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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 | ||
0b263ecb | 66 | # == Subsection title |
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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 | ||
bc52d03f | 120 | Each expression that isn't an include directive may be preceded by a |
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121 | documentation block. Such blocks are called expression documentation |
122 | blocks. | |
123 | ||
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124 | When documentation is required (see pragma 'doc-required'), expression |
125 | documentation blocks are mandatory. | |
126 | ||
3313b612 MAL |
127 | The documentation block consists of a first line naming the |
128 | expression, an optional overview, a description of each argument (for | |
129 | commands and events) or member (for structs, unions and alternates), | |
130 | and optional tagged sections. | |
131 | ||
132 | FIXME: the parser accepts these things in almost any order. | |
133 | ||
1d8bda12 MA |
134 | Extensions added after the expression was first released carry a |
135 | '(since x.y.z)' comment. | |
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136 | |
137 | A tagged section starts with one of the following words: | |
138 | "Note:"/"Notes:", "Since:", "Example"/"Examples", "Returns:", "TODO:". | |
139 | The section ends with the start of a new section. | |
140 | ||
141 | A 'Since: x.y.z' tagged section lists the release that introduced the | |
142 | expression. | |
143 | ||
144 | For example: | |
145 | ||
146 | ## | |
147 | # @BlockStats: | |
148 | # | |
149 | # Statistics of a virtual block device or a block backing device. | |
150 | # | |
1d8bda12 | 151 | # @device: If the stats are for a virtual block device, the name |
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152 | # corresponding to the virtual block device. |
153 | # | |
1d8bda12 | 154 | # @node-name: The node name of the device. (since 2.3) |
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155 | # |
156 | # ... more members ... | |
157 | # | |
158 | # Since: 0.14.0 | |
159 | ## | |
160 | { 'struct': 'BlockStats', | |
161 | 'data': {'*device': 'str', '*node-name': 'str', | |
162 | ... more members ... } } | |
163 | ||
164 | ## | |
165 | # @query-blockstats: | |
166 | # | |
167 | # Query the @BlockStats for all virtual block devices. | |
168 | # | |
1d8bda12 | 169 | # @query-nodes: If true, the command will query all the |
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170 | # block nodes ... explain, explain ... (since 2.3) |
171 | # | |
172 | # Returns: A list of @BlockStats for each virtual block devices. | |
173 | # | |
174 | # Since: 0.14.0 | |
175 | # | |
176 | # Example: | |
177 | # | |
178 | # -> { "execute": "query-blockstats" } | |
179 | # <- { | |
180 | # ... lots of output ... | |
181 | # } | |
182 | # | |
183 | ## | |
184 | { 'command': 'query-blockstats', | |
185 | 'data': { '*query-nodes': 'bool' }, | |
186 | 'returns': ['BlockStats'] } | |
187 | ||
188 | ==== Free-form documentation ==== | |
189 | ||
190 | A documentation block that isn't an expression documentation block is | |
191 | a free-form documentation block. These may be used to provide | |
192 | additional text and structuring content. | |
193 | ||
194 | ||
195 | === Schema overview === | |
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196 | |
197 | The schema sets up a series of types, as well as commands and events | |
198 | that will use those types. Forward references are allowed: the parser | |
199 | scans in two passes, where the first pass learns all type names, and | |
200 | the second validates the schema and generates the code. This allows | |
201 | the definition of complex structs that can have mutually recursive | |
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202 | types, and allows for indefinite nesting of Client JSON Protocol that |
203 | satisfies the schema. A type name should not be defined more than | |
204 | once. It is permissible for the schema to contain additional types | |
205 | not used by any commands or events in the Client JSON Protocol, for | |
206 | the side effect of generated C code used internally. | |
e790e666 | 207 | |
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208 | There are eight top-level expressions recognized by the parser: |
209 | 'include', 'pragma', 'command', 'struct', 'enum', 'union', | |
210 | 'alternate', and 'event'. There are several groups of types: simple | |
211 | types (a number of built-in types, such as 'int' and 'str'; as well as | |
212 | enumerations), complex types (structs and two flavors of unions), and | |
213 | alternate types (a choice between other types). The 'command' and | |
214 | 'event' expressions can refer to existing types by name, or list an | |
215 | anonymous type as a dictionary. Listing a type name inside an array | |
216 | refers to a single-dimension array of that type; multi-dimension | |
217 | arrays are not directly supported (although an array of a complex | |
218 | struct that contains an array member is possible). | |
e790e666 | 219 | |
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220 | All names must begin with a letter, and contain only ASCII letters, |
221 | digits, hyphen, and underscore. There are two exceptions: enum values | |
222 | may start with a digit, and names that are downstream extensions (see | |
223 | section Downstream extensions) start with underscore. | |
224 | ||
225 | Names beginning with 'q_' are reserved for the generator, which uses | |
226 | them for munging QMP names that resemble C keywords or other | |
227 | problematic strings. For example, a member named "default" in qapi | |
228 | becomes "q_default" in the generated C code. | |
229 | ||
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230 | Types, commands, and events share a common namespace. Therefore, |
231 | generally speaking, type definitions should always use CamelCase for | |
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232 | user-defined type names, while built-in types are lowercase. |
233 | ||
234 | Type names ending with 'Kind' or 'List' are reserved for the | |
235 | generator, which uses them for implicit union enums and array types, | |
236 | respectively. | |
237 | ||
238 | Command names, and member names within a type, should be all lower | |
239 | case with words separated by a hyphen. However, some existing older | |
240 | commands and complex types use underscore; when extending such | |
241 | expressions, consistency is preferred over blindly avoiding | |
242 | underscore. | |
243 | ||
244 | Event names should be ALL_CAPS with words separated by underscore. | |
245 | ||
246 | Member names starting with 'has-' or 'has_' are reserved for the | |
247 | generator, which uses them for tracking optional members. | |
e790e666 | 248 | |
9ee86b85 | 249 | Any name (command, event, type, member, or enum value) beginning with |
e790e666 | 250 | "x-" is marked experimental, and may be withdrawn or changed |
79f75981 | 251 | incompatibly in a future release. |
e790e666 | 252 | |
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253 | Pragma 'name-case-whitelist' lets you violate the rules on use of |
254 | upper and lower case. Use for new code is strongly discouraged. | |
255 | ||
e790e666 EB |
256 | In the rest of this document, usage lines are given for each |
257 | expression type, with literal strings written in lower case and | |
258 | placeholders written in capitals. If a literal string includes a | |
259 | prefix of '*', that key/value pair can be omitted from the expression. | |
3b2a8b85 | 260 | For example, a usage statement that includes '*base':STRUCT-NAME |
e790e666 | 261 | means that an expression has an optional key 'base', which if present |
