PageRenderTime 23ms CodeModel.GetById 11ms app.highlight 4ms RepoModel.GetById 2ms app.codeStats 0ms

/Documentation/kbuild/kconfig-language.txt

https://bitbucket.org/evzijst/gittest
Plain Text | 282 lines | 222 code | 60 blank | 0 comment | 0 complexity | 7f4ffe9537d2003c2a460ba0e7c024e0 MD5 | raw file
  1Introduction
  2------------
  3
  4The configuration database is collection of configuration options
  5organized in a tree structure:
  6
  7	+- Code maturity level options
  8	|  +- Prompt for development and/or incomplete code/drivers
  9	+- General setup
 10	|  +- Networking support
 11	|  +- System V IPC
 12	|  +- BSD Process Accounting
 13	|  +- Sysctl support
 14	+- Loadable module support
 15	|  +- Enable loadable module support
 16	|     +- Set version information on all module symbols
 17	|     +- Kernel module loader
 18	+- ...
 19
 20Every entry has its own dependencies. These dependencies are used
 21to determine the visibility of an entry. Any child entry is only
 22visible if its parent entry is also visible.
 23
 24Menu entries
 25------------
 26
 27Most entries define a config option, all other entries help to organize
 28them. A single configuration option is defined like this:
 29
 30config MODVERSIONS
 31	bool "Set version information on all module symbols"
 32	depends MODULES
 33	help
 34	  Usually, modules have to be recompiled whenever you switch to a new
 35	  kernel.  ...
 36
 37Every line starts with a key word and can be followed by multiple
 38arguments.  "config" starts a new config entry. The following lines
 39define attributes for this config option. Attributes can be the type of
 40the config option, input prompt, dependencies, help text and default
 41values. A config option can be defined multiple times with the same
 42name, but every definition can have only a single input prompt and the
 43type must not conflict.
 44
 45Menu attributes
 46---------------
 47
 48A menu entry can have a number of attributes. Not all of them are
 49applicable everywhere (see syntax).
 50
 51- type definition: "bool"/"tristate"/"string"/"hex"/"int"
 52  Every config option must have a type. There are only two basic types:
 53  tristate and string, the other types are based on these two. The type
 54  definition optionally accepts an input prompt, so these two examples
 55  are equivalent:
 56
 57	bool "Networking support"
 58  and
 59	bool
 60	prompt "Networking support"
 61
 62- input prompt: "prompt" <prompt> ["if" <expr>]
 63  Every menu entry can have at most one prompt, which is used to display
 64  to the user. Optionally dependencies only for this prompt can be added
 65  with "if".
 66
 67- default value: "default" <expr> ["if" <expr>]
 68  A config option can have any number of default values. If multiple
 69  default values are visible, only the first defined one is active.
 70  Default values are not limited to the menu entry, where they are
 71  defined, this means the default can be defined somewhere else or be
 72  overridden by an earlier definition.
 73  The default value is only assigned to the config symbol if no other
 74  value was set by the user (via the input prompt above). If an input
 75  prompt is visible the default value is presented to the user and can
 76  be overridden by him.
 77  Optionally dependencies only for this default value can be added with
 78  "if".
 79
 80- dependencies: "depends on"/"requires" <expr>
 81  This defines a dependency for this menu entry. If multiple
 82  dependencies are defined they are connected with '&&'. Dependencies
 83  are applied to all other options within this menu entry (which also
 84  accept an "if" expression), so these two examples are equivalent:
 85
 86	bool "foo" if BAR
 87	default y if BAR
 88  and
 89	depends on BAR
 90	bool "foo"
 91	default y
 92
 93- reverse dependencies: "select" <symbol> ["if" <expr>]
 94  While normal dependencies reduce the upper limit of a symbol (see
 95  below), reverse dependencies can be used to force a lower limit of
 96  another symbol. The value of the current menu symbol is used as the
 97  minimal value <symbol> can be set to. If <symbol> is selected multiple
 98  times, the limit is set to the largest selection.
 99  Reverse dependencies can only be used with boolean or tristate
100  symbols.
101
102- numerical ranges: "range" <symbol> <symbol> ["if" <expr>]
103  This allows to limit the range of possible input values for int
104  and hex symbols. The user can only input a value which is larger than
105  or equal to the first symbol and smaller than or equal to the second
106  symbol.
107
108- help text: "help" or "---help---"
109  This defines a help text. The end of the help text is determined by
110  the indentation level, this means it ends at the first line which has
111  a smaller indentation than the first line of the help text.
112  "---help---" and "help" do not differ in behaviour, "---help---" is
113  used to help visually seperate configuration logic from help within
114  the file as an aid to developers.
