kconfig-language.txt 9.4 KB

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  1. Introduction
  2. ------------
  3. The configuration database is a collection of configuration options
  4. organized in a tree structure:
  5. +- Code maturity level options
  6. | +- Prompt for development and/or incomplete code/drivers
  7. +- General setup
  8. | +- Networking support
  9. | +- System V IPC
  10. | +- BSD Process Accounting
  11. | +- Sysctl support
  12. +- Loadable module support
  13. | +- Enable loadable module support
  14. | +- Set version information on all module symbols
  15. | +- Kernel module loader
  16. +- ...
  17. Every entry has its own dependencies. These dependencies are used
  18. to determine the visibility of an entry. Any child entry is only
  19. visible if its parent entry is also visible.
  20. Menu entries
  21. ------------
  22. Most entries define a config option, all other entries help to organize
  23. them. A single configuration option is defined like this:
  24. config MODVERSIONS
  25. bool "Set version information on all module symbols"
  26. depends on MODULES
  27. help
  28. Usually, modules have to be recompiled whenever you switch to a new
  29. kernel. ...
  30. Every line starts with a key word and can be followed by multiple
  31. arguments. "config" starts a new config entry. The following lines
  32. define attributes for this config option. Attributes can be the type of
  33. the config option, input prompt, dependencies, help text and default
  34. values. A config option can be defined multiple times with the same
  35. name, but every definition can have only a single input prompt and the
  36. type must not conflict.
  37. Menu attributes
  38. ---------------
  39. A menu entry can have a number of attributes. Not all of them are
  40. applicable everywhere (see syntax).
  41. - type definition: "bool"/"tristate"/"string"/"hex"/"int"
  42. Every config option must have a type. There are only two basic types:
  43. tristate and string, the other types are based on these two. The type
  44. definition optionally accepts an input prompt, so these two examples
  45. are equivalent:
  46. bool "Networking support"
  47. and
  48. bool
  49. prompt "Networking support"
  50. - input prompt: "prompt" <prompt> ["if" <expr>]
  51. Every menu entry can have at most one prompt, which is used to display
  52. to the user. Optionally dependencies only for this prompt can be added
  53. with "if".
  54. - default value: "default" <expr> ["if" <expr>]
  55. A config option can have any number of default values. If multiple
  56. default values are visible, only the first defined one is active.
  57. Default values are not limited to the menu entry where they are
  58. defined. This means the default can be defined somewhere else or be
  59. overridden by an earlier definition.
  60. The default value is only assigned to the config symbol if no other
  61. value was set by the user (via the input prompt above). If an input
  62. prompt is visible the default value is presented to the user and can
  63. be overridden by him.
  64. Optionally, dependencies only for this default value can be added with
  65. "if".
  66. - dependencies: "depends on"/"requires" <expr>
  67. This defines a dependency for this menu entry. If multiple
  68. dependencies are defined, they are connected with '&&'. Dependencies
  69. are applied to all other options within this menu entry (which also
  70. accept an "if" expression), so these two examples are equivalent:
  71. bool "foo" if BAR
  72. default y if BAR
  73. and
  74. depends on BAR
  75. bool "foo"
  76. default y
  77. - reverse dependencies: "select" <symbol> ["if" <expr>]
  78. While normal dependencies reduce the upper limit of a symbol (see
  79. below), reverse dependencies can be used to force a lower limit of
  80. another symbol. The value of the current menu symbol is used as the
  81. minimal value <symbol> can be set to. If <symbol> is selected multiple
  82. times, the limit is set to the largest selection.
  83. Reverse dependencies can only be used with boolean or tristate
  84. symbols.
  85. - numerical ranges: "range" <symbol> <symbol> ["if" <expr>]
  86. This allows to limit the range of possible input values for int
  87. and hex symbols. The user can only input a value which is larger than
  88. or equal to the first symbol and smaller than or equal to the second
  89. symbol.
  90. - help text: "help" or "---help---"
  91. This defines a help text. The end of the help text is determined by
  92. the indentation level, this means it ends at the first line which has
  93. a smaller indentation than the first line of the help text.
  94. "---help---" and "help" do not differ in behaviour, "---help---" is
  95. used to help visually separate configuration logic from help within
  96. the file as an aid to developers.
  97. Menu dependencies
  98. -----------------
  99. Dependencies define the visibility of a menu entry and can also reduce
  100. the input range of tristate symbols. The tristate logic used in the
  101. expressions uses one more state than normal boolean logic to express the
  102. module state. Dependency expressions have the following syntax:
  103. <expr> ::= <symbol> (1)
  104. <symbol> '=' <symbol> (2)
  105. <symbol> '!=' <symbol> (3)
  106. '(' <expr> ')' (4)
  107. '!' <expr> (5)
  108. <expr> '&&' <expr> (6)
  109. <expr> '||' <expr> (7)
  110. Expressions are listed in decreasing order of precedence.
  111. (1) Convert the symbol into an expression. Boolean and tristate symbols
  112. are simply converted into the respective expression values. All
  113. other symbol types result in 'n'.
