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1 | = How to use the QAPI code generator = |
2 | ||
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3 | Copyright IBM Corp. 2011 |
4 | Copyright (C) 2012-2015 Red Hat, Inc. | |
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. | |
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46 | |
47 | Comments are allowed; anything between an unquoted # and the following | |
48 | newline is ignored. Although there is not yet a documentation | |
49 | generator, a form of stylized comments has developed for consistently | |
50 | documenting details about an expression and when it was added to the | |
51 | schema. The documentation is delimited between two lines of ##, then | |
52 | the first line names the expression, an optional overview is provided, | |
53 | then individual documentation about each member of 'data' is provided, | |
54 | and finally, a 'Since: x.y.z' tag lists the release that introduced | |
55 | the expression. Optional fields are tagged with the phrase | |
56 | '#optional', often with their default value; and extensions added | |
57 | after the expression was first released are also given a '(since | |
58 | x.y.z)' comment. For example: | |
59 | ||
60 | ## | |
61 | # @BlockStats: | |
62 | # | |
63 | # Statistics of a virtual block device or a block backing device. | |
64 | # | |
65 | # @device: #optional If the stats are for a virtual block device, the name | |
66 | # corresponding to the virtual block device. | |
67 | # | |
68 | # @stats: A @BlockDeviceStats for the device. | |
69 | # | |
70 | # @parent: #optional This describes the file block device if it has one. | |
71 | # | |
72 | # @backing: #optional This describes the backing block device if it has one. | |
73 | # (Since 2.0) | |
74 | # | |
75 | # Since: 0.14.0 | |
76 | ## | |
3b2a8b85 | 77 | { 'struct': 'BlockStats', |
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78 | 'data': {'*device': 'str', 'stats': 'BlockDeviceStats', |
79 | '*parent': 'BlockStats', | |
80 | '*backing': 'BlockStats'} } | |
81 | ||
82 | The schema sets up a series of types, as well as commands and events | |
83 | that will use those types. Forward references are allowed: the parser | |
84 | scans in two passes, where the first pass learns all type names, and | |
85 | the second validates the schema and generates the code. This allows | |
86 | the definition of complex structs that can have mutually recursive | |
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87 | types, and allows for indefinite nesting of Client JSON Protocol that |
88 | satisfies the schema. A type name should not be defined more than | |
89 | once. It is permissible for the schema to contain additional types | |
90 | not used by any commands or events in the Client JSON Protocol, for | |
91 | the side effect of generated C code used internally. | |
e790e666 | 92 | |
7b1b98c4 | 93 | There are seven top-level expressions recognized by the parser: |
3b2a8b85 | 94 | 'include', 'command', 'struct', 'enum', 'union', 'alternate', and |
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95 | 'event'. There are several groups of types: simple types (a number of |
96 | built-in types, such as 'int' and 'str'; as well as enumerations), | |
97 | complex types (structs and two flavors of unions), and alternate types | |
98 | (a choice between other types). The 'command' and 'event' expressions | |
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99 | can refer to existing types by name, or list an anonymous type as a |
100 | dictionary. Listing a type name inside an array refers to a | |
101 | single-dimension array of that type; multi-dimension arrays are not | |
102 | directly supported (although an array of a complex struct that | |
103 | contains an array member is possible). | |
104 | ||
105 | Types, commands, and events share a common namespace. Therefore, | |
106 | generally speaking, type definitions should always use CamelCase for | |
107 | user-defined type names, while built-in types are lowercase. Type | |
108 | definitions should not end in 'Kind', as this namespace is used for | |
109 | creating implicit C enums for visiting union types. Command names, | |
110 | and field names within a type, should be all lower case with words | |
111 | separated by a hyphen. However, some existing older commands and | |
112 | complex types use underscore; when extending such expressions, | |
113 | consistency is preferred over blindly avoiding underscore. Event | |
114 | names should be ALL_CAPS with words separated by underscore. The | |
115 | special string '**' appears for some commands that manually perform | |
116 | their own type checking rather than relying on the type-safe code | |
117 | produced by the qapi code generators. | |
118 | ||
119 | Any name (command, event, type, field, or enum value) beginning with | |
120 | "x-" is marked experimental, and may be withdrawn or changed | |
121 | incompatibly in a future release. Downstream vendors may add | |
122 | extensions; such extensions should begin with a prefix matching | |
123 | "__RFQDN_" (for the reverse-fully-qualified-domain-name of the | |
124 | vendor), even if the rest of the name uses dash (example: | |