115
116
117Menu dependencies
118-----------------
119
120Dependencies define the visibility of a menu entry and can also reduce
121the input range of tristate symbols. The tristate logic used in the
122expressions uses one more state than normal boolean logic to express the
123module state. Dependency expressions have the following syntax:
124
125<expr> ::= <symbol>                             (1)
126           <symbol> '=' <symbol>                (2)
127           <symbol> '!=' <symbol>               (3)
128           '(' <expr> ')'                       (4)
129           '!' <expr>                           (5)
130           <expr> '&&' <expr>                   (6)
131           <expr> '||' <expr>                   (7)
132
133Expressions are listed in decreasing order of precedence. 
134
135(1) Convert the symbol into an expression. Boolean and tristate symbols
136    are simply converted into the respective expression values. All
137    other symbol types result in 'n'.
138(2) If the values of both symbols are equal, it returns 'y',
139    otherwise 'n'.
140(3) If the values of both symbols are equal, it returns 'n',
141    otherwise 'y'.
142(4) Returns the value of the expression. Used to override precedence.
143(5) Returns the result of (2-/expr/).
144(6) Returns the result of min(/expr/, /expr/).
145(7) Returns the result of max(/expr/, /expr/).
146
147An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2
148respectively for calculations). A menu entry becomes visible when it's
149expression evaluates to 'm' or 'y'.
150
151There are two types of symbols: constant and nonconstant symbols.
152Nonconstant symbols are the most common ones and are defined with the
153'config' statement. Nonconstant symbols consist entirely of alphanumeric
154characters or underscores.
155Constant symbols are only part of expressions. Constant symbols are
156always surrounded by single or double quotes. Within the quote any
157other character is allowed and the quotes can be escaped using '\'.
158
159Menu structure
160--------------
161
162The position of a menu entry in the tree is determined in two ways. First
163it can be specified explicitly:
164
165menu "Network device support"
166	depends NET
167
168config NETDEVICES
169	...
170
171endmenu
172
173All entries within the "menu" ... "endmenu" block become a submenu of
174"Network device support". All subentries inherit the dependencies from
175the menu entry, e.g. this means the dependency "NET" is added to the
176dependency list of the config option NETDEVICES.
177
178The other way to generate the menu structure is done by analyzing the
179dependencies. If a menu entry somehow depends on the previous entry, it
180can be made a submenu of it. First, the previous (parent) symbol must
181be part of the dependency list and then one of these two conditions
182must be true:
183- the child entry must become invisible, if the parent is set to 'n'
184- the child entry must only be visible, if the parent is visible
185
186config MODULES
187	bool "Enable loadable module support"
188
189config MODVERSIONS
190	bool "Set version information on all module symbols"
191	depends MODULES
192
193comment "module support disabled"
194	depends !MODULES
195
196MODVERSIONS directly depends on MODULES, this means it's only visible if
197MODULES is different from 'n'. The comment on the other hand is always
198visible when MODULES is visible (the (empty) dependency of MODULES is
199also part of the comment dependencies).
200
201
202Kconfig syntax
203--------------
204
205The configuration file describes a series of menu entries, where every
206line starts with a keyword (except help texts). The following keywords
207end a menu entry:
208- config
209- menuconfig
210- choice/endchoice
211- comment
212- menu/endmenu
213- if/endif
214- source
215The first five also start the definition of a menu entry.
216
217config:
218
219	"config" <symbol>
220	<config options>
221
222This defines a config symbol <symbol> and accepts any of above
223attributes as options.
224
225menuconfig:
226	"menuconfig" <symbol>
227	<config options>
228
229This is similiar to the simple config entry above, but it also gives a
230hint to front ends, that all suboptions should be displayed as a
231separate list of options.
232
233choices:
234
235	"choice"
236	<choice options>
237	<choice block>
238	"endchoice"
239
240This defines a choice group and accepts any of above attributes as
241options. A choice can only be of type bool or tristate, while a boolean
242choice only allows a single config entry to be selected, a tristate
243choice also allows any number of config entries to be set to 'm'. This
244can be used if multiple drivers for a single hardware exists and only a
245single driver can be compiled/loaded into the kernel, but all drivers
246can be compiled as modules.
247A choice accepts another option "optional", which allows to set the
248choice to 'n' and no entry needs to be selected.
249
250comment:
251
252	"comment" <prompt>
253	<comment options>
254
255This defines a comment which is displayed to the user during the
256configuration process and is also echoed to the output files. The only
257possible options are dependencies.
258
259menu:
260
261	"menu" <prompt>
262	<menu options>
263	<menu block>
264	"endmenu"
265
266This defines a menu block, see "Menu structure" above for more
267information. The only possible options are dependencies.
268
269if:
270
271	"if" <expr>
272	<if block>
273	"endif"
274
275This defines an if block. The dependency expression <expr> is appended
276to all enclosed menu entries.
277
278source:
279
280	"source" <prompt>
281
282This reads the specified configuration file. This file is always parsed.