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1 | Introduction | ||
2 | ------------ | ||
3 | |||
4 | The configuration database is collection of configuration options | ||
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 visible 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" | ||
32 | depends MODULES | ||
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"/"integer" | ||
52 | Every config option must have a type. There are only two basic types: | ||
53 | tristate and string, the other types base 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" <symbol> ["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. | ||
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 | ||
72 | overriden 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. | ||
77 | Optionally dependencies only for this default value can be added with | ||
78 | "if". | ||
79 | |||
80 | - dependencies: "depends on"/"requires" <expr> | ||
81 | This defines a dependency for this menu entry. If multiple | ||
82 | dependencies are defined they are connected with '&&'. Dependencies | ||
83 | are applied to all other options within this menu entry (which also | ||
84 | accept "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 | - help text: "help" | ||
94 | This defines a help text. The end of the help text is determined by | ||
95 | the level indentation, this means it ends at the first line which has | ||
96 | a smaller indentation than the first line of the help text. | ||
97 | |||
98 | |||
99 | Menu dependencies | ||
100 | ----------------- | ||
101 | |||
102 | Dependencies define the visibility of a menu entry and can also reduce | ||
103 | the input range of tristate symbols. The tristate logic used in the | ||
104 | expressions uses one more state than normal boolean logic to express the | ||
105 | module state. Dependency expressions have the following syntax: | ||
106 | |||
107 | <expr> ::= <symbol> (1) | ||
108 | <symbol> '=' <symbol> (2) | ||
109 | <symbol> '!=' <symbol> (3) | ||
110 | '(' <expr> ')' (4) | ||
111 | '!' <expr> (5) | ||
112 | <expr> '||' <expr> (6) | ||
113 | <expr> '&&' <expr> (7) | ||
114 | |||
115 | Expressions are listed in decreasing order of precedence. | ||
116 | |||
117 | (1) Convert the symbol into an expression. Boolean and tristate symbols | ||
118 | are simply converted into the respective expression values. All | ||
119 | other symbol types result in 'n'. | ||
120 | (2) If the values of both symbols are equal, it returns 'y', | ||
121 | otherwise 'n'. | ||
122 | (3) If the values of both symbols are equal, it returns 'n', | ||
123 | otherwise 'y'. | ||
124 | (4) Returns the value of the expression. Used to override precedence. | ||
125 | (5) Returns the result of (2-/expr/). | ||
126 | (6) Returns the result of min(/expr/, /expr/). | ||
127 | (7) Returns the result of max(/expr/, /expr/). | ||
128 | |||
129 | An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2 | ||
130 | respectively for calculations). A menu entry becomes visible when it's | ||
131 | expression evaluates to 'm' or 'y'. | ||
132 | |||
133 | There are two type of symbols: constant and nonconstant symbols. | ||
134 | Nonconstant symbols are the most common ones and are defined with the | ||
135 | 'config' statement. Nonconstant symbols consist entirely of alphanumeric | ||
136 | characters or underscores. | ||
137 | Constant symbols are only part of expressions. Constant symbols are | ||
138 | always surrounded by single or double quotes. Within the quote any | ||
139 | other character is allowed and the quotes can be escaped using '\'. | ||
140 | |||
141 | Menu structure | ||
142 | -------------- | ||
143 | |||
144 | The position of a menu entry in the tree is determined in two ways. First | ||
145 | it can be specified explicitely: | ||
146 | |||
147 | menu "Network device support" | ||
148 | depends NET | ||
149 | |||
150 | config NETDEVICES | ||
151 | ... | ||
152 | |||
153 | endmenu | ||
154 | |||
155 | All entries within the "menu" ... "endmenu" block become a submenu of | ||
156 | "Network device support". All subentries inherit the dependencies from | ||
157 | the menu entry, e.g. this means the dependency "NET" is added to the | ||
158 | dependency list of the config option NETDEVICES. | ||
159 | |||
160 | The other way to generate the menu structure is done by analyzing the | ||
161 | dependencies. If a menu entry somehow depends on the previous entry, it | ||
162 | can be made a submenu of it. First the the previous (parent) symbol must | ||
163 | be part of the dependency list and then one of these two condititions | ||
164 | must be true: | ||
165 | - the child entry must become invisible, if the parent is set to 'n' | ||
166 | - the child entry must only be visible, if the parent is visible | ||
167 | |||
168 | config MODULES | ||
169 | bool "Enable loadable module support" | ||
170 | |||
171 | config MODVERSIONS | ||
172 | bool "Set version information on all module symbols" | ||
173 | depends MODULES | ||
174 | |||
175 | comment "module support disabled" | ||
176 | depends !MODULES | ||
177 | |||
178 | MODVERSIONS directly depends on MODULES, this means it's only visible if | ||
179 | MODULES is different from 'n'. The comment on the other hand is always | ||
180 | visible when MODULES it's visible (the (empty) dependency of MODULES is | ||
181 | also part of the comment dependencies). | ||
182 | |||
183 | |||
184 | Kconfig syntax | ||
185 | -------------- | ||
186 | |||
187 | The configuration file describes a series of menu entries, where every | ||
188 | line starts with a keyword (except help texts). The following keywords | ||
189 | end a menu entry: | ||
190 | - config | ||
191 | - choice/endchoice | ||
192 | - comment | ||
193 | - menu/endmenu | ||
194 | - if/endif | ||
195 | - source | ||
196 | The first four also start the definition of a menu entry. | ||
197 | |||
198 | config: | ||
199 | |||
200 | "config" <symbol> | ||
201 | <config options> | ||
202 | |||
203 | This defines a config symbol <symbol> and accepts any of above | ||
204 | attributes as options. | ||
205 | |||
206 | choices: | ||
207 | |||
208 | "choice" | ||
209 | <choice options> | ||
210 | <choice block> | ||
211 | "endchoice" | ||
212 | |||
213 | This defines a choice group and accepts any of above attributes as | ||
214 | options. A choice can only be of type bool or tristate, while a boolean | ||
215 | choice only allows a single config entry to be selected, a tristate | ||
216 | choice also allows any number of config entries to be set to 'm'. This | ||
217 | can be used if multiple drivers for a single hardware exists and only a | ||
218 | single driver can be compiled/loaded into the kernel, but all drivers | ||
219 | can be compiled as modules. | ||
220 | A choice accepts another option "optional", which allows to set the | ||
221 | choice to 'n' and no entry needs to be selected. | ||
222 | |||
223 | comment: | ||
224 | |||
225 | "comment" <prompt> | ||
226 | <comment options> | ||
227 | |||
228 | This defines a comment which is displayed to the user during the | ||
229 | configuration process and is also echoed to the output files. The only | ||
230 | possible options are dependencies. | ||
231 | |||
232 | menu: | ||
233 | |||
234 | "menu" <prompt> | ||
235 | <menu options> | ||
236 | <menu block> | ||
237 | "endmenu" | ||
238 | |||
239 | This defines a menu block, see "Menu structure" above for more | ||
240 | information. The only possible options are dependencies. | ||
241 | |||
242 | if: | ||
243 | |||
244 | "if" <expr> | ||
245 | <if block> | ||
246 | "endif" | ||
247 | |||
248 | This defines an if block. The dependency expression <expr> is appended | ||
249 | to all enclosed menu entries. | ||
250 | |||
251 | source: | ||
252 | |||
253 | "source" <prompt> | ||
254 | |||
255 | This reads the specified configuration file. This file is always parsed. | ||