125 | __com.redhat_drive-mirror). Other than downstream extensions (with | |
126 | leading underscore and the use of dots), all names should begin with a | |
127 | letter, and contain only ASCII letters, digits, dash, and underscore. | |
128 | It is okay to reuse names that match C keywords; the generator will | |
129 | rename a field named "default" in the QAPI to "q_default" in the | |
130 | generated C code. | |
131 | ||
132 | In the rest of this document, usage lines are given for each | |
133 | expression type, with literal strings written in lower case and | |
134 | placeholders written in capitals. If a literal string includes a | |
135 | prefix of '*', that key/value pair can be omitted from the expression. | |
3b2a8b85 | 136 | For example, a usage statement that includes '*base':STRUCT-NAME |
e790e666 | 137 | means that an expression has an optional key 'base', which if present |
3b2a8b85 | 138 | must have a value that forms a struct name. |
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139 | |
140 | ||
141 | === Built-in Types === | |
142 | ||
143 | The following types are built-in to the parser: | |
144 | 'str' - arbitrary UTF-8 string | |
145 | 'int' - 64-bit signed integer (although the C code may place further | |
146 | restrictions on acceptable range) | |
147 | 'number' - floating point number | |
148 | 'bool' - JSON value of true or false | |
149 | 'int8', 'int16', 'int32', 'int64' - like 'int', but enforce maximum | |
150 | bit size | |
151 | 'uint8', 'uint16', 'uint32', 'uint64' - unsigned counterparts | |
152 | 'size' - like 'uint64', but allows scaled suffix from command line | |
153 | visitor | |
51631493 | 154 | |
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155 | |
156 | === Includes === | |
157 | ||
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158 | Usage: { 'include': STRING } |
159 | ||
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160 | The QAPI schema definitions can be modularized using the 'include' directive: |
161 | ||
e790e666 | 162 | { 'include': 'path/to/file.json' } |
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163 | |
164 | The directive is evaluated recursively, and include paths are relative to the | |
e790e666 | 165 | file using the directive. Multiple includes of the same file are |
4247f839 | 166 | idempotent. No other keys should appear in the expression, and the include |
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167 | value should be a string. |
168 | ||
169 | As a matter of style, it is a good idea to have all files be | |
170 | self-contained, but at the moment, nothing prevents an included file | |
171 | from making a forward reference to a type that is only introduced by | |
172 | an outer file. The parser may be made stricter in the future to | |
173 | prevent incomplete include files. | |
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174 | |
175 | ||
3b2a8b85 | 176 | === Struct types === |
51631493 | 177 | |
3b2a8b85 | 178 | Usage: { 'struct': STRING, 'data': DICT, '*base': STRUCT-NAME } |
e790e666 | 179 | |
3b2a8b85 | 180 | A struct is a dictionary containing a single 'data' key whose |
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181 | value is a dictionary. This corresponds to a struct in C or an Object |
182 | in JSON. Each value of the 'data' dictionary must be the name of a | |
183 | type, or a one-element array containing a type name. An example of a | |
3b2a8b85 | 184 | struct is: |
b84da831 | 185 | |
3b2a8b85 | 186 | { 'struct': 'MyType', |
acf8394e | 187 | 'data': { 'member1': 'str', 'member2': 'int', '*member3': 'str' } } |
b84da831 | 188 | |
e790e666 | 189 | The use of '*' as a prefix to the name means the member is optional in |
363b4262 | 190 | the corresponding JSON protocol usage. |
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191 | |
192 | The default initialization value of an optional argument should not be changed | |
193 | between versions of QEMU unless the new default maintains backward | |
194 | compatibility to the user-visible behavior of the old default. | |
195 | ||
196 | With proper documentation, this policy still allows some flexibility; for | |
197 | example, documenting that a default of 0 picks an optimal buffer size allows | |
198 | one release to declare the optimal size at 512 while another release declares | |
199 | the optimal size at 4096 - the user-visible behavior is not the bytes used by | |
200 | the buffer, but the fact that the buffer was optimal size. | |
201 | ||
202 | On input structures (only mentioned in the 'data' side of a command), changing | |
203 | from mandatory to optional is safe (older clients will supply the option, and | |
204 | newer clients can benefit from the default); changing from optional to | |
205 | mandatory is backwards incompatible (older clients may be omitting the option, | |
206 | and must continue to work). | |
207 | ||
208 | On output structures (only mentioned in the 'returns' side of a command), | |
209 | changing from mandatory to optional is in general unsafe (older clients may be | |
210 | expecting the field, and could crash if it is missing), although it can be done | |
211 | if the only way that the optional argument will be omitted is when it is | |
