summaryrefslogtreecommitdiffstats
path: root/documentation/dev-manual/dev-manual-newbie.xml
blob: 7c21379b991b0e609bfba1db578067f97cbcf9d6 (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
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
<!DOCTYPE chapter 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; ] >

<chapter id='dev-manual-newbie'>

<title>The Yocto Project Open Source Development Environment</title>

<para>
    This chapter helps you understand the Yocto Project as an open source development project.
    In general, working in an open source environment is very different from working in a
    closed, proprietary environment.
    Additionally, the Yocto Project uses specific tools and constructs as part of its development
    environment.
    This chapter specifically addresses open source philosophy, licensing issues, code repositories,
    the open source distributed version control system Git, and best practices using the Yocto Project.
</para>

<section id='open-source-philosophy'>
    <title>Open Source Philosophy</title>

    <para>
        Open source philosophy is characterized by software development directed by peer production
        and collaboration through an active community of developers.
        Contrast this to the more standard centralized development models used by commercial software
        companies where a finite set of developers produces a product for sale using a defined set
        of procedures that ultimately result in an end product whose architecture and source material
        are closed to the public.
    </para>

    <para>
        Open source projects conceptually have differing concurrent agendas, approaches, and production.
        These facets of the development process can come from anyone in the public (community) that has a
        stake in the software project.
        The open source environment contains new copyright, licensing, domain, and consumer issues
        that differ from the more traditional development environment.
        In an open source environment, the end product, source material, and documentation are
        all available to the public at no cost.
    </para>

    <para>
        A benchmark example of an open source project is the Linux Kernel, which was initially conceived
        and created by Finnish computer science student Linus Torvalds in 1991.
        Conversely, a good example of a non-open source project is the
        <trademark class='registered'>Windows</trademark> family of operating
        systems developed by <trademark class='registered'>Microsoft</trademark> Corporation.
    </para>

    <para>
        Wikipedia has a good historical description of the Open Source Philosophy
        <ulink url='http://en.wikipedia.org/wiki/Open_source'>here</ulink>.
        You can also find helpful information on how to participate in the Linux Community
        <ulink url='http://ldn.linuxfoundation.org/book/how-participate-linux-community'>here</ulink>.
    </para>
</section>

<section id="usingpoky-changes-collaborate">
    <title>Using the Yocto Project in a Team Environment</title>

    <para>
        It might not be immediately clear how you can use the Yocto Project in a team environment,
        or scale it for a large team of developers.
        The specifics of any situation determine the best solution.
        Granted that the Yocto Project offers immense flexibility regarding this, practices do exist
        that experience has shown work well.
    </para>

    <para>
        The core component of any development effort with the Yocto Project is often an
        automated build and testing framework along with an image generation process.
        You can use these core components to check that the metadata can be built,
        highlight when commits break the build, and provide up-to-date images that
        allow developers to test the end result and use it as a base platform for further
        development.
        Experience shows that buildbot is a good fit for this role.
        What works well is to configure buildbot to make two types of builds:
        incremental and full (from scratch).
        See "<ulink url='http://autobuilder.yoctoproject.org:8010/'>Welcome to the buildbot for the Yocto Project</ulink>"
        for an example implementation that uses buildbot.
    </para>

    <para>
        You can tie an incremental build to a commit hook that triggers the build
        each time a commit is made to the metadata.
        This practice results in useful acid tests that determine whether a given commit
        breaks the build in some serious way.
        Associating a build to a commit can catch a lot of simple errors.
        Furthermore, the tests are fast so developers can get quick feedback on changes.
    </para>

    <para>
        Full builds build and test everything from the ground up.
        These types of builds usually happen at predetermined times like during the
        night when the machine load is low.
    </para>

    <para>
        Most teams have many pieces of software undergoing active development at any given time.
        You can derive large benefits by putting these pieces under the control of a source
        control system that is compatible (i.e. Git or Subversion (SVN)) with the OpenEmbedded
        build system that the Yocto Project uses.
        You can then set the autobuilder to pull the latest revisions of the packages
        and test the latest commits by the builds.
        This practice quickly highlights issues.
        The build system easily supports testing configurations that use both a
        stable known good revision and a floating revision.
        The build system can also take just the changes from specific source control branches.
        This capability allows you to track and test specific changes.
    </para>

    <para>
        Perhaps the hardest part of setting this up is defining the software project or
        the metadata policies that surround the different source control systems.
        Of course circumstances will be different in each case.
        However, this situation reveals one of the Yocto Project's advantages -
        the system itself does not
        force any particular policy on users, unlike a lot of build systems.
        The system allows the best policies to be chosen for the given circumstances.
    </para>

    <para>
        In general, best practices exist that make your work with the Yocto
        Project easier in a team environment.
        This list presents some of these practices you might consider following.
        Of course, you need to understand that you do not have to follow these
        practices and your setup can be totally controlled and customized by
        your team:
        <itemizedlist>
            <listitem><para>Use <link linkend='git'>Git</link>
                as the source control system.</para></listitem>
            <listitem><para>Maintain your metadata in layers that make sense
                for your situation.
                See the "<link linkend='understanding-and-creating-layers'>Understanding
                and Creating Layers</link>" section for more information on
                layers.</para></listitem>
            <listitem><para>Separate the project's metadata and code by using
                separate Git repositories.
                See the "<link linkend='yocto-project-repositories'>Yocto Project
                Source Repositories</link>" section for information on these
                repositories.
                See the "<link linkend='getting-setup'>Getting Set Up</link>" section
                for information on how to set up various Yocto Project related
                Git repositories.</para></listitem>
            <listitem><para>Set up the directory for the shared state cache
                (<ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_DIR'><filename>SSTATE_DIR</filename></ulink>)
                where they make sense.
                For example, set up the sstate cache for developers using the
                same office and share source directories on the developer's
                machines.</para></listitem>
            <listitem><para>Set up an autobuilder and have it populate the
                sstate cache and source directories.</para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='yocto-project-repositories'>
    <title>Yocto Project Source Repositories</title>

    <para>
        The Yocto Project team maintains complete source repositories for all Yocto Project files
        at <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi'></ulink>.
        This web-based source code browser is organized into categories by function such as
        IDE Plugins, Matchbox, Poky, Yocto Linux Kernel, and so forth.
        From the interface, you can click on any particular item in the "Name" column and
        see the URL at the bottom of the page that you need to set up a Git repository for
        that particular item.
        Having a local Git repository of the Source Directory (poky) allows you to
        make changes, contribute to the history, and ultimately enhance the Yocto Project's
        tools, Board Support Packages, and so forth.
    </para>

    <para>
        Conversely, if you are a developer that is not interested in contributing back to the
        Yocto Project, you have the ability to simply download and extract release tarballs
        and use them within the Yocto Project environment.
        All that is required is a particular release of the Yocto Project and
        your application source code.
    </para>

    <para>
<!DOCTYPE chapter 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; ] >

<chapter id='dev-manual-newbie'>

<title>The Yocto Project Open Source Development Environment</title>

<para>
    This chapter helps you understand the Yocto Project as an open source development project.
    In general, working in an open source environment is very different from working in a
    closed, proprietary environment.
    Additionally, the Yocto Project uses specific tools and constructs as part of its development
    environment.
    This chapter specifically addresses open source philosophy, licensing issues, code repositories,
    the open source distributed version control system Git, and best practices using the Yocto Project.
</para>

<section id='open-source-philosophy'>
    <title>Open Source Philosophy</title>

    <para>
        Open source philosophy is characterized by software development directed by peer production
        and collaboration through an active community of developers.
        Contrast this to the more standard centralized development models used by commercial software
        companies where a finite set of developers produces a product for sale using a defined set
        of procedures that ultimately result in an end product whose architecture and source material
        are closed to the public.
    </para>

