summaryrefslogtreecommitdiffstats
path: root/documentation/poky-ref-manual/ref-classes.xml
blob: d1b919f9b38f6785254275bb729f01c178eb34a2 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
<!DOCTYPE appendix PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >

<appendix id='ref-classes'>
<title>Reference: Classes</title>

<para>
    Class files are used to abstract common functionality and share it amongst multiple 
    <filename>.bb</filename> files. 
    Any metadata usually found in a <filename>.bb</filename> file can also be placed in a class 
    file. 
    Class files are identified by the extension <filename>.bbclass</filename> and are usually placed 
    in a <filename>classes/</filename> directory beneath the 
    <filename>meta*/</filename> directory found in the 
    <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>source directory</ulink>.
    Class files can also be pointed to by BUILDDIR (e.g. <filename>build/</filename>)in the same way as
    <filename>.conf</filename> files in the <filename>conf</filename> directory. 
    Class files are searched for in <link linkend='var-BBPATH'><filename>BBPATH</filename></link>
    using the same method by which <filename>.conf</filename> files are searched.
</para>

<para>
    In most cases inheriting the class is enough to enable its features, although 
    for some classes you might need to set variables or override some of the 
    default behaviour.
</para>

<section id='ref-classes-base'>
    <title>The base class - <filename>base.bbclass</filename></title>

    <para>
        The base class is special in that every <filename>.bb</filename> 
        file inherits it automatically. 
        This class contains definitions for standard basic 
        tasks such as fetching, unpacking, configuring (empty by default), compiling 
        (runs any <filename>Makefile</filename> present), installing (empty by default) and packaging 
        (empty by default). 
        These classes are often overridden or extended by other classes 
        such as <filename>autotools.bbclass</filename> or <filename>package.bbclass</filename>. 
        The class also contains some commonly used functions such as <filename>oe_runmake</filename>.
    </para>
</section>

<section id='ref-classes-autotools'>
    <title>Autotooled Packages - <filename>autotools.bbclass</filename></title>

    <para>
        Autotools (<filename>autoconf</filename>, <filename>automake</filename>, 
        and <filename>libtool</filename>) bring standardization. 
        This class defines a set of tasks (configure, compile etc.) that 
        work for all Autotooled packages.  
        It should usually be enough to define a few standard variables 
        and then simply <filename>inherit autotools</filename>.
        This class can also work with software that emulates Autotools.
        For more information, see the  
        "<ulink url='&YOCTO_DOCS_DEV_URL;#usingpoky-extend-addpkg-autotools'>Autotooled Package</ulink>"
        section in the Yocto Project Development Manual.
    </para>

    <para>
        It's useful to have some idea of how the tasks defined by this class work
        and what they do behind the scenes.
        <itemizedlist>
            <listitem><para><filename>do_configure</filename> &dash; regenerates the 
                configure script (using <filename>autoreconf</filename>) and then launches it 
                with a standard set of arguments used during cross-compilation. 
                You can pass additional parameters to <filename>configure</filename> through the 
                <filename><link linkend='var-EXTRA_OECONF'>EXTRA_OECONF</link></filename> variable.
                </para></listitem>
            <listitem><para><filename>do_compile</filename> &dash; runs <filename>make</filename> with 
                arguments that specify the compiler and linker. 
                You can pass additional arguments through 
                the <filename><link linkend='var-EXTRA_OEMAKE'>EXTRA_OEMAKE</link></filename> variable.
                </para></listitem>
            <listitem><para><filename>do_install</filename> &dash; runs <filename>make install</filename> 
                and passes a DESTDIR option, which takes its value from the standard 
                <filename><link linkend='var-DESTDIR'>DESTDIR</link></filename> variable.
                </para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-update-alternatives'>
    <title>Alternatives - <filename>update-alternatives.bbclass</filename></title>

