summaryrefslogtreecommitdiffstats
path: root/documentation/dev-manual/dev-manual-model.xml
blob: 0055bccfedd8093b6c163b7ef59b72a35dab7043 (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
<!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-model'>

<title>Common Development Models</title>

<para>
    Many development models exist for which you can use the Yocto Project.
    This chapter overviews simple methods that use tools provided by the
    Yocto Project:
    <itemizedlist>
        <listitem><para><emphasis>System Development:</emphasis>
             System Development covers Board Support Package (BSP) development
             and kernel modification or configuration.
             For an example on how to create a BSP, see the
             "<ulink url='&YOCTO_DOCS_BSP_URL;#creating-a-new-bsp-layer-using-the-yocto-bsp-script'>Creating a New BSP Layer Using the yocto-bsp Script</ulink>"
             section in the Yocto Project Board Support Package (BSP)
             Developer's Guide.
             For more complete information on how to work with the kernel,
             see the
             <ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;'>Yocto Project Linux Kernel Development Manual</ulink>.
             </para></listitem>
         <listitem><para><emphasis>Temporary Source Code Modification:</emphasis>
             Direct modification of temporary source code is a convenient
             development model to quickly iterate and develop towards a
             solution.
             Once you implement the solution, you should of course take
             steps to get the changes upstream and applied in the affected
             recipes.
             </para></listitem>
         <listitem><para><emphasis>Using a Development Shell:</emphasis>
             You can use a
             <link linkend='platdev-appdev-devshell'><filename>devshell</filename></link>
             to efficiently debug
             commands or simply edit packages.
             Working inside a development shell is a quick way to set up the
             OpenEmbedded build environment to work on parts of a project.
             </para></listitem>
     </itemizedlist>
</para>

<section id='system-development-model'>
    <title>System Development Workflow</title>

    <para>
        System development involves modification or creation of an image that you want to run on
        a specific hardware target.
        Usually, when you want to create an image that runs on embedded hardware, the image does
        not require the same number of features that a full-fledged Linux distribution provides.
        Thus, you can create a much smaller image that is designed to use only the
        features for your particular hardware.
    </para>

    <para>
        To help you understand how system development works in the Yocto Project, this section
        covers two types of image development:  BSP creation and kernel modification or
        configuration.
    </para>

    <section id='modifying-the-kernel'>
        <title><anchor id='kernel-spot' />Modifying the Kernel</title>

        <para>
            Kernel modification involves changing the Yocto Project kernel, which could involve changing
            configuration options as well as adding new kernel recipes.
            Configuration changes can be added in the form of configuration fragments, while recipe
            modification comes through the kernel's <filename>recipes-kernel</filename> area
            in a kernel layer you create.
        </para>

        <para>
            The remainder of this section presents a high-level overview of the Yocto Project
            kernel architecture and the steps to modify the kernel.
            You can reference the
            "<link linkend='patching-the-kernel'>Patching the Kernel</link>" section
            for an example that changes the source code of the kernel.
            For information on how to configure the kernel, see the
            "<link linkend='configuring-the-kernel'>Configuring the Kernel</link>" section.
            For more information on the kernel and on modifying the kernel, see the
            <ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;'>Yocto Project Linux Kernel Development Manual</ulink>.
        </para>

        <section id='kernel-modification-workflow'>
            <title>Kernel Modification Workflow</title>

            <para>
                This illustration and the following list summarizes the kernel modification general workflow.
            </para>

            <para>
                <imagedata fileref="figures/kernel-dev-flow.png"
                    width="6in" depth="5in" align="center" scalefit="1" />
            </para>

            <para>
                <orderedlist>
                    <listitem><para><emphasis>Set up your host development system to support
                        development using the Yocto Project</emphasis>:  See
                        "<ulink url='&YOCTO_DOCS_QS_URL;#the-linux-distro'>The Linux Distribution</ulink>" and
                        "<ulink url='&YOCTO_DOCS_QS_URL;#packages'>The Build Host Packages</ulink>" sections both
                        in the Yocto Project Quick Start for requirements.</para></listitem>
                    <listitem><para><emphasis>Establish a local copy of project files on your
                        system</emphasis>:  Having the
                        <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
                        on your system gives you access to the build process and tools
                        you need.
                        For information on how to get these files, see the
                        "<link linkend='cloning-the-poky-repository'>Cloning the <filename>poky</filename> Repository</link>"
                        section.
                        </para></listitem>
                    <listitem><para><emphasis>Establish the temporary kernel source files</emphasis>:
                        Temporary kernel source files are kept in the
                        <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
                        created by the
                        OpenEmbedded build system when you run BitBake.
                        If you have never built the kernel in which you are
                        interested, you need to run an initial build to
                        establish local kernel source files.</para>
                        <para>If you are building an image for the first time, you need to get the build
                        environment ready by sourcing an environment setup script
                        (i.e. <filename>oe-init-build-env</filename> or
                        <filename>oe-init-build-env-memres</filename>).
                        You also need to be sure two key configuration files
                        (<filename>local.conf</filename> and <filename>bblayers.conf</filename>)
                        are configured appropriately.</para>
                        <para>The entire process for building an image is overviewed in the
                        "<ulink url='&YOCTO_DOCS_QS_URL;#qs-building-images'>Building Images</ulink>"
                        section of the Yocto Project Quick Start.
                        You might want to reference this information.
                        You can find more information on BitBake in the
                        <ulink url='&YOCTO_DOCS_BB_URL;'>BitBake User Manual</ulink>.
                        </para>
                        <para>The build process supports several types of images to satisfy different needs.
                        See the "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>" chapter in
                        the Yocto Project Reference Manual for information on supported images.
                        </para></listitem>
                    <listitem><para><emphasis>Make changes to the kernel source code if
                        applicable</emphasis>:  Modifying the kernel does not always mean directly
                        changing source files.
                        However, if you have to do this, you make the changes to the files in the
                        Build Directory.</para></listitem>
                    <listitem><para><emphasis>Make kernel configuration changes if applicable</emphasis>:
                        If your situation calls for changing the kernel's
                        configuration, you can use
                        <ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#generating-configuration-files'><filename>menuconfig</filename></ulink>,
                        which allows you to interactively develop and test the
                        configuration changes you are making to the kernel.
                        Saving changes you make with
                        <filename>menuconfig</filename> updates
                        the kernel's <filename>.config</filename> file.
                        <note><title>Warning</title>
                            Try to resist the temptation to directly edit an
                            existing <filename>.config</filename> file, which is
                            found in the Build Directory among the source code
                            used for the build (e.g. see the workflow illustration
                            in the
                            "<link linkend='kernel-modification-workflow'>Kernel Modification Workflow</link>"
                            section).
                            Doing so, can produce unexpected results when the
                            OpenEmbedded build system regenerates the configuration
                            file.
                        </note>
                        Once you are satisfied with the configuration
                        changes made using <filename>menuconfig</filename>
                        and you have saved them, you can directly compare the
                        resulting <filename>.config</filename> file against an
                        existing original and gather those changes into a
                        <link linkend='creating-config-fragments'>configuration fragment file</link>
                        to be referenced from within the kernel's
                        <filename>.bbappend</filename> file.</para>

