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282 lines
9.4 KiB
282 lines
9.4 KiB
Introduction |
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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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+- 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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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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Menu entries |
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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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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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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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Menu attributes |
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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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- 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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bool "Networking support" |
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and |
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bool |
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prompt "Networking support" |
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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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- 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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- 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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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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- 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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- 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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- 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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Menu dependencies |
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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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<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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Expressions are listed in decreasing order of precedence. |
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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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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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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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Menu structure |
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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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menu "Network device support" |
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depends NET |
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config NETDEVICES |
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... |
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endmenu |
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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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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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config MODULES |
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bool "Enable loadable module support" |
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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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comment "module support disabled" |
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depends !MODULES |
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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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Kconfig syntax |
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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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config: |
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"config" <symbol> |
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<config options> |
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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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menuconfig: |
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"menuconfig" <symbol> |
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<config options> |
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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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choices: |
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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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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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comment: |
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"comment" <prompt> |
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<comment options> |
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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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menu: |
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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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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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if: |
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"if" <expr> |
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<if block> |
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"endif" |
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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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source: |
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"source" <prompt> |
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This reads the specified configuration file. This file is always parsed.
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