    <para>
        Several programs can fulfill the same or similar function and be installed with the same name. 
        For example, the <filename>ar</filename> command is available from the 
        <filename>busybox</filename>, <filename>binutils</filename> and 
        <filename>elfutils</filename> packages. 
        The <filename>update-alternatives.bbclass</filename> class handles renaming the 
        binaries so that multiple packages can be installed without conflicts. 
        The <filename>ar</filename> command still works regardless of which packages are installed
        or subsequently removed. 
        The class renames the conflicting binary in each package and symlinks the highest 
        priority binary during installation or removal of packages.
    </para>
    <para>
        Four variables control this class:
        <itemizedlist>
            <listitem><para><filename>ALTERNATIVE_NAME</filename> &dash; The name of the 
                binary that is replaced (<filename>ar</filename> in this example).</para></listitem>
            <listitem><para><filename>ALTERNATIVE_LINK</filename> &dash; The path to 
                the resulting binary (<filename>/bin/ar</filename> in this example).</para></listitem>
            <listitem><para><filename>ALTERNATIVE_PATH</filename> &dash; The path to the 
                real binary (<filename>/usr/bin/ar.binutils</filename> in this example).</para></listitem>
            <listitem><para><filename>ALTERNATIVE_PRIORITY</filename> &dash; The priority of 
                the binary. 
                The version with the most features should have the highest priority.</para></listitem>
        </itemizedlist>
    </para>

    <para>
	Currently, the OpenEmbedded build system supports only one binary per package.
    </para>
</section>

<section id='ref-classes-update-rc.d'>
    <title>Initscripts - <filename>update-rc.d.bbclass</filename></title>

    <para>
        This class uses <filename>update-rc.d</filename> to safely install an 
        initialization script on behalf of the package. 
        The OpenEmbedded build system takes care of details such as making sure the script is stopped before 
        a package is removed and started when the package is installed. 
        Three variables control this class: 
        <filename><link linkend='var-INITSCRIPT_PACKAGES'>INITSCRIPT_PACKAGES</link></filename>, 
        <filename><link linkend='var-INITSCRIPT_NAME'>INITSCRIPT_NAME</link></filename> and
        <filename><link linkend='var-INITSCRIPT_PARAMS'>INITSCRIPT_PARAMS</link></filename>.
        See the variable links for details.
    </para>
</section>

<section id='ref-classes-binconfig'>
    <title>Binary config scripts - <filename>binconfig.bbclass</filename></title>

    <para>
        Before <filename>pkg-config</filename> had become widespread, libraries shipped shell
        scripts to give information about the libraries and include paths needed 
        to build software (usually named <filename>LIBNAME-config</filename>).
        This class assists any recipe using such scripts.
    </para>

    <para>
        During staging, BitBake installs such scripts into the
        <filename>sysroots/</filename> directory. 
        BitBake also changes all paths to point into the <filename>sysroots/</filename>
        directory so all builds that use the script will use the correct 
        directories for the cross compiling layout.
    </para>
</section>

<section id='ref-classes-debian'>
    <title>Debian renaming - <filename>debian.bbclass</filename></title>

    <para>
        This class renames packages so that they follow the Debian naming
        policy (i.e. <filename>eglibc</filename> becomes <filename>libc6</filename>
        and <filename>eglibc-devel</filename> becomes <filename>libc6-dev</filename>.
    </para>
</section>

<section id='ref-classes-pkgconfig'>
    <title>Pkg-config - <filename>pkgconfig.bbclass</filename></title>

    <para>
        <filename>pkg-config</filename> brought standardization and this class aims to make its
        integration smooth for all libraries that make use of it.
    </para>

    <para>
        During staging, BitBake installs <filename>pkg-config</filename> data into the
        <filename>sysroots/</filename> directory. 
        By making use of sysroot functionality within <filename>pkg-config</filename>,
        this class no longer has to manipulate the files.
    </para>
</section>