212 | triggered by the presence of a new input flag to the command that older clients | |
213 | don't know to send. Changing from optional to mandatory is safe. | |
214 | ||
215 | A structure that is used in both input and output of various commands | |
216 | must consider the backwards compatibility constraints of both directions | |
217 | of use. | |
622f557f | 218 | |
3b2a8b85 | 219 | A struct definition can specify another struct as its base. |
622f557f | 220 | In this case, the fields of the base type are included as top-level fields |
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221 | of the new struct's dictionary in the Client JSON Protocol wire |
222 | format. An example definition is: | |
622f557f | 223 | |
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224 | { 'struct': 'BlockdevOptionsGenericFormat', 'data': { 'file': 'str' } } |
225 | { 'struct': 'BlockdevOptionsGenericCOWFormat', | |
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226 | 'base': 'BlockdevOptionsGenericFormat', |
227 | 'data': { '*backing': 'str' } } | |
228 | ||
229 | An example BlockdevOptionsGenericCOWFormat object on the wire could use | |
230 | both fields like this: | |
231 | ||
232 | { "file": "/some/place/my-image", | |
233 | "backing": "/some/place/my-backing-file" } | |
234 | ||
e790e666 | 235 | |
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236 | === Enumeration types === |
237 | ||
e790e666 | 238 | Usage: { 'enum': STRING, 'data': ARRAY-OF-STRING } |
351d36e4 | 239 | { 'enum': STRING, '*prefix': STRING, 'data': ARRAY-OF-STRING } |
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240 | |
241 | An enumeration type is a dictionary containing a single 'data' key | |
242 | whose value is a list of strings. An example enumeration is: | |
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243 | |
244 | { 'enum': 'MyEnum', 'data': [ 'value1', 'value2', 'value3' ] } | |
245 | ||
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246 | Nothing prevents an empty enumeration, although it is probably not |
247 | useful. The list of strings should be lower case; if an enum name | |
248 | represents multiple words, use '-' between words. The string 'max' is | |
249 | not allowed as an enum value, and values should not be repeated. | |
250 | ||
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251 | The enum constants will be named by using a heuristic to turn the |
252 | type name into a set of underscore separated words. For the example | |
253 | above, 'MyEnum' will turn into 'MY_ENUM' giving a constant name | |
254 | of 'MY_ENUM_VALUE1' for the first value. If the default heuristic | |
255 | does not result in a desirable name, the optional 'prefix' field | |
256 | can be used when defining the enum. | |
257 | ||
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258 | The enumeration values are passed as strings over the Client JSON |
259 | Protocol, but are encoded as C enum integral values in generated code. | |
260 | While the C code starts numbering at 0, it is better to use explicit | |
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261 | comparisons to enum values than implicit comparisons to 0; the C code |
262 | will also include a generated enum member ending in _MAX for tracking | |
263 | the size of the enum, useful when using common functions for | |
264 | converting between strings and enum values. Since the wire format | |
265 | always passes by name, it is acceptable to reorder or add new | |
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266 | enumeration members in any location without breaking clients of Client |
267 | JSON Protocol; however, removing enum values would break | |
268 | compatibility. For any struct that has a field that will only contain | |
269 | a finite set of string values, using an enum type for that field is | |
270 | better than open-coding the field to be type 'str'. | |
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271 | |
272 | ||
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273 | === Union types === |
274 | ||
e790e666 | 275 | Usage: { 'union': STRING, 'data': DICT } |
3b2a8b85 | 276 | or: { 'union': STRING, 'data': DICT, 'base': STRUCT-NAME, |
e790e666 | 277 | 'discriminator': ENUM-MEMBER-OF-BASE } |
51631493 | 278 | |
e790e666 | 279 | Union types are used to let the user choose between several different |
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280 | variants for an object. There are two flavors: simple (no |
281 | discriminator or base), flat (both discriminator and base). A union | |
282 | type is defined using a data dictionary as explained in the following | |
283 | paragraphs. | |
51631493 | 284 | |
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285 | A simple union type defines a mapping from automatic discriminator |
286 | values to data types like in this example: | |
51631493 | 287 | |
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288 | { 'struct': 'FileOptions', 'data': { 'filename': 'str' } } |
289 | { 'struct': 'Qcow2Options', | |
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290 | 'data': { 'backing-file': 'str', 'lazy-refcounts': 'bool' } } |
291 | ||
292 | { 'union': 'BlockdevOptions', | |
293 | 'data': { 'file': 'FileOptions', | |
294 | 'qcow2': 'Qcow2Options' } } | |