    <para>
        Open source projects conceptually have differing concurrent agendas, approaches, and production.
        These facets of the development process can come from anyone in the public (community) that has a
        stake in the software project.
        The open source environment contains new copyright, licensing, domain, and consumer issues
        that differ from the more traditional development environment.
        In an open source environment, the end product, source material, and documentation are
        all available to the public at no cost.
    </para>

    <para>
        A benchmark example of an open source project is the Linux Kernel, which was initially conceived
        and created by Finnish computer science student Linus Torvalds in 1991.
        Conversely, a good example of a non-open source project is the
        <trademark class='registered'>Windows</trademark> family of operating
        systems developed by <trademark class='registered'>Microsoft</trademark> Corporation.
    </para>

    <para>
        Wikipedia has a good historical description of the Open Source Philosophy
        <ulink url='http://en.wikipedia.org/wiki/Open_source'>here</ulink>.
        You can also find helpful information on how to participate in the Linux Community
        <ulink url='http://ldn.linuxfoundation.org/book/how-participate-linux-community'>here</ulink>.
    </para>
</section>

<section id="usingpoky-changes-collaborate">
    <title>Using the Yocto Project in a Team Environment</title>

    <para>
        It might not be immediately clear how you can use the Yocto Project in a team environment,
        or scale it for a large team of developers.
        The specifics of any situation determine the best solution.
        Granted that the Yocto Project offers immense flexibility regarding this, practices do exist
        that experience has shown work well.
    </para>

    <para>
        The core component of any development effort with the Yocto Project is often an
        automated build and testing framework along with an image generation process.
        You can use these core components to check that the metadata can be built,
        highlight when commits break the build, and provide up-to-date images that
        allow developers to test the end result and use it as a base platform for further
        development.
        Experience shows that buildbot is a good fit for this role.
        What works well is to configure buildbot to make two types of builds:
        incremental and full (from scratch).
        See "<ulink url='http://autobuilder.yoctoproject.org:8010/'>Welcome to the buildbot for the Yocto Project</ulink>"
        for an example implementation that uses buildbot.
    </para>

    <para>
        You can tie an incremental build to a commit hook that triggers the build
        each time a commit is made to the metadata.
        This practice results in useful acid tests that determine whether a given commit
        breaks the build in some serious way.
        Associating a build to a commit can catch a lot of simple errors.
        Furthermore, the tests are fast so developers can get quick feedback on changes.
    </para>

    <para>
        Full builds build and test everything from the ground up.
        These types of builds usually happen at predetermined times like during the
        night when the machine load is low.
    </para>

    <para>
        Most teams have many pieces of software undergoing active development at any given time.
        You can derive large benefits by putting these pieces under the control of a source
        control system that is compatible (i.e. Git or Subversion (SVN)) with the OpenEmbedded
        build system that the Yocto Project uses.
        You can then set the autobuilder to pull the latest revisions of the packages
        and test the latest commits by the builds.
        This practice quickly highlights issues.
        The build system easily supports testing configurations that use both a
        stable known good revision and a floating revision.
        The build system can also take just the changes from specific source control branches.
        This capability allows you to track and test specific changes.
    </para>

    <para>
        Perhaps the hardest part of setting this up is defining the software project or
        the metadata policies that surround the different source control systems.
        Of course circumstances will be different in each case.
        However, this situation reveals one of the Yocto Project's advantages -
        the system itself does not
        force any particular policy on users, unlike a lot of build systems.
        The system allows the best policies to be chosen for the given circumstances.
    </para>

    <para>
        In general, best practices exist that make your work with the Yocto
        Project easier in a team environment.
        This list presents some of these practices you might consider following.
        Of course, you need to understand that you do not have to follow these
        practices and your setup can be totally controlled and customized by
        your team:
        <itemizedlist>
            <listitem><para>Use <link linkend='git'>Git</link>
                as the source control system.</para></listitem>
            <listitem><para>Maintain your metadata in layers that make sense
                for your situation.
                See the "<link linkend='understanding-and-creating-layers'>Understanding
                and Creating Layers</link>" section for more information on
                layers.</para></listitem>
            <listitem><para>Separate the project's metadata and code by using
                separate Git repositories.
                See the "<link linkend='yocto-project-repositories'>Yocto Project
                Source Repositories</link>" section for information on these
                repositories.
                See the "<link linkend='getting-setup'>Getting Set Up</link>" section
                for information on how to set up various Yocto Project related
                Git repositories.</para></listitem>
            <listitem><para>Set up the directory for the shared state cache
                (<ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_DIR'><filename>SSTATE_DIR</filename></ulink>)
                where they make sense.
                For example, set up the sstate cache for developers using the
                same office and share source directories on the developer's
                machines.</para></listitem>
            <listitem><para>Set up an autobuilder and have it populate the
                sstate cache and source directories.</para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='yocto-project-repositories'>
    <title>Yocto Project Source Repositories</title>

    <para>
        The Yocto Project team maintains complete source repositories for all Yocto Project files
        at <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi'></ulink>.
        This web-based source code browser is organized into categories by function such as
        IDE Plugins, Matchbox, Poky, Yocto Linux Kernel, and so forth.
        From the interface, you can click on any particular item in the "Name" column and
        see the URL at the bottom of the page that you need to set up a Git repository for
        that particular item.
        Having a local Git repository of the Source Directory (poky) allows you to
        make changes, contribute to the history, and ultimately enhance the Yocto Project's
        tools, Board Support Packages, and so forth.
    </para>

    <para>
        Conversely, if you are a developer that is not interested in contributing back to the
        Yocto Project, you have the ability to simply download and extract release tarballs
        and use them within the Yocto Project environment.
        All that is required is a particular release of the Yocto Project and
        your application source code.
    </para>

    <para>
        For any supported release of Yocto Project, you can go to the Yocto Project website’s
        <ulink url='&YOCTO_HOME_URL;/download'>download page</ulink> and get a
        tarball of the release.
        You can also go to this site to download any supported BSP tarballs.
        Unpacking the tarball gives you a hierarchical Source Directory that lets you develop
        using the Yocto Project.
    </para>

    <para>
        Once you are set up through either tarball extraction or a checkout of Git repositories,
        you are ready to develop.
    </para>

    <para>
        In summary, here is where you can get the project files needed for development:
        <itemizedlist>
            <listitem><para id='source-repositories'><emphasis><ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi'>Source Repositories:</ulink></emphasis>
                This area contains IDE Plugins, Matchbox, Poky, Poky Support, Tools, Yocto Linux Kernel, and Yocto
                Metadata Layers.
                You can create local copies of Git repositories for each of these areas.</para>
                <para>
                <imagedata fileref="figures/source-repos.png" align="center" width="6in" depth="4in" />
                </para></listitem>
            <listitem><para><anchor id='index-downloads' /><emphasis><ulink url='&YOCTO_DL_URL;/releases/'>Index of /releases:</ulink></emphasis>
                This area contains index releases such as
                the <trademark class='trade'>Eclipse</trademark>
                Yocto Plug-in, miscellaneous support, poky, pseudo, installers for cross-development toolchains,
                and all released versions of Yocto Project in the form of images or tarballs.
                Downloading and extracting these files does not produce a local copy of the
                Git repository but rather a snapshot of a particular release or image.</para>
                <para>
                <imagedata fileref="figures/index-downloads.png" align="center" width="6in" depth="4in" />
                </para></listitem>
            <listitem><para><emphasis><ulink url='&YOCTO_HOME_URL;/download'>Yocto Project Download Page</ulink></emphasis>
                This page on the Yocto Project website allows you to download any Yocto Project
                release or Board Support Package (BSP) in tarball form.
                The tarballs are similar to those found in the
                <ulink url='&YOCTO_DL_URL;/releases/'>Index of /releases:</ulink> area.</para>
                <para>
                <imagedata fileref="figures/yp-download.png" align="center" width="6in" depth="4in" />
            </para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='yocto-project-terms'>
    <title>Yocto Project Terms</title>