<section id='ref-classes-src-distribute'>
    <title>Distribution of sources - <filename>src_distribute_local.bbclass</filename></title>

    <para>
        Many software licenses require that source files be provided along with the binaries.
        To simplify this process, two classes were created:
        <filename>src_distribute.bbclass</filename> and 
        <filename>src_distribute_local.bbclass</filename>.
    </para>

    <para>
        The results of these classes are <filename>tmp/deploy/source/</filename> 
        subdirs with sources sorted by 
        <filename><link linkend='var-LICENSE'>LICENSE</link></filename> field. 
        If recipes list few licenses (or have entries like "Bitstream Vera"),
        the source archive is placed in each license directory.
    </para>

    <para>
        This class operates using three modes:
        <itemizedlist>
            <listitem><para><emphasis>copy:</emphasis> Copies the files to the 
                distribute directory.</para></listitem>
            <listitem><para><emphasis>symlink:</emphasis> Symlinks the files to the 
                distribute directory.</para></listitem>
            <listitem><para><emphasis>move+symlink:</emphasis> Moves the files into 
                the distribute directory and then symlinks them back.</para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-perl'>
    <title>Perl modules - <filename>cpan.bbclass</filename></title>

    <para>
        Recipes for Perl modules are simple.
        These recipes usually only need to point to the source's archive and then inherit the 
        proper <filename>.bbclass</filename> file.
        Building is split into two methods depending on which method the module authors used.
    </para>
    
    <para>
        Modules that use old <filename>Makefile.PL</filename>-based build system require
        <filename>cpan.bbclass</filename> in their recipes.
    </para>

    <para>
        Modules that use <filename>Build.PL</filename>-based build system require
        using <filename>cpan_build.bbclass</filename> in their recipes.
    </para>
</section>

<section id='ref-classes-distutils'>
    <title>Python extensions - <filename>distutils.bbclass</filename></title>

    <para>
        Recipes for Python extensions are simple.
        These recipes usually only need to point to the source's archive and then inherit
        the proper <filename>.bbclass</filename> file.
        Building is split into two methods dependling on which method the module authors used.
    </para>

    <para>
        Extensions that use an Autotools-based build system require Autotools and 
        <filename>distutils</filename>-based <filename>.bbclasse</filename> files in their recipes.
    </para>

    <para>
        Extensions that use <filename>distutils</filename>-based build systems require 
        <filename>distutils.bbclass</filename> in their recipes.
    </para>
</section>

<section id='ref-classes-devshell'>
    <title>Developer Shell - <filename>devshell.bbclass</filename></title>

    <para>
        This class adds the <filename>devshell</filename> task. 
        Distribution policy dictates whether to include this class.
        See the 
        "<ulink url='&YOCTO_DOCS_DEV_URL;#platdev-appdev-devshell'>Using a Development Shell</ulink>" section 
        in the Yocto Project Development Manual for more information about using <filename>devshell</filename>.
    </para>
</section>

<section id='ref-classes-package'>
    <title>Packaging - <filename>package*.bbclass</filename></title>

    <para>
        The packaging classes add support for generating packages from a build's
        output. 
        The core generic functionality is in <filename>package.bbclass</filename>.
        The code specific to particular package types is contained in various sub-classes such as
        <filename>package_deb.bbclass</filename>, <filename>package_ipk.bbclass</filename>,
        and <filename>package_rpm.bbclass</filename>. 
        Most users will want one or more of these classes.
    </para>
 
    <para>
        You can control the list of resulting package formats by using the 
        <filename><link linkend='var-PACKAGE_CLASSES'>PACKAGE_CLASSES</link></filename> 
        variable defined in the <filename>local.conf</filename> configuration file, 
        which is located in the <filename>conf</filename> folder of the 
        <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>source directory</ulink>. 
        When defining the variable, you can specify one or more package types.
        Since images are generated from packages, a packaging class is 
        needed to enable image generation.
        The first class listed in this variable is used for image generation. 
    </para>