3b2a8b85 | 262 | must have a value that forms a struct name. |
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263 | |
264 | ||
265 | === Built-in Types === | |
266 | ||
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267 | The following types are predefined, and map to C as follows: |
268 | ||
269 | Schema C JSON | |
270 | str char * any JSON string, UTF-8 | |
271 | number double any JSON number | |
272 | int int64_t a JSON number without fractional part | |
273 | that fits into the C integer type | |
274 | int8 int8_t likewise | |
275 | int16 int16_t likewise | |
276 | int32 int32_t likewise | |
277 | int64 int64_t likewise | |
278 | uint8 uint8_t likewise | |
279 | uint16 uint16_t likewise | |
280 | uint32 uint32_t likewise | |
281 | uint64 uint64_t likewise | |
282 | size uint64_t like uint64_t, except StringInputVisitor | |
283 | accepts size suffixes | |
284 | bool bool JSON true or false | |
4d2d5c41 | 285 | null QNull * JSON null |
28770e05 | 286 | any QObject * any JSON value |
7264f5c5 | 287 | QType QType JSON string matching enum QType values |
51631493 | 288 | |
a719a27c | 289 | |
bc52d03f | 290 | === Include directives === |
a719a27c | 291 | |
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292 | Usage: { 'include': STRING } |
293 | ||
a719a27c LV |
294 | The QAPI schema definitions can be modularized using the 'include' directive: |
295 | ||
e790e666 | 296 | { 'include': 'path/to/file.json' } |
a719a27c LV |
297 | |
298 | The directive is evaluated recursively, and include paths are relative to the | |
e790e666 | 299 | file using the directive. Multiple includes of the same file are |
4247f839 | 300 | idempotent. No other keys should appear in the expression, and the include |
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301 | value should be a string. |
302 | ||
303 | As a matter of style, it is a good idea to have all files be | |
304 | self-contained, but at the moment, nothing prevents an included file | |
305 | from making a forward reference to a type that is only introduced by | |
306 | an outer file. The parser may be made stricter in the future to | |
307 | prevent incomplete include files. | |
a719a27c LV |
308 | |
309 | ||
bc52d03f MA |
310 | === Pragma directives === |
311 | ||
312 | Usage: { 'pragma': DICT } | |
313 | ||
314 | The pragma directive lets you control optional generator behavior. | |
315 | The dictionary's entries are pragma names and values. | |
316 | ||
317 | Pragma's scope is currently the complete schema. Setting the same | |
318 | pragma to different values in parts of the schema doesn't work. | |
319 | ||
320 | Pragma 'doc-required' takes a boolean value. If true, documentation | |
321 | is required. Default is false. | |
322 | ||
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323 | Pragma 'returns-whitelist' takes a list of command names that may |
324 | violate the rules on permitted return types. Default is none. | |
325 | ||
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326 | Pragma 'name-case-whitelist' takes a list of names that may violate |
327 | rules on use of upper- vs. lower-case letters. Default is none. | |
328 | ||
bc52d03f | 329 | |
3b2a8b85 | 330 | === Struct types === |
51631493 | 331 | |
3b2a8b85 | 332 | Usage: { 'struct': STRING, 'data': DICT, '*base': STRUCT-NAME } |
e790e666 | 333 | |
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334 | A struct is a dictionary containing a single 'data' key whose value is |
335 | a dictionary; the dictionary may be empty. This corresponds to a | |
336 | struct in C or an Object in JSON. Each value of the 'data' dictionary | |
337 | must be the name of a type, or a one-element array containing a type | |
338 | name. An example of a struct is: | |
b84da831 | 339 | |
3b2a8b85 | 340 | { 'struct': 'MyType', |
acf8394e | 341 | 'data': { 'member1': 'str', 'member2': 'int', '*member3': 'str' } } |
b84da831 | 342 | |
e790e666 | 343 | The use of '*' as a prefix to the name means the member is optional in |
363b4262 | 344 | the corresponding JSON protocol usage. |
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345 | |
346 | The default initialization value of an optional argument should not be changed | |
347 | between versions of QEMU unless the new default maintains backward | |
348 | compatibility to the user-visible behavior of the old default. | |
349 | ||
350 | With proper documentation, this policy still allows some flexibility; for | |
351 | example, documenting that a default of 0 picks an optimal buffer size allows | |
352 | one release to declare the optimal size at 512 while another release declares | |
353 | the optimal size at 4096 - the user-visible behavior is not the bytes used by | |
354 | the buffer, but the fact that the buffer was optimal size. | |
355 | ||
356 | On input structures (only mentioned in the 'data' side of a command), changing | |
357 | from mandatory to optional is safe (older clients will supply the option, and | |
358 | newer clients can benefit from the default); changing from optional to | |
359 | mandatory is backwards incompatible (older clients may be omitting the option, | |
360 | and must continue to work). | |
361 | ||
362 | On output structures (only mentioned in the 'returns' side of a command), | |
363 | changing from mandatory to optional is in general unsafe (older clients may be | |
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364 | expecting the member, and could crash if it is missing), although it |
365 | can be done if the only way that the optional argument will be omitted | |
366 | is when it is triggered by the presence of a new input flag to the | |
367 | command that older clients don't know to send. Changing from optional | |
368 | to mandatory is safe. | |
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369 | |
370 | A structure that is used in both input and output of various commands | |
371 | must consider the backwards compatibility constraints of both directions | |
372 | of use. | |
622f557f | 373 | |
3b2a8b85 | 374 | A struct definition can specify another struct as its base. |
9ee86b85 | 375 | In this case, the members of the base type are included as top-level members |
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376 | of the new struct's dictionary in the Client JSON Protocol wire |
377 | format. An example definition is: | |
622f557f | 378 | |
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379 | { 'struct': 'BlockdevOptionsGenericFormat', 'data': { 'file': 'str' } } |
380 | { 'struct': 'BlockdevOptionsGenericCOWFormat', | |
622f557f KW |
381 | 'base': 'BlockdevOptionsGenericFormat', |
382 | 'data': { '*backing': 'str' } } | |
383 | ||
384 | An example BlockdevOptionsGenericCOWFormat object on the wire could use | |
9ee86b85 | 385 | both members like this: |
622f557f KW |
386 | |
387 | { "file": "/some/place/my-image", | |
388 | "backing": "/some/place/my-backing-file" } | |
389 | ||
e790e666 | 390 | |
51631493 KW |
391 | === Enumeration types === |
392 | ||
e790e666 | 393 | Usage: { 'enum': STRING, 'data': ARRAY-OF-STRING } |
351d36e4 | 394 | { 'enum': STRING, '*prefix': STRING, 'data': ARRAY-OF-STRING } |
e790e666 EB |
395 | |
396 | An enumeration type is a dictionary containing a single 'data' key | |
397 | whose value is a list of strings. An example enumeration is: | |
b84da831 MR |
398 | |
399 | { 'enum': 'MyEnum', 'data': [ 'value1', 'value2', 'value3' ] } | |
400 | ||
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401 | Nothing prevents an empty enumeration, although it is probably not |
402 | useful. The list of strings should be lower case; if an enum name | |
403 | represents multiple words, use '-' between words. The string 'max' is | |
404 | not allowed as an enum value, and values should not be repeated. | |
405 | ||
351d36e4 DB |
406 | The enum constants will be named by using a heuristic to turn the |