    <para>
        Following is a list of terms and definitions users new to the Yocto Project development
        environment might find helpful.
        While some of these terms are universal, the list includes them just in case:
        <itemizedlist>
            <listitem><para><emphasis>Append Files:</emphasis> Files that append build information to
                a recipe file.
                Append files are known as BitBake append files and <filename>.bbappend</filename> files.
                The OpenEmbedded build system expects every append file to have a corresponding and
                underlying recipe (<filename>.bb</filename>) file.
                Furthermore, the append file and the underlying recipe must have the same root filename.
                The filenames can differ only in the file type suffix used (e.g.
                <filename>formfactor_0.0.bb</filename> and <filename>formfactor_0.0.bbappend</filename>).
                </para>
                <para>Information in append files overrides the information in the similarly-named recipe file.
                For an example of an append file in use, see the
                "<link linkend='using-bbappend-files'>Using .bbappend Files</link>" section.
                </para></listitem>
            <listitem><para id='bitbake-term'><emphasis>BitBake:</emphasis>
                The task executor and scheduler used by
                the OpenEmbedded build system to build images.
                For more information on BitBake, see the BitBake documentation
                in the <filename>bitbake/doc/manual</filename> directory of the
                <link linkend='source-directory'>Source Directory</link>.</para></listitem>
            <listitem>
                <para id='build-directory'><emphasis>Build Directory:</emphasis>
                This term refers to the area used by the OpenEmbedded build system for builds.
                The area is created when you <filename>source</filename> the setup
                environment script that is found in the Source Directory
                (i.e. <filename>&OE_INIT_FILE;</filename>).
                The <ulink url='&YOCTO_DOCS_REF_URL;#var-TOPDIR'><filename>TOPDIR</filename></ulink>
                variable points to the Build Directory.</para>

                <para>You have a lot of flexibility when creating the Build Directory.
                Following are some examples that show how to create the directory:
                   <itemizedlist>
                        <listitem><para>Create the Build Directory in your current working directory
                            and name it <filename>build</filename>.
                            This is the default behavior.
                            <literallayout class='monospaced'>
     $ source &OE_INIT_PATH;
                            </literallayout></para></listitem>
                        <listitem><para>Provide a directory path and specifically name the build
                            directory.
                            This next example creates a Build Directory named <filename>YP-&POKYVERSION;</filename>
                            in your home directory within the directory <filename>mybuilds</filename>.
                            If <filename>mybuilds</filename> does not exist, the directory is created for you:
                            <literallayout class='monospaced'>
     $ source &OE_INIT_PATH; $HOME/mybuilds/YP-&POKYVERSION;
                            </literallayout></para></listitem>
                        <listitem><para>Provide an existing directory to use as the Build Directory.
                            This example uses the existing <filename>mybuilds</filename> directory
                            as the Build Directory.
                            <literallayout class='monospaced'>
     $ source &OE_INIT_PATH; $HOME/mybuilds/
                            </literallayout></para></listitem>
                    </itemizedlist>
                </para></listitem>
            <listitem><para><emphasis>Build System:</emphasis> In the context of the Yocto Project
                this term refers to the OpenEmbedded build system used by the project.
                This build system is based on the project known as "Poky."
                For some historical information about Poky, see the
                <link linkend='poky'>Poky</link> term further along in this section.
                </para></listitem>
            <listitem><para><emphasis>Classes:</emphasis> Files that provide for logic encapsulation
                and inheritance allowing commonly used patterns to be defined once and easily used
                in multiple recipes.
                Class files end with the <filename>.bbclass</filename> filename extension.
                </para></listitem>
            <listitem><para><emphasis>Configuration File:</emphasis>  Configuration information in various
                <filename>.conf</filename> files provides global definitions of variables.
                The <filename>conf/local.conf</filename> configuration file in the
                <link linkend='build-directory'>Build Directory</link>
                contains user-defined variables that affect each build.
                The <filename>meta-yocto/conf/distro/poky.conf</filename> configuration file
                defines Yocto ‘distro’ configuration
                variables used only when building with this policy.
                Machine configuration files, which
                are located throughout the
                <link linkend='source-directory'>Source Directory</link>, define
                variables for specific hardware and are only used when building for that target
                (e.g. the <filename>machine/beagleboard.conf</filename> configuration file defines
                variables for the Texas Instruments ARM Cortex-A8 development board).
                Configuration files end with a <filename>.conf</filename> filename extension.
                </para></listitem>
            <listitem><para id='cross-development-toolchain'>
                <emphasis>Cross-Development Toolchain:</emphasis>
                A collection of software development
                tools and utilities that allow you to develop software for
                targeted architectures.
                This toolchain contains cross-compilers, linkers, and debuggers
                that are specific to an architecture.
                You can use the OpenEmbedded build system to build a
                cross-development toolchain installer that, when run, installs
                the toolchain that contains the development tools you
                need to cross-compile and test your software.
                The Yocto Project ships with images that contain installers for
                toolchains for supported architectures as well.
                Sometimes this toolchain is referred to as the
                meta-toolchain.</para>
                <para>Following is a list of toolchain recipes with brief
                descriptions of each:
                <itemizedlist>
                    <listitem><para><filename>gcc-cross-initial</filename>:
                        The initial compiler needed to bootstrap the toolchain
                        that runs on the host and is used to build software
                        for the target.
                        This tool is a 'native' package.</para></listitem>
                    <listitem><para><filename>gcc-cross-intermediate</filename>:
                        The second stage of the bootstrap process that runs
                        on the host and builds software for the target.
                        This tool is a 'native' package.</para></listitem>
                    <listitem><para><filename>gcc-cross</filename>:
                        The the final stage of the bootstrap process that
                        results in the cross compiler that runs on the host
                        and builds software for the target.
                        If you are replacing the cross compiler toolchain
                        with a custom version, this is what you must replace.
                        This tool is a 'native' package.</para></listitem>
                    <listitem><para><filename>gcc-runtime</filename>:
                        Runtime libraries from the toolchain bootstrapping
                        process.
                        This tool produces a binary for the target.
                        </para></listitem>
                    <listitem><para><filename>gcc-crosssdk-initial/intermediate</filename>:
                        Stage 1 and 2 of the a cross compiler that runs on the
                        host and builds for the SDK.
                        Often the SDK is not the same target as the host.
                        This tool is a 'native' binary.</para></listitem>
                    <listitem><para><filename>gcc-crosssdk</filename>:
                        The final stage of the SDK compiler.
                        This tool is a 'native' binary.
                        The tool runs on the host and builds for the SDK.
                        </para></listitem>
                    <listitem><para><filename>gcc-cross-canadian</filename>:
                        The compiler that runs on the SDK machine and is
                        included with the SDK that builds software for the
                        target.
                        This tool is a 'nativesdk' package.</para></listitem>
                </itemizedlist></para></listitem>
            <listitem><para><emphasis>Image:</emphasis> An image is the result produced when
                BitBake processes a given collection of recipes and related metadata.
                Images are the binary output that run on specific hardware or QEMU
                and for specific use cases.
                For a list of the supported image types that the Yocto Project provides, see the
                "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>"
                chapter in the Yocto Project Reference Manual.</para></listitem>
            <listitem><para id='layer'><emphasis>Layer:</emphasis> A collection of recipes representing the core,
                a BSP, or an application stack.
                For a discussion on BSP Layers, see the
                "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
                section in the Yocto Project Board Support Packages (BSP) Developer's Guide.</para></listitem>
            <listitem><para id='metadata'><emphasis>Metadata:</emphasis>
                The files that BitBake parses when building an image.
                In general, Metadata includes recipes, classes, and
                configuration files.
                In the context of the kernel ("kernel Metadata"),
                it refers to metadata in the <filename>meta</filename>
                branches of the kernel source Git repositories.
                </para></listitem>
            <listitem><para id='oe-core'><emphasis>OE-Core:</emphasis> A core set of metadata originating
                with OpenEmbedded (OE) that is shared between OE and the Yocto Project.
                This metadata is found in the <filename>meta</filename> directory of the source
                directory.</para></listitem>
            <listitem><para><emphasis>Package:</emphasis> In the context of the Yocto Project,
                this term refers to the packaged output from a baked recipe.
                A package is generally the compiled binaries produced from the recipe's sources.
                You ‘bake’ something by running it through BitBake.</para>
                <para>It is worth noting that the term "package" can, in general, have subtle
                meanings.  For example, the packages refered to in the
                "<ulink url='&YOCTO_DOCS_QS_URL;#packages'>The Packages</ulink>" section are
                compiled binaries that when installed add functionality to your Linux
                distribution.</para>
                <para>Another point worth noting is that historically within the Yocto Project,
                recipes were referred to as packages - thus, the existence of several BitBake
                variables that are seemingly mis-named,
                (e.g. <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>,
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PRINC'><filename>PRINC</filename></ulink>,
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>, and
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PE'><filename>PE</filename></ulink>).
                </para></listitem>
            <listitem><para id='poky'><emphasis>Poky:</emphasis> The term "poky" can mean several things.
                In its most general sense, it is an open-source project that was initially developed
                by OpenedHand.  With OpenedHand, poky was developed off of the existing OpenEmbedded
                build system becoming a build system for embedded images.
                After Intel Corporation acquired OpenedHand, the project poky became the basis for
                the Yocto Project's build system.
                Within the Yocto Project source repositories, poky exists as a separate Git repository
                that can be cloned to yield a local copy on the host system.
                Thus, "poky" can refer to the local copy of the Source Directory used to develop within
                the Yocto Project.</para></listitem>
            <listitem><para><emphasis>Recipe:</emphasis> A set of instructions for building packages.
                A recipe describes where you get source code and which patches to apply.
                Recipes describe dependencies for libraries or for other recipes, and they
                also contain configuration and compilation options.
                Recipes contain the logical unit of execution, the software/images to build, and
                use the <filename>.bb</filename> file extension.</para></listitem>
            <listitem>
                <para id='source-directory'><emphasis>Source Directory:</emphasis>
                This term refers to the directory structure created as a result of either downloading
                and unpacking a Yocto Project release tarball or creating a local copy of
                the <filename>poky</filename> Git repository
                <filename>git://git.yoctoproject.org/poky</filename>.
                Sometimes you might hear the term "poky directory" used to refer to this
                directory structure.
                <note>
                    The OpenEmbedded build system does not support file or directory names that
                    contain spaces.
                    Be sure that the Source Directory you use does not contain these types
                    of names.
                </note></para>
                <para>The Source Directory contains BitBake, Documentation, metadata and
                other files that all support the Yocto Project.
                Consequently, you must have the Source Directory in place on your development
                system in order to do any development using the Yocto Project.</para>

