1Config::Model::Manual::UMsoedrelCCCoornnetfaritigib:ou:ntMIeonddterPloe:dr:ulMcatDniouocanul(m:3e:)nMtoadteiloCnreationIntroduction(3)
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6 Config::Model::Manual::ModelCreationIntroduction - Introduction to
7 model creation with Config::Model
8
10 version 2.142
11
13 This page describes how to write a simple configuration model. Creation
14 of more complex models are described in Creating a model with advanced
15 features.
16 Note that this document shows a lot of Perl data structure to highlight
18 the content of a model. A Perl data structure is very similar to a JSON
19 structure. The only thing you need to know are:
20 • Curly braces "{ ... }" contain a dictionary of key, value pairs (a
22 "hash" in Perl land))
23 • Square brackets "[ ... ]" contain a list of items ("array" or
25 "list" in Perl land)
26
28 configuration file
29 Text file where configuration data are stored. This configuration
30 file is used by an application -- the target application
31 configuration tree
33 The semantic content of the configuration file stored in a tree
34 representation
35 configuration model
37 Structure and constraints of the configuration tree. Like a schema
38 for the configuration tree
39 target application
41 The application that uses the configuration file. The application
42 can be of type "system" (i.e. the configuration file is located in
43 "/etc"), "user" (i.e. the configuration file is located in a user
44 directory like "~/.config") or "application" (the configuration
45 file is in or below the current directory)
46 end user
48 User of the target application
49 application developer
51 Target application developer
52 model developer
54 People developing the configuration model. Not necessarily the
55 application developer
56
58 Most configuration files are actually organized mostly as a tree
59 structure. Depending on the syntax of the file, this structure may be
60 obvious to see (e.g. for XML, Apache) or not so obvious ("Xorg" syntax,
61 INI syntax).
62 For some files like "approx.conf" or "adduser.conf", this tree
64 structure is quite flat. It looks much like a rake than a tree, but
65 still, it's a tree.
66 For instance, this "approx.conf":
68 $pdiffs 1
70 $max_wait 14
71 debian http://ftp.fr.debian.org/debian
72 can have this tree representation:
74 root
76 |--pdiff=1
77 |--max_wait=14
78 `--distrib(debian)=http://ftp.fr.debian.org/debian
79 Other configuration files like "apache2.conf" or "xorg.conf" have a
81 structure that look more like a tree.
82 For instance, consider this "xorg.conf" snippet:
84 Section "Device"
86 Identifier "Device0"
87 Driver "nvidia"
88 EndSection
89 Section "Screen"
91 Identifier "Screen0"
92 Device "Device0"
93 Option "AllowGLXWithComposite" "True"
94 Option "DynamicTwinView" "True"
95 SubSection "Display"
96 Depth 24
97 EndSubSection
98 EndSection
99 Knowing that Xorg.conf can have several Device or Screen sections
101 identified by their "Identifiers", the configuration can be represented
102 in this tree as:
103 root
105 |--Device(Device0)
106 | `--Driver=nvidia
107 `--Screen(Screen0)
108 |--Device=Device0
109 |--Option
110 | |--AllowGLXWithComposite=True
111 | `--DynamicTwinView=True
112 `--Display
113 `--Depth=24
114 One may argue that some "Xorg" parameter refer to others (i.e."Device"
116 and "Monitor" value in "Screen" section) and so they cannot be
117 represented as a tree. That's right, there are some more complex
118 relations that are added to the tree structure. This will be covered in
119 more details when dealing with complex models.
120 In some other case, the structure of a tree is not fixed. For instance,
122 "Device" options in "Xorg.conf" are different depending on the value of
123 the "Device Driver". In this case, the structure of the configuration
124 tree must be adapted (morphed) depending on a parameter value.
125 Just like XML data can have Schema to validate their content, the
127 configuration tree structure needs to have its own schema to validate
128 its content. Since the tree structure cannot be represented as a static
129 tree without reference, XML like schema are not enough to validate
130 configuration data.
131 Config::Model provides a kind of schema for configuration data that
133 takes care of the cross references mentioned above and of the dynamic
134 nature of the configuration tree required for "Xorg" (and others).
135
137 A configuration model defines the configuration tree structure:
138 • A model defines one or more configuration class
140 • At least one class is required to define the configuration tree
142 root
143 • Each class contains several elements. An element can be:
145 • A leaf to represent one configuration parameter
147 • A list of hash of leaves to represent several parameter
149 • A node to hold a node of a configuration tree
151 • A list or hash of nodes
153 These basic relations enable to define the main parts of a
155 configuration tree.
