: the SchemaInfo for MyEnum from section Enumeration types | |
855 | ||
856 | { "name": "MyEnum", "meta-type": "enum", | |
857 | "values": [ "value1", "value2", "value3" ] } | |
858 | ||
859 | The SchemaInfo for a built-in type has the same name as the type in | |
860 | the QAPI schema (see section Built-in Types), with one exception | |
861 | detailed below. It has variant member "json-type" that shows how | |
862 | values of this type are encoded on the wire. | |
863 | ||
864 | Example: the SchemaInfo for str | |
865 | ||
866 | { "name": "str", "meta-type": "builtin", "json-type": "string" } | |
867 | ||
868 | The QAPI schema supports a number of integer types that only differ in | |
869 | how they map to C. They are identical as far as SchemaInfo is | |
870 | concerned. Therefore, they get all mapped to a single type "int" in | |
871 | SchemaInfo. | |
872 | ||
873 | As explained above, type names are not part of the wire ABI. Not even | |
874 | the names of built-in types. Clients should examine member | |
875 | "json-type" instead of hard-coding names of built-in types. | |
876 | ||
877 | ||
b84da831 MR |
878 | == Code generation == |
879 | ||
9ee86b85 | 880 | Schemas are fed into five scripts to generate all the code/files that, |
39a18158 MA |
881 | paired with the core QAPI libraries, comprise everything required to |
882 | take JSON commands read in by a Client JSON Protocol server, unmarshal | |
883 | the arguments into the underlying C types, call into the corresponding | |
9ee86b85 EB |
884 | C function, map the response back to a Client JSON Protocol response |
885 | to be returned to the user, and introspect the commands. | |
b84da831 | 886 | |
9ee86b85 EB |
887 | As an example, we'll use the following schema, which describes a |
888 | single complex user-defined type, along with command which takes a | |
889 | list of that type as a parameter, and returns a single element of that | |
890 | type. The user is responsible for writing the implementation of | |
891 | qmp_my_command(); everything else is produced by the generator. | |
b84da831 | 892 | |
87a560c4 | 893 | $ cat example-schema.json |
3b2a8b85 | 894 | { 'struct': 'UserDefOne', |
9ee86b85 | 895 | 'data': { 'integer': 'int', '*string': 'str' } } |
b84da831 MR |
896 | |
897 | { 'command': 'my-command', | |
9ee86b85 | 898 | 'data': { 'arg1': ['UserDefOne'] }, |
b84da831 | 899 | 'returns': 'UserDefOne' } |
b84da831 | 900 | |
59a2c4ce EB |
901 | { 'event': 'MY_EVENT' } |
902 | ||
9ee86b85 EB |
903 | For a more thorough look at generated code, the testsuite includes |
904 | tests/qapi-schema/qapi-schema-tests.json that covers more examples of | |
905 | what the generator will accept, and compiles the resulting C code as | |
906 | part of 'make check-unit'. | |
907 | ||
b84da831 MR |
908 | === scripts/qapi-types.py === |
909 | ||
9ee86b85 EB |
910 | Used to generate the C types defined by a schema, along with |
911 | supporting code. The following files are created: | |