407 | type name into a set of underscore separated words. For the example | |
408 | above, 'MyEnum' will turn into 'MY_ENUM' giving a constant name | |
409 | of 'MY_ENUM_VALUE1' for the first value. If the default heuristic | |
9ee86b85 | 410 | does not result in a desirable name, the optional 'prefix' member |
351d36e4 DB |
411 | can be used when defining the enum. |
412 | ||
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413 | The enumeration values are passed as strings over the Client JSON |
414 | Protocol, but are encoded as C enum integral values in generated code. | |
415 | While the C code starts numbering at 0, it is better to use explicit | |
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416 | comparisons to enum values than implicit comparisons to 0; the C code |
417 | will also include a generated enum member ending in _MAX for tracking | |
418 | the size of the enum, useful when using common functions for | |
419 | converting between strings and enum values. Since the wire format | |
420 | always passes by name, it is acceptable to reorder or add new | |
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421 | enumeration members in any location without breaking clients of Client |
422 | JSON Protocol; however, removing enum values would break | |
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423 | compatibility. For any struct that has a member that will only contain |
424 | a finite set of string values, using an enum type for that member is | |
425 | better than open-coding the member to be type 'str'. | |
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426 | |
427 | ||
51631493 KW |
428 | === Union types === |
429 | ||
e790e666 | 430 | Usage: { 'union': STRING, 'data': DICT } |
ac4338f8 | 431 | or: { 'union': STRING, 'data': DICT, 'base': STRUCT-NAME-OR-DICT, |
e790e666 | 432 | 'discriminator': ENUM-MEMBER-OF-BASE } |
51631493 | 433 | |
e790e666 | 434 | Union types are used to let the user choose between several different |
7b1b98c4 | 435 | variants for an object. There are two flavors: simple (no |
02a57ae3 | 436 | discriminator or base), and flat (both discriminator and base). A union |
7b1b98c4 | 437 | type is defined using a data dictionary as explained in the following |
02a57ae3 EB |
438 | paragraphs. The data dictionary for either type of union must not |
439 | be empty. | |
51631493 | 440 | |
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441 | A simple union type defines a mapping from automatic discriminator |
442 | values to data types like in this example: | |
51631493 | 443 | |
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444 | { 'struct': 'BlockdevOptionsFile', 'data': { 'filename': 'str' } } |
445 | { 'struct': 'BlockdevOptionsQcow2', | |
446 | 'data': { 'backing': 'str', '*lazy-refcounts': 'bool' } } | |
51631493 | 447 | |
bd59adce EB |
448 | { 'union': 'BlockdevOptionsSimple', |
449 | 'data': { 'file': 'BlockdevOptionsFile', | |
450 | 'qcow2': 'BlockdevOptionsQcow2' } } | |
51631493 | 451 | |
363b4262 | 452 | In the Client JSON Protocol, a simple union is represented by a |
9ee86b85 EB |
453 | dictionary that contains the 'type' member as a discriminator, and a |
454 | 'data' member that is of the specified data type corresponding to the | |
363b4262 | 455 | discriminator value, as in these examples: |
51631493 | 456 | |
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457 | { "type": "file", "data": { "filename": "/some/place/my-image" } } |
458 | { "type": "qcow2", "data": { "backing": "/some/place/my-image", | |
459 | "lazy-refcounts": true } } | |
51631493 | 460 | |
e790e666 EB |
461 | The generated C code uses a struct containing a union. Additionally, |
462 | an implicit C enum 'NameKind' is created, corresponding to the union | |
463 | 'Name', for accessing the various branches of the union. No branch of | |
464 | the union can be named 'max', as this would collide with the implicit | |
465 | enum. The value for each branch can be of any type. | |
51631493 | 466 | |
ac4338f8 EB |
467 | A flat union definition avoids nesting on the wire, and specifies a |
468 | set of common members that occur in all variants of the union. The | |
d33c8a7d | 469 | 'base' key must specify either a type name (the type must be a |
ac4338f8 EB |
470 | struct, not a union), or a dictionary representing an anonymous type. |
471 | All branches of the union must be complex types, and the top-level | |
472 | members of the union dictionary on the wire will be combination of | |
473 | members from both the base type and the appropriate branch type (when | |
474 | merging two dictionaries, there must be no keys in common). The | |
475 | 'discriminator' member must be the name of a non-optional enum-typed | |
476 | member of the base struct. | |
51631493 | 477 | |
e790e666 | 478 | The following example enhances the above simple union example by |
bd59adce EB |
479 | adding an optional common member 'read-only', renaming the |
480 | discriminator to something more applicable than the simple union's | |
481 | default of 'type', and reducing the number of {} required on the wire: | |
50f2bdc7 | 482 | |
94a3f0af | 483 | { 'enum': 'BlockdevDriver', 'data': [ 'file', 'qcow2' ] } |
50f2bdc7 | 484 | { 'union': 'BlockdevOptions', |
ac4338f8 | 485 | 'base': { 'driver': 'BlockdevDriver', '*read-only': 'bool' }, |
50f2bdc7 | 486 | 'discriminator': 'driver', |
bd59adce EB |
487 | 'data': { 'file': 'BlockdevOptionsFile', |
488 | 'qcow2': 'BlockdevOptionsQcow2' } } | |
50f2bdc7 | 489 | |
e790e666 EB |
490 | Resulting in these JSON objects: |
491 | ||
bd59adce | 492 | { "driver": "file", "read-only": true, |
e790e666 | 493 | "filename": "/some/place/my-image" } |
bd59adce EB |
494 | { "driver": "qcow2", "read-only": false, |
495 | "backing": "/some/place/my-image", "lazy-refcounts": true } | |
e790e666 EB |
496 | |
497 | Notice that in a flat union, the discriminator name is controlled by | |
498 | the user, but because it must map to a base member with enum type, the | |
499 | code generator can ensure that branches exist for all values of the | |
500 | enum (although the order of the keys need not match the declaration of | |
501 | the enum). In the resulting generated C data types, a flat union is | |
9ee86b85 EB |
502 | represented as a struct with the base members included directly, and |
503 | then a union of structures for each branch of the struct. | |
e790e666 EB |
504 | |
505 | A simple union can always be re-written as a flat union where the base | |
506 | class has a single member named 'type', and where each branch of the | |
3b2a8b85 | 507 | union has a struct with a single member named 'data'. That is, |
50f2bdc7 | 508 | |
e790e666 | 509 | { 'union': 'Simple', 'data': { 'one': 'str', 'two': 'int' } } |
50f2bdc7 | 510 | |
e790e666 | 511 | is identical on the wire to: |
50f2bdc7 | 512 | |
e790e666 | 513 | { 'enum': 'Enum', 'data': ['one', 'two'] } |
3b2a8b85 EB |
514 | { 'struct': 'Branch1', 'data': { 'data': 'str' } } |
515 | { 'struct': 'Branch2', 'data': { 'data': 'int' } } | |
ac4338f8 | 516 | { 'union': 'Flat': 'base': { 'type': 'Enum' }, 'discriminator': 'type', |
e790e666 | 517 | 'data': { 'one': 'Branch1', 'two': 'Branch2' } } |
69dd62df | 518 | |
e790e666 | 519 | |
7b1b98c4 | 520 | === Alternate types === |
69dd62df | 521 | |
7b1b98c4 EB |
522 | Usage: { 'alternate': STRING, 'data': DICT } |
523 | ||
524 | An alternate type is one that allows a choice between two or more JSON | |
525 | data types (string, integer, number, or object, but currently not | |
526 | array) on the wire. The definition is similar to a simple union type, | |
527 | where each branch of the union names a QAPI type. For example: | |
528 | ||
bd59adce | 529 | { 'alternate': 'BlockdevRef', |
69dd62df KW |
530 | 'data': { 'definition': 'BlockdevOptions', |
531 | 'reference': 'str' } } | |
