diff options
| -rw-r--r-- | config/Kconfig-language.txt | 190 |
1 files changed, 157 insertions, 33 deletions
diff --git a/config/Kconfig-language.txt b/config/Kconfig-language.txt index 493749b32..c412c2458 100644 --- a/config/Kconfig-language.txt +++ b/config/Kconfig-language.txt @@ -1,7 +1,7 @@ Introduction ------------ -The configuration database is collection of configuration options +The configuration database is a collection of configuration options organized in a tree structure: +- Code maturity level options @@ -18,18 +18,18 @@ organized in a tree structure: +- ... Every entry has its own dependencies. These dependencies are used -to determine the visible of an entry. Any child entry is only +to determine the visibility 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 +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 + depends on MODULES help Usually, modules have to be recompiled whenever you switch to a new kernel. ... @@ -48,9 +48,9 @@ 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" +- type definition: "bool"/"tristate"/"string"/"hex"/"int" 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 + tristate and string; the other types are based on these two. The type definition optionally accepts an input prompt, so these two examples are equivalent: @@ -64,24 +64,29 @@ applicable everywhere (see syntax). to the user. Optionally dependencies only for this prompt can be added with "if". -- default value: "default" <symbol> ["if" <expr>] +- default value: "default" <expr> ["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 - overriden by an earlier definition. + 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 + Optionally, dependencies only for this default value can be added with "if". -- dependencies: "depends on"/"requires" <expr> +- type definition + default value: + "def_bool"/"def_tristate" <expr> ["if" <expr>] + This is a shorthand notation for a type definition plus a value. + Optionally dependencies for this default value can be added with "if". + +- dependencies: "depends on" <expr> This defines a dependency for this menu entry. If multiple - dependencies are defined they are connected with '&&'. Dependencies + 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: + accept an "if" expression), so these two examples are equivalent: bool "foo" if BAR default y if BAR @@ -90,11 +95,60 @@ applicable everywhere (see syntax). bool "foo" default y -- help text: "help" +- reverse dependencies: "select" <symbol> ["if" <expr>] + While normal dependencies reduce the upper limit of a symbol (see + below), reverse dependencies can be used to force a lower limit of + another symbol. The value of the current menu symbol is used as the + minimal value <symbol> can be set to. If <symbol> is selected multiple + times, the limit is set to the largest selection. + Reverse dependencies can only be used with boolean or tristate + symbols. + Note: + select should be used with care. select will force + a symbol to a value without visiting the dependencies. + By abusing select you are able to select a symbol FOO even + if FOO depends on BAR that is not set. + In general use select only for non-visible symbols + (no prompts anywhere) and for symbols with no dependencies. + That will limit the usefulness but on the other hand avoid + the illegal configurations all over. + kconfig should one day warn about such things. + +- numerical ranges: "range" <symbol> <symbol> ["if" <expr>] + This allows to limit the range of possible input values for int + and hex symbols. The user can only input a value which is larger than + or equal to the first symbol and smaller than or equal to the second + symbol. + +- help text: "help" or "---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 + the indentation level, this means it ends at the first line which has a smaller indentation than the first line of the help text. - + "---help---" and "help" do not differ in behaviour, "---help---" is + used to help visually separate configuration logic from help within + the file as an aid to developers. + +- misc options: "option" <symbol>[=<value>] + Various less common options can be defined via this option syntax, + which can modify the behaviour of the menu entry and its config + symbol. These options are currently possible: + + - "defconfig_list" + This declares a list of default entries which can be used when + looking for the default configuration (which is used when the main + .config doesn't exists yet.) + + - "modules" + This declares the symbol to be used as the MODULES symbol, which + enables the third modular state for all config symbols. + + - "env"=<value> + This imports the environment variable into Kconfig. It behaves like + a default, except that the value comes from the environment, this + also means that the behaviour when mixing it with normal defaults is + undefined at this point. The symbol is currently not exported back + to the build environment (if this is desired, it can be done via + another symbol). Menu dependencies ----------------- @@ -109,10 +163,10 @@ module state. Dependency expressions have the following syntax: <symbol> '!=' <symbol> (3) '(' <expr> ')' (4) '!' <expr> (5) - <expr> '||' <expr> (6) - <expr> '&&' <expr> (7) + <expr> '&&' <expr> (6) + <expr> '||' <expr> (7) -Expressions are listed in decreasing order of precedence. +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 @@ -130,22 +184,22 @@ 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 +There are two types of symbols: constant and non-constant symbols. +Non-constant symbols are the most common ones and are defined with the +'config' statement. Non-constant 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 +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: +it can be specified explicitly: menu "Network device support" - depends NET + depends on NET config NETDEVICES ... @@ -159,8 +213,8 @@ 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 +can be made a submenu of it. First, the previous (parent) symbol must +be part of the dependency list and then one of these two conditions 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 @@ -170,14 +224,14 @@ config MODULES config MODVERSIONS bool "Set version information on all module symbols" - depends MODULES + depends on MODULES comment "module support disabled" - depends !MODULES + depends on !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 +visible when MODULES is visible (the (empty) dependency of MODULES is also part of the comment dependencies). @@ -188,12 +242,13 @@ 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 +- menuconfig - choice/endchoice - comment - menu/endmenu - if/endif - source -The first four also start the definition of a menu entry. +The first five also start the definition of a menu entry. config: @@ -203,6 +258,14 @@ config: This defines a config symbol <symbol> and accepts any of above attributes as options. +menuconfig: + "menuconfig" <symbol> + <config options> + +This is similar to the simple config entry above, but it also gives a +hint to front ends, that all suboptions should be displayed as a +separate list of options. + choices: "choice" @@ -210,7 +273,7 @@ choices: <choice block> "endchoice" -This defines a choice group and accepts any of above attributes as +This defines a choice group and accepts any of the 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 @@ -253,3 +316,64 @@ source: "source" <prompt> This reads the specified configuration file. This file is always parsed. + +mainmenu: + + "mainmenu" <prompt> + +This sets the config program's title bar if the config program chooses +to use it. + + +Kconfig hints +------------- +This is a collection of Kconfig tips, most of which aren't obvious at +first glance and most of which have become idioms in several Kconfig +files. + +Adding common features and make the usage configurable +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +It is a common idiom to implement a feature/functionality that are +relevant for some architectures but not all. +The recommended way to do so is to use a config variable named HAVE_* +that is defined in a common Kconfig file and selected by the relevant +architectures. +An example is the generic IOMAP functionality. + +We would in lib/Kconfig see: + +# Generic IOMAP is used to ... +config HAVE_GENERIC_IOMAP + +config GENERIC_IOMAP + depends on HAVE_GENERIC_IOMAP && FOO + +And in lib/Makefile we would see: +obj-$(CONFIG_GENERIC_IOMAP) += iomap.o + +For each architecture using the generic IOMAP functionality we would see: + +config X86 + select ... + select HAVE_GENERIC_IOMAP + select ... + +Note: we use the existing config option and avoid creating a new +config variable to select HAVE_GENERIC_IOMAP. + +Note: the use of the internal config variable HAVE_GENERIC_IOMAP, it is +introduced to overcome the limitation of select which will force a +config option to 'y' no matter the dependencies. +The dependencies are moved to the symbol GENERIC_IOMAP and we avoid the +situation where select forces a symbol equals to 'y'. + +Build as module only +~~~~~~~~~~~~~~~~~~~~ +To restrict a component build to module-only, qualify its config symbol +with "depends on m". E.g.: + +config FOO + depends on BAR && m + +limits FOO to module (=m) or disabled (=n). + |