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diff --git a/docs/Kconfig-language.txt b/docs/Kconfig-language.txt new file mode 100644 index 0000000..0ba8932 --- /dev/null +++ b/docs/Kconfig-language.txt @@ -0,0 +1,255 @@ +Introduction +------------ + +The configuration database is collection of configuration options +organized in a tree structure: + + +- Code maturity level options + | +- Prompt for development and/or incomplete code/drivers + +- General setup + | +- Networking support + | +- System V IPC + | +- BSD Process Accounting + | +- Sysctl support + +- Loadable module support + | +- Enable loadable module support + | +- Set version information on all module symbols + | +- Kernel module loader + +- ... + +Every entry has its own dependencies. These dependencies are used +to determine the visible of an entry. Any child entry is only +visible if its parent entry is also visible. + +Menu entries +------------ + +Most entries define a config option, all other entries help to organize +them. A single configuration option is defined like this: + +config MODVERSIONS + bool "Set version information on all module symbols" + depends MODULES + help + Usually, modules have to be recompiled whenever you switch to a new + kernel. ... + +Every line starts with a key word and can be followed by multiple +arguments. "config" starts a new config entry. The following lines +define attributes for this config option. Attributes can be the type of +the config option, input prompt, dependencies, help text and default +values. A config option can be defined multiple times with the same +name, but every definition can have only a single input prompt and the +type must not conflict. + +Menu attributes +--------------- + +A menu entry can have a number of attributes. Not all of them are +applicable everywhere (see syntax). + +- type definition: "bool"/"tristate"/"string"/"hex"/"integer" + Every config option must have a type. There are only two basic types: + tristate and string, the other types base on these two. The type + definition optionally accepts an input prompt, so these two examples + are equivalent: + + bool "Networking support" + and + bool + prompt "Networking support" + +- input prompt: "prompt" <prompt> ["if" <expr>] + Every menu entry can have at most one prompt, which is used to display + to the user. Optionally dependencies only for this prompt can be added + with "if". + +- default value: "default" <symbol> ["if" <expr>] + A config option can have any number of default values. If multiple + default values are visible, only the first defined one is active. + Default values are not limited to the menu entry, where they are + defined, this means the default can be defined somewhere else or be + overridden by an earlier definition. + The default value is only assigned to the config symbol if no other + value was set by the user (via the input prompt above). If an input + prompt is visible the default value is presented to the user and can + be overridden by him. + Optionally dependencies only for this default value can be added with + "if". + +- dependencies: "depends on"/"requires" <expr> + This defines a dependency for this menu entry. If multiple + dependencies are defined they are connected with '&&'. Dependencies + are applied to all other options within this menu entry (which also + accept "if" expression), so these two examples are equivalent: + + bool "foo" if BAR + default y if BAR + and + depends on BAR + bool "foo" + default y + +- help text: "help" + This defines a help text. The end of the help text is determined by + the level indentation, this means it ends at the first line which has + a smaller indentation than the first line of the help text. + + +Menu dependencies +----------------- + +Dependencies define the visibility of a menu entry and can also reduce +the input range of tristate symbols. The tristate logic used in the +expressions uses one more state than normal boolean logic to express the +module state. Dependency expressions have the following syntax: + +<expr> ::= <symbol> (1) + <symbol> '=' <symbol> (2) + <symbol> '!=' <symbol> (3) + '(' <expr> ')' (4) + '!' <expr> (5) + <expr> '||' <expr> (6) + <expr> '&&' <expr> (7) + +Expressions are listed in decreasing order of precedence. + +(1) Convert the symbol into an expression. Boolean and tristate symbols + are simply converted into the respective expression values. All + other symbol types result in 'n'. +(2) If the values of both symbols are equal, it returns 'y', + otherwise 'n'. +(3) If the values of both symbols are equal, it returns 'n', + otherwise 'y'. +(4) Returns the value of the expression. Used to override precedence. +(5) Returns the result of (2-/expr/). +(6) Returns the result of min(/expr/, /expr/). +(7) Returns the result of max(/expr/, /expr/). + +An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2 +respectively for calculations). A menu entry becomes visible when it's +expression evaluates to 'm' or 'y'. + +There are two type of symbols: constant and nonconstant symbols. +Nonconstant symbols are the most common ones and are defined with the +'config' statement. Nonconstant symbols consist entirely of alphanumeric +characters or underscores. +Constant symbols are only part of expressions. Constant symbols are +always surrounded by single or double quotes. Within the quote any +other character is allowed and the quotes can be escaped using '\'. + +Menu structure +-------------- + +The position of a menu entry in the tree is determined in two ways. First +it can be specified explicitely: + +menu "Network device support" + depends NET + +config NETDEVICES + ... + +endmenu + +All entries within the "menu" ... "endmenu" block become a submenu of +"Network device support". All subentries inherit the dependencies from +the menu entry, e.g. this means the dependency "NET" is added to the +dependency list of the config option NETDEVICES. + +The other way to generate the menu structure is done by analyzing the +dependencies. If a menu entry somehow depends on the previous entry, it +can be made a submenu of it. First the the previous (parent) symbol must +be part of the dependency list and then one of these two condititions +must be true: +- the child entry must become invisible, if the parent is set to 'n' +- the child entry must only be visible, if the parent is visible + +config MODULES + bool "Enable loadable module support" + +config MODVERSIONS + bool "Set version information on all module symbols" + depends MODULES + +comment "module support disabled" + depends !MODULES + +MODVERSIONS directly depends on MODULES, this means it's only visible if +MODULES is different from 'n'. The comment on the other hand is always +visible when MODULES it's visible (the (empty) dependency of MODULES is +also part of the comment dependencies). + + +Kconfig syntax +-------------- + +The configuration file describes a series of menu entries, where every +line starts with a keyword (except help texts). The following keywords +end a menu entry: +- config +- choice/endchoice +- comment +- menu/endmenu +- if/endif +- source +The first four also start the definition of a menu entry. + +config: + + "config" <symbol> + <config options> + +This defines a config symbol <symbol> and accepts any of above +attributes as options. + +choices: + + "choice" + <choice options> + <choice block> + "endchoice" + +This defines a choice group and accepts any of above attributes as +options. A choice can only be of type bool or tristate, while a boolean +choice only allows a single config entry to be selected, a tristate +choice also allows any number of config entries to be set to 'm'. This +can be used if multiple drivers for a single hardware exists and only a +single driver can be compiled/loaded into the kernel, but all drivers +can be compiled as modules. +A choice accepts another option "optional", which allows to set the +choice to 'n' and no entry needs to be selected. + +comment: + + "comment" <prompt> + <comment options> + +This defines a comment which is displayed to the user during the +configuration process and is also echoed to the output files. The only +possible options are dependencies. + +menu: + + "menu" <prompt> + <menu options> + <menu block> + "endmenu" + +This defines a menu block, see "Menu structure" above for more +information. The only possible options are dependencies. + +if: + + "if" <expr> + <if block> + "endif" + +This defines an if block. The dependency expression <expr> is appended +to all enclosed menu entries. + +source: + + "source" <prompt> + +This reads the specified configuration file. This file is always parsed. |