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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 | ||
27 | Most entries define a config option, all other entries help to organize | |
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: | |
53 | tristate and string, the other types are based on these two. The type | |
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 | ||
80 | - dependencies: "depends on"/"requires" <expr> | |
81 | This defines a dependency for this menu entry. If multiple | |
83dcde4e | 82 | dependencies are defined, they are connected with '&&'. Dependencies |
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83 | are applied to all other options within this menu entry (which also |
84 | accept an "if" expression), so these two examples are equivalent: | |
85 | ||
86 | bool "foo" if BAR | |
87 | default y if BAR | |
88 | and | |
89 | depends on BAR | |
90 | bool "foo" | |
91 | default y | |
92 | ||
93 | - reverse dependencies: "select" <symbol> ["if" <expr>] | |
94 | While normal dependencies reduce the upper limit of a symbol (see | |
95 | below), reverse dependencies can be used to force a lower limit of | |
96 | another symbol. The value of the current menu symbol is used as the | |
97 | minimal value <symbol> can be set to. If <symbol> is selected multiple | |
98 | times, the limit is set to the largest selection. | |
99 | Reverse dependencies can only be used with boolean or tristate | |
100 | symbols. | |
101 | ||
102 | - numerical ranges: "range" <symbol> <symbol> ["if" <expr>] | |
103 | This allows to limit the range of possible input values for int | |
104 | and hex symbols. The user can only input a value which is larger than | |
105 | or equal to the first symbol and smaller than or equal to the second | |
106 | symbol. | |
107 | ||
108 | - help text: "help" or "---help---" | |
109 | This defines a help text. The end of the help text is determined by | |
110 | the indentation level, this means it ends at the first line which has | |
111 | a smaller indentation than the first line of the help text. | |
112 | "---help---" and "help" do not differ in behaviour, "---help---" is | |
53cb4726 | 113 | used to help visually separate configuration logic from help within |
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114 | the file as an aid to developers. |
115 | ||
116 | ||
117 | Menu dependencies | |
118 | ----------------- | |
119 | ||
120 | Dependencies define the visibility of a menu entry and can also reduce | |
121 | the input range of tristate symbols. The tristate logic used in the | |
122 | expressions uses one more state than normal boolean logic to express the | |
123 | module state. Dependency expressions have the following syntax: | |
124 | ||
125 | <expr> ::= <symbol> (1) | |
126 | <symbol> '=' <symbol> (2) | |
127 | <symbol> '!=' <symbol> (3) | |
128 | '(' <expr> ')' (4) | |
129 | '!' <expr> (5) | |
130 | <expr> '&&' <expr> (6) | |
131 | <expr> '||' <expr> (7) | |
132 | ||
133 | Expressions are listed in decreasing order of precedence. | |
134 | ||
135 | (1) Convert the symbol into an expression. Boolean and tristate symbols | |
136 | are simply converted into the respective expression values. All | |
137 | other symbol types result in 'n'. | |
138 | (2) If the values of both symbols are equal, it returns 'y', | |
139 | otherwise 'n'. | |
140 | (3) If the values of both symbols are equal, it returns 'n', | |
141 | otherwise 'y'. | |
142 | (4) Returns the value of the expression. Used to override precedence. | |
143 | (5) Returns the result of (2-/expr/). | |
144 | (6) Returns the result of min(/expr/, /expr/). | |
145 | (7) Returns the result of max(/expr/, /expr/). | |
146 | ||
147 | An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2 | |
148 | respectively for calculations). A menu entry becomes visible when it's | |
149 | expression evaluates to 'm' or 'y'. | |
150 | ||
151 | There are two types of symbols: constant and nonconstant symbols. | |
152 | Nonconstant symbols are the most common ones and are defined with the | |
153 | 'config' statement. Nonconstant symbols consist entirely of alphanumeric | |
154 | characters or underscores. | |
155 | Constant symbols are only part of expressions. Constant symbols are | |
83dcde4e | 156 | always surrounded by single or double quotes. Within the quote, any |
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157 | other character is allowed and the quotes can be escaped using '\'. |
158 | ||
159 | Menu structure | |
160 | -------------- | |
161 | ||
162 | The position of a menu entry in the tree is determined in two ways. First | |