  114. (2) If the values of both symbols are equal, it returns 'y',
  115. otherwise 'n'.
  116. (3) If the values of both symbols are equal, it returns 'n',
  117. otherwise 'y'.
  118. (4) Returns the value of the expression. Used to override precedence.
  119. (5) Returns the result of (2-/expr/).
  120. (6) Returns the result of min(/expr/, /expr/).
  121. (7) Returns the result of max(/expr/, /expr/).
  122. An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2
  123. respectively for calculations). A menu entry becomes visible when it's
  124. expression evaluates to 'm' or 'y'.
  125. There are two types of symbols: constant and nonconstant symbols.
  126. Nonconstant symbols are the most common ones and are defined with the
  127. 'config' statement. Nonconstant symbols consist entirely of alphanumeric
  128. characters or underscores.
  129. Constant symbols are only part of expressions. Constant symbols are
  130. always surrounded by single or double quotes. Within the quote, any
  131. other character is allowed and the quotes can be escaped using '\'.
  132. Menu structure
  133. --------------
  134. The position of a menu entry in the tree is determined in two ways. First
  135. it can be specified explicitly:
  136. menu "Network device support"
  137. depends on NET
  138. config NETDEVICES
  139. ...
  140. endmenu
  141. All entries within the "menu" ... "endmenu" block become a submenu of
  142. "Network device support". All subentries inherit the dependencies from
  143. the menu entry, e.g. this means the dependency "NET" is added to the
  144. dependency list of the config option NETDEVICES.
  145. The other way to generate the menu structure is done by analyzing the
  146. dependencies. If a menu entry somehow depends on the previous entry, it
  147. can be made a submenu of it. First, the previous (parent) symbol must
  148. be part of the dependency list and then one of these two conditions
  149. must be true:
  150. - the child entry must become invisible, if the parent is set to 'n'
  151. - the child entry must only be visible, if the parent is visible
  152. config MODULES
  153. bool "Enable loadable module support"
  154. config MODVERSIONS
  155. bool "Set version information on all module symbols"
  156. depends on MODULES
  157. comment "module support disabled"
  158. depends on !MODULES
  159. MODVERSIONS directly depends on MODULES, this means it's only visible if
  160. MODULES is different from 'n'. The comment on the other hand is always
  161. visible when MODULES is visible (the (empty) dependency of MODULES is
  162. also part of the comment dependencies).
  163. Kconfig syntax
  164. --------------
  165. The configuration file describes a series of menu entries, where every
  166. line starts with a keyword (except help texts). The following keywords
  167. end a menu entry:
  168. - config
  169. - menuconfig
  170. - choice/endchoice
  171. - comment
  172. - menu/endmenu
  173. - if/endif
  174. - source
  175. The first five also start the definition of a menu entry.
  176. config:
  177. "config" <symbol>
  178. <config options>
  179. This defines a config symbol <symbol> and accepts any of above
  180. attributes as options.
  181. menuconfig:
  182. "menuconfig" <symbol>
  183. <config options>
  184. This is similar to the simple config entry above, but it also gives a
  185. hint to front ends, that all suboptions should be displayed as a
  186. separate list of options.
  187. choices:
  188. "choice"
  189. <choice options>
  190. <choice block>
  191. "endchoice"
  192. This defines a choice group and accepts any of the above attributes as
  193. options. A choice can only be of type bool or tristate, while a boolean
  194. choice only allows a single config entry to be selected, a tristate
  195. choice also allows any number of config entries to be set to 'm'. This
  196. can be used if multiple drivers for a single hardware exists and only a
  197. single driver can be compiled/loaded into the kernel, but all drivers
  198. can be compiled as modules.
  199. A choice accepts another option "optional", which allows to set the
  200. choice to 'n' and no entry needs to be selected.
  201. comment:
  202. "comment" <prompt>
  203. <comment options>
  204. This defines a comment which is displayed to the user during the
  205. configuration process and is also echoed to the output files. The only
  206. possible options are dependencies.
  207. menu:
  208. "menu" <prompt>
  209. <menu options>
  210. <menu block>
  211. "endmenu"
  212. This defines a menu block, see "Menu structure" above for more
  213. information. The only possible options are dependencies.
  214. if:
  215. "if" <expr>
  216. <if block>
  217. "endif"
  218. This defines an if block. The dependency expression <expr> is appended
  219. to all enclosed menu entries.
  220. source:
  221. "source" <prompt>
  222. This reads the specified configuration file. This file is always parsed.