                <para>For tarball expansion, the name of the top-level directory of the Source Directory
                is derived from the Yocto Project release tarball.
                For example, downloading and unpacking <filename>&YOCTO_POKY_TARBALL;</filename>
                results in a Source Directory whose top-level folder is named
                <filename>&YOCTO_POKY;</filename>.
                If you create a local copy of the Git repository, then you can name the repository
                anything you like.
                Throughout much of the documentation, <filename>poky</filename> is used as the name of
                the top-level folder of the local copy of the poky Git repository.
                So, for example, cloning the <filename>poky</filename> Git repository results in a
                local Git repository whose top-level folder is also named <filename>poky</filename>.</para>

                <para>It is important to understand the differences between the Source Directory created
                by unpacking a released tarball as compared to cloning
                <filename>git://git.yoctoproject.org/poky</filename>.
                When you unpack a tarball, you have an exact copy of the files based on the time of
                release - a fixed release point.
                Any changes you make to your local files in the Source Directory are on top of the release.
                On the other hand, when you clone the <filename>poky</filename> Git repository, you have an
                active development repository.
                In this case, any local changes you make to the Source Directory can be later applied
                to active development branches of the upstream <filename>poky</filename> Git
                repository.</para>

                <para>Finally, if you want to track a set of local changes while starting from the same point
                as a release tarball, you can create a local Git branch that
                reflects the exact copy of the files at the time of their release.
                You do this by using Git tags that are part of the repository.</para>

                <para>For more information on concepts related to Git repositories, branches, and tags,
                see the
                "<link linkend='repositories-tags-and-branches'>Repositories, Tags, and Branches</link>"
                section.</para></listitem>
            <listitem><para><emphasis>Tasks:</emphasis> Arbitrary groups of software Recipes.
                You simply use Tasks to hold recipes that, when built, usually accomplish a single task.
                For example, a task could contain the recipes for a company’s proprietary or value-add software.
                Or, the task could contain the recipes that enable graphics.
                A task is really just another recipe.
                Because task files are recipes, they end with the <filename>.bb</filename> filename
                extension.</para></listitem>
            <listitem><para><emphasis>Upstream:</emphasis> A reference to source code or repositories
                that are not local to the development system but located in a master area that is controlled
                by the maintainer of the source code.
                For example, in order for a developer to work on a particular piece of code, they need to
                first get a copy of it from an "upstream" source.</para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='licensing'>
    <title>Licensing</title>

    <para>
        Because open source projects are open to the public, they have different licensing structures in place.
        License evolution for both Open Source and Free Software has an interesting history.
        If you are interested in this history, you can find basic information here:
    <itemizedlist>
        <listitem><para><ulink url='http://en.wikipedia.org/wiki/Open-source_license'>Open source license history</ulink>
            </para></listitem>
        <listitem><para><ulink url='http://en.wikipedia.org/wiki/Free_software_license'>Free software license
            history</ulink></para></listitem>
    </itemizedlist>
    </para>

    <para>
        In general, the Yocto Project is broadly licensed under the Massachusetts Institute of Technology
        (MIT) License.
        MIT licensing permits the reuse of software within proprietary software as long as the
        license is distributed with that software.
        MIT is also compatible with the GNU General Public License (GPL).
        Patches to the Yocto Project follow the upstream licensing scheme.
        You can find information on the MIT license at
        <ulink url='http://www.opensource.org/licenses/mit-license.php'>here</ulink>.
        You can find information on the GNU GPL <ulink url='http://www.opensource.org/licenses/LGPL-3.0'>
        here</ulink>.
    </para>

    <para>
        When you build an image using the Yocto Project, the build process uses a
        known list of licenses to ensure compliance.
        You can find this list in the Yocto Project files directory at
        <filename>meta/files/common-licenses</filename>.
        Once the build completes, the list of all licenses found and used during that build are
        kept in the
        <link linkend='build-directory'>Build Directory</link> at
        <filename>tmp/deploy/images/licenses</filename>.
    </para>

    <para>
        If a module requires a license that is not in the base list, the build process
        generates a warning during the build.
        These tools make it easier for a developer to be certain of the licenses with which
        their shipped products must comply.
        However, even with these tools it is still up to the developer to resolve potential licensing issues.
    </para>

    <para>
        The base list of licenses used by the build process is a combination of the Software Package
        Data Exchange (SPDX) list and the Open Source Initiative (OSI) projects.
        <ulink url='http://spdx.org'>SPDX Group</ulink> is a working group of the Linux Foundation
        that maintains a specification
        for a standard format for communicating the components, licenses, and copyrights
        associated with a software package.
        <ulink url='http://opensource.org'>OSI</ulink> is a corporation dedicated to the Open Source
        Definition and the effort for reviewing and approving licenses that are OSD-conformant.
    </para>

    <para>
        You can find a list of the combined SPDX and OSI licenses that the Yocto Project uses
        <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/meta/files/common-licenses'>here</ulink>.
        This wiki page discusses the license infrastructure used by the Yocto Project.
    </para>