                        <para>Additionally, if you are working in a BSP layer
                        and need to modify the BSP's kernel's configuration,
                        you can use the
                        <ulink url='&YOCTO_DOCS_BSP_URL;#managing-kernel-patches-and-config-items-with-yocto-kernel'><filename>yocto-kernel</filename></ulink>
                        script as well as <filename>menuconfig</filename>.
                        The <filename>yocto-kernel</filename> script lets
                        you interactively set up kernel configurations.
                        </para></listitem>
                    <listitem><para><emphasis>Rebuild the kernel image with your changes</emphasis>:
                        Rebuilding the kernel image applies your changes.
                        </para></listitem>
                </orderedlist>
            </para>
        </section>
    </section>
</section>

<section id="dev-modifying-source-code">
    <title>Modifying Source Code</title>

    <para>
        A common development workflow consists of modifying project source
        files that are external to the Yocto Project and then integrating
        that project's build output into an image built using the
        OpenEmbedded build system.
        Given this scenario, development engineers typically want to stick
        to their familiar project development tools and methods, which allows
        them to just focus on the project.
    </para>

    <para>
        Several workflows exist that allow you to develop, build, and test
        code that is going to be integrated into an image built using the
        OpenEmbedded build system.
        This section describes two:
        <itemizedlist>
            <listitem><para><emphasis><filename>devtool</filename>:</emphasis>
                A set of tools to aid in working on the source code built by
                the OpenEmbedded build system.
                Section
                "<link linkend='using-devtool-in-your-workflow'>Using <filename>devtool</filename> in Your Workflow</link>"
                describes this workflow.
                If you want more information that showcases the workflow, click
                <ulink url='https://drive.google.com/a/linaro.org/file/d/0B3KGzY5fW7laTDVxUXo3UDRvd2s/view'>here</ulink>
                for a presentation by Trevor Woerner that, while somewhat dated,
                provides detailed background information and a complete
                working tutorial.
                </para></listitem>
            <listitem><para><emphasis><ulink url='http://savannah.nongnu.org/projects/quilt'>Quilt</ulink>:</emphasis>
                A powerful tool that allows you to capture source
                code changes without having a clean source tree.
                While Quilt is not the preferred workflow of the two, this
                section includes it for users that are committed to using
                the tool.
                See the
                "<link linkend='using-a-quilt-workflow'>Using Quilt in Your Workflow</link>"
                section for more information.
                </para></listitem>
        </itemizedlist>
    </para>

    <section id='using-devtool-in-your-workflow'>
        <title>Using <filename>devtool</filename> in Your Workflow</title>

        <para>
            As mentioned earlier, <filename>devtool</filename> helps
            you easily develop projects whose build output must be part of
            an image built using the OpenEmbedded build system.
        </para>

        <para>
            Three entry points exist that allow you to develop using
            <filename>devtool</filename>:
            <itemizedlist>
                <listitem><para><emphasis><filename>devtool add</filename></emphasis>
                    </para></listitem>
                <listitem><para><emphasis><filename>devtool modify</filename></emphasis>
                    </para></listitem>
                <listitem><para><emphasis><filename>devtool upgrade</filename></emphasis>
                    </para></listitem>
            </itemizedlist>
        </para>

        <para>
            The remainder of this section presents these workflows.
            See the
            "<ulink url='&YOCTO_DOCS_REF_URL;#ref-devtool-reference'><filename>devtool</filename>&nbsp;Quick Reference</ulink>"
            in the Yocto Project Reference Manual for a
            <filename>devtool</filename> quick reference.
        </para>

        <section id='use-devtool-to-integrate-new-code'>
            <title>Use <filename>devtool add</filename> to Add an Application</title>

            <para>
                The <filename>devtool add</filename> command generates
                a new recipe based on existing source code.
                This command takes advantage of the
                <ulink url='&YOCTO_DOCS_DEV_URL;#devtool-the-workspace-layer-structure'>workspace</ulink>
                layer that many <filename>devtool</filename> commands
                use.
                The command is flexible enough to allow you to extract source
                code into both the workspace or a separate local Git repository
                and to use existing code that does not need to be extracted.
            </para>

            <para>
                Depending on your particular scenario, the arguments and options
                you use with <filename>devtool add</filename> form different
                combinations.
                The following diagram shows common development flows
                you would use with the <filename>devtool add</filename>
                command:
            </para>

            <para>
                <imagedata fileref="figures/devtool-add-flow.png" align="center" />
            </para>