b84da831 MR |
912 | |
913 | $(prefix)qapi-types.h - C types corresponding to types defined in | |
914 | the schema you pass in | |
915 | $(prefix)qapi-types.c - Cleanup functions for the above C types | |
916 | ||
917 | The $(prefix) is an optional parameter used as a namespace to keep the | |
918 | generated code from one schema/code-generation separated from others so code | |
919 | can be generated/used from multiple schemas without clobbering previously | |
920 | created code. | |
921 | ||
922 | Example: | |
923 | ||
87a560c4 | 924 | $ python scripts/qapi-types.py --output-dir="qapi-generated" \ |
16d80f61 | 925 | --prefix="example-" example-schema.json |
9ee86b85 EB |
926 | $ cat qapi-generated/example-qapi-types.h |
927 | [Uninteresting stuff omitted...] | |
928 | ||
929 | #ifndef EXAMPLE_QAPI_TYPES_H | |
930 | #define EXAMPLE_QAPI_TYPES_H | |
931 | ||
932 | [Built-in types omitted...] | |
933 | ||
934 | typedef struct UserDefOne UserDefOne; | |
935 | ||
936 | typedef struct UserDefOneList UserDefOneList; | |
937 | ||
938 | struct UserDefOne { | |
939 | int64_t integer; | |
940 | bool has_string; | |
941 | char *string; | |
942 | }; | |
943 | ||
944 | void qapi_free_UserDefOne(UserDefOne *obj); | |
945 | ||
946 | struct UserDefOneList { | |
947 | UserDefOneList *next; | |
948 | UserDefOne *value; | |
949 | }; | |
950 | ||
951 | void qapi_free_UserDefOneList(UserDefOneList *obj); | |
952 | ||
953 | #endif | |
87a560c4 | 954 | $ cat qapi-generated/example-qapi-types.c |
6e2bb3ec MA |
955 | [Uninteresting stuff omitted...] |
956 | ||
2b162ccb | 957 | void qapi_free_UserDefOne(UserDefOne *obj) |
6e2bb3ec | 958 | { |
6e2bb3ec MA |
959 | Visitor *v; |
960 | ||
961 | if (!obj) { | |
962 | return; | |
963 | } | |
964 | ||
2c0ef9f4 | 965 | v = qapi_dealloc_visitor_new(); |
9ee86b85 | 966 | visit_type_UserDefOne(v, NULL, &obj, NULL); |
2c0ef9f4 | 967 | visit_free(v); |
6e2bb3ec | 968 | } |
b84da831 | 969 | |
2b162ccb | 970 | void qapi_free_UserDefOneList(UserDefOneList *obj) |
b84da831 | 971 | { |
b84da831 MR |
972 | Visitor *v; |
973 | ||
974 | if (!obj) { | |
975 | return; | |
976 | } | |
977 | ||
2c0ef9f4 | 978 | v = qapi_dealloc_visitor_new(); |
9ee86b85 | 979 | visit_type_UserDefOneList(v, NULL, &obj, NULL); |
2c0ef9f4 | 980 | visit_free(v); |
b84da831 | 981 | } |
b84da831 | 982 | |
b84da831 MR |
983 | === scripts/qapi-visit.py === |
984 | ||
9ee86b85 EB |
985 | Used to generate the visitor functions used to walk through and |
986 | convert between a native QAPI C data structure and some other format | |
987 | (such as QObject); the generated functions are named visit_type_FOO() | |
988 | and visit_type_FOO_members(). | |
b84da831 MR |
989 | |
990 | The following files are generated: | |
991 | ||
992 | $(prefix)qapi-visit.c: visitor function for a particular C type, used | |
993 | to automagically convert QObjects into the | |
994 | corresponding C type and vice-versa, as well | |