295 | ||
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296 | In the Client JSON Protocol, a simple union is represented by a |
297 | dictionary that contains the 'type' field as a discriminator, and a | |
298 | 'data' field that is of the specified data type corresponding to the | |
299 | discriminator value, as in these examples: | |
51631493 | 300 | |
e790e666 | 301 | { "type": "file", "data" : { "filename": "/some/place/my-image" } } |
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302 | { "type": "qcow2", "data" : { "backing-file": "/some/place/my-image", |
303 | "lazy-refcounts": true } } | |
304 | ||
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305 | The generated C code uses a struct containing a union. Additionally, |
306 | an implicit C enum 'NameKind' is created, corresponding to the union | |
307 | 'Name', for accessing the various branches of the union. No branch of | |
308 | the union can be named 'max', as this would collide with the implicit | |
309 | enum. The value for each branch can be of any type. | |
51631493 | 310 | |
3b2a8b85 | 311 | A flat union definition specifies a struct as its base, and |
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312 | avoids nesting on the wire. All branches of the union must be |
313 | complex types, and the top-level fields of the union dictionary on | |
314 | the wire will be combination of fields from both the base type and the | |
315 | appropriate branch type (when merging two dictionaries, there must be | |
316 | no keys in common). The 'discriminator' field must be the name of an | |
3b2a8b85 | 317 | enum-typed member of the base struct. |
51631493 | 318 | |
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319 | The following example enhances the above simple union example by |
320 | adding a common field 'readonly', renaming the discriminator to | |
321 | something more applicable, and reducing the number of {} required on | |
322 | the wire: | |
50f2bdc7 | 323 | |
94a3f0af | 324 | { 'enum': 'BlockdevDriver', 'data': [ 'file', 'qcow2' ] } |
3b2a8b85 | 325 | { 'struct': 'BlockdevCommonOptions', |
bceae769 | 326 | 'data': { 'driver': 'BlockdevDriver', 'readonly': 'bool' } } |
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327 | { 'union': 'BlockdevOptions', |
328 | 'base': 'BlockdevCommonOptions', | |
329 | 'discriminator': 'driver', | |
e790e666 | 330 | 'data': { 'file': 'FileOptions', |
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331 | 'qcow2': 'Qcow2Options' } } |
332 | ||
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333 | Resulting in these JSON objects: |
334 | ||
335 | { "driver": "file", "readonly": true, | |
336 | "filename": "/some/place/my-image" } | |
337 | { "driver": "qcow2", "readonly": false, | |
338 | "backing-file": "/some/place/my-image", "lazy-refcounts": true } | |
339 | ||
340 | Notice that in a flat union, the discriminator name is controlled by | |
341 | the user, but because it must map to a base member with enum type, the | |
342 | code generator can ensure that branches exist for all values of the | |
343 | enum (although the order of the keys need not match the declaration of | |
344 | the enum). In the resulting generated C data types, a flat union is | |
345 | represented as a struct with the base member fields included directly, | |
346 | and then a union of structures for each branch of the struct. | |
347 | ||
348 | A simple union can always be re-written as a flat union where the base | |
349 | class has a single member named 'type', and where each branch of the | |
3b2a8b85 | 350 | union has a struct with a single member named 'data'. That is, |
50f2bdc7 | 351 | |
e790e666 | 352 | { 'union': 'Simple', 'data': { 'one': 'str', 'two': 'int' } } |
50f2bdc7 | 353 | |
e790e666 | 354 | is identical on the wire to: |
50f2bdc7 | 355 | |
e790e666 | 356 | { 'enum': 'Enum', 'data': ['one', 'two'] } |
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357 | { 'struct': 'Base', 'data': { 'type': 'Enum' } } |
358 | { 'struct': 'Branch1', 'data': { 'data': 'str' } } | |
359 | { 'struct': 'Branch2', 'data': { 'data': 'int' } } | |
94a3f0af | 360 | { 'union': 'Flat', 'base': 'Base', 'discriminator': 'type', |
e790e666 | 361 | 'data': { 'one': 'Branch1', 'two': 'Branch2' } } |
69dd62df | 362 | |
e790e666 | 363 | |
7b1b98c4 | 364 | === Alternate types === |
69dd62df | 365 | |
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366 | Usage: { 'alternate': STRING, 'data': DICT } |
367 | ||
368 | An alternate type is one that allows a choice between two or more JSON | |
369 | data types (string, integer, number, or object, but currently not | |
370 | array) on the wire. The definition is similar to a simple union type, | |
371 | where each branch of the union names a QAPI type. For example: | |
372 | ||
373 | { 'alternate': 'BlockRef', | |
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374 | 'data': { 'definition': 'BlockdevOptions', |
375 | 'reference': 'str' } } | |
376 | ||
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377 | Just like for a simple union, an implicit C enum 'NameKind' is created |
378 | to enumerate the branches for the alternate 'Name'. | |
379 | ||
380 | Unlike a union, the discriminator string is never passed on the wire | |