    <para>
        The package class you choose can affect build-time performance and has space
        ramifications.
        In general, building a package with RPM takes about thirty percent more time as 
        compared to using IPK to build the same or similar package.
        This comparison takes into account a complete build of the package with all 
        dependencies previously built.
        The reason for this discrepancy is because the RPM package manager creates and 
        processes more metadata than the IPK package manager.
        Consequently, you might consider setting <filename>PACKAGE_CLASSES</filename>
        to "package_ipk" if you are building smaller systems.
    </para>

    <para>
        Keep in mind, however, that RPM starts to provide more abilities than IPK due to 
        the fact that it processes more metadata.
        For example, this information includes individual file types, file checksum generation
        and evaluation on install, sparse file support, conflict detection and resolution
        for multilib systems, ACID style upgrade, and repackaging abilities for rollbacks.
    </para>

    <para>
        Another consideration for packages built using the RPM package manager is space.
        For smaller systems, the extra space used for the Berkley Database and the amount 
        of metadata can affect your ability to do on-device upgrades.
    </para>

    <para>
        You can find additional information on the effects of the package class at these 
        two Yocto Project mailing list links:
        <itemizedlist>
            <listitem><para><ulink url='&YOCTO_LISTS_URL;/pipermail/poky/2011-May/006362.html'>
                https://lists.yoctoproject.org/pipermail/poky/2011-May/006362.html</ulink></para></listitem>
            <listitem><para><ulink url='&YOCTO_LISTS_URL;/pipermail/poky/2011-May/006363.html'>
                https://lists.yoctoproject.org/pipermail/poky/2011-May/006363.html</ulink></para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-kernel'>
    <title>Building kernels - <filename>kernel.bbclass</filename></title>

    <para>
        This class handles building Linux kernels. 
        The class contains code to build all kernel trees. 
        All needed headers are staged into the
        <filename><link linkend='var-STAGING_KERNEL_DIR'>STAGING_KERNEL_DIR</link></filename>
        directory to allow out-of-tree module builds using <filename>module.bbclass</filename>.
    </para>

    <para>
        This means that each built kernel module is packaged separately and inter-module 
        dependencies are created by parsing the <filename>modinfo</filename> output. 
        If all modules are required, then installing the <filename>kernel-modules</filename>
        package installs all packages with modules and various other kernel packages 
        such as <filename>kernel-vmlinux</filename>.
    </para>

    <para>
        Various other classes are used by the kernel and module classes internally including 
        <filename>kernel-arch.bbclass</filename>, <filename>module_strip.bbclass</filename>, 
        <filename>module-base.bbclass</filename>, and <filename>linux-kernel-base.bbclass</filename>.
    </para>
</section>

<section id='ref-classes-image'>
    <title>Creating images - <filename>image.bbclass</filename> and <filename>rootfs*.bbclass</filename></title>

    <para>
        These classes add support for creating images in several formats. 
        First, the root filesystem is created from packages using
        one of the <filename>rootfs_*.bbclass</filename> 
        files (depending on the package format used) and then the image is created.
    </para>

    <para>
        The <filename><link linkend='var-IMAGE_FSTYPES'>IMAGE_FSTYPES</link></filename>
        variable controls the types of images to generate.
    </para>

    <para>        
        The <filename><link linkend='var-IMAGE_INSTALL'>IMAGE_INSTALL</link></filename>
        variable controls the list of packages to install into the image.
    </para>
</section>

<section id='ref-classes-sanity'>
    <title>Host System sanity checks - <filename>sanity.bbclass</filename></title>

    <para>
        This class checks to see if prerequisite software is present so that 
        users can be notified of potential problems that might affect their build. 
        The class also performs basic user configuration checks from 
        the <filename>local.conf</filename> configuration file to
        prevent common mistakes that cause build failures. 
        Distribution policy usually determines whether to include this class.
    </para>
</section>