995 | as for deallocating memory for an existing C | |
996 | type | |
997 | ||
998 | $(prefix)qapi-visit.h: declarations for previously mentioned visitor | |
999 | functions | |
1000 | ||
1001 | Example: | |
1002 | ||
87a560c4 | 1003 | $ python scripts/qapi-visit.py --output-dir="qapi-generated" |
16d80f61 | 1004 | --prefix="example-" example-schema.json |
9ee86b85 EB |
1005 | $ cat qapi-generated/example-qapi-visit.h |
1006 | [Uninteresting stuff omitted...] | |
1007 | ||
1008 | #ifndef EXAMPLE_QAPI_VISIT_H | |
1009 | #define EXAMPLE_QAPI_VISIT_H | |
1010 | ||
1011 | [Visitors for built-in types omitted...] | |
1012 | ||
1013 | void visit_type_UserDefOne_members(Visitor *v, UserDefOne *obj, Error **errp); | |
1014 | void visit_type_UserDefOne(Visitor *v, const char *name, UserDefOne **obj, Error **errp); | |
1015 | void visit_type_UserDefOneList(Visitor *v, const char *name, UserDefOneList **obj, Error **errp); | |
1016 | ||
1017 | #endif | |
87a560c4 | 1018 | $ cat qapi-generated/example-qapi-visit.c |
6e2bb3ec | 1019 | [Uninteresting stuff omitted...] |
b84da831 | 1020 | |
9ee86b85 | 1021 | void visit_type_UserDefOne_members(Visitor *v, UserDefOne *obj, Error **errp) |
6e2bb3ec MA |
1022 | { |
1023 | Error *err = NULL; | |
3a864e7c | 1024 | |
9ee86b85 | 1025 | visit_type_int(v, "integer", &obj->integer, &err); |
297a3646 MA |
1026 | if (err) { |
1027 | goto out; | |
1028 | } | |
9ee86b85 EB |
1029 | if (visit_optional(v, "string", &obj->has_string)) { |
1030 | visit_type_str(v, "string", &obj->string, &err); | |
1031 | if (err) { | |
1032 | goto out; | |
1033 | } | |
297a3646 | 1034 | } |
6e2bb3ec | 1035 | |
297a3646 | 1036 | out: |
6e2bb3ec MA |
1037 | error_propagate(errp, err); |
1038 | } | |
b84da831 | 1039 | |
9ee86b85 | 1040 | void visit_type_UserDefOne(Visitor *v, const char *name, UserDefOne **obj, Error **errp) |
b84da831 | 1041 | { |
297a3646 MA |
1042 | Error *err = NULL; |
1043 | ||
9ee86b85 EB |
1044 | visit_start_struct(v, name, (void **)obj, sizeof(UserDefOne), &err); |
1045 | if (err) { | |
1046 | goto out; | |
1047 | } | |
1048 | if (!*obj) { | |
1049 | goto out_obj; | |
6e2bb3ec | 1050 | } |
9ee86b85 | 1051 | visit_type_UserDefOne_members(v, *obj, &err); |
15c2f669 EB |
1052 | if (err) { |
1053 | goto out_obj; | |
1054 | } | |
1055 | visit_check_struct(v, &err); | |
9ee86b85 | 1056 | out_obj: |
1158bb2a | 1057 | visit_end_struct(v, (void **)obj); |
68ab47e4 EB |
1058 | if (err && visit_is_input(v)) { |
1059 | qapi_free_UserDefOne(*obj); | |
1060 | *obj = NULL; | |
1061 | } | |
9ee86b85 | 1062 | out: |
297a3646 | 1063 | error_propagate(errp, err); |
b84da831 MR |
1064 | } |
1065 | ||
9ee86b85 | 1066 | void visit_type_UserDefOneList(Visitor *v, const char *name, UserDefOneList **obj, Error **errp) |
b84da831 | 1067 | { |
6e2bb3ec | 1068 | Error *err = NULL; |
d9f62dde EB |
1069 | UserDefOneList *tail; |
1070 | size_t size = sizeof(**obj); | |
6e2bb3ec | 1071 | |
d9f62dde | 1072 | visit_start_list(v, name, (GenericList **)obj, size, &err); |