    <para>
        For information that can help you to maintain compliance with various open source licensing
        during the lifecycle of a product created using the Yocto Project, see the
        "<link linkend='maintaining-open-source-license-compliance-during-your-products-lifecycle'>Maintaining Open Source License Compliance During Your Product's Lifecycle</link>" section.
    </para>
</section>

<section id='git'>
    <title>Git</title>

    <para>
        The Yocto Project uses Git, which is a free, open source distributed version control system.
        Git supports distributed development, non-linear development, and can handle large projects.
        It is best that you have some fundamental understanding of how Git tracks projects and
        how to work with Git if you are going to use Yocto Project for development.
        This section provides a quick overview of how Git works and provides you with a summary
        of some essential Git commands.
    </para>

    <para>
        For more information on Git, see
        <ulink url='http://git-scm.com/documentation'></ulink>.
        If you need to download Git, go to <ulink url='http://git-scm.com/download'></ulink>.
    </para>

    <section id='repositories-tags-and-branches'>
        <title>Repositories, Tags, and Branches</title>

        <para>
            As mentioned earlier in section
            "<link linkend='yocto-project-repositories'>Yocto Project Source Repositories</link>",
            the Yocto Project maintains source repositories at
            <ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>.
            If you look at this web-interface of the repositories, each item is a separate
            Git repository.
        </para>

        <para>
            Git repositories use branching techniques that track content change (not files)
            within a project (e.g. a new feature or updated documentation).
            Creating a tree-like structure based on project divergence allows for excellent historical
            information over the life of a project.
            This methodology also allows for an environment in which you can do lots of
            local experimentation on a project as you develop changes or new features.
        </para>

        <para>
            A Git repository represents all development efforts for a given project.
            For example, the Git repository <filename>poky</filename> contains all changes
            and developments for Poky over the course of its entire life.
            That means that all changes that make up all releases are captured.
            The repository maintains a complete history of changes.
        </para>

        <para>
            You can create a local copy of any repository by "cloning" it with the Git
            <filename>clone</filename> command.
            When you clone a Git repository, you end up with an identical copy of the
            repository on your development system.
            Once you have a local copy of a repository, you can take steps to develop locally.
            For examples on how to clone Git repositories, see the section
            "<link linkend='getting-setup'>Getting Set Up</link>" earlier in this manual.
        </para>

        <para>
            It is important to understand that Git tracks content change and not files.
            Git uses "branches" to organize different development efforts.
            For example, the <filename>poky</filename> repository has
            <filename>bernard</filename>,
            <filename>edison</filename>, <filename>denzil</filename>, <filename>danny</filename>
            and <filename>master</filename> branches among others.
            You can see all the branches by going to
            <ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/'></ulink> and
            clicking on the
            <filename><ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/refs/heads'>[...]</ulink></filename>
            link beneath the "Branch" heading.
        </para>

        <para>
            Each of these branches represents a specific area of development.
            The <filename>master</filename> branch represents the current or most recent
            development.
            All other branches represent off-shoots of the <filename>master</filename>
            branch.
        </para>

        <para>
            When you create a local copy of a Git repository, the copy has the same set
            of branches as the original.
            This means you can use Git to create a local working area (also called a branch)
            that tracks a specific development branch from the source Git repository.
            in other words, you can define your local Git environment to work on any development
            branch in the repository.
            To help illustrate, here is a set of commands that creates a local copy of the
            <filename>poky</filename> Git repository and then creates and checks out a local
            Git branch that tracks the Yocto Project &DISTRO; Release (&DISTRO_NAME;) development:
            <literallayout class='monospaced'>
     $ cd ~
     $ git clone git://git.yoctoproject.org/poky
     $ cd poky
     $ git checkout -b &DISTRO_NAME; origin/&DISTRO_NAME;
            </literallayout>
            In this example, the name of the top-level directory of your local Yocto Project
            Files Git repository is <filename>poky</filename>,
            and the name of the local working area (or local branch) you have created and checked
            out is <filename>&DISTRO_NAME;</filename>.
            The files in your repository now reflect the same files that are in the
            <filename>&DISTRO_NAME;</filename> development branch of the Yocto Project's
            <filename>poky</filename> repository.
            It is important to understand that when you create and checkout a
            local working branch based on a branch name,
            your local environment matches the "tip" of that development branch
            at the time you created your local branch, which could be
            different than the files at the time of a similarly named release.
            In other words, creating and checking out a local branch based on the
            <filename>&DISTRO_NAME;</filename> branch name is not the same as
            cloning and checking out the <filename>master</filename> branch.
            Keep reading to see how you create a local snapshot of a Yocto Project Release.
        </para>

        <para>
            Git uses "tags" to mark specific changes in a repository.
            Typically, a tag is used to mark a special point such as the final change
            before a project is released.
            You can see the tags used with the <filename>poky</filename> Git repository
            by going to <ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/'></ulink> and
            clicking on the
            <filename><ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/refs/tags'>[...]</ulink></filename>
            link beneath the "Tag" heading.
        </para>

        <para>
            Some key tags are <filename>bernard-5.0</filename>, <filename>denzil-7.0</filename>,
            and <filename>&DISTRO_NAME;-&POKYVERSION;</filename>.
            These tags represent Yocto Project releases.
        </para>

        <para>
            When you create a local copy of the Git repository, you also have access to all the
            tags.
            Similar to branches, you can create and checkout a local working Git branch based
            on a tag name.
            When you do this, you get a snapshot of the Git repository that reflects
            the state of the files when the change was made associated with that tag.
            The most common use is to checkout a working branch that matches a specific
            Yocto Project release.
            Here is an example:
            <literallayout class='monospaced'>
     $ cd ~
     $ git clone git://git.yoctoproject.org/poky
     $ cd poky
     $ git checkout -b my-&DISTRO_NAME;-&POKYVERSION; &DISTRO_NAME;-&POKYVERSION;
            </literallayout>
            In this example, the name of the top-level directory of your local Yocto Project
            Files Git repository is <filename>poky</filename>.
            And, the name of the local branch you have created and checked out is
            <filename>my-&DISTRO_NAME;-&POKYVERSION;</filename>.
            The files in your repository now exactly match the Yocto Project &DISTRO;
            Release tag (<filename>&DISTRO_NAME;-&POKYVERSION;</filename>).
            It is important to understand that when you create and checkout a local
            working branch based on a tag, your environment matches a specific point
            in time and not a development branch.
        </para>
    </section>

    <section id='basic-commands'>
        <title>Basic Commands</title>

        <para>
            Git has an extensive set of commands that lets you manage changes and perform
            collaboration over the life of a project.
            Conveniently though, you can manage with a small set of basic operations and workflows
            once you understand the basic philosophy behind Git.
            You do not have to be an expert in Git to be functional.
            A good place to look for instruction on a minimal set of Git commands is
            <ulink url='http://git-scm.com/documentation'>here</ulink>.
            If you need to download Git, you can do so
            <ulink url='http://git-scm.com/download'>here</ulink>.
        </para>

        <para>
            If you don’t know much about Git, we suggest you educate
            yourself by visiting the links previously mentioned.
        </para>