            <para>
                <orderedlist>
                    <listitem><para><emphasis>Generating the New Recipe</emphasis>:
                        The top part of the flow shows three scenarios by which
                        you could use <filename>devtool add</filename> to
                        generate a recipe based on existing source code.</para>

                        <para>In a shared development environment, it is
                        typical where other developers are responsible for
                        various areas of source code.
                        As a developer, you are probably interested in using
                        that source code as part of your development using
                        the Yocto Project.
                        All you need is access to the code, a recipe, and a
                        controlled area in which to do your work.</para>

                        <para>Within the diagram, three possible scenarios
                        feed into the <filename>devtool add</filename> workflow:
                        <itemizedlist>
                            <listitem><para><emphasis>Left</emphasis>:
                                The left scenario represents a common situation
                                where the source code does not exist locally
                                and needs to be extracted.
                                In this situation, you just let it get
                                extracted to the default workspace - you do not
                                want it in some specific location outside of the
                                workspace.
                                Thus, everything you need will be located in the
                                workspace:
                                <literallayout class='monospaced'>
     $ devtool add <replaceable>recipe fetchuri</replaceable>
                                </literallayout>
                                With this command, <filename>devtool</filename>
                                creates a recipe and an append file in the
                                workspace as well as extracts the upstream
                                source files into a local Git repository also
                                within the <filename>sources</filename> folder.
                                </para></listitem>
                            <listitem><para><emphasis>Middle</emphasis>:
                                The middle scenario also represents a situation where
                                the source code does not exist locally.
                                In this case, the code is again upstream
                                and needs to be extracted to some
                                local area - this time outside of the default
                                workspace.
                                If required, <filename>devtool</filename>
                                always creates
                                a Git repository locally during the extraction.
                                Furthermore, the first positional argument
                                <replaceable>srctree</replaceable> in this case
                                identifies where the
                                <filename>devtool add</filename> command
                                will locate the extracted code outside of the
                                workspace:
                                <literallayout class='monospaced'>
     $ devtool add <replaceable>recipe srctree fetchuri</replaceable>
                                </literallayout>
                                In summary, the source code is pulled from
                                <replaceable>fetchuri</replaceable> and extracted
                                into the location defined by
                                <replaceable>srctree</replaceable> as a local
                                Git repository.</para>

                                <para>Within workspace, <filename>devtool</filename>
                                creates both the recipe and an append file
                                for the recipe.
                                </para></listitem>
                            <listitem><para><emphasis>Right</emphasis>:
                                The right scenario represents a situation
                                where the source tree (srctree) has been
                                previously prepared outside of the
                                <filename>devtool</filename> workspace.
                                </para>

                                <para>The following command names the recipe
                                and identifies where the existing source tree
                                is located:
                                <literallayout class='monospaced'>
     $ devtool add <replaceable>recipe srctree</replaceable>
                                </literallayout>
                                The command examines the source code and creates
                                a recipe for it placing the recipe into the
                                workspace.</para>

                                <para>Because the extracted source code already exists,
                                <filename>devtool</filename> does not try to
                                relocate it into the workspace - just the new
                                the recipe is placed in the workspace.</para>

                                <para>Aside from a recipe folder, the command
                                also creates an append folder and places an initial
                                <filename>*.bbappend</filename> within.
                                </para></listitem>
                        </itemizedlist>
                        </para></listitem>
                    <listitem><para><emphasis>Edit the Recipe</emphasis>:
                        At this point, you can use <filename>devtool edit-recipe</filename>
                        to open up the editor as defined by the
                        <filename>$EDITOR</filename> environment variable
                        and modify the file:
                        <literallayout class='monospaced'>
     $ devtool edit-recipe <replaceable>recipe</replaceable>
                        </literallayout>
                        From within the editor, you can make modifications to the
                        recipe that take affect when you build it later.
                        </para></listitem>
                    <listitem><para><emphasis>Build the Recipe or Rebuild the Image</emphasis>:
                        At this point in the flow, the next step you
                        take depends on what you are going to do with
                        the new code.</para>
                        <para>If you need to take the build output and eventually
                        move it to the target hardware, you would use
                        <filename>devtool build</filename>:
                        <literallayout class='monospaced'>
     $ devtool build <replaceable>recipe</replaceable>
                        </literallayout></para>
                        <para>On the other hand, if you want an image to
                        contain the recipe's packages for immediate deployment
                        onto a device (e.g. for testing purposes), you can use
                        the <filename>devtool build-image</filename> command:
                        <literallayout class='monospaced'>
     $ devtool build-image <replaceable>image</replaceable>
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Deploy the Build Output</emphasis>:
                        When you use the <filename>devtool build</filename>
                        command to build out your recipe, you probably want to
                        see if the resulting build output works as expected on target
                        hardware.
                        <note>
                            This step assumes you have a previously built
                            image that is already either running in QEMU or
                            running on actual hardware.
                            Also, it is assumed that for deployment of the image
                            to the target, SSH is installed in the image and if
                            the image is running on real hardware that you have
                            network access to and from your development machine.
                        </note>
                        You can deploy your build output to that target hardware by
                        using the <filename>devtool deploy-target</filename> command:
                        <literallayout class='monospaced'>
     $ devtool deploy-target <replaceable>recipe target</replaceable>
                        </literallayout>
                        The <replaceable>target</replaceable> is a live target machine
                        running as an SSH server.</para>

                        <para>You can, of course, also deploy the image you build
                        using the <filename>devtool build-image</filename> command
                        to actual hardware.
                        However, <filename>devtool</filename> does not provide a
                        specific command that allows you to do this.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Finish Your Work With the Recipe</emphasis>:
                        The <filename>devtool finish</filename> command creates
                        any patches corresponding to commits in the local
                        Git repository, moves the new recipe to a more permanent
                        layer, and then resets the recipe so that the recipe is
                        built normally rather than from the workspace.
                        <literallayout class='monospaced'>
     $ devtool finish <replaceable>recipe layer</replaceable>
                        </literallayout>
                        <note>
                            Any changes you want to turn into patches must be
                            committed to the Git repository in the source tree.
                        </note></para>