<section id='ref-classes-insane'>
    <title>Generated output quality assurance checks - <filename>insane.bbclass</filename></title>

    <para>
        This class adds a step to the package generation process that sanity checks the
        packages generated by the OpenEmbedded build system.
        A range of checks are performed that check the build's output
        for common problems that show up during runtime.
        Distribution policy usually dictates whether to include this class.
    </para>

    <para>
        You can configure the sanity checks so that specific test failures either raise a warning or 
        an error message.  
        Typically, failures for new tests generate a warning.
        Subsequent failures for the same test would then generate an error message 
        once the metadata is in a known and good condition.
        You use the <filename>WARN_QA</filename> variable to specify tests for which you 
        want to generate a warning message on failure.
        You use the <filename>ERROR_QA</filename> variable to specify tests for which you 
        want to generate an error message on failure.
    </para>

    <para>
        The following list shows the tests you can list with the <filename>WARN_QA</filename>
        and <filename>ERROR_QA</filename> variables:
        <itemizedlist>
            <listitem><para><emphasis><filename>ldflags:</filename></emphasis>
                Ensures that the binaries were linked with the 
                <filename>LDFLAGS</filename> options provided by the build system. 
                If this test fails, check that the <filename>LDFLAGS</filename> variable
                is being passed to the linker command.</para></listitem>
            <listitem><para><emphasis><filename>useless-rpaths:</filename></emphasis>
                Checks for dynamic library load paths (rpaths) in the binaries that 
                by default on a standard system are searched by the linker (e.g.
                <filename>/lib</filename> and <filename>/usr/lib</filename>). 
                While these paths will not cause any breakage, they do waste space and 
                are unnecessary.</para></listitem>
            <listitem><para><emphasis><filename>rpaths:</filename></emphasis>
                Checks for rpaths in the binaries that contain build system paths such
                as <filename>TMPDIR</filename>.
                If this test fails, bad <filename>-rpath</filename> options are being 
                passed to the linker commands and your binaries have potential security 
                issues.</para></listitem>
            <listitem><para><emphasis><filename>dev-so:</filename></emphasis>
                Checks that the <filename>.so</filename> symbolic links are in the 
                <filename>-dev</filename> package and not in any of the other packages. 
                In general, these symlinks are only useful for development purposes.
                Thus, the <filename>-dev</filename> package is the correct location for
                them. 
                Some very rare cases do exist for dynamically loaded modules where 
                these symlinks are needed instead in the main package.
                </para></listitem>
            <listitem><para><emphasis><filename>debug-files:</filename></emphasis>
                Checks for <filename>.debug</filename> directories in anything but the 
                <filename>-dbg</filename> package. 
                The debug files should all be in the <filename>-dbg</filename> package.
                Thus, anything packaged elsewhere is incorrect packaging.</para></listitem>
            <listitem><para><emphasis><filename>arch:</filename></emphasis>
                Checks the Executable and Linkable Format (ELF) type, bit size and endianness 
                of any binaries to ensure it matches the target architecture. 
                This test fails if any binaries don't match the type since there would be an 
                incompatibility. 
                Sometimes software, like bootloaders, might need to bypass this check.
                </para></listitem>
            <listitem><para><emphasis><filename>debug-deps:</filename></emphasis>
                Checks that <filename>-dbg</filename> packages only depend on other
                <filename>-dbg</filename> packages and not on any other types of packages,
                which would cause a packaging bug.</para></listitem>
            <listitem><para><emphasis><filename>dev-deps:</filename></emphasis>
                Checks that <filename>-dev</filename> packages only depend on other 
                <filename>-dev</filename> packages and not on any other types of packages,
                which would be a packaging bug.</para></listitem>
            <listitem><para><emphasis><filename>pkgconfig:</filename></emphasis>
                Checks <filename>.pc</filename> files for any 
                <filename>TMPDIR/WORKDIR</filename> paths. 
                Any <filename>.pc</filename> file containing these paths is incorrect 
                since <filename>pkg-config</filename> itself adds the correct sysroot prefix 
                when the files are accessed.</para></listitem>
            <listitem><para><emphasis><filename>la:</filename></emphasis>
                Checks <filename>.la</filename> files for any <filename>TMPDIR</filename>
                paths. 
                Any <filename>.la</filename> file continaing these paths is incorrect since 
                <filename>libtool</filename> adds the correct sysroot prefix when using the 
                files automatically itself.</para></listitem>
            <listitem><para><emphasis><filename>desktop:</filename></emphasis>
                Runs the <filename>desktop-file-validate</filename> program against any 
                <filename>.desktop</filename> files to validate their contents against 
                the specification for <filename>.desktop</filename> files.</para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-siteinfo'>
    <title>Autotools configuration data cache - <filename>siteinfo.bbclass</filename></title>