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381 | for the Client JSON Protocol. Instead, the value's JSON type serves |
382 | as an implicit discriminator, which in turn means that an alternate | |
383 | can only express a choice between types represented differently in | |
384 | JSON. If a branch is typed as the 'bool' built-in, the alternate | |
385 | accepts true and false; if it is typed as any of the various numeric | |
386 | built-ins, it accepts a JSON number; if it is typed as a 'str' | |
387 | built-in or named enum type, it accepts a JSON string; and if it is | |
388 | typed as a complex type (struct or union), it accepts a JSON object. | |
389 | Two different complex types, for instance, aren't permitted, because | |
390 | both are represented as a JSON object. | |
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391 | |
392 | The example alternate declaration above allows using both of the | |
393 | following example objects: | |
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394 | |
395 | { "file": "my_existing_block_device_id" } | |
396 | { "file": { "driver": "file", | |
397 | "readonly": false, | |
63922c64 | 398 | "filename": "/tmp/mydisk.qcow2" } } |
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399 | |
400 | ||
51631493 | 401 | === Commands === |
b84da831 | 402 | |
e790e666 | 403 | Usage: { 'command': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT, |
9b090d42 | 404 | '*returns': TYPE-NAME, |
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405 | '*gen': false, '*success-response': false } |
406 | ||
407 | Commands are defined by using a dictionary containing several members, | |
408 | where three members are most common. The 'command' member is a | |
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409 | mandatory string, and determines the "execute" value passed in a |
410 | Client JSON Protocol command exchange. | |
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411 | |
412 | The 'data' argument maps to the "arguments" dictionary passed in as | |
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413 | part of a Client JSON Protocol command. The 'data' member is optional |
414 | and defaults to {} (an empty dictionary). If present, it must be the | |
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415 | string name of a complex type, or a dictionary that declares an |
416 | anonymous type with the same semantics as a 'struct' expression, with | |
417 | one exception noted below when 'gen' is used. | |
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418 | |
419 | The 'returns' member describes what will appear in the "return" field | |
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420 | of a Client JSON Protocol reply on successful completion of a command. |
421 | The member is optional from the command declaration; if absent, the | |
422 | "return" field will be an empty dictionary. If 'returns' is present, | |
423 | it must be the string name of a complex or built-in type, a | |
424 | one-element array containing the name of a complex or built-in type, | |
9b090d42 MA |
425 | with one exception noted below when 'gen' is used. Although it is |
426 | permitted to have the 'returns' member name a built-in type or an | |
427 | array of built-in types, any command that does this cannot be extended | |
428 | to return additional information in the future; thus, new commands | |
429 | should strongly consider returning a dictionary-based type or an array | |
430 | of dictionaries, even if the dictionary only contains one field at the | |
431 | present. | |
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432 | |
433 | All commands in Client JSON Protocol use a dictionary to report | |
434 | failure, with no way to specify that in QAPI. Where the error return | |
435 | is different than the usual GenericError class in order to help the | |
436 | client react differently to certain error conditions, it is worth | |
437 | documenting this in the comments before the command declaration. | |
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438 | |
439 | Some example commands: | |
440 | ||
441 | { 'command': 'my-first-command', | |
442 | 'data': { 'arg1': 'str', '*arg2': 'str' } } | |
3b2a8b85 | 443 | { 'struct': 'MyType', 'data': { '*value': 'str' } } |
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444 | { 'command': 'my-second-command', |
445 | 'returns': [ 'MyType' ] } | |
446 | ||
363b4262 | 447 | which would validate this Client JSON Protocol transaction: |
e790e666 EB |
448 | |
449 | => { "execute": "my-first-command", | |
450 | "arguments": { "arg1": "hello" } } | |
451 | <= { "return": { } } | |
452 | => { "execute": "my-second-command" } | |
453 | <= { "return": [ { "value": "one" }, { } ] } | |
454 | ||
455 | In rare cases, QAPI cannot express a type-safe representation of a | |
363b4262 EB |
456 | corresponding Client JSON Protocol command. In these cases, if the |
457 | command expression includes the key 'gen' with boolean value false, | |
458 | then the 'data' or 'returns' member that intends to bypass generated | |
459 | type-safety and do its own manual validation should use an inline | |
460 | dictionary definition, with a value of '**' rather than a valid type | |
