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1 | Introduction |
2 | ------------ | |
3 | ||
e95be9a5 | 4 | The configuration database is a collection of configuration options |
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5 | organized in a tree structure: |
6 | ||
7 | +- Code maturity level options | |
8 | | +- Prompt for development and/or incomplete code/drivers | |
9 | +- General setup | |
10 | | +- Networking support | |
11 | | +- System V IPC | |
12 | | +- BSD Process Accounting | |
13 | | +- Sysctl support | |
14 | +- Loadable module support | |
15 | | +- Enable loadable module support | |
16 | | +- Set version information on all module symbols | |
17 | | +- Kernel module loader | |
18 | +- ... | |
19 | ||
20 | Every entry has its own dependencies. These dependencies are used | |
21 | to determine the visibility of an entry. Any child entry is only | |
22 | visible if its parent entry is also visible. | |
23 | ||
24 | Menu entries | |
25 | ------------ | |
26 | ||
0486bc90 | 27 | Most entries define a config option; all other entries help to organize |
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28 | them. A single configuration option is defined like this: |
29 | ||
30 | config MODVERSIONS | |
31 | bool "Set version information on all module symbols" | |
bef1f402 | 32 | depends on MODULES |
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33 | help |
34 | Usually, modules have to be recompiled whenever you switch to a new | |
35 | kernel. ... | |
36 | ||
37 | Every line starts with a key word and can be followed by multiple | |
38 | arguments. "config" starts a new config entry. The following lines | |
39 | define attributes for this config option. Attributes can be the type of | |
40 | the config option, input prompt, dependencies, help text and default | |
41 | values. A config option can be defined multiple times with the same | |
42 | name, but every definition can have only a single input prompt and the | |
43 | type must not conflict. | |
44 | ||
45 | Menu attributes | |
46 | --------------- | |
47 | ||
48 | A menu entry can have a number of attributes. Not all of them are | |
49 | applicable everywhere (see syntax). | |
50 | ||
51 | - type definition: "bool"/"tristate"/"string"/"hex"/"int" | |
52 | Every config option must have a type. There are only two basic types: | |
0486bc90 | 53 | tristate and string; the other types are based on these two. The type |
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54 | definition optionally accepts an input prompt, so these two examples |
55 | are equivalent: | |
56 | ||
57 | bool "Networking support" | |
58 | and | |
59 | bool | |
60 | prompt "Networking support" | |
61 | ||
62 | - input prompt: "prompt" <prompt> ["if" <expr>] | |
63 | Every menu entry can have at most one prompt, which is used to display | |
64 | to the user. Optionally dependencies only for this prompt can be added | |
65 | with "if". | |
66 | ||
67 | - default value: "default" <expr> ["if" <expr>] | |
68 | A config option can have any number of default values. If multiple | |
69 | default values are visible, only the first defined one is active. | |
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70 | Default values are not limited to the menu entry where they are |
71 | defined. This means the default can be defined somewhere else or be | |
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72 | overridden by an earlier definition. |
73 | The default value is only assigned to the config symbol if no other | |
74 | value was set by the user (via the input prompt above). If an input | |
75 | prompt is visible the default value is presented to the user and can | |
76 | be overridden by him. | |
83dcde4e | 77 | Optionally, dependencies only for this default value can be added with |
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78 | "if". |
79 | ||
6e66b900 RD |
80 | - type definition + default value: |
81 | "def_bool"/"def_tristate" <expr> ["if" <expr>] | |
82 | This is a shorthand notation for a type definition plus a value. | |
83 | Optionally dependencies for this default value can be added with "if". | |
84 | ||
85 | - dependencies: "depends on" <expr> | |
1da177e4 | 86 | This defines a dependency for this menu entry. If multiple |
83dcde4e | 87 | dependencies are defined, they are connected with '&&'. Dependencies |