297a3646 MA |
1073 | if (err) { |
1074 | goto out; | |
1075 | } | |
1076 | ||
d9f62dde EB |
1077 | for (tail = *obj; tail; |
1078 | tail = (UserDefOneList *)visit_next_list(v, (GenericList *)tail, size)) { | |
1079 | visit_type_UserDefOne(v, NULL, &tail->value, &err); | |
1080 | if (err) { | |
1081 | break; | |
1082 | } | |
b84da831 | 1083 | } |
297a3646 | 1084 | |
1158bb2a | 1085 | visit_end_list(v, (void **)obj); |
68ab47e4 EB |
1086 | if (err && visit_is_input(v)) { |
1087 | qapi_free_UserDefOneList(*obj); | |
1088 | *obj = NULL; | |
1089 | } | |
297a3646 MA |
1090 | out: |
1091 | error_propagate(errp, err); | |
b84da831 | 1092 | } |
b84da831 | 1093 | |
b84da831 MR |
1094 | === scripts/qapi-commands.py === |
1095 | ||
9ee86b85 EB |
1096 | Used to generate the marshaling/dispatch functions for the commands |
1097 | defined in the schema. The generated code implements | |
bd6092e4 MAL |
1098 | qmp_marshal_COMMAND() (registered automatically), and declares |
1099 | qmp_COMMAND() that the user must implement. The following files are | |
1100 | generated: | |
b84da831 MR |
1101 | |
1102 | $(prefix)qmp-marshal.c: command marshal/dispatch functions for each | |
1103 | QMP command defined in the schema. Functions | |
1104 | generated by qapi-visit.py are used to | |
2542bfd5 | 1105 | convert QObjects received from the wire into |
b84da831 MR |
1106 | function parameters, and uses the same |
1107 | visitor functions to convert native C return | |
1108 | values to QObjects from transmission back | |
1109 | over the wire. | |
1110 | ||
1111 | $(prefix)qmp-commands.h: Function prototypes for the QMP commands | |
1112 | specified in the schema. | |
1113 | ||
1114 | Example: | |
1115 | ||
59a2c4ce | 1116 | $ python scripts/qapi-commands.py --output-dir="qapi-generated" |
16d80f61 | 1117 | --prefix="example-" example-schema.json |
9ee86b85 EB |
1118 | $ cat qapi-generated/example-qmp-commands.h |
1119 | [Uninteresting stuff omitted...] | |
1120 | ||
1121 | #ifndef EXAMPLE_QMP_COMMANDS_H | |
1122 | #define EXAMPLE_QMP_COMMANDS_H | |
1123 | ||
1124 | #include "example-qapi-types.h" | |
1125 | #include "qapi/qmp/qdict.h" | |
1126 | #include "qapi/error.h" | |
1127 | ||
1128 | UserDefOne *qmp_my_command(UserDefOneList *arg1, Error **errp); | |
1129 | ||
1130 | #endif | |
87a560c4 | 1131 | $ cat qapi-generated/example-qmp-marshal.c |
6e2bb3ec | 1132 | [Uninteresting stuff omitted...] |
b84da831 | 1133 | |
56d92b00 | 1134 | static void qmp_marshal_output_UserDefOne(UserDefOne *ret_in, QObject **ret_out, Error **errp) |
b84da831 | 1135 | { |
2a0f50e8 | 1136 | Error *err = NULL; |
b84da831 MR |
1137 | Visitor *v; |
1138 | ||
7d5e199a | 1139 | v = qobject_output_visitor_new(ret_out); |
9ee86b85 | 1140 | visit_type_UserDefOne(v, "unused", &ret_in, &err); |
3b098d56 EB |
1141 | if (!err) { |
1142 | visit_complete(v, ret_out); | |
6e2bb3ec | 1143 | } |
2a0f50e8 | 1144 | error_propagate(errp, err); |
2c0ef9f4 EB |