532 | ||
7b1b98c4 | 533 | Unlike a union, the discriminator string is never passed on the wire |
363b4262 EB |
534 | for the Client JSON Protocol. Instead, the value's JSON type serves |
535 | as an implicit discriminator, which in turn means that an alternate | |
536 | can only express a choice between types represented differently in | |
537 | JSON. If a branch is typed as the 'bool' built-in, the alternate | |
538 | accepts true and false; if it is typed as any of the various numeric | |
539 | built-ins, it accepts a JSON number; if it is typed as a 'str' | |
4d2d5c41 MA |
540 | built-in or named enum type, it accepts a JSON string; if it is typed |
541 | as the 'null' built-in, it accepts JSON null; and if it is typed as a | |
542 | complex type (struct or union), it accepts a JSON object. Two | |
543 | different complex types, for instance, aren't permitted, because both | |
544 | are represented as a JSON object. | |
7b1b98c4 EB |
545 | |
546 | The example alternate declaration above allows using both of the | |
547 | following example objects: | |
69dd62df KW |
548 | |
549 | { "file": "my_existing_block_device_id" } | |
550 | { "file": { "driver": "file", | |
bd59adce | 551 | "read-only": false, |
63922c64 | 552 | "filename": "/tmp/mydisk.qcow2" } } |
69dd62df KW |
553 | |
554 | ||
51631493 | 555 | === Commands === |
b84da831 | 556 | |
378112b0 PX |
557 | --- General Command Layout --- |
558 | ||
e790e666 | 559 | Usage: { 'command': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT, |
c818408e | 560 | '*returns': TYPE-NAME, '*boxed': true, |
378112b0 PX |
561 | '*gen': false, '*success-response': false, |
562 | '*allow-oob': true } | |
e790e666 EB |
563 | |
564 | Commands are defined by using a dictionary containing several members, | |
565 | where three members are most common. The 'command' member is a | |
363b4262 EB |
566 | mandatory string, and determines the "execute" value passed in a |
567 | Client JSON Protocol command exchange. | |
e790e666 EB |
568 | |
569 | The 'data' argument maps to the "arguments" dictionary passed in as | |
363b4262 EB |
570 | part of a Client JSON Protocol command. The 'data' member is optional |
571 | and defaults to {} (an empty dictionary). If present, it must be the | |
315932b5 | 572 | string name of a complex type, or a dictionary that declares an |
700dc9f5 | 573 | anonymous type with the same semantics as a 'struct' expression. |
e790e666 | 574 | |
9ee86b85 | 575 | The 'returns' member describes what will appear in the "return" member |
363b4262 EB |
576 | of a Client JSON Protocol reply on successful completion of a command. |
577 | The member is optional from the command declaration; if absent, the | |
9ee86b85 | 578 | "return" member will be an empty dictionary. If 'returns' is present, |
363b4262 | 579 | it must be the string name of a complex or built-in type, a |
700dc9f5 | 580 | one-element array containing the name of a complex or built-in type. |
1554a8fa MA |
581 | To return anything else, you have to list the command in pragma |
582 | 'returns-whitelist'. If you do this, the command cannot be extended | |
583 | to return additional information in the future. Use of | |
584 | 'returns-whitelist' for new commands is strongly discouraged. | |
363b4262 EB |
585 | |
586 | All commands in Client JSON Protocol use a dictionary to report | |
587 | failure, with no way to specify that in QAPI. Where the error return | |
588 | is different than the usual GenericError class in order to help the | |
589 | client react differently to certain error conditions, it is worth | |
590 | documenting this in the comments before the command declaration. | |
e790e666 EB |
591 | |
592 | Some example commands: | |
593 | ||
594 | { 'command': 'my-first-command', | |
595 | 'data': { 'arg1': 'str', '*arg2': 'str' } } | |
3b2a8b85 | 596 | { 'struct': 'MyType', 'data': { '*value': 'str' } } |
e790e666 EB |
597 | { 'command': 'my-second-command', |
598 | 'returns': [ 'MyType' ] } | |
599 | ||
363b4262 | 600 | which would validate this Client JSON Protocol transaction: |
e790e666 EB |
601 | |
602 | => { "execute": "my-first-command", | |
603 | "arguments": { "arg1": "hello" } } | |
604 | <= { "return": { } } | |
605 | => { "execute": "my-second-command" } | |
606 | <= { "return": [ { "value": "one" }, { } ] } | |
607 | ||
c818408e EB |
608 | The generator emits a prototype for the user's function implementing |
609 | the command. Normally, 'data' is a dictionary for an anonymous type, | |
610 | or names a struct type (possibly empty, but not a union), and its | |
611 | members are passed as separate arguments to this function. If the | |
612 | command definition includes a key 'boxed' with the boolean value true, | |
613 | then 'data' is instead the name of any non-empty complex type | |
614 | (struct, union, or alternate), and a pointer to that QAPI type is | |
615 | passed as a single argument. | |
616 | ||
617 | The generator also emits a marshalling function that extracts | |
618 | arguments for the user's function out of an input QDict, calls the | |
619 | user's function, and if it succeeded, builds an output QObject from | |
620 | its return value. | |
621 | ||
e790e666 | 622 | In rare cases, QAPI cannot express a type-safe representation of a |
2d21291a MA |
623 | corresponding Client JSON Protocol command. You then have to suppress |
624 | generation of a marshalling function by including a key 'gen' with | |
625 | boolean value false, and instead write your own function. Please try | |
626 | to avoid adding new commands that rely on this, and instead use | |
627 | type-safe unions. For an example of this usage: | |
e790e666 EB |
628 | |
629 | { 'command': 'netdev_add', | |
b8a98326 | 630 | 'data': {'type': 'str', 'id': 'str'}, |
e790e666 EB |
631 | 'gen': false } |
632 | ||
633 | Normally, the QAPI schema is used to describe synchronous exchanges, | |
634 | where a response is expected. But in some cases, the action of a | |
635 | command is expected to change state in a way that a successful | |
636 | response is not possible (although the command will still return a | |
637 | normal dictionary error on failure). When a successful reply is not | |
638 | possible, the command expression should include the optional key | |
639 | 'success-response' with boolean value false. So far, only QGA makes | |
9ee86b85 | 640 | use of this member. |
b84da831 | 641 | |
378112b0 PX |
642 | A command can be declared to support Out-Of-Band (OOB) execution. By |
643 | default, commands do not support OOB. To declare a command that | |
644 | supports it, the schema includes an extra 'allow-oob' field. For | |
645 | example: | |
646 | ||
647 | { 'command': 'migrate_recover', | |
648 | 'data': { 'uri': 'str' }, 'allow-oob': true } | |
649 | ||
650 | To execute a command with out-of-band priority, the client specifies | |
651 | the "control" field in the request, with "run-oob" set to | |
652 | true. Example: | |
653 | ||
654 | => { "execute": "command-support-oob", | |
655 | "arguments": { ... }, | |
656 | "control": { "run-oob": true } } | |
657 | <= { "return": { } } | |
658 | ||
659 | Without it, even the commands that support out-of-band execution will | |
660 | still be run in-band. | |
661 | ||
662 | Under normal QMP command execution, the following apply to each | |
663 | command: | |
664 | ||
665 | - They are executed in order, | |
666 | - They run only in main thread of QEMU, | |
667 | - They have the BQL taken during execution. | |
668 | ||
669 | When a command is executed with OOB, the following changes occur: | |
670 | ||
671 | - They can be completed before a pending in-band command, | |
672 | - They run in a dedicated monitor thread, | |
673 | - They do not take the BQL during execution. | |
674 | ||
675 | OOB command handlers must satisfy the following conditions: | |
676 | ||
