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" 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. 112 113 114Menu dependencies 115----------------- 116 117Dependencies define the visibility of a menu entry and can also reduce 118the input range of tristate symbols. The tristate logic used in the 119expressions uses one more state than normal boolean logic to express the 120module state. Dependency expressions have the following syntax: 121 122<expr> ::= <symbol> (1) 123 <symbol> '=' <symbol> (2) 124 <symbol> '!=' <symbol> (3) 125 '(' <expr> ')' (4) 126 '!' <expr> (5) 127 <expr> '||' <expr> (6) 128 <expr> '&&' <expr> (7) 129 130Expressions are listed in decreasing order of precedence. 131 132(1) Convert the symbol into an expression. Boolean and tristate symbols 133 are simply converted into the respective expression values. All 134 other symbol types result in 'n'. 135(2) If the values of both symbols are equal, it returns 'y', 136 otherwise 'n'. 137(3) If the values of both symbols are equal, it returns 'n', 138 otherwise 'y'. 139(4) Returns the value of the expression. Used to override precedence. 140(5) Returns the result of (2-/expr/). 141(6) Returns the result of max(/expr/, /expr/). 142(7) Returns the result of min(/expr/, /expr/). 143 144An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2 145respectively for calculations). A menu entry becomes visible when it's 146expression evaluates to 'm' or 'y'. 147 148There are two types of symbols: constant and nonconstant symbols. 149Nonconstant symbols are the most common ones and are defined with the 150'config' statement. Nonconstant symbols consist entirely of alphanumeric 151characters or underscores. 152Constant symbols are only part of expressions. Constant symbols are 153always surrounded by single or double quotes. Within the quote any 154other character is allowed and the quotes can be escaped using '\'. 155 156Menu structure 157-------------- 158 159The position of a menu entry in the tree is determined in two ways. First 160it can be specified explicitly: 161 162menu "Network device support" 163 depends NET 164 165config NETDEVICES 166 ... 167 168endmenu 169 170All entries within the "menu" ... "endmenu" block become a submenu of 171"Network device support". All subentries inherit the dependencies from 172the menu entry, e.g. this means the dependency "NET" is added to the 173dependency list of the config option NETDEVICES. 174 175The other way to generate the menu structure is done by analyzing the 176dependencies. If a menu entry somehow depends on the previous entry, it 177can be made a submenu of it. First, the previous (parent) symbol must 178be part of the dependency list and then one of these two conditions 179must be true: 180- the child entry must become invisible, if the parent is set to 'n' 181- the child entry must only be visible, if the parent is visible 182 183config MODULES 184 bool "Enable loadable module support" 185 186config MODVERSIONS 187 bool "Set version information on all module symbols" 188 depends MODULES 189 190comment "module support disabled" 191 depends !MODULES 192 193MODVERSIONS directly depends on MODULES, this means it's only visible if 194MODULES is different from 'n'. The comment on the other hand is always 195visible when MODULES is visible (the (empty) dependency of MODULES is 196also part of the comment dependencies). 197 198 199Kconfig syntax 200-------------- 201 202The configuration file describes a series of menu entries, where every 203line starts with a keyword (except help texts). The following keywords 204end a menu entry: 205- config 206- menuconfig 207- choice/endchoice 208- comment 209- menu/endmenu 210- if/endif 211- source 212The first five also start the definition of a menu entry. 213 214config: 215 216 "config" <symbol> 217 <config options> 218 219This defines a config symbol <symbol> and accepts any of above 220attributes as options. 221 222menuconfig: 223 "menuconfig" <symbol> 224 <config options> 225 226This is similiar to the simple config entry above, but it also gives a 227hint to front ends, that all suboptions should be displayed as a 228separate list of options. 229 230choices: 231 232 "choice" 233 <choice options> 234 <choice block> 235 "endchoice" 236 237This defines a choice group and accepts any of above attributes as 238options. A choice can only be of type bool or tristate, while a boolean 239choice only allows a single config entry to be selected, a tristate 240choice also allows any number of config entries to be set to 'm'. This 241can be used if multiple drivers for a single hardware exists and only a 242single driver can be compiled/loaded into the kernel, but all drivers 243can be compiled as modules. 244A choice accepts another option "optional", which allows to set the 245choice to 'n' and no entry needs to be selected. 246 247comment: 248 249 "comment" <prompt> 250 <comment options> 251 252This defines a comment which is displayed to the user during the 253configuration process and is also echoed to the output files. The only 254possible options are dependencies. 255 256menu: 257 258 "menu" <prompt> 259 <menu options> 260 <menu block> 261 "endmenu" 262 263This defines a menu block, see "Menu structure" above for more 264information. The only possible options are dependencies. 265 266if: 267 268 "if" <expr> 269 <if block> 270 "endif" 271 272This defines an if block. The dependency expression <expr> is appended 273to all enclosed menu entries. 274 275source: 276 277 "source" <prompt> 278 279This reads the specified configuration file. This file is always parsed. 280