163 | it can be specified explicitly: | |
164 | ||
165 | menu "Network device support" | |
bef1f402 | 166 | depends on NET |
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167 | |
168 | config NETDEVICES | |
169 | ... | |
170 | ||
171 | endmenu | |
172 | ||
173 | All entries within the "menu" ... "endmenu" block become a submenu of | |
174 | "Network device support". All subentries inherit the dependencies from | |
175 | the menu entry, e.g. this means the dependency "NET" is added to the | |
176 | dependency list of the config option NETDEVICES. | |
177 | ||
178 | The other way to generate the menu structure is done by analyzing the | |
179 | dependencies. If a menu entry somehow depends on the previous entry, it | |
180 | can be made a submenu of it. First, the previous (parent) symbol must | |
181 | be part of the dependency list and then one of these two conditions | |
182 | must be true: | |
183 | - the child entry must become invisible, if the parent is set to 'n' | |
184 | - the child entry must only be visible, if the parent is visible | |
185 | ||
186 | config MODULES | |
187 | bool "Enable loadable module support" | |
188 | ||
189 | config MODVERSIONS | |
190 | bool "Set version information on all module symbols" | |
bef1f402 | 191 | depends on MODULES |
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192 | |
193 | comment "module support disabled" | |
bef1f402 | 194 | depends on !MODULES |
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195 | |
196 | MODVERSIONS directly depends on MODULES, this means it's only visible if | |
197 | MODULES is different from 'n'. The comment on the other hand is always | |
198 | visible when MODULES is visible (the (empty) dependency of MODULES is | |
199 | also part of the comment dependencies). | |
200 | ||
201 | ||
202 | Kconfig syntax | |
203 | -------------- | |
204 | ||
205 | The configuration file describes a series of menu entries, where every | |
206 | line starts with a keyword (except help texts). The following keywords | |
207 | end a menu entry: | |
208 | - config | |
209 | - menuconfig | |
210 | - choice/endchoice | |
211 | - comment | |
212 | - menu/endmenu | |
213 | - if/endif | |
214 | - source | |
215 | The first five also start the definition of a menu entry. | |
216 | ||
217 | config: | |
218 | ||
219 | "config" <symbol> | |
220 | <config options> | |
221 | ||
222 | This defines a config symbol <symbol> and accepts any of above | |
223 | attributes as options. | |
224 | ||
225 | menuconfig: | |
226 | "menuconfig" <symbol> | |
227 | <config options> | |
228 | ||
53cb4726 | 229 | This is similar to the simple config entry above, but it also gives a |
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230 | hint to front ends, that all suboptions should be displayed as a |
231 | separate list of options. | |
232 | ||
233 | choices: | |
234 | ||
235 | "choice" | |
236 | <choice options> | |
237 | <choice block> | |
238 | "endchoice" | |
239 | ||
83dcde4e | 240 | This defines a choice group and accepts any of the above attributes as |
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241 | options. A choice can only be of type bool or tristate, while a boolean |
242 | choice only allows a single config entry to be selected, a tristate | |
243 | choice also allows any number of config entries to be set to 'm'. This | |
244 | can be used if multiple drivers for a single hardware exists and only a | |
245 | single driver can be compiled/loaded into the kernel, but all drivers | |
246 | can be compiled as modules. | |
247 | A choice accepts another option "optional", which allows to set the | |
248 | choice to 'n' and no entry needs to be selected. | |
249 | ||
250 | comment: | |
251 | ||
252 | "comment" <prompt> | |
253 | <comment options> | |
254 | ||
255 | This defines a comment which is displayed to the user during the | |
256 | configuration process and is also echoed to the output files. The only | |
257 | possible options are dependencies. | |
258 | ||
259 | menu: | |
260 | ||
261 | "menu" <prompt> | |
262 | <menu options> | |
263 | <menu block> | |
264 | "endmenu" | |
265 | ||
266 | This defines a menu block, see "Menu structure" above for more | |
267 | information. The only possible options are dependencies. | |
268 | ||
269 | if: | |
270 | ||
271 | "if" <expr> | |
272 | <if block> | |
273 | "endif" | |
274 | ||
275 | This defines an if block. The dependency expression <expr> is appended | |
276 | to all enclosed menu entries. | |
277 | ||
278 | source: | |
279 | ||
280 | "source" <prompt> | |
281 | ||
282 | This reads the specified configuration file. This file is always parsed. |