677 | - It executes extremely fast, | |
678 | - It does not take any lock, or, it can take very small locks if all | |
679 | critical regions also follow the rules for OOB command handler code, | |
680 | - It does not invoke system calls that may block, | |
681 | - It does not access guest RAM that may block when userfaultfd is | |
682 | enabled for postcopy live migration. | |
683 | ||
684 | If in doubt, do not implement OOB execution support. | |
b84da831 | 685 | |
21cd70df WX |
686 | === Events === |
687 | ||
c818408e EB |
688 | Usage: { 'event': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT, |
689 | '*boxed': true } | |
e790e666 EB |
690 | |
691 | Events are defined with the keyword 'event'. It is not allowed to | |
692 | name an event 'MAX', since the generator also produces a C enumeration | |
693 | of all event names with a generated _MAX value at the end. When | |
694 | 'data' is also specified, additional info will be included in the | |
3b2a8b85 | 695 | event, with similar semantics to a 'struct' expression. Finally there |
eb815e24 | 696 | will be C API generated in qapi-events.h; when called by QEMU code, a |
e790e666 | 697 | message with timestamp will be emitted on the wire. |
21cd70df WX |
698 | |
699 | An example event is: | |
700 | ||
701 | { 'event': 'EVENT_C', | |
702 | 'data': { '*a': 'int', 'b': 'str' } } | |
703 | ||
704 | Resulting in this JSON object: | |
705 | ||
706 | { "event": "EVENT_C", | |
707 | "data": { "b": "test string" }, | |
708 | "timestamp": { "seconds": 1267020223, "microseconds": 435656 } } | |
b84da831 | 709 | |
c818408e EB |
710 | The generator emits a function to send the event. Normally, 'data' is |
711 | a dictionary for an anonymous type, or names a struct type (possibly | |
712 | empty, but not a union), and its members are passed as separate | |
713 | arguments to this function. If the event definition includes a key | |
714 | 'boxed' with the boolean value true, then 'data' is instead the name of | |
715 | any non-empty complex type (struct, union, or alternate), and a | |
716 | pointer to that QAPI type is passed as a single argument. | |
717 | ||
59a2c4ce | 718 | |
79f75981 MA |
719 | === Downstream extensions === |
720 | ||
721 | QAPI schema names that are externally visible, say in the Client JSON | |
722 | Protocol, need to be managed with care. Names starting with a | |
723 | downstream prefix of the form __RFQDN_ are reserved for the downstream | |
724 | who controls the valid, reverse fully qualified domain name RFQDN. | |
725 | RFQDN may only contain ASCII letters, digits, hyphen and period. | |
726 | ||
727 | Example: Red Hat, Inc. controls redhat.com, and may therefore add a | |
728 | downstream command __com.redhat_drive-mirror. | |
729 | ||
730 | ||
39a18158 MA |
731 | == Client JSON Protocol introspection == |
732 | ||
733 | Clients of a Client JSON Protocol commonly need to figure out what | |
734 | exactly the server (QEMU) supports. | |
735 | ||
736 | For this purpose, QMP provides introspection via command | |
737 | query-qmp-schema. QGA currently doesn't support introspection. | |
738 | ||
39a65e2c EB |
739 | While Client JSON Protocol wire compatibility should be maintained |
740 | between qemu versions, we cannot make the same guarantees for | |
741 | introspection stability. For example, one version of qemu may provide | |
742 | a non-variant optional member of a struct, and a later version rework | |
743 | the member to instead be non-optional and associated with a variant. | |
744 | Likewise, one version of qemu may list a member with open-ended type | |
745 | 'str', and a later version could convert it to a finite set of strings | |
746 | via an enum type; or a member may be converted from a specific type to | |
747 | an alternate that represents a choice between the original type and | |
748 | something else. | |
749 | ||
39a18158 MA |
750 | query-qmp-schema returns a JSON array of SchemaInfo objects. These |
751 | objects together describe the wire ABI, as defined in the QAPI schema. | |
f5455044 EB |
752 | There is no specified order to the SchemaInfo objects returned; a |
753 | client must search for a particular name throughout the entire array | |
754 | to learn more about that name, but is at least guaranteed that there | |
755 | will be no collisions between type, command, and event names. | |
39a18158 MA |
756 | |
757 | However, the SchemaInfo can't reflect all the rules and restrictions | |
758 | that apply to QMP. It's interface introspection (figuring out what's | |
759 | there), not interface specification. The specification is in the QAPI | |
760 | schema. To understand how QMP is to be used, you need to study the | |
761 | QAPI schema. | |
762 | ||
763 | Like any other command, query-qmp-schema is itself defined in the QAPI | |
764 | schema, along with the SchemaInfo type. This text attempts to give an | |
765 | overview how things work. For details you need to consult the QAPI | |
766 | schema. | |
767 | ||
768 | SchemaInfo objects have common members "name" and "meta-type", and | |
769 | additional variant members depending on the value of meta-type. | |
770 | ||
771 | Each SchemaInfo object describes a wire ABI entity of a certain | |
772 | meta-type: a command, event or one of several kinds of type. | |
773 | ||
1a9a507b MA |
774 | SchemaInfo for commands and events have the same name as in the QAPI |
775 | schema. | |
39a18158 MA |
776 | |
777 | Command and event names are part of the wire ABI, but type names are | |
1a9a507b MA |
778 | not. Therefore, the SchemaInfo for types have auto-generated |
779 | meaningless names. For readability, the examples in this section use | |
780 | meaningful type names instead. | |
781 | ||
782 | To examine a type, start with a command or event using it, then follow | |
783 | references by name. | |
39a18158 MA |
784 | |
785 | QAPI schema definitions not reachable that way are omitted. | |
786 | ||
787 | The SchemaInfo for a command has meta-type "command", and variant | |
378112b0 PX |
788 | members "arg-type", "ret-type" and "allow-oob". On the wire, the |
789 | "arguments" member of a client's "execute" command must conform to the | |
790 | object type named by "arg-type". The "return" member that the server | |
791 | passes in a success response conforms to the type named by | |
792 | "ret-type". When "allow-oob" is set, it means the command supports | |
793 | out-of-band execution. | |
39a18158 MA |
794 | |
795 | If the command takes no arguments, "arg-type" names an object type | |
796 | without members. Likewise, if the command returns nothing, "ret-type" | |
797 | names an object type without members. | |
798 | ||
799 | Example: the SchemaInfo for command query-qmp-schema | |
800 | ||
801 | { "name": "query-qmp-schema", "meta-type": "command", | |
7599697c | 802 | "arg-type": "q_empty", "ret-type": "SchemaInfoList" } |
39a18158 | 803 | |
7599697c | 804 | Type "q_empty" is an automatic object type without members, and type |
39a18158 MA |
805 | "SchemaInfoList" is the array of SchemaInfo type. |
806 | ||
807 | The SchemaInfo for an event has meta-type "event", and variant member | |
808 | "arg-type". On the wire, a "data" member that the server passes in an | |
809 | event conforms to the object type named by "arg-type". | |
810 | ||
811 | If the event carries no additional information, "arg-type" names an | |
812 | object type without members. The event may not have a data member on | |
813 | the wire then. | |
814 | ||
815 | Each command or event defined with dictionary-valued 'data' in the | |
1a9a507b | 816 | QAPI schema implicitly defines an object type. |
39a18158 MA |
817 | |
818 | Example: the SchemaInfo for EVENT_C from section Events | |
819 | ||
820 | { "name": "EVENT_C", "meta-type": "event", | |
7599697c | 821 | "arg-type": "q_obj-EVENT_C-arg" } |
39a18158 | 822 | |
