Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | Introduction |
| 2 | ------------ |
| 3 | |
Daniel Walker | e95be9a | 2006-10-04 02:15:21 -0700 | [diff] [blame] | 4 | The configuration database is a collection of configuration options |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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 visibility of an entry. Any child entry is only |
| 22 | visible if its parent entry is also visible. |
| 23 | |
| 24 | Menu entries |
| 25 | ------------ |
| 26 | |
Randy Dunlap | 0486bc9 | 2007-11-12 16:17:55 -0800 | [diff] [blame] | 27 | Most entries define a config option; all other entries help to organize |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 28 | them. A single configuration option is defined like this: |
| 29 | |
| 30 | config MODVERSIONS |
| 31 | bool "Set version information on all module symbols" |
Robert P. J. Day | bef1f40 | 2006-12-12 20:04:19 +0100 | [diff] [blame] | 32 | depends on MODULES |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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"/"int" |
| 52 | Every config option must have a type. There are only two basic types: |
Randy Dunlap | 0486bc9 | 2007-11-12 16:17:55 -0800 | [diff] [blame] | 53 | tristate and string; the other types are based on these two. The type |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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. |
Jan Engelhardt | 83dcde4 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 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 |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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. |
Jan Engelhardt | 83dcde4 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 77 | Optionally, dependencies only for this default value can be added with |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 78 | "if". |
| 79 | |
Randy Dunlap | 6e66b90 | 2007-10-19 10:53:48 -0700 | [diff] [blame] | 80 | - type definition + default value: |
| 81 | "def_bool"/"def_tristate" <expr> ["if" <expr>] |
| 82 | This is a shorthand notation for a type definition plus a value. |
| 83 | Optionally dependencies for this default value can be added with "if". |
| 84 | |
| 85 | - dependencies: "depends on" <expr> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 86 | This defines a dependency for this menu entry. If multiple |
Jan Engelhardt | 83dcde4 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 87 | dependencies are defined, they are connected with '&&'. Dependencies |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 88 | are applied to all other options within this menu entry (which also |
| 89 | accept an "if" expression), so these two examples are equivalent: |
| 90 | |
| 91 | bool "foo" if BAR |
| 92 | default y if BAR |
| 93 | and |
| 94 | depends on BAR |
| 95 | bool "foo" |
| 96 | default y |
| 97 | |
| 98 | - reverse dependencies: "select" <symbol> ["if" <expr>] |
| 99 | While normal dependencies reduce the upper limit of a symbol (see |
| 100 | below), reverse dependencies can be used to force a lower limit of |
| 101 | another symbol. The value of the current menu symbol is used as the |
| 102 | minimal value <symbol> can be set to. If <symbol> is selected multiple |
| 103 | times, the limit is set to the largest selection. |
| 104 | Reverse dependencies can only be used with boolean or tristate |
| 105 | symbols. |
Jarek Poplawski | f8a7459 | 2007-08-10 13:01:04 -0700 | [diff] [blame] | 106 | Note: |
| 107 | select is evil.... select will by brute force set a symbol |
| 108 | equal to 'y' without visiting the dependencies. So abusing |
| 109 | select you are able to select a symbol FOO even if FOO depends |
| 110 | on BAR that is not set. In general use select only for |
Randy Dunlap | 0486bc9 | 2007-11-12 16:17:55 -0800 | [diff] [blame] | 111 | non-visible symbols (no prompts anywhere) and for symbols with |
Jarek Poplawski | f8a7459 | 2007-08-10 13:01:04 -0700 | [diff] [blame] | 112 | no dependencies. That will limit the usefulness but on the |
| 113 | other hand avoid the illegal configurations all over. kconfig |
| 114 | should one day warn about such things. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 115 | |
| 116 | - numerical ranges: "range" <symbol> <symbol> ["if" <expr>] |
| 117 | This allows to limit the range of possible input values for int |