156 If we refer to the "approx.conf" example mentioned above, one only
158 class is required (let's say the "Approx" class). This class must
159 contain (see approx.conf man page):
160 • A boolean leaf for "pdiff" (1 if not specified)
162 • An integer leaf for "max_wait" (10 seconds unless specified
164 otherwise)
165 • A hash of string leaves for "distrib" (no default).
167 A configuration model is stored this way by Config::Model:
169 {
171 name => 'Approx',
172 element => [
173 pdiffs => {
174 type => 'leaf',
175 value_type => 'boolean',
176 upstream_default => '1'
177 },
178 max_wait => {
179 type => 'leaf',
180 value_type => 'integer',
181 upstream_default => '10'
182 },
183 distributions'=> {
184 type => 'hash',
185 index_type => 'string' ,
186 cargo => {
187 value_type => 'uniline',
188 type => 'leaf',
189 },
190 }
191 ]
192 }
193 The "Xorg" example leads to a slightly more complex model with several
195 classes:
196 • "Xorg" (root class)
198 • "Xorg::Device"
200 • "Xorg::Screen"
202 • "Xorg::Screen::Option" for the Screen options
204 • "Xorg::Screen::Display" for the"Display" subsection
206 The root class is declared this way:
208 {
210 name => 'Xorg',
211 element => [
212 Device => {
213 type => 'hash',
214 index_type => 'string'
215 cargo => {
216 type => 'node',
217 config_class_name => 'Xorg::Device'
218 },
219 },
220 Screen => {
221 type => 'hash',
222 index_type => 'string'
223 cargo => {
224 type => 'node',
225 config_class_name => 'Xorg::Screen'
226 },
227 },
228 ]
229 }
230 The"Xorg::Screen" class is:
232 {
234 name => 'Xorg::Screen',
235 element => [
236 Device => {
237 type' => 'leaf',
238 value_type => 'uniline',
239 },
240 Display => {
241 type => 'hash',
242 index_type => 'integer'
243 cargo => {
244 type => 'node',
245 config_class_name => 'Xorg::Screen::Display'
246 },
247 }
248 Option => {
249 type => 'node',
250 config_class_name => 'Xorg::Screen::Option'
251 },
252 ]
253 }
254 It's now time to detail how the elements of a class are constructed.
256
258 To define the required configuration classes, you should read the
259 documentation of the target application to :
260 • Find the structure of the configuration tree
262 • Identify configuration parameters, their constraints and relations
264 Last but not least, you should also find several valid examples of your
266 application configuration. These examples can be used as non-regression
267 tests and to verify that the application documentation was understood.
268
270 Configuration class declaration
271 Since writing the data structure shown below is not fun (even with
272 Perl), you are encouraged to use the model editor provided by cme using
273 "cme meta edit" command (provided by Config::Model::Itself). This
274 commands provides a GUI to create or update your model.
275 When saving, "cme" writes the data structure in the correct directory.
277 Configuration class declaration (the hard way)
279 In summary, configuration documentation is translated in a format
280 usable by Config::Model:
281 • The structure is translated into configuration classes
283 • Configuration parameters are translated into elements
285 • Constraints are translated into element attributes
287 All models files must be written in a specific directory. For instance,
289 for model "Xorg", you must create "./lib/Config/Model/models/Xorg.pl".
290 Other classes like "Xorg::Screen" can be stored in their own file
291 "./lib/Config/Model/models/Xorg/Screen.pl" or included in "Xorg.pl"
292 A model file is a Perl file containing an array for hash ref. Each Hash
294 ref contains a class declaration:
295 [ { name => 'Xorg', ... } , { name => 'Xorg::Screen', ... } ] ;
297 A class can have the following parameters:
299 • name: mandatory name of the class
301 • class_description: Description of the configuration class.
303 • generated_by: Mention with a descriptive string if this class was
305 generated by a program. This parameter is currently reserved for
306 "Config::Model::Itself" model editor.
307 • include: Include element description from another class.
309 For more details, see "Configuration_Model" in Config::Model.
311 For instance:
313 $ cat lib/Config/Model/models/Xorg.pl
315 [
316 {
317 name => 'Xorg',
318 class_description => 'Top level Xorg configuration.',
319 include => [ 'Xorg::ConfigDir'],
320 element => [
321 Files => {
322 type => 'node',
323 description => 'File pathnames',
324 config_class_name => 'Xorg::Files'
325 },
326 # snip
327 ]
328 },
329 {
330 name => 'Xorg::DRI',
331 element => [
332 Mode => {
333 type => 'leaf',
334 value_type => 'uniline',
335 description => 'DRI mode, usually set to 0666'
336 }
337 ]
338 }
339 ];
340 Common attributes for all elements
342 This first set of attributes helps the user by providing guidance (with
343 "level" and "status") and documentation ("summary" and "description").