7599697c | 823 | Type "q_obj-EVENT_C-arg" is an implicitly defined object type with |
39a18158 MA |
824 | the two members from the event's definition. |
825 | ||
826 | The SchemaInfo for struct and union types has meta-type "object". | |
827 | ||
828 | The SchemaInfo for a struct type has variant member "members". | |
829 | ||
830 | The SchemaInfo for a union type additionally has variant members "tag" | |
831 | and "variants". | |
832 | ||
833 | "members" is a JSON array describing the object's common members, if | |
834 | any. Each element is a JSON object with members "name" (the member's | |
835 | name), "type" (the name of its type), and optionally "default". The | |
836 | member is optional if "default" is present. Currently, "default" can | |
837 | only have value null. Other values are reserved for future | |
f5455044 EB |
838 | extensions. The "members" array is in no particular order; clients |
839 | must search the entire object when learning whether a particular | |
840 | member is supported. | |
39a18158 MA |
841 | |
842 | Example: the SchemaInfo for MyType from section Struct types | |
843 | ||
844 | { "name": "MyType", "meta-type": "object", | |
845 | "members": [ | |
846 | { "name": "member1", "type": "str" }, | |
847 | { "name": "member2", "type": "int" }, | |
848 | { "name": "member3", "type": "str", "default": null } ] } | |
849 | ||
850 | "tag" is the name of the common member serving as type tag. | |
851 | "variants" is a JSON array describing the object's variant members. | |
852 | Each element is a JSON object with members "case" (the value of type | |
853 | tag this element applies to) and "type" (the name of an object type | |
f5455044 EB |
854 | that provides the variant members for this type tag value). The |
855 | "variants" array is in no particular order, and is not guaranteed to | |
856 | list cases in the same order as the corresponding "tag" enum type. | |
39a18158 MA |
857 | |
858 | Example: the SchemaInfo for flat union BlockdevOptions from section | |
859 | Union types | |
860 | ||
861 | { "name": "BlockdevOptions", "meta-type": "object", | |
862 | "members": [ | |
863 | { "name": "driver", "type": "BlockdevDriver" }, | |
bd59adce | 864 | { "name": "read-only", "type": "bool", "default": null } ], |
39a18158 MA |
865 | "tag": "driver", |
866 | "variants": [ | |
bd59adce EB |
867 | { "case": "file", "type": "BlockdevOptionsFile" }, |
868 | { "case": "qcow2", "type": "BlockdevOptionsQcow2" } ] } | |
39a18158 MA |
869 | |
870 | Note that base types are "flattened": its members are included in the | |
871 | "members" array. | |
872 | ||
873 | A simple union implicitly defines an enumeration type for its implicit | |
874 | discriminator (called "type" on the wire, see section Union types). | |
39a18158 MA |
875 | |
876 | A simple union implicitly defines an object type for each of its | |
1a9a507b | 877 | variants. |
39a18158 | 878 | |
bd59adce | 879 | Example: the SchemaInfo for simple union BlockdevOptionsSimple from section |
39a18158 MA |
880 | Union types |
881 | ||
bd59adce | 882 | { "name": "BlockdevOptionsSimple", "meta-type": "object", |
39a18158 | 883 | "members": [ |
bd59adce | 884 | { "name": "type", "type": "BlockdevOptionsSimpleKind" } ], |
39a18158 MA |
885 | "tag": "type", |
886 | "variants": [ | |
bd59adce EB |
887 | { "case": "file", "type": "q_obj-BlockdevOptionsFile-wrapper" }, |
888 | { "case": "qcow2", "type": "q_obj-BlockdevOptionsQcow2-wrapper" } ] } | |
39a18158 | 889 | |
bd59adce EB |
890 | Enumeration type "BlockdevOptionsSimpleKind" and the object types |
891 | "q_obj-BlockdevOptionsFile-wrapper", "q_obj-BlockdevOptionsQcow2-wrapper" | |
892 | are implicitly defined. | |
39a18158 MA |
893 | |
894 | The SchemaInfo for an alternate type has meta-type "alternate", and | |
895 | variant member "members". "members" is a JSON array. Each element is | |
896 | a JSON object with member "type", which names a type. Values of the | |
f5455044 EB |
897 | alternate type conform to exactly one of its member types. There is |
898 | no guarantee on the order in which "members" will be listed. | |
39a18158 | 899 | |
bd59adce | 900 | Example: the SchemaInfo for BlockdevRef from section Alternate types |
39a18158 | 901 | |
bd59adce | 902 | { "name": "BlockdevRef", "meta-type": "alternate", |
39a18158 MA |
903 | "members": [ |
904 | { "type": "BlockdevOptions" }, | |
905 | { "type": "str" } ] } | |
906 | ||
907 | The SchemaInfo for an array type has meta-type "array", and variant | |
908 | member "element-type", which names the array's element type. Array | |
ce5fcb47 EB |
909 | types are implicitly defined. For convenience, the array's name may |
910 | resemble the element type; however, clients should examine member | |
911 | "element-type" instead of making assumptions based on parsing member | |
912 | "name". | |
39a18158 MA |
913 | |
914 | Example: the SchemaInfo for ['str'] | |
915 | ||
ce5fcb47 | 916 | { "name": "[str]", "meta-type": "array", |
39a18158 MA |
917 | "element-type": "str" } |
918 | ||
919 | The SchemaInfo for an enumeration type has meta-type "enum" and | |
f5455044 EB |
920 | variant member "values". The values are listed in no particular |
921 | order; clients must search the entire enum when learning whether a | |
922 | particular value is supported. | |
39a18158 MA |
923 | |
924 | Example: the SchemaInfo for MyEnum from section Enumeration types | |
925 | ||
926 | { "name": "MyEnum", "meta-type": "enum", | |
927 | "values": [ "value1", "value2", "value3" ] } | |
928 | ||
929 | The SchemaInfo for a built-in type has the same name as the type in | |
930 | the QAPI schema (see section Built-in Types), with one exception | |
931 | detailed below. It has variant member "json-type" that shows how | |
932 | values of this type are encoded on the wire. | |
933 | ||
934 | Example: the SchemaInfo for str | |
935 | ||
936 | { "name": "str", "meta-type": "builtin", "json-type": "string" } | |
937 | ||
938 | The QAPI schema supports a number of integer types that only differ in | |
939 | how they map to C. They are identical as far as SchemaInfo is | |
940 | concerned. Therefore, they get all mapped to a single type "int" in | |
941 | SchemaInfo. | |
942 | ||
943 | As explained above, type names are not part of the wire ABI. Not even | |
944 | the names of built-in types. Clients should examine member | |
945 | "json-type" instead of hard-coding names of built-in types. | |
946 | ||
947 | ||
b84da831 MR |
948 | == Code generation == |
949 | ||
fb0bc835 MA |
950 | The QAPI code generator qapi-gen.py generates code and documentation |
951 | from the schema. Together with the core QAPI libraries, this code | |
952 | provides everything required to take JSON commands read in by a Client | |
953 | JSON Protocol server, unmarshal the arguments into the underlying C | |
954 | types, call into the corresponding C function, map the response back | |
955 | to a Client JSON Protocol response to be returned to the user, and | |
956 | introspect the commands. | |
b84da831 | 957 | |
9ee86b85 EB |
958 | As an example, we'll use the following schema, which describes a |
959 | single complex user-defined type, along with command which takes a | |
960 | list of that type as a parameter, and returns a single element of that | |
961 | type. The user is responsible for writing the implementation of | |
962 | qmp_my_command(); everything else is produced by the generator. | |
b84da831 | 963 | |
87a560c4 | 964 | $ cat example-schema.json |
3b2a8b85 | 965 | { 'struct': 'UserDefOne', |
9ee86b85 | 966 | 'data': { 'integer': 'int', '*string': 'str' } } |
b84da831 MR |
967 | |
968 | { 'command': 'my-command', | |
9ee86b85 | 969 | 'data': { 'arg1': ['UserDefOne'] }, |
b84da831 | 970 | 'returns': 'UserDefOne' } |
b84da831 | 971 | |
59a2c4ce EB |
972 | { 'event': 'MY_EVENT' } |
973 | ||
fb0bc835 MA |
974 | We run qapi-gen.py like this: |