        <para>
            The following list briefly describes some basic Git operations as a way to get started.
            As with any set of commands, this list (in most cases) simply shows the base command and
            omits the many arguments they support.
            See the Git documentation for complete descriptions and strategies on how to use these commands:
            <itemizedlist>
                <listitem><para><emphasis><filename>git init</filename>:</emphasis> Initializes an empty Git repository.
                    You cannot use Git commands unless you have a <filename>.git</filename> repository.</para></listitem>
                <listitem><para><emphasis><filename>git clone</filename>:</emphasis> Creates a clone of a repository.
                    During collaboration, this command allows you to create a local repository that is on
                    equal footing with a fellow developer’s repository.</para></listitem>
                <listitem><para><emphasis><filename>git add</filename>:</emphasis> Adds updated file contents
                    to the index that
                    Git uses to track changes.
                    You must add all files that have changed before you can commit them.</para></listitem>
                <listitem><para><emphasis><filename>git commit</filename>:</emphasis> Creates a “commit” that documents
                    the changes you made.
                    Commits are used for historical purposes, for determining if a maintainer of a project
                    will allow the change, and for ultimately pushing the change from your local Git repository
                    into the project’s upstream (or master) repository.</para></listitem>
                <listitem><para><emphasis><filename>git status</filename>:</emphasis> Reports any modified files that
                    possibly need to be added and committed.</para></listitem>
                <listitem><para><emphasis><filename>git checkout &lt;branch-name&gt;</filename>:</emphasis> Changes
                    your working branch.
                    This command is analogous to “cd”.</para></listitem>
                <listitem><para><emphasis><filename>git checkout –b &lt;working-branch&gt;</filename>:</emphasis> Creates
                    a working branch on your local machine where you can isolate work.
                    It is a good idea to use local branches when adding specific features or changes.
                    This way if you don’t like what you have done you can easily get rid of the work.</para></listitem>
                <listitem><para><emphasis><filename>git branch</filename>:</emphasis> Reports
                    existing local branches and
                    tells you the branch in which you are currently working.</para></listitem>
                <listitem><para><emphasis><filename>git branch -D &lt;branch-name&gt;</filename>:</emphasis>
                    Deletes an existing local branch.
                    You need to be in a local branch other than the one you are deleting
                    in order to delete <filename>&lt;branch-name&gt;</filename>.</para></listitem>
                <listitem><para><emphasis><filename>git pull</filename>:</emphasis> Retrieves information
                    from an upstream Git
                    repository and places it in your local Git repository.
                    You use this command to make sure you are synchronized with the repository
                    from which you are basing changes (.e.g. the master branch).</para></listitem>
                <listitem><para><emphasis><filename>git push</filename>:</emphasis> Sends all your local changes you
                    have committed to an upstream Git repository (e.g. a contribution repository).
                    The maintainer of the project draws from these repositories when adding your changes to the
                    project’s master repository.</para></listitem>
                <listitem><para><emphasis><filename>git merge</filename>:</emphasis> Combines or adds changes from one
                    local branch of your repository with another branch.
                    When you create a local Git repository, the default branch is named “master”.
                    A typical workflow is to create a temporary branch for isolated work, make and commit your
                    changes, switch to your local master branch, merge the changes from the temporary branch into the
                    local master branch, and then delete the temporary branch.</para></listitem>
                <listitem><para><emphasis><filename>git cherry-pick</filename>:</emphasis> Choose and apply specific
                    commits from one branch into another branch.
                    There are times when you might not be able to merge all the changes in one branch with
                    another but need to pick out certain ones.</para></listitem>
                <listitem><para><emphasis><filename>gitk</filename>:</emphasis> Provides a GUI view of the branches
                    and changes in your local Git repository.
                    This command is a good way to graphically see where things have diverged in your
                    local repository.</para></listitem>
                <listitem><para><emphasis><filename>git log</filename>:</emphasis> Reports a history of your changes to the
                    repository.</para></listitem>
                <listitem><para><emphasis><filename>git diff</filename>:</emphasis> Displays line-by-line differences
                    between your local working files and the same files in the upstream Git repository that your
                    branch currently tracks.</para></listitem>
            </itemizedlist>
        </para>
    </section>
</section>

<section id='workflows'>
    <title>Workflows</title>

    <para>
        This section provides some overview on workflows using Git.
        In particular, the information covers basic practices that describe roles and actions in a
        collaborative development environment.
        Again, if you are familiar with this type of development environment, you might want to just
        skip this section.
    </para>

    <para>
        The Yocto Project files are maintained using Git in a "master" branch whose Git history
        tracks every change and whose structure provides branches for all diverging functionality.
        Although there is no need to use Git, many open source projects do so.
        For the Yocto Project, a key individual called the "maintainer" is responsible for the "master"
        branch of the Git repository.
        The "master" branch is the “upstream” repository where the final builds of the project occur.
        The maintainer is responsible for allowing changes in from other developers and for
        organizing the underlying branch structure to reflect release strategies and so forth.
        <note>You can see who is the maintainer for Yocto Project files by examining the
        <filename>maintainers.inc</filename> file in the Yocto Project
        <filename>meta-yocto/conf/distro/include</filename> directory.</note>
    </para>

    <para>
        The project also has contribution repositories known as “contrib” areas.
        These areas temporarily hold changes to the project that have been submitted or committed
        by the Yocto Project development team and by community members that contribute to the project.
        The maintainer determines if the changes are qualified to be moved from the "contrib" areas
        into the "master" branch of the Git repository.
    </para>

    <para>
        Developers (including contributing community members) create and maintain cloned repositories
        of the upstream "master" branch.
        These repositories are local to their development platforms and are used to develop changes.
        When a developer is satisfied with a particular feature or change, they “push” the changes
        to the appropriate "contrib" repository.
    </para>

    <para>
        Developers are responsible for keeping their local repository up-to-date with "master".
        They are also responsible for straightening out any conflicts that might arise within files
        that are being worked on simultaneously by more than one person.
        All this work is done locally on the developer’s machine before anything is pushed to a
        "contrib" area and examined at the maintainer’s level.
    </para>

    <para>
        A somewhat formal method exists by which developers commit changes and push them into the
        "contrib" area and subsequently request that the maintainer include them into "master"
        This process is called “submitting a patch” or “submitting a change.”
        For information on submitting patches and changes, see the
        "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>" section.
    </para>

    <para>
        To summarize the environment:  we have a single point of entry for changes into the project’s
        "master" branch of the Git repository, which is controlled by the project’s maintainer.
        And, we have a set of developers who independently develop, test, and submit changes
        to "contrib" areas for the maintainer to examine.
        The maintainer then chooses which changes are going to become a permanent part of the project.
    </para>

    <para>
        <imagedata fileref="figures/git-workflow.png" width="6in" depth="3in" align="left" scalefit="1" />
    </para>

    <para>
        While each development environment is unique, there are some best practices or methods
        that help development run smoothly.
        The following list describes some of these practices.
        For more information about Git workflows, see the workflow topics in the
        <ulink url='http://book.git-scm.com'>Git Community Book</ulink>.
        <itemizedlist>
            <listitem><para><emphasis>Make Small Changes:</emphasis> It is best to keep the changes you commit
                small as compared to bundling many disparate changes into a single commit.
                This practice not only keeps things manageable but also allows the maintainer
                to more easily include or refuse changes.</para>
                <para>It is also good practice to leave the repository in a state that allows you to
                still successfully build your project.  In other words, do not commit half of a feature,
                then add the other half in a separate, later commit.
                Each commit should take you from one buildable project state to another
                buildable state.</para></listitem>
            <listitem><para><emphasis>Use Branches Liberally:</emphasis> It is very easy to create, use, and
                delete local branches in your working Git repository.
                You can name these branches anything you like.
                It is helpful to give them names associated with the particular feature or change
                on which you are working.
                Once you are done with a feature or change, simply discard the branch.</para></listitem>
            <listitem><para><emphasis>Merge Changes:</emphasis> The <filename>git merge</filename>
                command allows you to take the
                changes from one branch and fold them into another branch.
                This process is especially helpful when more than a single developer might be working
                on different parts of the same feature.
                Merging changes also automatically identifies any collisions or “conflicts”
                that might happen as a result of the same lines of code being altered by two different
                developers.</para></listitem>
            <listitem><para><emphasis>Manage Branches:</emphasis> Because branches are easy to use, you should
                use a system where branches indicate varying levels of code readiness.
                For example, you can have a “work” branch to develop in, a “test” branch where the code or
                change is tested, a “stage” branch where changes are ready to be committed, and so forth.
                As your project develops, you can merge code across the branches to reflect ever-increasing
                stable states of the development.</para></listitem>
            <listitem><para><emphasis>Use Push and Pull:</emphasis> The push-pull workflow is based on the
                concept of developers “pushing” local commits to a remote repository, which is
                usually a contribution repository.
                This workflow is also based on developers “pulling” known states of the project down into their
                local development repositories.
                The workflow easily allows you to pull changes submitted by other developers from the
                upstream repository into your work area ensuring that you have the most recent software
                on which to develop.
                The Yocto Project has two scripts named <filename>create-pull-request</filename> and
                <filename>send-pull-request</filename> that ship with the release to facilitate this
                workflow.
                You can find these scripts in the local Yocto Project files Git repository in
                the <filename>scripts</filename> directory.</para>
                <para>You can find more information on these scripts in the
                "<link linkend='pushing-a-change-upstream'>Using
                Scripts to Push a Change Upstream and Request a Pull</link>" section.
                </para></listitem>
            <listitem><para><emphasis>Patch Workflow:</emphasis> This workflow allows you to notify the
                maintainer through an email that you have a change (or patch) you would like considered
                for the "master" branch of the Git repository.
                To send this type of change you format the patch and then send the email using the Git commands
                <filename>git format-patch</filename> and <filename>git send-email</filename>.
                You can find information on how to submit changes
                later in this chapter.</para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='tracking-bugs'>
    <title>Tracking Bugs</title>