461 | name for the keys that the generated code will not validate. Please | |
462 | try to avoid adding new commands that rely on this, and instead use | |
463 | type-safe unions. For an example of bypass usage: | |
e790e666 EB |
464 | |
465 | { 'command': 'netdev_add', | |
466 | 'data': {'type': 'str', 'id': 'str', '*props': '**'}, | |
467 | 'gen': false } | |
468 | ||
469 | Normally, the QAPI schema is used to describe synchronous exchanges, | |
470 | where a response is expected. But in some cases, the action of a | |
471 | command is expected to change state in a way that a successful | |
472 | response is not possible (although the command will still return a | |
473 | normal dictionary error on failure). When a successful reply is not | |
474 | possible, the command expression should include the optional key | |
475 | 'success-response' with boolean value false. So far, only QGA makes | |
476 | use of this field. | |
b84da831 | 477 | |
b84da831 | 478 | |
21cd70df WX |
479 | === Events === |
480 | ||
e790e666 EB |
481 | Usage: { 'event': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT } |
482 | ||
483 | Events are defined with the keyword 'event'. It is not allowed to | |
484 | name an event 'MAX', since the generator also produces a C enumeration | |
485 | of all event names with a generated _MAX value at the end. When | |
486 | 'data' is also specified, additional info will be included in the | |
3b2a8b85 | 487 | event, with similar semantics to a 'struct' expression. Finally there |
e790e666 EB |
488 | will be C API generated in qapi-event.h; when called by QEMU code, a |
489 | message with timestamp will be emitted on the wire. | |
21cd70df WX |
490 | |
491 | An example event is: | |
492 | ||
493 | { 'event': 'EVENT_C', | |
494 | 'data': { '*a': 'int', 'b': 'str' } } | |
495 | ||
496 | Resulting in this JSON object: | |
497 | ||
498 | { "event": "EVENT_C", | |
499 | "data": { "b": "test string" }, | |
500 | "timestamp": { "seconds": 1267020223, "microseconds": 435656 } } | |
b84da831 | 501 | |
59a2c4ce | 502 | |
b84da831 MR |
503 | == Code generation == |
504 | ||
505 | Schemas are fed into 3 scripts to generate all the code/files that, paired | |
506 | with the core QAPI libraries, comprise everything required to take JSON | |
363b4262 | 507 | commands read in by a Client JSON Protocol server, unmarshal the arguments into |
b84da831 | 508 | the underlying C types, call into the corresponding C function, and map the |
363b4262 | 509 | response back to a Client JSON Protocol response to be returned to the user. |
b84da831 MR |
510 | |
511 | As an example, we'll use the following schema, which describes a single | |
512 | complex user-defined type (which will produce a C struct, along with a list | |
513 | node structure that can be used to chain together a list of such types in | |
514 | case we want to accept/return a list of this type with a command), and a | |
515 | command which takes that type as a parameter and returns the same type: | |
516 | ||
87a560c4 | 517 | $ cat example-schema.json |
3b2a8b85 | 518 | { 'struct': 'UserDefOne', |
b84da831 MR |
519 | 'data': { 'integer': 'int', 'string': 'str' } } |
520 | ||
521 | { 'command': 'my-command', | |
522 | 'data': {'arg1': 'UserDefOne'}, | |
523 | 'returns': 'UserDefOne' } | |
b84da831 | 524 | |
59a2c4ce EB |
525 | { 'event': 'MY_EVENT' } |
526 | ||
b84da831 MR |
527 | === scripts/qapi-types.py === |
528 | ||
529 | Used to generate the C types defined by a schema. The following files are | |
530 | created: | |
531 | ||
532 | $(prefix)qapi-types.h - C types corresponding to types defined in | |
533 | the schema you pass in | |
534 | $(prefix)qapi-types.c - Cleanup functions for the above C types | |
535 | ||
536 | The $(prefix) is an optional parameter used as a namespace to keep the | |
537 | generated code from one schema/code-generation separated from others so code | |
538 | can be generated/used from multiple schemas without clobbering previously | |
539 | created code. | |
540 | ||
541 | Example: | |
542 | ||
87a560c4 | 543 | $ python scripts/qapi-types.py --output-dir="qapi-generated" \ |
16d80f61 | 544 | --prefix="example-" example-schema.json |
87a560c4 | 545 | $ cat qapi-generated/example-qapi-types.c |
6e2bb3ec MA |
546 | [Uninteresting stuff omitted...] |
547 | ||
2b162ccb | 548 | void qapi_free_UserDefOne(UserDefOne *obj) |
6e2bb3ec MA |
549 | { |
550 | QapiDeallocVisitor *md; | |
551 | Visitor *v; | |
552 | ||
553 | if (!obj) { | |
554 | return; | |
555 | } | |
556 | ||
557 | md = qapi_dealloc_visitor_new(); | |
558 | v = qapi_dealloc_get_visitor(md); | |
2b162ccb | 559 | visit_type_UserDefOne(v, &obj, NULL, NULL); |
6e2bb3ec MA |
560 | qapi_dealloc_visitor_cleanup(md); |
561 | } | |
b84da831 | 562 | |
2b162ccb | 563 | void qapi_free_UserDefOneList(UserDefOneList *obj) |
b84da831 MR |
564 | { |
565 | QapiDeallocVisitor *md; | |
566 | Visitor *v; | |
567 | ||
568 | if (!obj) { | |
569 | return; | |
570 | } | |
571 | ||
572 | md = qapi_dealloc_visitor_new(); | |
573 | v = qapi_dealloc_get_visitor(md); | |
2b162ccb | 574 | visit_type_UserDefOneList(v, &obj, NULL, NULL); |
b84da831 MR |
575 | qapi_dealloc_visitor_cleanup(md); |
576 | } | |
87a560c4 | 577 | $ cat qapi-generated/example-qapi-types.h |