975 | ||
976 | $ python scripts/qapi-gen.py --output-dir="qapi-generated" \ | |
977 | --prefix="example-" example-schema.json | |
978 | ||
9ee86b85 EB |
979 | For a more thorough look at generated code, the testsuite includes |
980 | tests/qapi-schema/qapi-schema-tests.json that covers more examples of | |
981 | what the generator will accept, and compiles the resulting C code as | |
982 | part of 'make check-unit'. | |
983 | ||
fb0bc835 | 984 | === Code generated for QAPI types === |
b84da831 | 985 | |
fb0bc835 | 986 | The following files are created: |
b84da831 MR |
987 | |
988 | $(prefix)qapi-types.h - C types corresponding to types defined in | |
fb0bc835 MA |
989 | the schema |
990 | ||
b84da831 MR |
991 | $(prefix)qapi-types.c - Cleanup functions for the above C types |
992 | ||
993 | The $(prefix) is an optional parameter used as a namespace to keep the | |
994 | generated code from one schema/code-generation separated from others so code | |
995 | can be generated/used from multiple schemas without clobbering previously | |
996 | created code. | |
997 | ||
998 | Example: | |
999 | ||
9ee86b85 EB |
1000 | $ cat qapi-generated/example-qapi-types.h |
1001 | [Uninteresting stuff omitted...] | |
1002 | ||
1003 | #ifndef EXAMPLE_QAPI_TYPES_H | |
1004 | #define EXAMPLE_QAPI_TYPES_H | |
1005 | ||
1006 | [Built-in types omitted...] | |
1007 | ||
1008 | typedef struct UserDefOne UserDefOne; | |
1009 | ||
1010 | typedef struct UserDefOneList UserDefOneList; | |
1011 | ||
64355088 MA |
1012 | typedef struct q_obj_my_command_arg q_obj_my_command_arg; |
1013 | ||
9ee86b85 EB |
1014 | struct UserDefOne { |
1015 | int64_t integer; | |
1016 | bool has_string; | |
1017 | char *string; | |
1018 | }; | |
1019 | ||
1020 | void qapi_free_UserDefOne(UserDefOne *obj); | |
1021 | ||
1022 | struct UserDefOneList { | |
1023 | UserDefOneList *next; | |
1024 | UserDefOne *value; | |
1025 | }; | |
1026 | ||
1027 | void qapi_free_UserDefOneList(UserDefOneList *obj); | |
1028 | ||
64355088 MA |
1029 | struct q_obj_my_command_arg { |
1030 | UserDefOneList *arg1; | |
1031 | }; | |
1032 | ||
9ee86b85 | 1033 | #endif |
87a560c4 | 1034 | $ cat qapi-generated/example-qapi-types.c |
6e2bb3ec MA |
1035 | [Uninteresting stuff omitted...] |
1036 | ||
2b162ccb | 1037 | void qapi_free_UserDefOne(UserDefOne *obj) |
6e2bb3ec | 1038 | { |
6e2bb3ec MA |
1039 | Visitor *v; |
1040 | ||
1041 | if (!obj) { | |
1042 | return; | |
1043 | } | |
1044 | ||
2c0ef9f4 | 1045 | v = qapi_dealloc_visitor_new(); |
9ee86b85 | 1046 | visit_type_UserDefOne(v, NULL, &obj, NULL); |
2c0ef9f4 | 1047 | visit_free(v); |
6e2bb3ec | 1048 | } |
b84da831 | 1049 | |
2b162ccb | 1050 | void qapi_free_UserDefOneList(UserDefOneList *obj) |
b84da831 | 1051 | { |
b84da831 MR |
1052 | Visitor *v; |
1053 | ||
1054 | if (!obj) { | |
1055 | return; | |
1056 | } | |
1057 | ||
2c0ef9f4 | 1058 | v = qapi_dealloc_visitor_new(); |
9ee86b85 | 1059 | visit_type_UserDefOneList(v, NULL, &obj, NULL); |
2c0ef9f4 | 1060 | visit_free(v); |
b84da831 | 1061 | } |
b84da831 | 1062 | |
fb0bc835 | 1063 | === Code generated for visiting QAPI types === |
b84da831 | 1064 | |
fb0bc835 MA |
1065 | These are the visitor functions used to walk through and convert |
1066 | between a native QAPI C data structure and some other format (such as | |
1067 | QObject); the generated functions are named visit_type_FOO() and | |
1068 | visit_type_FOO_members(). | |
b84da831 MR |
1069 | |
1070 | The following files are generated: | |
1071 | ||
fb0bc835 | 1072 | $(prefix)qapi-visit.c: Visitor function for a particular C type, used |
b84da831 MR |
1073 | to automagically convert QObjects into the |
1074 | corresponding C type and vice-versa, as well | |
1075 | as for deallocating memory for an existing C | |
1076 | type | |
1077 | ||
fb0bc835 | 1078 | $(prefix)qapi-visit.h: Declarations for previously mentioned visitor |
b84da831 MR |
1079 | functions |
1080 | ||
1081 | Example: | |
1082 | ||
9ee86b85 EB |
1083 | $ cat qapi-generated/example-qapi-visit.h |
1084 | [Uninteresting stuff omitted...] | |
1085 | ||
1086 | #ifndef EXAMPLE_QAPI_VISIT_H | |
1087 | #define EXAMPLE_QAPI_VISIT_H | |
1088 | ||
1089 | [Visitors for built-in types omitted...] | |
1090 | ||
1091 | void visit_type_UserDefOne_members(Visitor *v, UserDefOne *obj, Error **errp); | |
1092 | void visit_type_UserDefOne(Visitor *v, const char *name, UserDefOne **obj, Error **errp); | |
1093 | void visit_type_UserDefOneList(Visitor *v, const char *name, UserDefOneList **obj, Error **errp); | |
1094 | ||
64355088 MA |
1095 | void visit_type_q_obj_my_command_arg_members(Visitor *v, q_obj_my_command_arg *obj, Error **errp); |
1096 | ||
9ee86b85 | 1097 | #endif |
87a560c4 | 1098 | $ cat qapi-generated/example-qapi-visit.c |
6e2bb3ec | 1099 | [Uninteresting stuff omitted...] |
b84da831 | 1100 | |
9ee86b85 | 1101 | void visit_type_UserDefOne_members(Visitor *v, UserDefOne *obj, Error **errp) |
6e2bb3ec MA |
1102 | { |
1103 | Error *err = NULL; | |
3a864e7c | 1104 | |
9ee86b85 | 1105 | visit_type_int(v, "integer", &obj->integer, &err); |
297a3646 MA |
1106 | if (err) { |
1107 | goto out; | |
1108 | } | |
9ee86b85 EB |
1109 | if (visit_optional(v, "string", &obj->has_string)) { |
1110 | visit_type_str(v, "string", &obj->string, &err); | |
1111 | if (err) { | |
1112 | goto out; | |
1113 | } | |
297a3646 | 1114 | } |
6e2bb3ec | 1115 | |
297a3646 | 1116 | out: |
6e2bb3ec MA |
1117 | error_propagate(errp, err); |
1118 | } | |
b84da831 | 1119 | |
9ee86b85 | 1120 | void visit_type_UserDefOne(Visitor *v, const char *name, UserDefOne **obj, Error **errp) |
b84da831 | 1121 | { |
297a3646 MA |
1122 | Error *err = NULL; |
1123 | ||
9ee86b85 EB |
1124 | visit_start_struct(v, name, (void **)obj, sizeof(UserDefOne), &err); |
1125 | if (err) { | |
1126 | goto out; | |
1127 | } | |
1128 | if (!*obj) { | |
1129 | goto out_obj; | |
6e2bb3ec | 1130 | } |
9ee86b85 | 1131 | visit_type_UserDefOne_members(v, *obj, &err); |
15c2f669 EB |
1132 | if (err) { |
1133 | goto out_obj; | |
1134 | } | |
1135 | visit_check_struct(v, &err); | |
9ee86b85 | 1136 | out_obj: |
1158bb2a | 1137 | visit_end_struct(v, (void **)obj); |
68ab47e4 EB |
1138 | if (err && visit_is_input(v)) { |
1139 | qapi_free_UserDefOne(*obj); | |
1140 | *obj = NULL; | |
1141 | } | |
9ee86b85 | 1142 | out: |
297a3646 | 1143 | error_propagate(errp, err); |
b84da831 MR |
1144 | } |
1145 | ||
9ee86b85 | 1146 | void visit_type_UserDefOneList(Visitor *v, const char *name, UserDefOneList **obj, Error **errp) |
b84da831 | 1147 | { |
6e2bb3ec | 1148 | Error *err = NULL; |
d9f62dde EB |
1149 | UserDefOneList *tail; |
1150 | size_t size = sizeof(**obj); | |
6e2bb3ec | 1151 | |
d9f62dde | 1152 | visit_start_list(v, name, (GenericList **)obj, size, &err); |
297a3646 MA |
1153 | if (err) { |
1154 | goto out; | |
1155 | } | |
1156 | ||
d9f62dde EB |
1157 | for (tail = *obj; tail; |
1158 | tail = (UserDefOneList *)visit_next_list(v, (GenericList *)tail, size)) { | |
1159 | visit_type_UserDefOne(v, NULL, &tail->value, &err); | |
1160 | if (err) { | |
1161 | break; | |
1162 | } | |
b84da831 | 1163 | } |
297a3646 | 1164 | |
64355088 MA |
1165 | if (!err) { |
1166 | visit_check_list(v, &err); | |
1167 | } | |
1158bb2a | 1168 | visit_end_list(v, (void **)obj); |
68ab47e4 EB |
1169 | if (err && visit_is_input(v)) { |
1170 | qapi_free_UserDefOneList(*obj); | |
1171 | *obj = NULL; | |
1172 | } | |
297a3646 MA |
1173 | out: |
1174 | error_propagate(errp, err); | |
b84da831 | 1175 | } |
b84da831 | 1176 | |
64355088 MA |
1177 | void visit_type_q_obj_my_command_arg_members(Visitor *v, q_obj_my_command_arg *obj, Error **errp) |
1178 | { | |
1179 | Error *err = NULL; | |
1180 | ||
1181 | visit_type_UserDefOneList(v, "arg1", &obj->arg1, &err); | |
1182 | if (err) { | |
1183 | goto out; | |
1184 | } | |
1185 | ||
1186 | out: | |
1187 | error_propagate(errp, err); | |
1188 | } | |