    <para>
        The Yocto Project uses its own implementation of
        <ulink url='http://www.bugzilla.org/about/'>Bugzilla</ulink> to track bugs.
        Implementations of Bugzilla work well for group development because they track bugs and code
        changes, can be used to communicate changes and problems with developers, can be used to
        submit and review patches, and can be used to manage quality assurance.
        The home page for the Yocto Project implementation of Bugzilla is
        <ulink url='&YOCTO_BUGZILLA_URL;'>&YOCTO_BUGZILLA_URL;</ulink>.
    </para>

    <para>
        Sometimes it is helpful to submit, investigate, or track a bug against the Yocto Project itself
        such as when discovering an issue with some component of the build system that acts contrary
        to the documentation or your expectations.
        Following is the general procedure for submitting a new bug using the Yocto Project
        Bugzilla.
        You can find more information on defect management, bug tracking, and feature request
        processes all accomplished through the Yocto Project Bugzilla on the wiki page
        <ulink url='&YOCTO_WIKI_URL;/wiki/Bugzilla_Configuration_and_Bug_Tracking'>here</ulink>.
        <orderedlist>
            <listitem><para>Always use the Yocto Project implementation of Bugzilla to submit
                a bug.</para></listitem>
            <listitem><para>When submitting a new bug, be sure to choose the appropriate
                Classification, Product, and Component for which the issue was found.
                Defects for Yocto Project fall into one of six classifications:  Yocto Project
                Components, Infrastructure, Build System &amp; Metadata, Documentation,
                QA/Testing, and Runtime.
                Each of these Classifications break down into multiple Products and, in some
                cases, multiple Components.</para></listitem>
            <listitem><para>Use the bug form to choose the correct Hardware and Architecture
                for which the bug applies.</para></listitem>
            <listitem><para>Indicate the Yocto Project version you were using when the issue
                occurred.</para></listitem>
            <listitem><para>Be sure to indicate the Severity of the bug.
                Severity communicates how the bug impacted your work.</para></listitem>
            <listitem><para>Provide a brief summary of the issue.
                Try to limit your summary to just a line or two and be sure to capture the
                essence of the issue.</para></listitem>
            <listitem><para>Provide a detailed description of the issue.
                You should provide as much detail as you can about the context, behavior, output,
                and so forth that surround the issue.
                You can even attach supporting files for output or log by using the "Add an attachment"
                button.</para></listitem>
            <listitem><para>Submit the bug by clicking the "Submit Bug" button.</para></listitem>
        </orderedlist>
    </para>
</section>

<section id='how-to-submit-a-change'>
    <title>How to Submit a Change</title>

    <para>
        Contributions to the Yocto Project and OpenEmbedded are very welcome.
        Because the system is extremely configurable and flexible, we recognize that developers
        will want to extend, configure or optimize it for their specific uses.
        You should send patches to the appropriate mailing list so that they
        can be reviewed and merged by the appropriate maintainer.
        For a list of the Yocto Project and related mailing lists, see the
        "<ulink url='&YOCTO_DOCS_REF_URL;#resources-mailinglist'>Mailing lists</ulink>" section in
        the Yocto Project Reference Manual.
    </para>

    <para>
        The following is some guidance on which mailing list to use for what type of change:
        <itemizedlist>
            <listitem><para>For changes to the core metadata, send your patch to the
                <ulink url='&OE_LISTS_URL;/listinfo/openembedded-core'>openembedded-core</ulink> mailing list.
                For example, a change to anything under the <filename>meta</filename> or
                <filename>scripts</filename> directories
                should be sent to this mailing list.</para></listitem>
            <listitem><para>For changes to BitBake (anything under the <filename>bitbake</filename>
                directory), send your patch to the
                <ulink url='&OE_LISTS_URL;/listinfo/bitbake-devel'>bitbake-devel</ulink> mailing list.</para></listitem>
            <listitem><para>For changes to <filename>meta-yocto</filename>, send your patch to the
                <ulink url='&YOCTO_LISTS_URL;/listinfo/poky'>poky</ulink> mailing list.</para></listitem>
            <listitem><para>For changes to other layers hosted on
                <filename>yoctoproject.org</filename> (unless the
                layer's documentation specifies otherwise), tools, and Yocto Project
                documentation, use the
                <ulink url='&YOCTO_LISTS_URL;/listinfo/yocto'>yocto</ulink> mailing list.</para></listitem>
            <listitem><para>For additional recipes that do not fit into the core metadata,
                you should determine which layer the recipe should go into and submit the
                change in the manner recommended by the documentation (e.g. README) supplied
                with the layer. If in doubt, please ask on the
                <ulink url='&YOCTO_LISTS_URL;/listinfo/yocto'>yocto</ulink> or
                <ulink url='&OE_LISTS_URL;/listinfo/openembedded-devel'>openembedded-devel</ulink>
                mailing lists.</para></listitem>
        </itemizedlist>
    </para>

    <para>
        When you send a patch, be sure to include a "Signed-off-by:"
        line in the same style as required by the Linux kernel.
        Adding this line signifies that you, the submitter, have agreed to the Developer's Certificate of Origin 1.1
        as follows:
        <literallayout class='monospaced'>
     Developer's Certificate of Origin 1.1

     By making a contribution to this project, I certify that:

     (a) The contribution was created in whole or in part by me and I
         have the right to submit it under the open source license
         indicated in the file; or

     (b) The contribution is based upon previous work that, to the best
         of my knowledge, is covered under an appropriate open source
         license and I have the right under that license to submit that
         work with modifications, whether created in whole or in part
         by me, under the same open source license (unless I am
         permitted to submit under a different license), as indicated
         in the file; or

     (c) The contribution was provided directly to me by some other
         person who certified (a), (b) or (c) and I have not modified
         it.