1145 | visit_free(v); |
1146 | v = qapi_dealloc_visitor_new(); | |
9ee86b85 | 1147 | visit_type_UserDefOne(v, "unused", &ret_in, NULL); |
2c0ef9f4 | 1148 | visit_free(v); |
b84da831 MR |
1149 | } |
1150 | ||
7fad30f0 | 1151 | static void qmp_marshal_my_command(QDict *args, QObject **ret, Error **errp) |
b84da831 | 1152 | { |
2a0f50e8 | 1153 | Error *err = NULL; |
3f99144c | 1154 | UserDefOne *retval; |
b84da831 | 1155 | Visitor *v; |
9ee86b85 | 1156 | UserDefOneList *arg1 = NULL; |
b84da831 | 1157 | |
048abb7b | 1158 | v = qobject_input_visitor_new(QOBJECT(args)); |
ed841535 EB |
1159 | visit_start_struct(v, NULL, NULL, 0, &err); |
1160 | if (err) { | |
1161 | goto out; | |
1162 | } | |
9ee86b85 | 1163 | visit_type_UserDefOneList(v, "arg1", &arg1, &err); |
15c2f669 EB |
1164 | if (!err) { |
1165 | visit_check_struct(v, &err); | |
1166 | } | |
1158bb2a | 1167 | visit_end_struct(v, NULL); |
2a0f50e8 | 1168 | if (err) { |
b84da831 MR |
1169 | goto out; |
1170 | } | |
297a3646 | 1171 | |
2a0f50e8 EB |
1172 | retval = qmp_my_command(arg1, &err); |
1173 | if (err) { | |
297a3646 | 1174 | goto out; |
6e2bb3ec | 1175 | } |
b84da831 | 1176 | |
2a0f50e8 | 1177 | qmp_marshal_output_UserDefOne(retval, ret, &err); |
297a3646 | 1178 | |
b84da831 | 1179 | out: |
2a0f50e8 | 1180 | error_propagate(errp, err); |
2c0ef9f4 EB |
1181 | visit_free(v); |
1182 | v = qapi_dealloc_visitor_new(); | |
ed841535 | 1183 | visit_start_struct(v, NULL, NULL, 0, NULL); |
9ee86b85 | 1184 | visit_type_UserDefOneList(v, "arg1", &arg1, NULL); |
1158bb2a | 1185 | visit_end_struct(v, NULL); |
2c0ef9f4 | 1186 | visit_free(v); |
b84da831 MR |
1187 | } |
1188 | ||
1189 | static void qmp_init_marshal(void) | |
1190 | { | |
7fad30f0 | 1191 | qmp_register_command("my-command", qmp_marshal_my_command, QCO_NO_OPTIONS); |
b84da831 MR |
1192 | } |
1193 | ||
1194 | qapi_init(qmp_init_marshal); | |
59a2c4ce EB |
1195 | |
1196 | === scripts/qapi-event.py === | |
1197 | ||
9ee86b85 EB |
1198 | Used to generate the event-related C code defined by a schema, with |
1199 | implementations for qapi_event_send_FOO(). The following files are | |
1200 | created: | |
59a2c4ce EB |
1201 | |
1202 | $(prefix)qapi-event.h - Function prototypes for each event type, plus an | |
1203 | enumeration of all event names | |
1204 | $(prefix)qapi-event.c - Implementation of functions to send an event | |
1205 | ||
1206 | Example: | |
1207 | ||
1208 | $ python scripts/qapi-event.py --output-dir="qapi-generated" | |
16d80f61 | 1209 | --prefix="example-" example-schema.json |
9ee86b85 EB |
1210 | $ cat qapi-generated/example-qapi-event.h |
1211 | [Uninteresting stuff omitted...] | |
1212 | ||
1213 | #ifndef EXAMPLE_QAPI_EVENT_H | |
1214 | #define EXAMPLE_QAPI_EVENT_H | |
1215 | ||
1216 | #include "qapi/error.h" | |
1217 | #include "qapi/qmp/qdict.h" | |
1218 | #include "example-qapi-types.h" | |
1219 | ||
1220 | ||
1221 | void qapi_event_send_my_event(Error **errp); | |
1222 | ||