1189 | ||
fb0bc835 MA |
1190 | === Code generated for commands === |
1191 | ||
1192 | These are the marshaling/dispatch functions for the commands defined | |
1193 | in the schema. The generated code provides qmp_marshal_COMMAND(), and | |
1194 | declares qmp_COMMAND() that the user must implement. | |
b84da831 | 1195 | |
fb0bc835 | 1196 | The following files are generated: |
b84da831 | 1197 | |
eb815e24 MA |
1198 | $(prefix)qapi-commands.c: Command marshal/dispatch functions for each |
1199 | QMP command defined in the schema | |
b84da831 | 1200 | |
eb815e24 MA |
1201 | $(prefix)qapi-commands.h: Function prototypes for the QMP commands |
1202 | specified in the schema | |
b84da831 MR |
1203 | |
1204 | Example: | |
1205 | ||
eb815e24 | 1206 | $ cat qapi-generated/example-qapi-commands.h |
9ee86b85 EB |
1207 | [Uninteresting stuff omitted...] |
1208 | ||
1209 | #ifndef EXAMPLE_QMP_COMMANDS_H | |
1210 | #define EXAMPLE_QMP_COMMANDS_H | |
1211 | ||
1212 | #include "example-qapi-types.h" | |
1213 | #include "qapi/qmp/qdict.h" | |
64355088 | 1214 | #include "qapi/qmp/dispatch.h" |
9ee86b85 | 1215 | |
64355088 | 1216 | void example_qmp_init_marshal(QmpCommandList *cmds); |
9ee86b85 | 1217 | UserDefOne *qmp_my_command(UserDefOneList *arg1, Error **errp); |
64355088 | 1218 | void qmp_marshal_my_command(QDict *args, QObject **ret, Error **errp); |
9ee86b85 EB |
1219 | |
1220 | #endif | |
eb815e24 | 1221 | $ cat qapi-generated/example-qapi-commands.c |
6e2bb3ec | 1222 | [Uninteresting stuff omitted...] |
b84da831 | 1223 | |
56d92b00 | 1224 | static void qmp_marshal_output_UserDefOne(UserDefOne *ret_in, QObject **ret_out, Error **errp) |
b84da831 | 1225 | { |
2a0f50e8 | 1226 | Error *err = NULL; |
b84da831 MR |
1227 | Visitor *v; |
1228 | ||
7d5e199a | 1229 | v = qobject_output_visitor_new(ret_out); |
9ee86b85 | 1230 | visit_type_UserDefOne(v, "unused", &ret_in, &err); |
3b098d56 EB |
1231 | if (!err) { |
1232 | visit_complete(v, ret_out); | |
6e2bb3ec | 1233 | } |
2a0f50e8 | 1234 | error_propagate(errp, err); |
2c0ef9f4 EB |
1235 | visit_free(v); |
1236 | v = qapi_dealloc_visitor_new(); | |
9ee86b85 | 1237 | visit_type_UserDefOne(v, "unused", &ret_in, NULL); |
2c0ef9f4 | 1238 | visit_free(v); |
b84da831 MR |
1239 | } |
1240 | ||
64355088 | 1241 | void qmp_marshal_my_command(QDict *args, QObject **ret, Error **errp) |
b84da831 | 1242 | { |
2a0f50e8 | 1243 | Error *err = NULL; |
3f99144c | 1244 | UserDefOne *retval; |
b84da831 | 1245 | Visitor *v; |
64355088 | 1246 | q_obj_my_command_arg arg = {0}; |
b84da831 | 1247 | |
048abb7b | 1248 | v = qobject_input_visitor_new(QOBJECT(args)); |
ed841535 EB |
1249 | visit_start_struct(v, NULL, NULL, 0, &err); |
1250 | if (err) { | |
1251 | goto out; | |
1252 | } | |
64355088 | 1253 | visit_type_q_obj_my_command_arg_members(v, &arg, &err); |
15c2f669 EB |
1254 | if (!err) { |
1255 | visit_check_struct(v, &err); | |
1256 | } | |
1158bb2a | 1257 | visit_end_struct(v, NULL); |
2a0f50e8 | 1258 | if (err) { |
b84da831 MR |
1259 | goto out; |
1260 | } | |
297a3646 | 1261 | |
64355088 | 1262 | retval = qmp_my_command(arg.arg1, &err); |
2a0f50e8 | 1263 | if (err) { |
297a3646 | 1264 | goto out; |
6e2bb3ec | 1265 | } |
b84da831 | 1266 | |
2a0f50e8 | 1267 | qmp_marshal_output_UserDefOne(retval, ret, &err); |
297a3646 | 1268 | |
b84da831 | 1269 | out: |
2a0f50e8 | 1270 | error_propagate(errp, err); |
2c0ef9f4 EB |
1271 | visit_free(v); |
1272 | v = qapi_dealloc_visitor_new(); | |
ed841535 | 1273 | visit_start_struct(v, NULL, NULL, 0, NULL); |
64355088 | 1274 | visit_type_q_obj_my_command_arg_members(v, &arg, NULL); |
1158bb2a | 1275 | visit_end_struct(v, NULL); |
2c0ef9f4 | 1276 | visit_free(v); |
b84da831 MR |
1277 | } |
1278 | ||
64355088 | 1279 | void example_qmp_init_marshal(QmpCommandList *cmds) |
b84da831 | 1280 | { |
64355088 | 1281 | QTAILQ_INIT(cmds); |
b84da831 | 1282 | |
64355088 MA |
1283 | qmp_register_command(cmds, "my-command", |
1284 | qmp_marshal_my_command, QCO_NO_OPTIONS); | |
1285 | } | |
59a2c4ce | 1286 | |
fb0bc835 | 1287 | === Code generated for events === |
59a2c4ce | 1288 | |
fb0bc835 MA |
1289 | This is the code related to events defined in the schema, providing |
1290 | qapi_event_send_EVENT(). | |
1291 | ||
1292 | The following files are created: | |
59a2c4ce | 1293 | |
eb815e24 | 1294 | $(prefix)qapi-events.h - Function prototypes for each event type, plus an |
59a2c4ce | 1295 | enumeration of all event names |
fb0bc835 | 1296 | |
eb815e24 | 1297 | $(prefix)qapi-events.c - Implementation of functions to send an event |
59a2c4ce EB |
1298 | |
1299 | Example: | |
1300 | ||
eb815e24 | 1301 | $ cat qapi-generated/example-qapi-events.h |
9ee86b85 EB |
1302 | [Uninteresting stuff omitted...] |
1303 | ||
1304 | #ifndef EXAMPLE_QAPI_EVENT_H | |
1305 | #define EXAMPLE_QAPI_EVENT_H | |
1306 | ||
9ee86b85 EB |
1307 | #include "qapi/qmp/qdict.h" |
1308 | #include "example-qapi-types.h" | |
1309 | ||
1310 | ||
1311 | void qapi_event_send_my_event(Error **errp); | |
1312 | ||
1313 | typedef enum example_QAPIEvent { | |
1314 | EXAMPLE_QAPI_EVENT_MY_EVENT = 0, | |
1315 | EXAMPLE_QAPI_EVENT__MAX = 1, | |
1316 | } example_QAPIEvent; | |
1317 | ||
5b5f825d MA |
1318 | #define example_QAPIEvent_str(val) \ |
1319 | qapi_enum_lookup(example_QAPIEvent_lookup, (val)) | |
1320 | ||
9ee86b85 EB |
1321 | extern const char *const example_QAPIEvent_lookup[]; |
1322 | ||
1323 | #endif | |
eb815e24 | 1324 | $ cat qapi-generated/example-qapi-events.c |
59a2c4ce EB |
1325 | [Uninteresting stuff omitted...] |
1326 | ||
1327 | void qapi_event_send_my_event(Error **errp) | |
1328 | { | |
1329 | QDict *qmp; | |
2a0f50e8 | 1330 | Error *err = NULL; |
59a2c4ce | 1331 | QMPEventFuncEmit emit; |
64355088 | 1332 | |
59a2c4ce EB |
1333 | emit = qmp_event_get_func_emit(); |
1334 | if (!emit) { | |
1335 | return; | |
1336 | } | |
1337 | ||
1338 | qmp = qmp_event_build_dict("MY_EVENT"); | |
1339 | ||
2a0f50e8 | 1340 | emit(EXAMPLE_QAPI_EVENT_MY_EVENT, qmp, &err); |
59a2c4ce | 1341 | |
2a0f50e8 | 1342 | error_propagate(errp, err); |
cb3e7f08 | 1343 | qobject_unref(qmp); |
59a2c4ce EB |
1344 | } |
1345 | ||
fb0bc835 MA |
1346 | const QEnumLookup example_QAPIEvent_lookup = { |
1347 | .array = (const char *const[]) { | |
1348 | [EXAMPLE_QAPI_EVENT_MY_EVENT] = "MY_EVENT", | |
1349 | }, | |
1350 | .size = EXAMPLE_QAPI_EVENT__MAX | |
59a2c4ce | 1351 | }; |
39a18158 | 1352 | |
fb0bc835 | 1353 | === Code generated for introspection === |
39a18158 | 1354 | |
fb0bc835 | 1355 | The following files are created: |
39a18158 | 1356 | |
eb815e24 | 1357 | $(prefix)qapi-introspect.c - Defines a string holding a JSON |
fb0bc835 MA |
1358 | description of the schema |
1359 | ||
eb815e24 | 1360 | $(prefix)qapi-introspect.h - Declares the above string |
39a18158 MA |
1361 | |
1362 | Example: | |
1363 | ||
eb815e24 | 1364 | $ cat qapi-generated/example-qapi-introspect.h |
39a18158 MA |
1365 | [Uninteresting stuff omitted...] |
1366 | ||
1367 | #ifndef EXAMPLE_QMP_INTROSPECT_H | |
1368 | #define EXAMPLE_QMP_INTROSPECT_H | |
1369 | ||
7d0f982b | 1370 | extern const QLitObject qmp_schema_qlit; |
39a18158 MA |
1371 | |
1372 | #endif | |
eb815e24 | 1373 | $ cat qapi-generated/example-qapi-introspect.c |
9ee86b85 EB |
1374 | [Uninteresting stuff omitted...] |
1375 | ||
7d0f982b MAL |
1376 | const QLitObject example_qmp_schema_qlit = QLIT_QLIST(((QLitObject[]) { |
1377 | QLIT_QDICT(((QLitDictEntry[]) { | |
1378 | { "arg-type", QLIT_QSTR("0") }, | |
1379 | { "meta-type", QLIT_QSTR("event") }, | |
1380 | { "name", QLIT_QSTR("Event") }, | |
1381 | { } | |
1382 | })), | |
1383 | QLIT_QDICT(((QLitDictEntry[]) { | |
1384 | { "members", QLIT_QLIST(((QLitObject[]) { | |
1385 | { } | |
1386 | })) }, | |
1387 | { "meta-type", QLIT_QSTR("object") }, | |
1388 | { "name", QLIT_QSTR("0") }, | |
1389 | { } | |
1390 | })), | |
1391 | ... | |
1392 | { } | |
1393 | })); |