                        <para>As mentioned, the <filename>devtool finish</filename>
                        command moves the final recipe to its permanent layer.
                        </para>

                        <para>As a final process of the
                        <filename>devtool finish</filename> command, the state
                        of the standard layers and the upstream source is
                        restored so that you can build the recipe from those
                        areas rather than the workspace.
                        <note>
                            You can use the <filename>devtool reset</filename>
                            command to put things back should you decide you
                            do not want to proceed with your work.
                            If you do use this command, realize that the source
                            tree is preserved.
                        </note>
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='devtool-use-devtool-modify-to-enable-work-on-code-associated-with-an-existing-recipe'>
            <title>Use <filename>devtool modify</filename> to Modify the Source of an Existing Component</title>

            <para>
                The <filename>devtool modify</filename> command prepares the
                way to work on existing code that already has a recipe in
                place.
                The command is flexible enough to allow you to extract code,
                specify the existing recipe, and keep track of and gather any
                patch files from other developers that are
                associated with the code.
            </para>

            <para>
                Depending on your particular scenario, the arguments and options
                you use with <filename>devtool modify</filename> form different
                combinations.
                The following diagram shows common development flows
                you would use with the <filename>devtool modify</filename>
                command:
            </para>

            <para>
                <imagedata fileref="figures/devtool-modify-flow.png" align="center" />
            </para>

            <para>
                <orderedlist>
                    <listitem><para><emphasis>Preparing to Modify the Code</emphasis>:
                        The top part of the flow shows three scenarios by which
                        you could use <filename>devtool modify</filename> to
                        prepare to work on source files.
                        Each scenario assumes the following:
                        <itemizedlist>
                            <listitem><para>The recipe exists in some layer external
                                to the <filename>devtool</filename> workspace.
                                </para></listitem>
                            <listitem><para>The source files exist upstream in an
                                un-extracted state or locally in a previously
                                extracted state.
                                </para></listitem>
                        </itemizedlist>
                        The typical situation is where another developer has
                        created some layer for use with the Yocto Project and
                        their recipe already resides in that layer.
                        Furthermore, their source code is readily available
                        either upstream or locally.
                        <itemizedlist>
                            <listitem><para><emphasis>Left</emphasis>:
                                The left scenario represents a common situation
                                where the source code does not exist locally
                                and needs to be extracted.
                                In this situation, the source is extracted
                                into the default workspace location.
                                The recipe, in this scenario, is in its own
                                layer outside the workspace
                                (i.e.
                                <filename>meta-</filename><replaceable>layername</replaceable>).
                                </para>

                                <para>The following command identifies the recipe
                                and by default extracts the source files:
                                <literallayout class='monospaced'>
     $ devtool modify <replaceable>recipe</replaceable>
                                </literallayout>
                                Once <filename>devtool</filename>locates the recipe,
                                it uses the
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                                variable to locate the source code and
                                any local patch files from other developers are
                                located.
                                <note>
                                    You cannot provide an URL for
                                    <replaceable>srctree</replaceable> when using the
                                    <filename>devtool modify</filename> command.
                                </note>
                                With this scenario, however, since no
                                <replaceable>srctree</replaceable> argument exists, the
                                <filename>devtool modify</filename> command by default
                                extracts the source files to a Git structure.
                                Furthermore, the location for the extracted source is the
                                default area within the workspace.
                                The result is that the command sets up both the source
                                code and an append file within the workspace with the
                                recipe remaining in its original location.
                                </para></listitem>
                            <listitem><para><emphasis>Middle</emphasis>:
                                The middle scenario represents a situation where
                                the source code also does not exist locally.
                                In this case, the code is again upstream
                                and needs to be extracted to some
                                local area as a Git repository.
                                The recipe, in this scenario, is again in its own
                                layer outside the workspace.</para>

                                <para>The following command tells
                                <filename>devtool</filename> what recipe with
                                which to work and, in this case, identifies a local
                                area for the extracted source files that is outside
                                of the default workspace:
                                <literallayout class='monospaced'>
     $ devtool modify <replaceable>recipe srctree</replaceable>
                                </literallayout>
                                As with all extractions, the command uses
                                the recipe's <filename>SRC_URI</filename> to locate the
                                source files.
                                Once the files are located, the command by default
                                extracts them.
                                Providing the <replaceable>srctree</replaceable>
                                argument instructs <filename>devtool</filename> where
                                to place the extracted source.</para>

                                <para>Within workspace, <filename>devtool</filename>
                                creates an append file for the recipe.
                                The recipe remains in its original location but
                                the source files are extracted to the location you
                                provided with <replaceable>srctree</replaceable>.
                                </para></listitem>
                            <listitem><para><emphasis>Right</emphasis>:
                                The right scenario represents a situation
                                where the source tree
                                (<replaceable>srctree</replaceable>) exists as a
                                previously extracted Git structure outside of
                                the <filename>devtool</filename> workspace.
                                In this example, the recipe also exists
                                elsewhere in its own layer.
                                </para>

                                <para>The following command tells
                                <filename>devtool</filename> the recipe
                                with which to work, uses the "-n" option to indicate
                                source does not need to be extracted, and uses
                                <replaceable>srctree</replaceable> to point to the
                                previously extracted source files:
                                <literallayout class='monospaced'>
     $ devtool modify -n <replaceable>recipe srctree</replaceable>
                                </literallayout>
                                </para>

