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Introduction ------------ The configuration database is a 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 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 them. A single configuration option is defined like this: config MODVERSIONS bool "Set version information on all module symbols" depends on 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"/"int" Every config option must have a type. There are only two basic types: 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: 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" <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 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". - 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 are applied to all other options within this menu entry (which also accept an "if" expression), so these two examples are equivalent: bool "foo" if BAR default y if BAR and depends on BAR bool "foo" default y - 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. - weak reverse dependencies: "imply" <symbol> ["if" <expr>] This is similar to "select" as it enforces a lower limit on another symbol except that the "implied" symbol's value may still be set to n from a direct dependency or with a visible prompt. Given the following example: config FOO tristate imply BAZ config BAZ tristate depends on BAR The following values are possible: FOO BAR BAZ's default choice for BAZ --- --- ------------- -------------- n y n N/m/y m y m M/y/n y y y Y/n y n * N This is useful e.g. with multiple drivers that want to indicate their ability to hook into a secondary subsystem while allowing the user to configure that subsystem out without also having to unset these drivers. - limiting menu display: "visible if" <expr> This attribute is only applicable to menu blocks, if the condition is false, the menu block is not displayed to the user (the symbols contained there can still be selected by other symbols, though). It is similar to a conditional "prompt" attribute for individual menu entries. Default value of "visible" is true. - 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 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. At most one symbol may have the "modules" option set. - "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). - "allnoconfig_y" This declares the symbol as one that should have the value y when using "allnoconfig". Used for symbols that hide other symbols. 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> '||' <e