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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 visibility 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 are based 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" <expr> ["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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- overridden 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 an "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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-- reverse dependencies: "select" <symbol> ["if" <expr>]
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- While normal dependencies reduce the upper limit of a symbol (see
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- below), reverse dependencies can be used to force a lower limit of
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- another symbol. The value of the current menu symbol is used as the
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- minimal value <symbol> can be set to. If <symbol> is selected multiple
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- times, the limit is set to the largest selection.
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- Reverse dependencies can only be used with boolean or tristate
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- symbols.
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-
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-- numerical ranges: "range" <symbol> <symbol> ["if" <expr>]
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- This allows to limit the range of possible input values for integer
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- and hex symbols. The user can only input a value which is larger than
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- or equal to the first symbol and smaller than or equal to the second
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- symbol.
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-
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-- help text: "help" or "---help---"
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- This defines a help text. The end of the help text is determined by
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- the indentation level, 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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- "---help---" and "help" do not differ in behaviour, "---help---" is
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- used to help visually separate configuration logic from help within
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- the file as an aid to developers.
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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 types 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 explicitly:
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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 previous (parent) symbol must
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-be part of the dependency list and then one of these two conditions
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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 is 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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-- menuconfig
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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 five 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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-menuconfig:
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- "menuconfig" <symbol>
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- <config options>
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-
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-This is similiar to the simple config entry above, but it also gives a
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-hint to front ends, that all suboptions should be displayed as a
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-separate list of 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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