344 All elements (simple or complex) can have the following attributes:
346 • "description": full length description of the attribute
348 • "summary": one line summary of the above description
350 • "level": is "important", "normal" or "hidden". The level is used to
352 set how configuration data is presented to the user in browsing
353 mode. Important elements are shown to the user no matter what.
354 hidden elements are explained with the warp notion.
355 • "status": is "obsolete", "deprecated" or "standard" (default).
357 Warnings are shown when using a deprecated element and an exception
358 is raised when an obsolete element is used.
359 See "Configuration_class" in Config::Model for details.
361 Leaf elements
363 Leaf element is the most common type to represent configuration data.
364 A leaf element represents a specific configuration parameter.
365 In more details, a leaf element have the following attributes (See
367 "Value_model_declaration" in Config::Model::Value doc):
368 type
370 Set to "leaf" (mandatory)
371 value_type
373 Either "boolean", "integer", "number", "enum", "string", "uniline"
374 (i.e. a string without "\n") (mandatory)
375 min Minimum value (for "integer" or "number")
377 max Maximum value (for "integer" or "number")
379 choice
381 Possible values for an enum
382 mandatory
384 Whether the value is mandatory or not
385 default
387 Default value that must be written in the configuration file
388 upstream_default
390 Default value that is known by the target application and thus does
391 not need to be written in the configuration file.
392 To know which attributes to use, you should read the documentation of
394 the target application.
395 For instance, "AddressFamily" parameter (sshd_config(5)) is specified
397 with: Specifies which address family should be used by sshd(8). Valid
398 arguments are "any", "inet" (use IPv4 only), or "inet6" (use IPv6
399 only). The default is "any".
400 For Config::Model, "AddressFamily" is a type "leaf" element, value_type
402 "enum" and the application falls back to "any" if this parameter is
403 left blank in "sshd_config" file.
404 Thus the model of this element is :
406 AddressFamily => {
408 type => 'leaf',
409 value_type => 'enum',
410 upstream_default => 'any',
411 description => 'Specifies which address family should be used by sshd(8).',
412 choice => [ 'any', 'inet', 'inet6' ]
413 }
414 Simple list or hash element
416 Some configuration parameters are in fact a list or a hash of
417 parameters. For instance, "approx.conf" can feature a list of remote
418 repositories:
419 # remote repositories
421 debian http://ftp.fr.debian.org/debian
422 multimedia http://www.debian-multimedia.org
423 These repositorie URLs must be stored as a hash where the key is debian
425 or multimedia and the associated value is a URL. But this hash must
426 have something which is not explicit in "approx.conf" file: a parameter
427 name. Approx man page mentions that: The name/value pairs [not
428 beginning with '$' are used to map distribution names to remote
429 repositories.. So let's use "distribution" as a parameter name.
430 The example is stored this way in the configuration tree:
432 root
434 |--distribution(debian)=http://ftp.fr.debian.org/debian
435 `--distribution(multimedia)=http://www.debian-multimedia.org
436 The model needs to declare that "distribution" is:
438 • a type "hash" parameter
440 • the hash key is a string
442 • the values of the hash are of type "leaf" and value_type "uniline"
444 distribution => {
446 type => 'hash',
447 index_type => 'string',
448 cargo => {
449 type => 'leaf',
450 value_type => 'uniline',
451 },
452 summary => 'remote repositories',
453 description => 'The other name/value pairs are ...',
454 }
455 For more details on list and hash elements, see hash or list model
457 declaration man page.
458 node element
460 A node element is necessary if the configuration file has more than a
461 list of variable. In this case, the tree is deeper than a rake and a
462 node element if necessary to provide a new node within the tree.
463 In the Xorg example above, the options of "Xorg::Screen" need their own
465 sub-branch in the tree:
466 Screen(Screen0)
468 `--Option
469 |--AllowGLXWithComposite=True
470 `--DynamicTwinView=True
471 For this, a new dedicated class is necessary>Xorg::Screen::Option> (see
473 its declaration above). This new class must be tied to the Screen class
474 with a node element.
