package/config/Kconfig-language.txt

   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.