    <para>
        Autotools can require tests that must execute on the target hardware.
        Since this is not possible in general when cross compiling, site information is
        used to provide cached test results so these tests can be skipped over but
        still make the correct values available.
        The <filename><link linkend='structure-meta-site'>meta/site directory</link></filename>
        contains test results sorted into different categories such as architecture, endianness, and
        the <filename>libc</filename> used. 
        Site information provides a list of files containing data relevant to 
        the current build in the 
        <filename><link linkend='var-CONFIG_SITE'>CONFIG_SITE</link></filename> variable 
        that Autotools automatically picks up.
    </para>

    <para>
        The class also provides variables like 
        <filename><link linkend='var-SITEINFO_ENDIANNESS'>SITEINFO_ENDIANNESS</link></filename> 
        and <filename><link linkend='var-SITEINFO_BITS'>SITEINFO_BITS</link></filename> 
        that can be used elsewhere in the metadata.
    </para>

    <para>
        Because this class is included from <filename>base.bbclass</filename>, it is always active.
    </para>
</section>

<section id='ref-classes-useradd'>
    <title>Adding Users - <filename>useradd.bbclass</filename></title>

    <para>
        If you have packages that install files that are owned by custom users or groups, 
        you can use this class to specify those packages and associate the users and groups
        with those packages.
        The <filename>meta-skeleton/recipes-skeleton/useradd/useradd-example.bb</filename> 
        recipe in the <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>source directory</ulink>
        provides a simple exmample that shows how to add three 
        users and groups to two packages.
        See the <filename>useradd-example.bb</filename> for more information on how to 
        use this class.
    </para>
</section>

<section id='ref-classes-externalsrc'>
    <title>Using External Source - <filename>externalsrc.bbclass</filename></title>

    <para>
        You can use this class to build software from source code that is external to the 
        OpenEmbedded build system.  
        In other words, your source code resides in an external tree outside of the Yocto Project.
        Building software from an external source tree means that the normal fetch, unpack, and 
        patch process is not used.
    </para>

    <para>
        To use the class, you need to define the 
        <link linkend='var-S'><filename>S</filename></link> variable to point to the directory that contains the source files. 
        You also need to have your recipe inherit the <filename>externalsrc.bbclass</filename> class.
    </para>

    <para>
        This class expects the source code to support recipe builds that use the 
        <link linkend='var-B'><filename>B</filename></link> variable to point to the directory in 
        which the OpenEmbedded build system places the generated objects built from the recipes.
        By default, the <filename>B</filename> directory is set to the following, which is separate from the 
        source directory (<filename>S</filename>):
        <literallayout class='monospaced'>
     ${WORKDIR}/${BPN}-{PV}/
        </literallayout>
        See the glossary entries for the
        <link linkend='var-WORKDIR'><filename>WORKDIR</filename></link>, 
        <link linkend='var-BPN'><filename>BPN</filename></link>, 
        <link linkend='var-PV'><filename>PV</filename></link>,
        <link linkend='var-S'><filename>S</filename></link>, and 
        <link linkend='var-B'><filename>B</filename></link> for more information.
    </para>

