docs/Kconfig-language.txt - busybox - Git at Google

 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.
	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.