本文，不是嚴格的逐字翻譯，且只對關心的部分進行翻譯，來源於linux-4.1.15/Documentation/kbuild/kconfig-language.txt
Introduction
The configuration database is a collection of configuration options
organized in a tree structure:
組織好的數據是樹狀結構的，像下面這樣的
+- 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.
每一個入口（編譯項）都 有自己的依賴。這些依賴決定着入口的可見性，如果子項要可見，則上一級的選項也要可見才行
Menu entries
大部分的編譯項都是可配置的，下面是一個例子。
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.
每一行都有一個關鍵字，然後跟着若干參數，config 定義了一個新的配置項，接下的的幾行決定這個配置項的屬性，屬性有：是否配置，提示，依賴，幫助信息和默認值，一個配置屬性可以定義多次，但是提示不能相同類型也不能衝突。
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:
類型有： “bool”，“tristate”，“string”，“hex”，“int”
每一個配置項必須要有一個類型，有兩種基本類型：tristate和string，其它的類型都是基於這兩種類型的，類型這一行可以允許有提示信息
bool "Networking support"
and
bool
prompt "Networking support"
這兩種寫法的效果是一樣的
-
input prompt: “prompt” [“if” ]
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”.
每個菜單選項最多只能有一個顯示給用戶的輸入提示。可以用 “if” 來表示該提示的依賴關係 -
default value: “default” [“if” ]
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”.
一個配置選項可以有任意多個默認值。如果有多個默認值，那麼只有第一個被定義的值是有效的，默認值不一定是定義在配置項的定義的地方，這就意味着默認值可以定義在任何地方或被更早的定義覆蓋
如果用戶沒有設置(通過上面的輸入提示)，配置選項的值就是默認值。如果可以顯示輸入提示的話，就會把默認值顯示給用戶，並可以讓用戶進行修改。
默認值的依賴關係可以用 “if” 添加
-
type definition + default value:
“def_bool”/“def_tristate” [“if” ]
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”
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:
爲配置項定義一個依賴，如果有多個依賴可以使用 “&&”符號，配置項的其它條目也可以使用依賴，同樣也接受 “if”，如下的寫法是等價的
只有depends on A,這個A被配置了，這一個配置項目纔可以配置
bool "foo" if BAR
default y if BAR
and
depends on BAR
bool "foo"
default y
-
reverse dependencies: “select” [“if” ]
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 can be set to. If is selected multiple
times, the limit is set to the largest selection.
Reverse dependencies can only be used with boolean or tristate
symbols.
反向依賴使用“select”，
我自己配置好了，其它 select的都得配置上
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. -
limiting menu display: “visible if”
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” [“if” ]
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.
help：定義了一個幫助文本，幫助文本的末尾由縮進級別決定的 -
misc options: “option” [=]
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”=
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
依賴決定着編譯項的可見性，同時也限制了tristate 屬性的輸入範圍，tristate 比boolean多了一個狀態，依賴表達式有如下的符號
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.
表達式以優先級順序列出
(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 its
expression evaluates to ‘m’ or ‘y’.
一個表達式可能有 ‘n’, ‘m’ or ‘y’（ 0, 1, 2，用於計算），一個配置項如果配置成 ‘m’ or ‘y’，則是可見的
There are two types of symbols: constant and non-constant symbols.
Non-constant symbols are the most common ones and are defined with the
‘config’ statement. Non-constant 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
有兩種方法來定義菜單項，第一種是顯式的
The position of a menu entry in the tree is determined in two ways. First
it can be specified explicitly:
menu "Network device support"
depends on 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.