| 118 | and hex symbols. The user can only input a value which is larger than |
| 119 | or equal to the first symbol and smaller than or equal to the second |
| 120 | symbol. |
| 121 | |
| 122 | - help text: "help" or "---help---" |
| 123 | This defines a help text. The end of the help text is determined by |
| 124 | the indentation level, this means it ends at the first line which has |
| 125 | a smaller indentation than the first line of the help text. |
| 126 | "---help---" and "help" do not differ in behaviour, "---help---" is |
Matt LaPlante | 53cb472 | 2006-10-03 22:55:17 +0200 | [diff] [blame] | 127 | used to help visually separate configuration logic from help within |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 128 | the file as an aid to developers. |
| 129 | |
Roman Zippel | 9344908 | 2008-01-14 04:50:54 +0100 | [diff] [blame] | 130 | - misc options: "option" <symbol>[=<value>] |
| 131 | Various less common options can be defined via this option syntax, |
| 132 | which can modify the behaviour of the menu entry and its config |
| 133 | symbol. These options are currently possible: |
| 134 | |
| 135 | - "defconfig_list" |
| 136 | This declares a list of default entries which can be used when |
| 137 | looking for the default configuration (which is used when the main |
| 138 | .config doesn't exists yet.) |
| 139 | |
| 140 | - "modules" |
| 141 | This declares the symbol to be used as the MODULES symbol, which |
| 142 | enables the third modular state for all config symbols. |
| 143 | |
| 144 | - "env"=<value> |
| 145 | This imports the environment variable into Kconfig. It behaves like |
| 146 | a default, except that the value comes from the environment, this |
| 147 | also means that the behaviour when mixing it with normal defaults is |
| 148 | undefined at this point. The symbol is currently not exported back |
| 149 | to the build environment (if this is desired, it can be done via |
| 150 | another symbol). |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 151 | |
| 152 | Menu dependencies |
| 153 | ----------------- |
| 154 | |
| 155 | Dependencies define the visibility of a menu entry and can also reduce |
| 156 | the input range of tristate symbols. The tristate logic used in the |
| 157 | expressions uses one more state than normal boolean logic to express the |
| 158 | module state. Dependency expressions have the following syntax: |
| 159 | |
| 160 | <expr> ::= <symbol> (1) |
| 161 | <symbol> '=' <symbol> (2) |
| 162 | <symbol> '!=' <symbol> (3) |
| 163 | '(' <expr> ')' (4) |
| 164 | '!' <expr> (5) |
| 165 | <expr> '&&' <expr> (6) |
| 166 | <expr> '||' <expr> (7) |
| 167 | |
| 168 | Expressions are listed in decreasing order of precedence. |
| 169 | |
| 170 | (1) Convert the symbol into an expression. Boolean and tristate symbols |
| 171 | are simply converted into the respective expression values. All |
| 172 | other symbol types result in 'n'. |
| 173 | (2) If the values of both symbols are equal, it returns 'y', |
| 174 | otherwise 'n'. |
| 175 | (3) If the values of both symbols are equal, it returns 'n', |
| 176 | otherwise 'y'. |
| 177 | (4) Returns the value of the expression. Used to override precedence. |
| 178 | (5) Returns the result of (2-/expr/). |
| 179 | (6) Returns the result of min(/expr/, /expr/). |
| 180 | (7) Returns the result of max(/expr/, /expr/). |
| 181 | |
| 182 | An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2 |
| 183 | respectively for calculations). A menu entry becomes visible when it's |
| 184 | expression evaluates to 'm' or 'y'. |
| 185 | |
Randy Dunlap | 0486bc9 | 2007-11-12 16:17:55 -0800 | [diff] [blame] | 186 | There are two types of symbols: constant and non-constant symbols. |
| 187 | Non-constant symbols are the most common ones and are defined with the |
| 188 | 'config' statement. Non-constant symbols consist entirely of alphanumeric |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 189 | characters or underscores. |
| 190 | Constant symbols are only part of expressions. Constant symbols are |
Jan Engelhardt | 83dcde4 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 191 | always surrounded by single or double quotes. Within the quote, any |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 192 | other character is allowed and the quotes can be escaped using '\'. |
| 193 | |
| 194 | Menu structure |
| 195 | -------------- |
| 196 | |