                                <para>Once the command finishes, it creates only
                                an append file for the recipe in the workspace.
                                The recipe and the source code remain in their
                                original locations.
                                </para></listitem>
                            </itemizedlist>
                        </para></listitem>
                    <listitem><para><emphasis>Edit the Source</emphasis>:
                        Once you have used the <filename>devtool modify</filename>
                        command, you are free to make changes to the source
                        files.
                        You can use any editor you like to make and save
                        your source code modifications.
                        </para></listitem>
                    <listitem><para><emphasis>Build the Recipe</emphasis>:
                        Once you have updated the source files, you can build
                        the recipe.
                        </para></listitem>
                    <listitem><para><emphasis>Deploy the Build Output</emphasis>:
                        When you use the <filename>devtool build</filename>
                        command to build out your recipe, you probably want to see
                        if the resulting build output works as expected on target
                        hardware.
                        <note>
                            This step assumes you have a previously built
                            image that is already either running in QEMU or
                            running on actual hardware.
                            Also, it is assumed that for deployment of the image
                            to the target, SSH is installed in the image and if
                            the image is running on real hardware that you have
                            network access to and from your development machine.
                        </note>
                        You can deploy your build output to that target hardware by
                        using the <filename>devtool deploy-target</filename> command:
                        <literallayout class='monospaced'>
     $ devtool deploy-target <replaceable>recipe target</replaceable>
                        </literallayout>
                        The <replaceable>target</replaceable> is a live target machine
                        running as an SSH server.</para>

                        <para>You can, of course, also deploy the image you build
                        using the <filename>devtool build-image</filename> command
                        to actual hardware.
                        However, <filename>devtool</filename> does not provide a
                        specific command that allows you to do this.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Finish Your Work With the Recipe</emphasis>:
                        The <filename>devtool finish</filename> command creates
                        any patches corresponding to commits in the local
                        Git repository, updates the recipe to point to them
                        (or creates a <filename>.bbappend</filename> file to do
                        so, depending on the specified destination layer), and
                        then resets the recipe so that the recipe is built normally
                        rather than from the workspace.
                        <literallayout class='monospaced'>
     $ devtool finish <replaceable>recipe layer</replaceable>
                        </literallayout>
                        <note>
                            Any changes you want to turn into patches must be
                            committed to the Git repository in the source tree.
                        </note></para>

                        <para>Because there is no need to move the recipe,
                        <filename>devtool finish</filename> either updates the
                        original recipe in the original layer or the command
                        creates a <filename>.bbappend</filename> in a different
                        layer as provided by <replaceable>layer</replaceable>.
                        </para>

                        <para>As a final process of the
                        <filename>devtool finish</filename> command, the state
                        of the standard layers and the upstream source is
                        restored so that you can build the recipe from those
                        areas rather than the workspace.
                        <note>
                            You can use the <filename>devtool reset</filename>
                            command to put things back should you decide you
                            do not want to proceed with your work.
                            If you do use this command, realize that the source
                            tree is preserved.
                        </note>
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='devtool-use-devtool-upgrade-to-create-a-version-of-the-recipe-that-supports-a-newer-version-of-the-software'>
            <title>Use <filename>devtool upgrade</filename> to Create a Version of the Recipe that Supports a Newer Version of the Software</title>

            <para>
                The <filename>devtool upgrade</filename> command updates
                an existing recipe so that you can build it for an updated
                set of source files.
                The command is flexible enough to allow you to specify
                source code revision and versioning schemes, extract code into
                or out of the <filename>devtool</filename> workspace, and
                work with any source file forms that the fetchers support.
            </para>

            <para>
                The following diagram shows the common development flow
                you would use with the <filename>devtool upgrade</filename>
                command:
            </para>

            <para>
                <imagedata fileref="figures/devtool-upgrade-flow.png" align="center" />
            </para>

            <para>
                <orderedlist>
                    <listitem><para><emphasis>Initiate the Upgrade</emphasis>:
                        The top part of the flow shows a typical scenario by which
                        you could use <filename>devtool upgrade</filename>.
                        The following conditions exist:
                        <itemizedlist>
                            <listitem><para>The recipe exists in some layer external
                                to the <filename>devtool</filename> workspace.
                                </para></listitem>
                            <listitem><para>The source files for the new release
                                exist adjacent to the same location pointed to by
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                                in the recipe (e.g. a tarball with the new version
                                number in the name, or as a different revision in
                                the upstream Git repository).
                                </para></listitem>
                        </itemizedlist>
                        A common situation is where third-party software has
                        undergone a revision so that it has been upgraded.
                        The recipe you have access to is likely in your own layer.
                        Thus, you need to upgrade the recipe to use the
                        newer version of the software:
                        <literallayout class='monospaced'>
     $ devtool upgrade -V <replaceable>version recipe</replaceable>
                        </literallayout>
                        By default, the <filename>devtool upgrade</filename> command
                        extracts source code into the <filename>sources</filename>
                        directory in the workspace.
                        If you want the code extracted to any other location, you
                        need to provide the <replaceable>srctree</replaceable>
                        positional argument with the command as follows:
                        <literallayout class='monospaced'>
     $ devtool upgrade -V <replaceable>version recipe srctree</replaceable>
                        </literallayout>
                        Also, in this example, the "-V" option is used to specify
                        the new version.
                        If the source files pointed to by the
                        <filename>SRC_URI</filename> statement in the recipe are
                        in a Git repository, you must provide the "-S" option and
                        specify a revision for the software.</para>

                        <para>Once <filename>devtool</filename> locates the recipe,
                        it uses the <filename>SRC_URI</filename> variable to locate
                        the source code and any local patch files from other
                        developers are located.
                        The result is that the command sets up the source
                        code, the new version of the recipe, and an append file
                        all within the workspace.
                        </para></listitem>
                    <listitem><para><emphasis>Resolve any Conflicts created by the Upgrade</emphasis>:
                        At this point, there could be some conflicts due to the
                        software being upgraded to a new version.
                        This would occur if your recipe specifies some patch files in
                        <filename>SRC_URI</filename> that conflict with changes
                        made in the new version of the software.
                        If this is the case, you need to resolve the conflicts
                        by editing the source and following the normal
                        <filename>git rebase</filename> conflict resolution
                        process.</para>

