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