6e2bb3ec MA |
578 | [Uninteresting stuff omitted...] |
579 | ||
580 | #ifndef EXAMPLE_QAPI_TYPES_H | |
581 | #define EXAMPLE_QAPI_TYPES_H | |
b84da831 | 582 | |
e790e666 | 583 | [Built-in types omitted...] |
b84da831 MR |
584 | |
585 | typedef struct UserDefOne UserDefOne; | |
586 | ||
2b162ccb MA |
587 | typedef struct UserDefOneList UserDefOneList; |
588 | ||
589 | struct UserDefOne { | |
590 | int64_t integer; | |
591 | char *string; | |
592 | }; | |
593 | ||
594 | void qapi_free_UserDefOne(UserDefOne *obj); | |
595 | ||
596 | struct UserDefOneList { | |
6e2bb3ec MA |
597 | union { |
598 | UserDefOne *value; | |
599 | uint64_t padding; | |
600 | }; | |
e98859a9 | 601 | UserDefOneList *next; |
b84da831 MR |
602 | }; |
603 | ||
59a2c4ce | 604 | void qapi_free_UserDefOneList(UserDefOneList *obj); |
b84da831 MR |
605 | |
606 | #endif | |
607 | ||
b84da831 MR |
608 | === scripts/qapi-visit.py === |
609 | ||
610 | Used to generate the visitor functions used to walk through and convert | |
611 | a QObject (as provided by QMP) to a native C data structure and | |
612 | vice-versa, as well as the visitor function used to dealloc a complex | |
613 | schema-defined C type. | |
614 | ||
615 | The following files are generated: | |
616 | ||
617 | $(prefix)qapi-visit.c: visitor function for a particular C type, used | |
618 | to automagically convert QObjects into the | |
619 | corresponding C type and vice-versa, as well | |
620 | as for deallocating memory for an existing C | |
621 | type | |
622 | ||
623 | $(prefix)qapi-visit.h: declarations for previously mentioned visitor | |
624 | functions | |
625 | ||
626 | Example: | |
627 | ||
87a560c4 | 628 | $ python scripts/qapi-visit.py --output-dir="qapi-generated" |
16d80f61 | 629 | --prefix="example-" example-schema.json |
87a560c4 | 630 | $ cat qapi-generated/example-qapi-visit.c |
6e2bb3ec | 631 | [Uninteresting stuff omitted...] |
b84da831 | 632 | |
59a2c4ce | 633 | static void visit_type_UserDefOne_fields(Visitor *m, UserDefOne **obj, Error **errp) |
6e2bb3ec MA |
634 | { |
635 | Error *err = NULL; | |
3a864e7c | 636 | |
6e2bb3ec | 637 | visit_type_int(m, &(*obj)->integer, "integer", &err); |
297a3646 MA |
638 | if (err) { |
639 | goto out; | |
640 | } | |
6e2bb3ec | 641 | visit_type_str(m, &(*obj)->string, "string", &err); |
297a3646 MA |
642 | if (err) { |
643 | goto out; | |
644 | } | |
6e2bb3ec | 645 | |
297a3646 | 646 | out: |
6e2bb3ec MA |
647 | error_propagate(errp, err); |
648 | } | |
b84da831 | 649 | |
59a2c4ce | 650 | void visit_type_UserDefOne(Visitor *m, UserDefOne **obj, const char *name, Error **errp) |
b84da831 | 651 | { |
297a3646 MA |
652 | Error *err = NULL; |
653 | ||
654 | visit_start_struct(m, (void **)obj, "UserDefOne", name, sizeof(UserDefOne), &err); | |
655 | if (!err) { | |
656 | if (*obj) { | |
657 | visit_type_UserDefOne_fields(m, obj, errp); | |
6e2bb3ec | 658 | } |
297a3646 | 659 | visit_end_struct(m, &err); |
6e2bb3ec | 660 | } |
297a3646 | 661 | error_propagate(errp, err); |
b84da831 MR |
662 | } |
663 | ||
59a2c4ce | 664 | void visit_type_UserDefOneList(Visitor *m, UserDefOneList **obj, const char *name, Error **errp) |
b84da831 | 665 | { |
6e2bb3ec | 666 | Error *err = NULL; |
297a3646 | 667 | GenericList *i, **prev; |
6e2bb3ec | 668 | |
297a3646 MA |
669 | visit_start_list(m, name, &err); |
670 | if (err) { | |
671 | goto out; | |
672 | } | |
673 | ||
674 | for (prev = (GenericList **)obj; | |
675 | !err && (i = visit_next_list(m, prev, &err)) != NULL; | |
676 | prev = &i) { | |
677 | UserDefOneList *native_i = (UserDefOneList *)i; | |
678 | visit_type_UserDefOne(m, &native_i->value, NULL, &err); | |
b84da831 | 679 | } |
297a3646 MA |
680 | |
681 | error_propagate(errp, err); | |
682 | err = NULL; | |
683 | visit_end_list(m, &err); | |
684 | out: | |
685 | error_propagate(errp, err); | |
b84da831 | 686 | } |
87a560c4 | 687 | $ cat qapi-generated/example-qapi-visit.h |
6e2bb3ec | 688 | [Uninteresting stuff omitted...] |
b84da831 | 689 | |
6e2bb3ec MA |
690 | #ifndef EXAMPLE_QAPI_VISIT_H |
691 | #define EXAMPLE_QAPI_VISIT_H | |
b84da831 | 692 | |
e790e666 | 693 | [Visitors for built-in types omitted...] |
b84da831 | 694 | |
59a2c4ce EB |
695 | void visit_type_UserDefOne(Visitor *m, UserDefOne **obj, const char *name, Error **errp); |
696 | void visit_type_UserDefOneList(Visitor *m, UserDefOneList **obj, const char *name, Error **errp); | |
b84da831 MR |
697 | |
698 | #endif | |
b84da831 | 699 | |
b84da831 MR |
700 | === scripts/qapi-commands.py === |
701 | ||
702 | Used to generate the marshaling/dispatch functions for the commands defined | |
703 | in the schema. The following files are generated: | |
704 | ||
705 | $(prefix)qmp-marshal.c: command marshal/dispatch functions for each | |
706 | QMP command defined in the schema. Functions | |
707 | generated by qapi-visit.py are used to | |
2542bfd5 | 708 | convert QObjects received from the wire into |
b84da831 MR |
709 | function parameters, and uses the same |
710 | visitor functions to convert native C return | |
711 | values to QObjects from transmission back | |
712 | over the wire. | |
713 | ||
714 | $(prefix)qmp-commands.h: Function prototypes for the QMP commands | |
715 | specified in the schema. | |
716 | ||
717 | Example: | |
