4 The configuration database is a collection of configuration options
5 organized in a tree structure:
7 +- Code maturity level options
8 | +- Prompt for development and/or incomplete code/drivers
10 | +- Networking support
12 | +- BSD Process Accounting
14 +- Loadable module support
15 | +- Enable loadable module support
16 | +- Set version information on all module symbols
17 | +- Kernel module loader
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.
27 Most entries define a config option, all other entries help to organize
28 them. A single configuration option is defined like this:
31 bool "Set version information on all module symbols"
34 Usually, modules have to be recompiled whenever you switch to a new
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.
48 A menu entry can have a number of attributes. Not all of them are
49 applicable everywhere (see syntax).
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
57 bool "Networking support"
60 prompt "Networking support"
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
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.
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 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
77 Optionally, dependencies only for this default value can be added with
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 an "if" expression), so these two examples are equivalent:
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
102 select is evil.... select will by brute force set a symbol
103 equal to 'y' without visiting the dependencies. So abusing
104 select you are able to select a symbol FOO even if FOO depends
105 on BAR that is not set. In general use select only for
106 non-visible symbols (no promts anywhere) and for symbols with
107 no dependencies. That will limit the usefulness but on the
108 other hand avoid the illegal configurations all over. kconfig
109 should one day warn about such things.
111 - numerical ranges: "range" <symbol> <symbol> ["if" <expr>]
112 This allows to limit the range of possible input values for int
113 and hex symbols. The user can only input a value which is larger than
114 or equal to the first symbol and smaller than or equal to the second
117 - help text: "help" or "---help---"
118 This defines a help text. The end of the help text is determined by
119 the indentation level, this means it ends at the first line which has
120 a smaller indentation than the first line of the help text.
121 "---help---" and "help" do not differ in behaviour, "---help---" is
122 used to help visually separate configuration logic from help within
123 the file as an aid to developers.
129 Dependencies define the visibility of a menu entry and can also reduce
130 the input range of tristate symbols. The tristate logic used in the
131 expressions uses one more state than normal boolean logic to express the
132 module state. Dependency expressions have the following syntax:
134 <expr> ::= <symbol> (1)
135 <symbol> '=' <symbol> (2)
136 <symbol> '!=' <symbol> (3)
139 <expr> '&&' <expr> (6)
140 <expr> '||' <expr> (7)
142 Expressions are listed in decreasing order of precedence.
144 (1) Convert the symbol into an expression. Boolean and tristate symbols
145 are simply converted into the respective expression values. All
146 other symbol types result in 'n'.
147 (2) If the values of both symbols are equal, it returns 'y',
149 (3) If the values of both symbols are equal, it returns 'n',
151 (4) Returns the value of the expression. Used to override precedence.
152 (5) Returns the result of (2-/expr/).
153 (6) Returns the result of min(/expr/, /expr/).
154 (7) Returns the result of max(/expr/, /expr/).
156 An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2
157 respectively for calculations). A menu entry becomes visible when it's
158 expression evaluates to 'm' or 'y'.
160 There are two types of symbols: constant and nonconstant symbols.
161 Nonconstant symbols are the most common ones and are defined with the
162 'config' statement. Nonconstant symbols consist entirely of alphanumeric
163 characters or underscores.
164 Constant symbols are only part of expressions. Constant symbols are
165 always surrounded by single or double quotes. Within the quote, any
166 other character is allowed and the quotes can be escaped using '\'.
171 The position of a menu entry in the tree is determined in two ways. First
172 it can be specified explicitly:
174 menu "Network device support"
182 All entries within the "menu" ... "endmenu" block become a submenu of
183 "Network device support". All subentries inherit the dependencies from
184 the menu entry, e.g. this means the dependency "NET" is added to the
185 dependency list of the config option NETDEVICES.
187 The other way to generate the menu structure is done by analyzing the
188 dependencies. If a menu entry somehow depends on the previous entry, it
189 can be made a submenu of it. First, the previous (parent) symbol must
190 be part of the dependency list and then one of these two conditions
192 - the child entry must become invisible, if the parent is set to 'n'
193 - the child entry must only be visible, if the parent is visible
196 bool "Enable loadable module support"
199 bool "Set version information on all module symbols"
202 comment "module support disabled"
205 MODVERSIONS directly depends on MODULES, this means it's only visible if
206 MODULES is different from 'n'. The comment on the other hand is always
207 visible when MODULES is visible (the (empty) dependency of MODULES is
208 also part of the comment dependencies).
214 The configuration file describes a series of menu entries, where every
215 line starts with a keyword (except help texts). The following keywords
224 The first five also start the definition of a menu entry.
231 This defines a config symbol <symbol> and accepts any of above
232 attributes as options.
235 "menuconfig" <symbol>
238 This is similar to the simple config entry above, but it also gives a
239 hint to front ends, that all suboptions should be displayed as a
240 separate list of options.
249 This defines a choice group and accepts any of the above attributes as
250 options. A choice can only be of type bool or tristate, while a boolean
251 choice only allows a single config entry to be selected, a tristate
252 choice also allows any number of config entries to be set to 'm'. This
253 can be used if multiple drivers for a single hardware exists and only a
254 single driver can be compiled/loaded into the kernel, but all drivers
255 can be compiled as modules.
256 A choice accepts another option "optional", which allows to set the
257 choice to 'n' and no entry needs to be selected.
264 This defines a comment which is displayed to the user during the
265 configuration process and is also echoed to the output files. The only
266 possible options are dependencies.
275 This defines a menu block, see "Menu structure" above for more
276 information. The only possible options are dependencies.
284 This defines an if block. The dependency expression <expr> is appended
285 to all enclosed menu entries.
291 This reads the specified configuration file. This file is always parsed.
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