     (d) I understand and agree that this project and the contribution
         are public and that a record of the contribution (including all
         personal information I submit with it, including my sign-off) is
         maintained indefinitely and may be redistributed consistent with
         this project or the open source license(s) involved.
        </literallayout>
    </para>

    <para>
        In a collaborative environment, it is necessary to have some sort of standard
        or method through which you submit changes.
        Otherwise, things could get quite chaotic.
        One general practice to follow is to make small, controlled changes.
        Keeping changes small and isolated aids review, makes merging/rebasing easier
        and keeps the change history clean when anyone needs to refer to it in future.
    </para>

    <para>
        When you make a commit, you must follow certain standards established by the
        OpenEmbedded and Yocto Project development teams.
        For each commit, you must provide a single-line summary of the change and you
        should almost always provide a more detailed description of what you did (i.e.
        the body of the commit message).
        The only exceptions for not providing a detailed description would be if your
        change is a simple, self-explanatory change that needs no further description
        beyond the summary.
        Here are the guidelines for composing a commit message:
        <itemizedlist>
            <listitem><para>Provide a single-line, short summary of the change.
                This summary is typically viewable in the "shortlist" of changes.
                Thus, providing something short and descriptive that gives the reader
                a summary of the change is useful when viewing a list of many commits.
                This should be prefixed by the recipe name (if changing a recipe), or
                else the short form path to the file being changed.
                </para></listitem>
            <listitem><para>For the body of the commit message, provide detailed information
                that describes what you changed, why you made the change, and the approach
                you used. It may also be helpful if you mention how you tested the change.
                Provide as much detail as you can in the body of the commit message.
                </para></listitem>
            <listitem><para>If the change addresses a specific bug or issue that is
                associated with a bug-tracking ID, include a reference to that ID in
                your detailed description.
                For example, the Yocto Project uses a specific convention for bug
                references - any commit that addresses a specific bug should include the
                bug ID in the description (typically at the beginning) as follows:
                <literallayout class='monospaced'>
     [YOCTO #&lt;bug-id&gt;]

     &lt;detailed description of change&gt;
                </literallayout></para></listitem>
                Where &lt;bug-id&gt; is replaced with the specific bug ID from the
                Yocto Project Bugzilla instance.
        </itemizedlist>
    </para>

    <para>
        You can find more guidance on creating well-formed commit messages at this OpenEmbedded
        wiki page:
        <ulink url='&OE_HOME_URL;/wiki/Commit_Patch_Message_Guidelines'></ulink>.
    </para>

    <para>
        Following are general instructions for both pushing changes upstream and for submitting
        changes as patches.
    </para>

    <section id='pushing-a-change-upstream'>
        <title>Using Scripts to Push a Change Upstream and Request a Pull</title>

        <para>
            The basic flow for pushing a change to an upstream "contrib" Git repository is as follows:
            <itemizedlist>
                <listitem><para>Make your changes in your local Git repository.</para></listitem>
                <listitem><para>Stage your changes by using the <filename>git add</filename>
                    command on each file you changed.</para></listitem>
                <listitem><para>Commit the change by using the <filename>git commit</filename>
                    command and push it to the "contrib" repository.
                    Be sure to provide a commit message that follows the project’s commit message standards
                    as described earlier.</para></listitem>
                <listitem><para>Notify the maintainer that you have pushed a change by making a pull
                    request.
                    The Yocto Project provides two scripts that conveniently let you generate and send
                    pull requests to the Yocto Project.
                    These scripts are <filename>create-pull-request</filename> and
                    <filename>send-pull-request</filename>.
                    You can find these scripts in the <filename>scripts</filename> directory
                    within the <link linkend='source-directory'>Source Directory</link>.</para>
                    <para>Using these scripts correctly formats the requests without introducing any
                    whitespace or HTML formatting.
                    The maintainer that receives your patches needs to be able to save and apply them
                    directly from your emails.
                    Using these scripts is the preferred method for sending patches.</para>
                    <para>For help on using these scripts, simply provide the
                    <filename>-h</filename> argument as follows:
                    <literallayout class='monospaced'>
     $ ~/poky/scripts/create-pull-request -h
     $ ~/poky/scripts/send-pull-request -h
                    </literallayout></para></listitem>
            </itemizedlist>
        </para>

        <para>
            You can find general Git information on how to push a change upstream in the
            <ulink url='http://book.git-scm.com/3_distributed_workflows.html'>Git Community Book</ulink>.
        </para>
    </section>

    <section id='submitting-a-patch'>
        <title>Using Email to Submit a Patch</title>

        <para>
            You can submit patches without using the <filename>create-pull-request</filename> and
            <filename>send-pull-request</filename> scripts described in the previous section.
            Keep in mind, the preferred method is to use the scripts, however.
        </para>

        <para>
            Depending on the components changed, you need to submit the email to a specific
            mailing list.
            For some guidance on which mailing list to use, see the list in the
            "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>" section
            earlier in this manual.
            For a description of the available mailing lists, see
            "<ulink url='&YOCTO_DOCS_REF_URL;#resources-mailinglist'>Mailing Lists</ulink>"
            section in the Yocto Project Reference Manual.
        </para>

        <para>
            Here is the general procedure on how to submit a patch through email without using the
            scripts:
            <itemizedlist>
                <listitem><para>Make your changes in your local Git repository.</para></listitem>
                <listitem><para>Stage your changes by using the <filename>git add</filename>
                    command on each file you changed.</para></listitem>
                <listitem><para>Commit the change by using the
                    <filename>git commit --signoff</filename> command.
                    Using the <filename>--signoff</filename> option identifies you as the person
                    making the change and also satisfies the Developer's Certificate of
                    Origin (DCO) shown earlier.</para>
                    <para>When you form a commit you must follow certain standards established by the
                    Yocto Project development team.
                    See the earlier section
                    "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>"
                    for Yocto Project commit message standards.</para></listitem>
                <listitem><para>Format the commit into an email message.
                    To format commits, use the <filename>git format-patch</filename> command.
                    When you provide the command, you must include a revision list or a number of patches
                    as part of the command.
                    For example, these two commands each take the most recent single commit and
                    format it as an email message in the current directory:
                    <literallayout class='monospaced'>
     $ git format-patch -1
     $ git format-patch HEAD~
                    </literallayout></para>
                    <para>After the command is run, the current directory contains a
                    numbered <filename>.patch</filename> file for the commit.</para>
                    <para>If you provide several commits as part of the command,
                    the <filename>git format-patch</filename> command produces a numbered
                    series of files in the current directory – one for each commit.
                    If you have more than one patch, you should also use the
                    <filename>--cover</filename> option with the command, which generates a
                    cover letter as the first "patch" in the series.
                    You can then edit the cover letter to provide a description for
                    the series of patches.
                    For information on the <filename>git format-patch</filename> command,
                    see <filename>GIT_FORMAT_PATCH(1)</filename> displayed using the
                    <filename>man git-format-patch</filename> command.</para>
                    <note>If you are or will be a frequent contributor to the Yocto Project
                    or to OpenEmbedded, you might consider requesting a contrib area and the
                    necessary associated rights.</note></listitem>
                <listitem><para>Import the files into your mail client by using the
                    <filename>git send-email</filename> command.
                    <note>In order to use <filename>git send-email</filename>, you must have the
                    the proper Git packages installed.
                    For Ubuntu and Fedora the package is <filename>git-email</filename>.</note></para>
                    <para>The <filename>git send-email</filename> command sends email by using a local
                    or remote Mail Transport Agent (MTA) such as
                    <filename>msmtp</filename>, <filename>sendmail</filename>, or through a direct
                    <filename>smtp</filename> configuration in your Git <filename>config</filename>
                    file.
                    If you are submitting patches through email only, it is very important
                    that you submit them without any whitespace or HTML formatting that
                    either you or your mailer introduces.
                    The maintainer that receives your patches needs to be able to save and
                    apply them directly from your emails.
                    A good way to verify that what you are sending will be applicable by the
                    maintainer is to do a dry run and send them to yourself and then
                    save and apply them as the maintainer would.</para>
                    <para>The <filename>git send-email</filename> command is the preferred method
                    for sending your patches since there is no risk of compromising whitespace
                    in the body of the message, which can occur when you use your own mail client.
                    The command also has several options that let you
                    specify recipients and perform further editing of the email message.
                    For information on how to use the <filename>git send-email</filename> command,
                    use the <filename>man git-send-email</filename> command.</para></listitem>
            </itemizedlist>
        </para>
    </section>
</section>
</chapter>
<!--
vim: expandtab tw=80 ts=4
-->