                        <para>Before moving onto the next step, be sure to resolve any
                        such conflicts created through use of a newer or different
                        version of the software.
                        </para></listitem>
                    <listitem><para><emphasis>Build the Recipe</emphasis>:
                        Once you have your recipe in order, you can build it.
                        You can either use <filename>devtool build</filename> or
                        <filename>bitbake</filename>.
                        Either method produces build output that is stored
                        in
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>.
                        </para></listitem>
                    <listitem><para><emphasis>Deploy the Build Output</emphasis>:
                        When you use the <filename>devtool build</filename>
                        command or <filename>bitbake</filename> to build out your
                        recipe, you probably want to see if the resulting build
                        output works as expected on target hardware.
                        <note>
                            This step assumes you have a previously built
                            image that is already either running in QEMU or
                            running on actual hardware.
                            Also, it is assumed that for deployment of the image
                            to the target, SSH is installed in the image and if
                            the image is running on real hardware that you have
                            network access to and from your development machine.
                        </note>
                        You can deploy your build output to that target hardware by
                        using the <filename>devtool deploy-target</filename> command:
                        <literallayout class='monospaced'>
     $ devtool deploy-target <replaceable>recipe target</replaceable>
                        </literallayout>
                        The <replaceable>target</replaceable> is a live target machine
                        running as an SSH server.</para>

                        <para>You can, of course, also deploy the image you build
                        using the <filename>devtool build-image</filename> command
                        to actual hardware.
                        However, <filename>devtool</filename> does not provide a
                        specific command that allows you to do this.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Finish Your Work With the Recipe</emphasis>:
                        The <filename>devtool finish</filename> command creates
                        any patches corresponding to commits in the local
                        Git repository, moves the new recipe to a more permanent
                        layer, and then resets the recipe so that the recipe is
                        built normally rather than from the workspace.
                        If you specify a destination layer that is the same as
                        the original source, then the old version of the
                        recipe and associated files will be removed prior to
                        adding the new version.
                        <literallayout class='monospaced'>
     $ devtool finish <replaceable>recipe layer</replaceable>
                        </literallayout>
                        <note>
                            Any changes you want to turn into patches must be
                            committed to the Git repository in the source tree.
                        </note></para>
                        <para>As a final process of the
                        <filename>devtool finish</filename> command, the state
                        of the standard layers and the upstream source is
                        restored so that you can build the recipe from those
                        areas rather than the workspace.
                        <note>
                            You can use the <filename>devtool reset</filename>
                            command to put things back should you decide you
                            do not want to proceed with your work.
                            If you do use this command, realize that the source
                            tree is preserved.
                        </note>
                        </para></listitem>
                </orderedlist>
            </para>
        </section>
    </section>

    <section id="using-a-quilt-workflow">
        <title>Using Quilt in Your Workflow</title>

        <para>
            <ulink url='http://savannah.nongnu.org/projects/quilt'>Quilt</ulink>
            is a powerful tool that allows you to capture source code changes
            without having a clean source tree.
            This section outlines the typical workflow you can use to modify
            source code, test changes, and then preserve the changes in the
            form of a patch all using Quilt.
            <note><title>Tip</title>
                With regard to preserving changes to source files if you
                clean a recipe or have <filename>rm_work</filename> enabled,
                the workflow described in the
                "<link linkend='using-devtool-in-your-workflow'>Using <filename>devtool</filename> in Your Workflow</link>"
                section is a safer development flow than the flow that
                uses Quilt.
            </note>
        </para>

        <para>
            Follow these general steps:
            <orderedlist>
                <listitem><para><emphasis>Find the Source Code:</emphasis>
                    Temporary source code used by the OpenEmbedded build system
                    is kept in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
                    See the
                    "<link linkend='finding-the-temporary-source-code'>Finding Temporary Source Code</link>"
                    section to learn how to locate the directory that has the
                    temporary source code for a particular package.
                    </para></listitem>
                <listitem><para><emphasis>Change Your Working Directory:</emphasis>
                    You need to be in the directory that has the temporary source code.
                    That directory is defined by the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>
                    variable.</para></listitem>
                <listitem><para><emphasis>Create a New Patch:</emphasis>
                    Before modifying source code, you need to create a new patch.
                    To create a new patch file, use <filename>quilt new</filename> as below:
                    <literallayout class='monospaced'>
     $ quilt new my_changes.patch
                    </literallayout></para></listitem>
                <listitem><para><emphasis>Notify Quilt and Add Files:</emphasis>
                    After creating the patch, you need to notify Quilt about the files
                    you plan to edit.
                    You notify Quilt by adding the files to the patch you just created:
                    <literallayout class='monospaced'>
     $ quilt add file1.c file2.c file3.c
                    </literallayout>
                    </para></listitem>
                <listitem><para><emphasis>Edit the Files:</emphasis>
                    Make your changes in the source code to the files you added
                    to the patch.
                    </para></listitem>
                <listitem><para><emphasis>Test Your Changes:</emphasis>
                    Once you have modified the source code, the easiest way to
                    test your changes is by calling the
                    <filename>do_compile</filename> task as shown in the
                    following example:
                    <literallayout class='monospaced'>
     $ bitbake -c compile -f <replaceable>package</replaceable>
                    </literallayout>
                    The <filename>-f</filename> or <filename>--force</filename>
                    option forces the specified task to execute.
                    If you find problems with your code, you can just keep editing and
                    re-testing iteratively until things work as expected.
                    <note>All the modifications you make to the temporary source code
                    disappear once you run the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-clean'><filename>do_clean</filename></ulink>
                    or
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-cleanall'><filename>do_cleanall</filename></ulink>
                    tasks using BitBake (i.e.
                    <filename>bitbake -c clean <replaceable>package</replaceable></filename>
                    and
                    <filename>bitbake -c cleanall <replaceable>package</replaceable></filename>).
                    Modifications will also disappear if you use the <filename>rm_work</filename>
                    feature as described in the
                    "<ulink url='&YOCTO_DOCS_QS_URL;#qs-building-images'>Building Images</ulink>"
                    section of the Yocto Project Quick Start.
                    </note></para></listitem>
                <listitem><para><emphasis>Generate the Patch:</emphasis>
                    Once your changes work as expected, you need to use Quilt to generate the final patch that
                    contains all your modifications.
                    <literallayout class='monospaced'>
     $ quilt refresh
                    </literallayout>
                    At this point, the <filename>my_changes.patch</filename> file has all your edits made
                    to the <filename>file1.c</filename>, <filename>file2.c</filename>, and
                    <filename>file3.c</filename> files.</para>
                    <para>You can find the resulting patch file in the <filename>patches/</filename>
                    subdirectory of the source (<filename>S</filename>) directory.</para></listitem>
                <listitem><para><emphasis>Copy the Patch File:</emphasis>
                    For simplicity, copy the patch file into a directory named <filename>files</filename>,
                    which you can create in the same directory that holds the recipe
                    (<filename>.bb</filename>) file or the
                    append (<filename>.bbappend</filename>) file.
                    Placing the patch here guarantees that the OpenEmbedded build system will find
                    the patch.
                    Next, add the patch into the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>
                    of the recipe.
                    Here is an example:
                    <literallayout class='monospaced'>
     SRC_URI += "file://my_changes.patch"
                    </literallayout></para></listitem>
            </orderedlist>
        </para>
    </section>