718 | ||
59a2c4ce | 719 | $ python scripts/qapi-commands.py --output-dir="qapi-generated" |
16d80f61 | 720 | --prefix="example-" example-schema.json |
87a560c4 | 721 | $ cat qapi-generated/example-qmp-marshal.c |
6e2bb3ec | 722 | [Uninteresting stuff omitted...] |
b84da831 | 723 | |
59a2c4ce | 724 | static void qmp_marshal_output_my_command(UserDefOne *ret_in, QObject **ret_out, Error **errp) |
b84da831 | 725 | { |
297a3646 | 726 | Error *local_err = NULL; |
b84da831 | 727 | QmpOutputVisitor *mo = qmp_output_visitor_new(); |
f9bee751 | 728 | QapiDeallocVisitor *md; |
b84da831 MR |
729 | Visitor *v; |
730 | ||
731 | v = qmp_output_get_visitor(mo); | |
297a3646 MA |
732 | visit_type_UserDefOne(v, &ret_in, "unused", &local_err); |
733 | if (local_err) { | |
734 | goto out; | |
6e2bb3ec | 735 | } |
297a3646 MA |
736 | *ret_out = qmp_output_get_qobject(mo); |
737 | ||
738 | out: | |
739 | error_propagate(errp, local_err); | |
6e2bb3ec | 740 | qmp_output_visitor_cleanup(mo); |
f9bee751 | 741 | md = qapi_dealloc_visitor_new(); |
b84da831 | 742 | v = qapi_dealloc_get_visitor(md); |
6e2bb3ec | 743 | visit_type_UserDefOne(v, &ret_in, "unused", NULL); |
b84da831 | 744 | qapi_dealloc_visitor_cleanup(md); |
b84da831 MR |
745 | } |
746 | ||
6e2bb3ec | 747 | static void qmp_marshal_input_my_command(QDict *args, QObject **ret, Error **errp) |
b84da831 | 748 | { |
297a3646 | 749 | Error *local_err = NULL; |
3f99144c | 750 | UserDefOne *retval; |
f9bee751 | 751 | QmpInputVisitor *mi = qmp_input_visitor_new_strict(QOBJECT(args)); |
b84da831 MR |
752 | QapiDeallocVisitor *md; |
753 | Visitor *v; | |
59a2c4ce | 754 | UserDefOne *arg1 = NULL; |
b84da831 | 755 | |
b84da831 | 756 | v = qmp_input_get_visitor(mi); |
297a3646 MA |
757 | visit_type_UserDefOne(v, &arg1, "arg1", &local_err); |
758 | if (local_err) { | |
b84da831 MR |
759 | goto out; |
760 | } | |
297a3646 MA |
761 | |
762 | retval = qmp_my_command(arg1, &local_err); | |
763 | if (local_err) { | |
764 | goto out; | |
6e2bb3ec | 765 | } |
b84da831 | 766 | |
297a3646 MA |
767 | qmp_marshal_output_my_command(retval, ret, &local_err); |
768 | ||
b84da831 | 769 | out: |
297a3646 | 770 | error_propagate(errp, local_err); |
f9bee751 | 771 | qmp_input_visitor_cleanup(mi); |
b84da831 MR |
772 | md = qapi_dealloc_visitor_new(); |
773 | v = qapi_dealloc_get_visitor(md); | |
6e2bb3ec | 774 | visit_type_UserDefOne(v, &arg1, "arg1", NULL); |
b84da831 | 775 | qapi_dealloc_visitor_cleanup(md); |
b84da831 MR |
776 | } |
777 | ||
778 | static void qmp_init_marshal(void) | |
779 | { | |
6e2bb3ec | 780 | qmp_register_command("my-command", qmp_marshal_input_my_command, QCO_NO_OPTIONS); |
b84da831 MR |
781 | } |
782 | ||
783 | qapi_init(qmp_init_marshal); | |
87a560c4 | 784 | $ cat qapi-generated/example-qmp-commands.h |
6e2bb3ec | 785 | [Uninteresting stuff omitted...] |
b84da831 | 786 | |
6e2bb3ec MA |
787 | #ifndef EXAMPLE_QMP_COMMANDS_H |
788 | #define EXAMPLE_QMP_COMMANDS_H | |
b84da831 MR |
789 | |
790 | #include "example-qapi-types.h" | |
6e2bb3ec MA |
791 | #include "qapi/qmp/qdict.h" |
792 | #include "qapi/error.h" | |
b84da831 | 793 | |
59a2c4ce EB |
794 | UserDefOne *qmp_my_command(UserDefOne *arg1, Error **errp); |
795 | ||
796 | #endif | |
797 | ||
798 | === scripts/qapi-event.py === | |
799 | ||
800 | Used to generate the event-related C code defined by a schema. The | |
801 | following files are created: | |
802 | ||
803 | $(prefix)qapi-event.h - Function prototypes for each event type, plus an | |
804 | enumeration of all event names | |
805 | $(prefix)qapi-event.c - Implementation of functions to send an event | |
806 | ||
807 | Example: | |
808 | ||
809 | $ python scripts/qapi-event.py --output-dir="qapi-generated" | |
16d80f61 | 810 | --prefix="example-" example-schema.json |
59a2c4ce EB |
811 | $ cat qapi-generated/example-qapi-event.c |
812 | [Uninteresting stuff omitted...] | |
813 | ||
814 | void qapi_event_send_my_event(Error **errp) | |
815 | { | |
816 | QDict *qmp; | |
817 | Error *local_err = NULL; | |
818 | QMPEventFuncEmit emit; | |
819 | emit = qmp_event_get_func_emit(); | |
820 | if (!emit) { | |
821 | return; | |
822 | } | |
823 | ||
824 | qmp = qmp_event_build_dict("MY_EVENT"); | |
825 | ||
826 | emit(EXAMPLE_QAPI_EVENT_MY_EVENT, qmp, &local_err); | |
827 | ||
828 | error_propagate(errp, local_err); | |
829 | QDECREF(qmp); | |
830 | } | |
831 | ||
efd2eaa6 MA |
832 | const char *const example_QAPIEvent_lookup[] = { |
833 | [EXAMPLE_QAPI_EVENT_MY_EVENT] = "MY_EVENT", | |
834 | [EXAMPLE_QAPI_EVENT_MAX] = NULL, | |
59a2c4ce EB |
835 | }; |
836 | $ cat qapi-generated/example-qapi-event.h | |
837 | [Uninteresting stuff omitted...] | |
838 | ||
839 | #ifndef EXAMPLE_QAPI_EVENT_H | |
840 | #define EXAMPLE_QAPI_EVENT_H | |
841 | ||
842 | #include "qapi/error.h" | |
843 | #include "qapi/qmp/qdict.h" | |
844 | #include "example-qapi-types.h" | |
845 | ||
846 | ||
847 | void qapi_event_send_my_event(Error **errp); | |
848 | ||
3a864e7c | 849 | typedef enum example_QAPIEvent { |
59a2c4ce EB |
850 | EXAMPLE_QAPI_EVENT_MY_EVENT = 0, |
851 | EXAMPLE_QAPI_EVENT_MAX = 1, | |
016a335b | 852 | } example_QAPIEvent; |
b84da831 | 853 | |
efd2eaa6 MA |
854 | extern const char *const example_QAPIEvent_lookup[]; |
855 | ||
b84da831 | 856 | #endif |