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88 | are applied to all other options within this menu entry (which also |
89 | accept an "if" expression), so these two examples are equivalent: | |
90 | ||
91 | bool "foo" if BAR | |
92 | default y if BAR | |
93 | and | |
94 | depends on BAR | |
95 | bool "foo" | |
96 | default y | |
97 | ||
98 | - reverse dependencies: "select" <symbol> ["if" <expr>] | |
99 | While normal dependencies reduce the upper limit of a symbol (see | |
100 | below), reverse dependencies can be used to force a lower limit of | |
101 | another symbol. The value of the current menu symbol is used as the | |
102 | minimal value <symbol> can be set to. If <symbol> is selected multiple | |
103 | times, the limit is set to the largest selection. | |
104 | Reverse dependencies can only be used with boolean or tristate | |
105 | symbols. | |
f8a74594 | 106 | Note: |
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107 | select should be used with care. select will force |
108 | a symbol to a value without visiting the dependencies. | |
109 | By abusing select you are able to select a symbol FOO even | |
110 | if FOO depends on BAR that is not set. | |
111 | In general use select only for non-visible symbols | |
112 | (no prompts anywhere) and for symbols with no dependencies. | |
113 | That will limit the usefulness but on the other hand avoid | |
114 | the illegal configurations all over. | |
115 | kconfig should one day warn about such things. | |
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116 | |
117 | - numerical ranges: "range" <symbol> <symbol> ["if" <expr>] | |
118 | This allows to limit the range of possible input values for int | |
119 | and hex symbols. The user can only input a value which is larger than | |
120 | or equal to the first symbol and smaller than or equal to the second | |
121 | symbol. | |
122 | ||
123 | - help text: "help" or "---help---" | |
124 | This defines a help text. The end of the help text is determined by | |
125 | the indentation level, this means it ends at the first line which has | |
126 | a smaller indentation than the first line of the help text. | |
127 | "---help---" and "help" do not differ in behaviour, "---help---" is | |
53cb4726 | 128 | used to help visually separate configuration logic from help within |
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129 | the file as an aid to developers. |
130 | ||
93449082 RZ |
131 | - misc options: "option" <symbol>[=<value>] |
132 | Various less common options can be defined via this option syntax, | |
133 | which can modify the behaviour of the menu entry and its config | |
134 | symbol. These options are currently possible: | |
135 | ||
136 | - "defconfig_list" | |
137 | This declares a list of default entries which can be used when | |
138 | looking for the default configuration (which is used when the main | |
139 | .config doesn't exists yet.) | |
140 | ||
141 | - "modules" | |
142 | This declares the symbol to be used as the MODULES symbol, which | |
143 | enables the third modular state for all config symbols. | |
144 | ||
145 | - "env"=<value> | |
146 | This imports the environment variable into Kconfig. It behaves like | |
147 | a default, except that the value comes from the environment, this | |
148 | also means that the behaviour when mixing it with normal defaults is | |
149 | undefined at this point. The symbol is currently not exported back | |
150 | to the build environment (if this is desired, it can be done via | |
151 | another symbol). | |
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152 | |
153 | Menu dependencies | |
154 | ----------------- | |
155 | ||
156 | Dependencies define the visibility of a menu entry and can also reduce | |
157 | the input range of tristate symbols. The tristate logic used in the | |
158 | expressions uses one more state than normal boolean logic to express the | |
159 | module state. Dependency expressions have the following syntax: | |
160 | ||
161 | <expr> ::= <symbol> (1) | |
162 | <symbol> '=' <symbol> (2) | |
163 | <symbol> '!=' <symbol> (3) | |
164 | '(' <expr> ')' (4) | |
165 | '!' <expr> (5) | |
166 | <expr> '&&' <expr> (6) | |
167 | <expr> '||' <expr> (7) | |
168 | ||
169 | Expressions are listed in decreasing order of precedence. | |
170 | ||