“Network device support”菜單的配置項目被包在"menu" … "endmenu"的結構中，所有的下級配置項的依賴都繼承了上級菜單。也就是說，NETDEVICES配置項也依賴於 “NET”
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 previous (parent) symbol must
be part of the dependency list and then one of these two conditions
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
第二種產生菜單的方法是分析依賴，如果配置項依賴於前面定義的配置項，那麼本配置項目就是前一個配置項的子菜單
首先，父項目（前）要是本項目的依賴，且如下的兩個條件必須滿足
1,如果父菜單設置成“n”，子菜單必須是可見的，
1,如果父菜單可見，子菜單必須是可見的，
config MODULES
bool "Enable loadable module support"
config MODVERSIONS
bool "Set version information on all module symbols"
depends on MODULES
comment "module support disabled"
depends on !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 is visible (the (empty) dependency of MODULES is
also part of the comment dependencies).
MODVERSIONS直接依賴於MODULES，意味着只要MODULES不爲“n”，MODVERSIONS都是可見的
Kconfig syntax（語法）
配置文件 有很多的菜單，關鍵字如下：
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
- menuconfig
- choice/endchoice
- comment
- menu/endmenu
- if/endif
- source
The first five also start the definition of a menu entry.
前面的五個用於定義一個菜單的入口
config:
"config" <symbol>
<config options>
This defines a config symbol and accepts any of above
attributes as options.
menuconfig:
"menuconfig" <symbol>
<config options>
This is similar to the simple config entry above, but it also gives a
hint to front ends, that all suboptions should be displayed as a
separate list of options.
choices:
"choice" [symbol]
<choice options>
<choice block>
"endchoice"
choice 內的內定義的配置項只以有兩種類型：bool or tristate，bool類型的在這個choice塊內只能有一個可以被選上（類似於單選），tristate類型可以把不限制個數的配置項目配置成 “m”，（模塊），這種特性可以用於，一個硬件設備對應於多個驅動程序，這樣可以把所有的驅動程序都以模塊的形式編譯出來，但是隻有一個能被編譯進內核
This defines a choice group and accepts any of the 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.
If no [symbol] is associated with a choice, then you can not have multiple
definitions of that choice. If a [symbol] is associated to the choice,
then you may define the same choice (ie. with the same entries) in another
place.
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"
定義一個菜單塊
This defines a menu block, see “Menu structure” above for more
information. The only possible options are dependencies and “visible”
attributes.
if:
"if" <expr>
<if block>
"endif"
This defines an if block. The dependency expression is appended
to all enclosed menu entries.
source:
"source" <prompt>
作用類似於include
This reads the specified configuration file. This file is always parsed.
mainmenu:
"mainmenu" <prompt>
最頂層的菜單
This sets the config program’s title bar if the config program chooses
to use it. It should be placed at the top of the configuration, before any
other statement.
Kconfig hints
This is a collection of Kconfig tips, most of which aren’t obvious at
first glance and most of which have become idioms in several Kconfig
files.
Adding common features and make the usage configurable
It is a common idiom to implement a feature/functionality that are
relevant for some architectures but not all.
The recommended way to do so is to use a config variable named HAVE_*
that is defined in a common Kconfig file and selected by the relevant
architectures.
An example is the generic IOMAP functionality.
We would in lib/Kconfig see:
# Generic IOMAP is used to ...
config HAVE_GENERIC_IOMAP
config GENERIC_IOMAP
depends on HAVE_GENERIC_IOMAP && FOO
And in lib/Makefile we would see:
obj-$(CONFIG_GENERIC_IOMAP) += iomap.o
For each architecture using the generic IOMAP functionality we would see:
config X86
select ...
select HAVE_GENERIC_IOMAP
select ...
Note: we use the existing config option and avoid creating a new
config variable to select HAVE_GENERIC_IOMAP.
Note: the use of the internal config variable HAVE_GENERIC_IOMAP, it is
introduced to overcome the limitation of select which will force a
config option to 'y' no matter the dependencies.
The dependencies are moved to the symbol GENERIC_IOMAP and we avoid the
situation where select forces a symbol equals to 'y'.
Build as module only
~~~~~~~~~~~~~~~~~~~~
To restrict a component build to module-only, qualify its config symbol
with "depends on m". E.g.:
config FOO
depends on BAR && m
limits FOO to module (=m) or disabled (=n).