| 197 | The position of a menu entry in the tree is determined in two ways. First |
| 198 | it can be specified explicitly: |
| 199 | |
| 200 | menu "Network device support" |
Robert P. J. Day | bef1f40 | 2006-12-12 20:04:19 +0100 | [diff] [blame] | 201 | depends on NET |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 202 | |
| 203 | config NETDEVICES |
| 204 | ... |
| 205 | |
| 206 | endmenu |
| 207 | |
| 208 | All entries within the "menu" ... "endmenu" block become a submenu of |
| 209 | "Network device support". All subentries inherit the dependencies from |
| 210 | the menu entry, e.g. this means the dependency "NET" is added to the |
| 211 | dependency list of the config option NETDEVICES. |
| 212 | |
| 213 | The other way to generate the menu structure is done by analyzing the |
| 214 | dependencies. If a menu entry somehow depends on the previous entry, it |
| 215 | can be made a submenu of it. First, the previous (parent) symbol must |
| 216 | be part of the dependency list and then one of these two conditions |
| 217 | must be true: |
| 218 | - the child entry must become invisible, if the parent is set to 'n' |
| 219 | - the child entry must only be visible, if the parent is visible |
| 220 | |
| 221 | config MODULES |
| 222 | bool "Enable loadable module support" |
| 223 | |
| 224 | config MODVERSIONS |
| 225 | bool "Set version information on all module symbols" |
Robert P. J. Day | bef1f40 | 2006-12-12 20:04:19 +0100 | [diff] [blame] | 226 | depends on MODULES |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 227 | |
| 228 | comment "module support disabled" |
Robert P. J. Day | bef1f40 | 2006-12-12 20:04:19 +0100 | [diff] [blame] | 229 | depends on !MODULES |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 230 | |
| 231 | MODVERSIONS directly depends on MODULES, this means it's only visible if |
| 232 | MODULES is different from 'n'. The comment on the other hand is always |
| 233 | visible when MODULES is visible (the (empty) dependency of MODULES is |
| 234 | also part of the comment dependencies). |
| 235 | |
| 236 | |
| 237 | Kconfig syntax |
| 238 | -------------- |
| 239 | |
| 240 | The configuration file describes a series of menu entries, where every |
| 241 | line starts with a keyword (except help texts). The following keywords |
| 242 | end a menu entry: |
| 243 | - config |
| 244 | - menuconfig |
| 245 | - choice/endchoice |
| 246 | - comment |
| 247 | - menu/endmenu |
| 248 | - if/endif |
| 249 | - source |
| 250 | The first five also start the definition of a menu entry. |
| 251 | |
| 252 | config: |
| 253 | |
| 254 | "config" <symbol> |
| 255 | <config options> |
| 256 | |
| 257 | This defines a config symbol <symbol> and accepts any of above |
| 258 | attributes as options. |
| 259 | |
| 260 | menuconfig: |
| 261 | "menuconfig" <symbol> |
| 262 | <config options> |
| 263 | |
Matt LaPlante | 53cb472 | 2006-10-03 22:55:17 +0200 | [diff] [blame] | 264 | This is similar to the simple config entry above, but it also gives a |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 265 | hint to front ends, that all suboptions should be displayed as a |
| 266 | separate list of options. |
| 267 | |
| 268 | choices: |
| 269 | |
| 270 | "choice" |
| 271 | <choice options> |
| 272 | <choice block> |
| 273 | "endchoice" |
| 274 | |
Jan Engelhardt | 83dcde4 | 2006-07-27 22:14:29 +0200 | [diff] [blame] | 275 | This defines a choice group and accepts any of the above attributes as |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 276 | options. A choice can only be of type bool or tristate, while a boolean |
| 277 | choice only allows a single config entry to be selected, a tristate |
| 278 | choice also allows any number of config entries to be set to 'm'. This |
| 279 | can be used if multiple drivers for a single hardware exists and only a |
| 280 | single driver can be compiled/loaded into the kernel, but all drivers |
| 281 | can be compiled as modules. |
| 282 | A choice accepts another option "optional", which allows to set the |
| 283 | choice to 'n' and no entry needs to be selected. |
| 284 | |
| 285 | comment: |
| 286 | |
| 287 | "comment" <prompt> |
| 288 | <comment options> |
| 289 | |
| 290 | This defines a comment which is displayed to the user during the |
| 291 | configuration process and is also echoed to the output files. The only |
| 292 | possible options are dependencies. |
| 293 | |
| 294 | menu: |
| 295 | |
