1Introduction 2------------ 3 4The configuration database is collection of configuration options 5organized 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 20Every entry has its own dependencies. These dependencies are used 21to determine the visibility of an entry. Any child entry is only 22visible if its parent entry is also visible. 23 24Menu entries 25------------ 26 27Most entries define a config option, all other entries help to organize 28them. A single configuration option is defined like this: 29 30config 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 37Every line starts with a key word and can be followed by multiple 38arguments. "config" starts a new config entry. The following lines 39define attributes for this config option. Attributes can be the type of 40the config option, input prompt, dependencies, help text and default 41values. A config option can be defined multiple times with the same 42name, but every definition can have only a single input prompt and the 43type must not conflict. 44 45Menu attributes 46--------------- 47 48A menu entry can have a number of attributes. Not all of them are 49applicable 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 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. 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 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 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 integer 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 113 used to help visually seperate configuration logic from help within 114 the file as an aid to developers. 115 116 117Menu dependencies 118----------------- 119 120Dependencies define the visibility of a menu entry and can also reduce 121the input range of tristate symbols. The tristate logic used in the 122expressions uses one more state than normal boolean logic to express the 123module 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 133Expressions 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 max(/expr/, /expr/). 145(7) Returns the result of min(/expr/, /expr/). 146 147An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2 148respectively for calculations). A menu entry becomes visible when it's 149expression evaluates to 'm' or 'y'. 150 151There are two types of symbols: constant and nonconstant symbols. 152Nonconstant symbols are the most common ones and are defined with the 153'config' statement. Nonconstant symbols consist entirely of alphanumeric 154characters or underscores. 155Constant symbols are only part of expressions. Constant symbols are 156always surrounded by single or double quotes. Within the quote any 157other character is allowed and the quotes can be escaped using '\'. 158 159Menu structure 160-------------- 161 162The position of a menu entry in the tree is determined in two ways. First 163it can be specified explicitly: 164 165menu "Network device support" 166 depends NET 167 168config NETDEVICES 169 ... 170 171endmenu 172 173All entries within the "menu" ... "endmenu" block become a submenu of 174"Network device support". All subentries inherit the dependencies from 175the menu entry, e.g. this means the dependency "NET" is added to the 176dependency list of the config option NETDEVICES. 177 178The other way to generate the menu structure is done by analyzing the 179dependencies. If a menu entry somehow depends on the previous entry, it 180can be made a submenu of it. First, the previous (parent) symbol must 181be part of the dependency list and then one of these two conditions 182must 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 186config MODULES 187 bool "Enable loadable module support" 188 189config MODVERSIONS 190 bool "Set version information on all module symbols" 191 depends MODULES 192 193comment "module support disabled" 194 depends !MODULES 195 196MODVERSIONS directly depends on MODULES, this means it's only visible if 197MODULES is different from 'n'. The comment on the other hand is always 198visible when MODULES is visible (the (empty) dependency of MODULES is 199also part of the comment dependencies). 200 201 202Kconfig syntax 203-------------- 204 205The configuration file describes a series of menu entries, where every 206line starts with a keyword (except help texts). The following keywords 207end a menu entry: 208- config 209- menuconfig 210- choice/endchoice 211- comment 212- menu/endmenu 213- if/endif 214- source 215The first five also start the definition of a menu entry. 216 217config: 218 219 "config" <symbol> 220 <config options> 221 222This defines a config symbol <symbol> and accepts any of above 223attributes as options. 224 225menuconfig: 226 "menuconfig" <symbol> 227 <config options> 228 229This is similiar to the simple config entry above, but it also gives a 230hint to front ends, that all suboptions should be displayed as a 231separate list of options. 232 233choices: 234 235 "choice" 236 <choice options> 237 <choice block> 238 "endchoice" 239 240This defines a choice group and accepts any of above attributes as 241options. A choice can only be of type bool or tristate, while a boolean 242choice only allows a single config entry to be selected, a tristate 243choice also allows any number of config entries to be set to 'm'. This 244can be used if multiple drivers for a single hardware exists and only a 245single driver can be compiled/loaded into the kernel, but all drivers 246can be compiled as modules. 247A choice accepts another option "optional", which allows to set the 248choice to 'n' and no entry needs to be selected. 249 250comment: 251 252 "comment" <prompt> 253 <comment options> 254 255This defines a comment which is displayed to the user during the 256configuration process and is also echoed to the output files. The only 257possible options are dependencies. 258 259menu: 260 261 "menu" <prompt> 262 <menu options> 263 <menu block> 264 "endmenu" 265 266This defines a menu block, see "Menu structure" above for more 267information. The only possible options are dependencies. 268 269if: 270 271 "if" <expr> 272 <if block> 273 "endif" 274 275This defines an if block. The dependency expression <expr> is appended 276to all enclosed menu entries. 277 278source: 279 280 "source" <prompt> 281 282This reads the specified configuration file. This file is always parsed. 283