1223 | typedef enum example_QAPIEvent { | |
1224 | EXAMPLE_QAPI_EVENT_MY_EVENT = 0, | |
1225 | EXAMPLE_QAPI_EVENT__MAX = 1, | |
1226 | } example_QAPIEvent; | |
1227 | ||
1228 | extern const char *const example_QAPIEvent_lookup[]; | |
1229 | ||
1230 | #endif | |
59a2c4ce EB |
1231 | $ cat qapi-generated/example-qapi-event.c |
1232 | [Uninteresting stuff omitted...] | |
1233 | ||
1234 | void qapi_event_send_my_event(Error **errp) | |
1235 | { | |
1236 | QDict *qmp; | |
2a0f50e8 | 1237 | Error *err = NULL; |
59a2c4ce EB |
1238 | QMPEventFuncEmit emit; |
1239 | emit = qmp_event_get_func_emit(); | |
1240 | if (!emit) { | |
1241 | return; | |
1242 | } | |
1243 | ||
1244 | qmp = qmp_event_build_dict("MY_EVENT"); | |
1245 | ||
2a0f50e8 | 1246 | emit(EXAMPLE_QAPI_EVENT_MY_EVENT, qmp, &err); |
59a2c4ce | 1247 | |
2a0f50e8 | 1248 | error_propagate(errp, err); |
59a2c4ce EB |
1249 | QDECREF(qmp); |
1250 | } | |
1251 | ||
efd2eaa6 MA |
1252 | const char *const example_QAPIEvent_lookup[] = { |
1253 | [EXAMPLE_QAPI_EVENT_MY_EVENT] = "MY_EVENT", | |
7fb1cf16 | 1254 | [EXAMPLE_QAPI_EVENT__MAX] = NULL, |
59a2c4ce | 1255 | }; |
39a18158 MA |
1256 | |
1257 | === scripts/qapi-introspect.py === | |
1258 | ||
1259 | Used to generate the introspection C code for a schema. The following | |
1260 | files are created: | |
1261 | ||
1262 | $(prefix)qmp-introspect.c - Defines a string holding a JSON | |
1263 | description of the schema. | |
1264 | $(prefix)qmp-introspect.h - Declares the above string. | |
1265 | ||
1266 | Example: | |
1267 | ||
1268 | $ python scripts/qapi-introspect.py --output-dir="qapi-generated" | |
1269 | --prefix="example-" example-schema.json | |
39a18158 MA |
1270 | $ cat qapi-generated/example-qmp-introspect.h |
1271 | [Uninteresting stuff omitted...] | |
1272 | ||
1273 | #ifndef EXAMPLE_QMP_INTROSPECT_H | |
1274 | #define EXAMPLE_QMP_INTROSPECT_H | |
1275 | ||
1276 | extern const char example_qmp_schema_json[]; | |
1277 | ||
1278 | #endif | |
9ee86b85 EB |
1279 | $ cat qapi-generated/example-qmp-introspect.c |
1280 | [Uninteresting stuff omitted...] | |
1281 | ||
1282 | const char example_qmp_schema_json[] = "[" | |
1283 | "{\"arg-type\": \"0\", \"meta-type\": \"event\", \"name\": \"MY_EVENT\"}, " | |
1284 | "{\"arg-type\": \"1\", \"meta-type\": \"command\", \"name\": \"my-command\", \"ret-type\": \"2\"}, " | |
1285 | "{\"members\": [], \"meta-type\": \"object\", \"name\": \"0\"}, " | |
1286 | "{\"members\": [{\"name\": \"arg1\", \"type\": \"[2]\"}], \"meta-type\": \"object\", \"name\": \"1\"}, " | |
1287 | "{\"members\": [{\"name\": \"integer\", \"type\": \"int\"}, {\"default\": null, \"name\": \"string\", \"type\": \"str\"}], \"meta-type\": \"object\", \"name\": \"2\"}, " | |
1288 | "{\"element-type\": \"2\", \"meta-type\": \"array\", \"name\": \"[2]\"}, " | |
1289 | "{\"json-type\": \"int\", \"meta-type\": \"builtin\", \"name\": \"int\"}, " | |
1290 | "{\"json-type\": \"string\", \"meta-type\": \"builtin\", \"name\": \"str\"}]"; |