| 296 | "menu" <prompt> |
| 297 | <menu options> |
| 298 | <menu block> |
| 299 | "endmenu" |
| 300 | |
| 301 | This defines a menu block, see "Menu structure" above for more |
| 302 | information. The only possible options are dependencies. |
| 303 | |
| 304 | if: |
| 305 | |
| 306 | "if" <expr> |
| 307 | <if block> |
| 308 | "endif" |
| 309 | |
| 310 | This defines an if block. The dependency expression <expr> is appended |
| 311 | to all enclosed menu entries. |
| 312 | |
| 313 | source: |
| 314 | |
| 315 | "source" <prompt> |
| 316 | |
| 317 | This reads the specified configuration file. This file is always parsed. |
Randy Dunlap | 6e66b90 | 2007-10-19 10:53:48 -0700 | [diff] [blame] | 318 | |
| 319 | mainmenu: |
| 320 | |
| 321 | "mainmenu" <prompt> |
| 322 | |
| 323 | This sets the config program's title bar if the config program chooses |
| 324 | to use it. |
Randy Dunlap | 0486bc9 | 2007-11-12 16:17:55 -0800 | [diff] [blame] | 325 | |
| 326 | |
| 327 | Kconfig hints |
| 328 | ------------- |
| 329 | This is a collection of Kconfig tips, most of which aren't obvious at |
| 330 | first glance and most of which have become idioms in several Kconfig |
| 331 | files. |
| 332 | |
Sam Ravnborg | 9b3e4da | 2008-01-28 21:49:46 +0100 | [diff] [blame] | 333 | Adding common features and make the usage configurable |
| 334 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| 335 | It is a common idiom to implement a feature/functionality that are |
| 336 | relevant for some architectures but not all. |
| 337 | The recommended way to do so is to use a config variable named HAVE_* |
| 338 | that is defined in a common Kconfig file and selected by the relevant |
| 339 | architectures. |
| 340 | An example is the generic IOMAP functionality. |
| 341 | |
| 342 | We would in lib/Kconfig see: |
| 343 | |
| 344 | # Generic IOMAP is used to ... |
| 345 | config HAVE_GENERIC_IOMAP |
| 346 | |
| 347 | config GENERIC_IOMAP |
| 348 | depends on HAVE_GENERIC_IOMAP && FOO |
| 349 | |
| 350 | And in lib/Makefile we would see: |
| 351 | obj-$(CONFIG_GENERIC_IOMAP) += iomap.o |
| 352 | |
| 353 | For each architecture using the generic IOMAP functionality we would see: |
| 354 | |
| 355 | config X86 |
| 356 | select ... |
| 357 | select HAVE_GENERIC_IOMAP |
| 358 | select ... |
| 359 | |
| 360 | Note: we use the existing config option and avoid creating a new |
| 361 | config variable to select HAVE_GENERIC_IOMAP. |
| 362 | |
| 363 | Note: the use of the internal config variable HAVE_GENERIC_IOMAP, it is |
| 364 | introduced to overcome the limitation of select which will force a |
| 365 | config option to 'y' no matter the dependencies. |
| 366 | The dependencies are moved to the symbol GENERIC_IOMAP and we avoid the |
| 367 | situation where select forces a symbol equals to 'y'. |
| 368 | |
Randy Dunlap | 0486bc9 | 2007-11-12 16:17:55 -0800 | [diff] [blame] | 369 | Build as module only |
| 370 | ~~~~~~~~~~~~~~~~~~~~ |
| 371 | To restrict a component build to module-only, qualify its config symbol |
| 372 | with "depends on m". E.g.: |
| 373 | |
| 374 | config FOO |
| 375 | depends on BAR && m |
| 376 | |
| 377 | limits FOO to module (=m) or disabled (=n). |
| 378 | |
| 379 | |
| 380 | Build limited by a third config symbol which may be =y or =m |
| 381 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| 382 | A common idiom that we see (and sometimes have problems with) is this: |
| 383 | |
| 384 | When option C in B (module or subsystem) uses interfaces from A (module |
| 385 | or subsystem), and both A and B are tristate (could be =y or =m if they |
| 386 | were independent of each other, but they aren't), then we need to limit |
| 387 | C such that it cannot be built statically if A is built as a loadable |
| 388 | module. (C already depends on B, so there is no dependency issue to |
| 389 | take care of here.) |
| 390 | |
| 391 | If A is linked statically into the kernel image, C can be built |
| 392 | statically or as loadable module(s). However, if A is built as loadable |
| 393 | module(s), then C must be restricted to loadable module(s) also. This |
| 394 | can be expressed in kconfig language as: |
| 395 | |
| 396 | config C |
| 397 | depends on A = y || A = B |
| 398 | |
| 399 | or for real examples, use this command in a kernel tree: |
| 400 | |
| 401 | $ find . -name Kconfig\* | xargs grep -ns "depends on.*=.*||.*=" | grep -v orig |
| 402 | |