    <section id='finding-the-temporary-source-code'>
        <title>Finding Temporary Source Code</title>

        <para>
            You might find it helpful during development to modify the
            temporary source code used by recipes to build packages.
            For example, suppose you are developing a patch and you need to
            experiment a bit to figure out your solution.
            After you have initially built the package, you can iteratively
            tweak the source code, which is located in the
            <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>,
            and then you can force a re-compile and quickly test your altered code.
            Once you settle on a solution, you can then preserve your changes
            in the form of patches.
            If you are using Quilt for development, see the
            "<link linkend='using-a-quilt-workflow'>Using Quilt in Your Workflow</link>"
            section for more information.
        </para>

        <para>
            During a build, the unpacked temporary source code used by recipes
            to build packages is available in the Build Directory as
            defined by the
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename> variable.
            Below is the default value for the <filename>S</filename> variable as defined in the
            <filename>meta/conf/bitbake.conf</filename> configuration file in the
            <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>:
            <literallayout class='monospaced'>
     S = "${WORKDIR}/${BP}"
            </literallayout>
            You should be aware that many recipes override the <filename>S</filename> variable.
            For example, recipes that fetch their source from Git usually set
            <filename>S</filename> to <filename>${WORKDIR}/git</filename>.
            <note>
                The
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BP'><filename>BP</filename></ulink>
                represents the base recipe name, which consists of the name and version:
                <literallayout class='monospaced'>
     BP = "${BPN}-${PV}"
                </literallayout>
            </note>
        </para>

        <para>
            The path to the work directory for the recipe
            (<ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>)
            is defined as follows:
            <literallayout class='monospaced'>
     ${TMPDIR}/work/${MULTIMACH_TARGET_SYS}/${PN}/${EXTENDPE}${PV}-${PR}
            </literallayout>
            The actual directory depends on several things:
            <itemizedlist>
                <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>:
                    The top-level build output directory</listitem>
                <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-MULTIMACH_TARGET_SYS'><filename>MULTIMACH_TARGET_SYS</filename></ulink>:
                    The target system identifier</listitem>
                <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>:
                    The recipe name</listitem>
                <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-EXTENDPE'><filename>EXTENDPE</filename></ulink>:
                    The epoch - (if
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PE'><filename>PE</filename></ulink>
                    is not specified, which is usually the case for most
                    recipes, then <filename>EXTENDPE</filename> is blank)</listitem>
                <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>:
                    The recipe version</listitem>
                <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>:
                    The recipe revision</listitem>
            </itemizedlist>
        </para>

        <para>
            As an example, assume a Source Directory top-level folder
            named <filename>poky</filename>, a default Build Directory at
            <filename>poky/build</filename>, and a
            <filename>qemux86-poky-linux</filename> machine target
            system.
            Furthermore, suppose your recipe is named
            <filename>foo_1.3.0.bb</filename>.
            In this case, the work directory the build system uses to
            build the package would be as follows:
            <literallayout class='monospaced'>
     poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0
            </literallayout>
        </para>

        <para>
            Now that you know where to locate the directory that has the
            temporary source code, you can use Quilt as described in section
            "<link linkend='using-a-quilt-workflow'>Using Quilt in Your Workflow</link>"
            to make your edits, test the changes, and preserve the changes in
            the form of patches.
        </para>
    </section>
</section>

<section id="platdev-appdev-devshell">
    <title>Using a Development Shell</title>

    <para>
        When debugging certain commands or even when just editing packages,
        <filename>devshell</filename> can be a useful tool.
        When you invoke <filename>devshell</filename>, all tasks up to and
        including
        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>
        are run for the specified target.
        Then, a new terminal is opened and you are placed in
        <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink><filename>}</filename>,
        the source directory.
        In the new terminal, all the OpenEmbedded build-related environment variables are
        still defined so you can use commands such as <filename>configure</filename> and
        <filename>make</filename>.
        The commands execute just as if the OpenEmbedded build system were executing them.
        Consequently, working this way can be helpful when debugging a build or preparing
        software to be used with the OpenEmbedded build system.
    </para>