171 | (1) Convert the symbol into an expression. Boolean and tristate symbols | |
172 | are simply converted into the respective expression values. All | |
173 | other symbol types result in 'n'. | |
174 | (2) If the values of both symbols are equal, it returns 'y', | |
175 | otherwise 'n'. | |
176 | (3) If the values of both symbols are equal, it returns 'n', | |
177 | otherwise 'y'. | |
178 | (4) Returns the value of the expression. Used to override precedence. | |
179 | (5) Returns the result of (2-/expr/). | |
180 | (6) Returns the result of min(/expr/, /expr/). | |
181 | (7) Returns the result of max(/expr/, /expr/). | |
182 | ||
183 | An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2 | |
184 | respectively for calculations). A menu entry becomes visible when it's | |
185 | expression evaluates to 'm' or 'y'. | |
186 | ||
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187 | There are two types of symbols: constant and non-constant symbols. |
188 | Non-constant symbols are the most common ones and are defined with the | |
189 | 'config' statement. Non-constant symbols consist entirely of alphanumeric | |
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190 | characters or underscores. |
191 | Constant symbols are only part of expressions. Constant symbols are | |
83dcde4e | 192 | always surrounded by single or double quotes. Within the quote, any |
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193 | other character is allowed and the quotes can be escaped using '\'. |
194 | ||
195 | Menu structure | |
196 | -------------- | |
197 | ||
198 | The position of a menu entry in the tree is determined in two ways. First | |
199 | it can be specified explicitly: | |
200 | ||
201 | menu "Network device support" | |
bef1f402 | 202 | depends on NET |
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203 | |
204 | config NETDEVICES | |
205 | ... | |
206 | ||
207 | endmenu | |
208 | ||
209 | All entries within the "menu" ... "endmenu" block become a submenu of | |
210 | "Network device support". All subentries inherit the dependencies from | |
211 | the menu entry, e.g. this means the dependency "NET" is added to the | |
212 | dependency list of the config option NETDEVICES. | |
213 | ||
214 | The other way to generate the menu structure is done by analyzing the | |
215 | dependencies. If a menu entry somehow depends on the previous entry, it | |
216 | can be made a submenu of it. First, the previous (parent) symbol must | |
217 | be part of the dependency list and then one of these two conditions | |
218 | must be true: | |
219 | - the child entry must become invisible, if the parent is set to 'n' | |
220 | - the child entry must only be visible, if the parent is visible | |
221 | ||
222 | config MODULES | |
223 | bool "Enable loadable module support" | |
224 | ||
225 | config MODVERSIONS | |
226 | bool "Set version information on all module symbols" | |
bef1f402 | 227 | depends on MODULES |
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228 | |
229 | comment "module support disabled" | |
bef1f402 | 230 | depends on !MODULES |
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231 | |
232 | MODVERSIONS directly depends on MODULES, this means it's only visible if | |
233 | MODULES is different from 'n'. The comment on the other hand is always | |
234 | visible when MODULES is visible (the (empty) dependency of MODULES is | |
235 | also part of the comment dependencies). | |
236 | ||
237 | ||
238 | Kconfig syntax | |
239 | -------------- | |
240 | ||
241 | The configuration file describes a series of menu entries, where every | |
242 | line starts with a keyword (except help texts). The following keywords | |
243 | end a menu entry: | |
244 | - config | |
245 | - menuconfig | |
246 | - choice/endchoice | |
247 | - comment | |
248 | - menu/endmenu | |
249 | - if/endif | |
250 | - source | |
251 | The first five also start the definition of a menu entry. | |
252 | ||
253 | config: | |
254 | ||
255 | "config" <symbol> | |
256 | <config options> | |
257 | ||
258 | This defines a config symbol <symbol> and accepts any of above | |
259 | attributes as options. | |
260 | ||
261 | menuconfig: | |
262 | "menuconfig" <symbol> | |
263 | <config options> | |
264 | ||
53cb4726 | 265 | This is similar to the simple config entry above, but it also gives a |