475 A node element has the following parameters:
477 • type (set to "node")
479 • the name of the configuration class name (>config_class_name>)
481 So the "Option" node element is declared with:
483 Option => {
485 type => 'node',
486 config_class_name => 'Xorg::Screen::Option'
487 },
488 Hash or list of nodes
490 Some configuration files can feature a set of rather complex
491 configuration entities. For instance "Xorg.pl" can feature several
492 Screen or Device definitions. These definitions are identified by the
493 "Identifier" parameter:
494 Section "Device"
496 Identifier "Device0"
497 Driver "nvidia"
498 BusID "PCI:3:0:1"
499 EndSection
500 Section "Screen"
502 Identifier "Screen0"
503 Device "Device0"
504 DefaultDepth 24
505 EndSection
506 The Xorg configuration tree features 2 elements (Screen and Device)
508 that use the Identifier parameters as hash keys:
509 root
511 |--Device(Device0)
512 | |--Driver=nvidia
513 | `--BusId=PCI:3:0:1
514 `--Screen(Screen0)
515 |--Device=Device0
516 `--DefaultDepth=24
517 And the Xorg model must define these 2 parameters as "hash". The cargo
519 of this hash is of type "node" and refers to 2 different configuration
520 classes, one for "Device" ("Xorg::Device") and one for "Screen"
521 ("Xorg::Screen"):
522 {
524 name => 'Xorg',
525 element => [
526 Device => {
527 type => 'hash',
528 index_type => 'string'
529 cargo => {
530 type => 'node',
531 config_class_name => 'Xorg::Device'
532 },
533 },
534 Screen => {
535 type => 'hash',
536 index_type => 'string'
537 cargo => {
538 type => 'node',
539 config_class_name => 'Xorg::Screen'
540 },
541 },
542 ]
543 }
544
546 Both Perl/Tk and Curses interfaces feature a configuration wizard
547 generated from a configuration model.
548 The wizard works by exploring the configuration tree and stopping on
550 each important element and on each error (mostly missing mandatory
551 parameter).
552 When designing a model, you have to ponder for each element:
554 • The importance level of the parameter (important, normal or
556 hidden). "level" is used to set how configuration data is presented
557 to the user in wizard and browsing mode. Important elements are
558 shown in the wizard. hidden elements are explained with the warp
559 notion in Creating a model with advanced features.
560
562 Once the model is specified, Config::Model can generate a nice user
563 interface, but there's still no way to load or write the configuration
564 file.
565 For Config::Model to read the file, the model designer must declare in
567 the model how to read and write the file (the read/write backend).
568 The read/write functionality is provided by a class inheriting
570 "Config::Model::Backend::Any" class like
571 "Config::Model::Backend::IniFile"
572 The name of the backend parameter must match the backend class name
574 without "Config::Model::Backend". As syntactic sugar, lower case
575 backend name are transformed into upper case to match the backend class
576 name.
577 E.g.
579 Yaml -> Config::Model::Backend::Yaml
581 plain_file -> Config::Model::Backend::PlainFile
582 ini_file -> Config::Model::Backend::IniFile
583 With the backend name, the following parameters must be defined:
585 config_dir
587 The configuration directory
588 file
590 Config file name (optional). defaults to
591 "<config_class_name>.[pl|ini|cds]"
592 rw_config => { backend => 'ini_file' ,
594 config_dir => '/etc/cfg_dir',
595 file => 'cfg_file.ini',
596 },
597 See Config::Model::Backend::IniFile for details
599 Note that these parameters can also be set with the graphical
601 configuration model editor ("cme meta edit").
602 "rw_config" can also have custom parameters that are passed verbatim to
604 "Config::Model::Backend::Foo" methods:
605 rw_config => {
607 backend => 'my_backend',
608 config_dir => '/etc/cfg_dir',
609 my_param => 'my_value',
610 }
611 This "Config::Model::Backend::MyBackend" class is expected to inherit
613 Config::Model::Backend::Any and provide the following methods:
614 new
616 read
617 write
618 Their signatures are explained in Config::Model::BackendMgr doc on
620 plugin backends
621
623 • More complex models: Config::Model::Manual::ModelCreationAdvanced
624 • Config::Model::Manual::ModelForUpgrade: Writing a model for
626 configuration upgrades
627 • Configuration upgrades within Debian packages
629 <http://wiki.debian.org/PackageConfigUpgrade>
630
632 Feel free to send comments and suggestion about this page at
633 config-model-users at lists dot sourceforge dot net.
635
637 Dominique Dumont <ddumont at cpan.org>
638
640 Dominique Dumont
641
643 This software is Copyright (c) 2005-2021 by Dominique Dumont.
644 This is free software, licensed under:
646 The GNU Lesser General Public License, Version 2.1, February 1999
648perl v5.34.0 Config:2:0M2o1d-e0l7:-:2M2anual::ModelCreationIntroduction(3)