    <para>
        Following is an example that uses <filename>devshell</filename> on a target named
        <filename>matchbox-desktop</filename>:
        <literallayout class='monospaced'>
     $ bitbake matchbox-desktop -c devshell
        </literallayout>
    </para>

    <para>
        This command spawns a terminal with a shell prompt within the OpenEmbedded build environment.
        The <ulink url='&YOCTO_DOCS_REF_URL;#var-OE_TERMINAL'><filename>OE_TERMINAL</filename></ulink>
        variable controls what type of shell is opened.
    </para>

    <para>
        For spawned terminals, the following occurs:
        <itemizedlist>
            <listitem><para>The <filename>PATH</filename> variable includes the
                cross-toolchain.</para></listitem>
            <listitem><para>The <filename>pkgconfig</filename> variables find the correct
                <filename>.pc</filename> files.</para></listitem>
                <listitem><para>The <filename>configure</filename> command finds the
                Yocto Project site files as well as any other necessary files.</para></listitem>
        </itemizedlist>
    </para>

    <para>
        Within this environment, you can run configure or compile
        commands as if they were being run by
        the OpenEmbedded build system itself.
        As noted earlier, the working directory also automatically changes to the
        Source Directory (<ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>).
    </para>

    <para>
        To manually run a specific task using <filename>devshell</filename>,
        run the corresponding <filename>run.*</filename> script in
        the
        <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}/temp</filename>
        directory (e.g.,
        <filename>run.do_configure.</filename><replaceable>pid</replaceable>).
        If a task's script does not exist, which would be the case if the task was
        skipped by way of the sstate cache, you can create the task by first running
        it outside of the <filename>devshell</filename>:
        <literallayout class='monospaced'>
     $ bitbake -c <replaceable>task</replaceable>
        </literallayout>
        <note><title>Notes</title>
            <itemizedlist>
                <listitem><para>Execution of a task's <filename>run.*</filename>
                    script and BitBake's execution of a task are identical.
                    In other words, running the script re-runs the task
                    just as it would be run using the
                    <filename>bitbake -c</filename> command.
                    </para></listitem>
                <listitem><para>Any <filename>run.*</filename> file that does not
                    have a <filename>.pid</filename> extension is a
                    symbolic link (symlink) to the most recent version of that
                    file.
                    </para></listitem>
            </itemizedlist>
        </note>
    </para>

    <para>
        Remember, that the <filename>devshell</filename> is a mechanism that allows
        you to get into the BitBake task execution environment.
        And as such, all commands must be called just as BitBake would call them.
        That means you need to provide the appropriate options for
        cross-compilation and so forth as applicable.
    </para>

    <para>
        When you are finished using <filename>devshell</filename>, exit the shell
        or close the terminal window.
    </para>

    <note><title>Notes</title>
        <itemizedlist>
            <listitem><para>
                It is worth remembering that when using <filename>devshell</filename>
                you need to use the full compiler name such as <filename>arm-poky-linux-gnueabi-gcc</filename>
                instead of just using <filename>gcc</filename>.
                The same applies to other applications such as <filename>binutils</filename>,
                <filename>libtool</filename> and so forth.
                BitBake sets up environment variables such as <filename>CC</filename>
                to assist applications, such as <filename>make</filename> to find the correct tools.
                </para></listitem>
            <listitem><para>
                It is also worth noting that <filename>devshell</filename> still works over
                X11 forwarding and similar situations.
                </para></listitem>
        </itemizedlist>
    </note>
</section>

<section id="platdev-appdev-devpyshell">
    <title>Using a Development Python Shell</title>

    <para>
        Similar to working within a development shell as described in
        the previous section, you can also spawn and work within an
        interactive Python development shell.
        When debugging certain commands or even when just editing packages,
        <filename>devpyshell</filename> can be a useful tool.
        When you invoke <filename>devpyshell</filename>, all tasks up to and
        including
        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>
        are run for the specified target.
        Then a new terminal is opened.
        Additionally, key Python objects and code are available in the same
        way they are to BitBake tasks, in particular, the data store 'd'.
        So, commands such as the following are useful when exploring the data
        store and running functions:
        <literallayout class='monospaced'>
     pydevshell> d.getVar("STAGING_DIR", True)
     '/media/build1/poky/build/tmp/sysroots'
     pydevshell> d.getVar("STAGING_DIR", False)
     '${TMPDIR}/sysroots'
     pydevshell> d.setVar("FOO", "bar")
     pydevshell> d.getVar("FOO", True)
     'bar'
     pydevshell> d.delVar("FOO")
     pydevshell> d.getVar("FOO", True)
     pydevshell> bb.build.exec_func("do_unpack", d)
     pydevshell>
        </literallayout>
        The commands execute just as if the OpenEmbedded build system were executing them.
        Consequently, working this way can be helpful when debugging a build or preparing
        software to be used with the OpenEmbedded build system.
    </para>

    <para>
        Following is an example that uses <filename>devpyshell</filename> on a target named
        <filename>matchbox-desktop</filename>:
        <literallayout class='monospaced'>
     $ bitbake matchbox-desktop -c devpyshell
        </literallayout>
    </para>

    <para>
        This command spawns a terminal and places you in an interactive
        Python interpreter within the OpenEmbedded build environment.
        The <ulink url='&YOCTO_DOCS_REF_URL;#var-OE_TERMINAL'><filename>OE_TERMINAL</filename></ulink>
        variable controls what type of shell is opened.
    </para>

    <para>
        When you are finished using <filename>devpyshell</filename>, you
        can exit the shell either by using Ctrl+d or closing the terminal
        window.
    </para>
</section>

</chapter>