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266 | hint to front ends, that all suboptions should be displayed as a |
267 | separate list of options. | |
268 | ||
269 | choices: | |
270 | ||
271 | "choice" | |
272 | <choice options> | |
273 | <choice block> | |
274 | "endchoice" | |
275 | ||
83dcde4e | 276 | This defines a choice group and accepts any of the above attributes as |
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277 | options. A choice can only be of type bool or tristate, while a boolean |
278 | choice only allows a single config entry to be selected, a tristate | |
279 | choice also allows any number of config entries to be set to 'm'. This | |
280 | can be used if multiple drivers for a single hardware exists and only a | |
281 | single driver can be compiled/loaded into the kernel, but all drivers | |
282 | can be compiled as modules. | |
283 | A choice accepts another option "optional", which allows to set the | |
284 | choice to 'n' and no entry needs to be selected. | |
285 | ||
286 | comment: | |
287 | ||
288 | "comment" <prompt> | |
289 | <comment options> | |
290 | ||
291 | This defines a comment which is displayed to the user during the | |
292 | configuration process and is also echoed to the output files. The only | |
293 | possible options are dependencies. | |
294 | ||
295 | menu: | |
296 | ||
297 | "menu" <prompt> | |
298 | <menu options> | |
299 | <menu block> | |
300 | "endmenu" | |
301 | ||
302 | This defines a menu block, see "Menu structure" above for more | |
303 | information. The only possible options are dependencies. | |
304 | ||
305 | if: | |
306 | ||
307 | "if" <expr> | |
308 | <if block> | |
309 | "endif" | |
310 | ||
311 | This defines an if block. The dependency expression <expr> is appended | |
312 | to all enclosed menu entries. | |
313 | ||
314 | source: | |
315 | ||
316 | "source" <prompt> | |
317 | ||
318 | This reads the specified configuration file. This file is always parsed. | |
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319 | |
320 | mainmenu: | |
321 | ||
322 | "mainmenu" <prompt> | |
323 | ||
324 | This sets the config program's title bar if the config program chooses | |
325 | to use it. | |
0486bc90 RD |
326 | |
327 | ||
328 | Kconfig hints | |
329 | ------------- | |
330 | This is a collection of Kconfig tips, most of which aren't obvious at | |
331 | first glance and most of which have become idioms in several Kconfig | |
332 | files. | |
333 | ||
9b3e4dad SR |
334 | Adding common features and make the usage configurable |
335 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
336 | It is a common idiom to implement a feature/functionality that are | |
337 | relevant for some architectures but not all. | |
338 | The recommended way to do so is to use a config variable named HAVE_* | |
339 | that is defined in a common Kconfig file and selected by the relevant | |
340 | architectures. | |
341 | An example is the generic IOMAP functionality. | |
342 | ||
343 | We would in lib/Kconfig see: | |
344 | ||
345 | # Generic IOMAP is used to ... | |
346 | config HAVE_GENERIC_IOMAP | |
347 | ||
348 | config GENERIC_IOMAP | |
349 | depends on HAVE_GENERIC_IOMAP && FOO | |
350 | ||
351 | And in lib/Makefile we would see: | |
352 | obj-$(CONFIG_GENERIC_IOMAP) += iomap.o | |
353 | ||
354 | For each architecture using the generic IOMAP functionality we would see: | |
355 | ||
356 | config X86 | |
357 | select ... | |
358 | select HAVE_GENERIC_IOMAP | |
359 | select ... | |
360 | ||
361 | Note: we use the existing config option and avoid creating a new | |
362 | config variable to select HAVE_GENERIC_IOMAP. | |
363 | ||
364 | Note: the use of the internal config variable HAVE_GENERIC_IOMAP, it is | |
365 | introduced to overcome the limitation of select which will force a | |
366 | config option to 'y' no matter the dependencies. | |
367 | The dependencies are moved to the symbol GENERIC_IOMAP and we avoid the | |
368 | situation where select forces a symbol equals to 'y'. | |
369 | ||
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370 | Build as module only |
371 | ~~~~~~~~~~~~~~~~~~~~ | |
372 | To restrict a component build to module-only, qualify its config symbol | |
373 | with "depends on m". E.g.: | |
374 | ||
375 | config FOO | |
376 | depends on BAR && m | |
377 | ||
378 | limits FOO to module (=m) or disabled (=n). | |
379 |