    <para>
        You can build object files in the external tree by setting the
        <filename>B</filename> variable equal to <filename>"${S}"</filename>.
        However, this practice does not work well if you use the source for more than one variant
        (i.e., "natives" such as <filename>quilt-native</filename>, 
        or "crosses" such as <filename>gcc-cross</filename>).
        So, be sure there are no "native", "cross", or "multilib" variants of the recipe.
    </para>

    <para>
        If you do want to build different variants of a recipe, you can use the 
        <link linkend='var-BBCLASSEXTEND'><filename>BBCLASSEXTEND</filename></link> variable. 
        When you do, the <link linkend='var-B'><filename>B</filename></link> variable must support the 
        recipe's ability to build variants in different working directories.
        Most autotools-based recipes support separating these directories.
        The OpenEmbedded build system defaults to using separate directories for <filename>gcc</filename>
        and some kernel recipes.
        Alternatively, you can make sure that separate recipes exist that each 
        use the <filename>BBCLASSEXTEND</filename> variable to build each variant.
        The separate recipes can inherit a single target recipe.
    </para>

    <para>
        For information on how to use this class, see the 
        "<ulink url='&YOCTO_DOCS_DEV_URL;#building-software-from-an-external-source'>Building
        Software from an External Source</ulink>" section in the Yocto Project Development Manual.
    </para>
</section>

<section id='ref-classes-others'>
    <title>Other Classes</title>

    <para>
        Thus far, this appendix has discussed only the most useful and important 
        classes.
        However, other classes exist within the <filename>meta/classes</filename> directory 
        in the <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>source directory</ulink>.
        You can examine the <filename>.bbclass</filename> files directly for more 
        information. 
    </para>
</section>

<!-- Undocumented classes are:
        allarch.bbclass
        binconfig.bbclass
        bootimg.bbclass
        buildstats.bbclass
        ccache.inc
        cmake.bbclass
        cml1.bbclass
        cross.bbclass
        cross-canadian.bbclass
        deploy.bbclass
        distrodata.bbclass
        gconf.bbclass
        gettext.bbclass
        gnome.bbclass
        gtk-doc.bbclass
        gtk-icon-cache.bbclass
        icecc.bbclass
        image-mklibs.bbclass
        image-prelink.bbclass
        image-swab.bbclass
        imagetest-dummy.bbclass
        imagetest-qemu.bbclass
        insserv.bbclass
        lib_package.bbclass
        license.bbclass
        logging.bbclass
        meta.bbclass
        metadata_scm.bbclass
        mirrors.bbclass
        multilib*.bbclass
        native.bbclass
        nativesdk.bbclass
        oelint.bbclass
        own-mirrors.bbclass
        packagedata.bbclass
        packagehistory.bbclass
        patch.bbclass
        perlnative.bbclass
        pkg_distribute.bbclass
        pkg_metainfo.bbclass
        populate_sdk*.bbclass
        prserv.bbclass
        python-dir.bbclass
        qemu.bbclass
        qmake*.bbclass
        qt4*.bbclass
        recipe_sanity.bbclass
        relocatable.bbclass
        rm_work.bbclass
        scons.bbclass
        sdl.bbclass
        setuptools.bbclass
        sip.bbclass
        siteconfig.bbclass
        sourcepkg.bbclass
        sstate.bbclass
        staging.bbclass
        syslinux.bbclass
        task.bbclass
        terminal.bbclass
        tinderclient.bbclass
        toolchain-scripts.bbclass
        typecheck.bbclass
        utility-tasks.bbclass
        utils.bbclass
-->


</appendix>
<!-- 
vim: expandtab tw=80 ts=4 
-->