summaryrefslogtreecommitdiffstats
path: root/documentation/dev-manual/dev-manual-common-tasks.xml
blob: 4e32f300c3ac0bf66f1885d4a8f4d60bbcc5cff3 (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
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
<!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='extendpoky'>

<title>Common Tasks</title>
    <para>
        This chapter describes standard tasks such as adding new
        software packages, extending or customizing images or porting the Yocto Project to
        new hardware (adding a new machine). 
        The chapter also describes ways to modify package source code, combine multiple 
        versions of library files into a single image, and handle a package name alias.
        Finally, the chapter contains advice about how to make changes to the 
        Yocto Project to achieve the best results.
    </para>

    <section id="understanding-and-creating-layers">
        <title>Understanding and Creating Layers</title>

        <para>
            The Yocto Project build system supports organizing <link linkend='metadata'>metadata</link> 
            into multiple layers. 
            Layers allow you to isolate different types of customizations from each other.
            You might find it tempting to keep everything in one layer when working on a single project.
            However, the more modular you organize your metadata, the easier it is to cope with future changes.
        </para>

        <para>
            To illustrate how layers are used to keep things modular, consider machine customizations.
            These types of customizations typically reside in a BSP Layer.
            Furthermore, the machine customizations should be isolated from recipes and metadata that support 
            a new GUI environment, for example. 
            This situation gives you a couple a layers: one for the machine configurations, and one for the 
            GUI environment.
            It is important to understand, however, that the BSP layer can still make machine-specific 
            additions to recipes within the GUI environment layer without polluting the GUI layer itself 
            with those machine-specific changes. 
            You can accomplish this through a recipe that is a BitBake append 
            (<filename>.bbappend</filename>) file, which is described later in this section.
        </para>

        <para>
        </para>

        <section id='yocto-project-layers'>
            <title>Yocto Project Layers</title>

            <para>
                The Yocto Project contains several layers right out of the box.
                You can easily identify a layer in the Yocto Project by the name of its folder.
                Folders that are layers begin with the string <filename>meta</filename>.
                For example, when you set up the <link linkend='yocto-project-files'>Yocto Project Files</link>
                structure, you will see several layers: <filename>meta</filename>, <filename>meta-demoapps</filename>,
                <filename>meta-skeleton</filename>, and <filename>meta-yocto</filename>.
                Each of these folders is a layer.
            </para>

            <para>
                Furthermore, if you set up a local copy of the <filename>meta-intel</filename> Git repository
                and then explore that folder, you will discover many BSP layers within the 
                <filename>meta-intel</filename> layer.
                For more information on BSP layers, see the 
                "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
                section in the Yocto Project Board Support Package (BSP) Developer's Guide.
            </para>
        </section>

        <section id='creating-your-own-layer'>
            <title>Creating Your Own Layer</title>

            <para>
                It is very easy to create your own layer to use with the Yocto Project.
                Follow these general steps to create your layer:
                <orderedlist>
                    <listitem><para><emphasis>Check Existing Layers:</emphasis> Before creating a new layer, 
                        you should be sure someone has not already created a layer containing the metadata 
                        you need.
                        You can see the
                        <ulink url='&OE_HOME_URL;/wiki/LayerIndex'><filename>LayerIndex</filename></ulink>
                        for a list of layers from the OpenEmbedded community that can be used in the 
                        Yocto Project.</para></listitem>
                    <listitem><para><emphasis>Create a Directory:</emphasis> Create the directory 
                        for your layer.
                        Traditionally, prepend the name of the folder with the string
                        <filename>meta</filename>.
                        For example:
                        <literallayout class='monospaced'>
     meta-mylayer
     meta-GUI_xyz
     meta-mymachine
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Create a Layer Configuration File:</emphasis> Inside your new
                       layer folder, you need to create a <filename>conf/layer.conf</filename> file.
                       It is easiest to take an existing layer configuration file and copy that to your 
                       layer's <filename>conf</filename> directory and then modify the file as needed.</para>
                       <para>The <filename>meta-yocto/conf/layer.conf</filename> file demonstrates the 
                       required syntax:
                       <literallayout class='monospaced'>
     # We have a conf and classes directory, add to BBPATH
     BBPATH := "${LAYERDIR}:${BBPATH}"

     # We have a packages directory, add to BBFILES
     BBFILES := "${BBFILES} ${LAYERDIR}/recipes-*/*/*.bb \
                 ${LAYERDIR}/recipes-*/*/*.bbappend"

     BBFILE_COLLECTIONS += "yocto"
     BBFILE_PATTERN_yocto := "^${LAYERDIR}/"
     BBFILE_PRIORITY_yocto = "5" 
                        </literallayout></para>
                        <para>In the previous example, the recipes for the layers are added to 
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILES'>BBFILES</ulink></filename>. 
                        The 
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_COLLECTIONS'>BBFILE_COLLECTIONS</ulink></filename>
                        variable is then appended with the layer name. 
                        The 
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PATTERN'>BBFILE_PATTERN</ulink></filename> 
                        variable is set to a regular expression and is used to match files
                        from <filename>BBFILES</filename> into a particular layer.
                        In this case, immediate expansion of 
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERDIR'>LAYERDIR</ulink></filename> 
                        sets <filename>BBFILE_PATTERN</filename> to the layer's path.
                        The 
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PRIORITY'>BBFILE_PRIORITY</ulink></filename> 
                        variable then assigns a priority to the layer. 
                        Applying priorities is useful in situations where the same package might appear in multiple
                        layers and allows you to choose what layer should take precedence.</para>
                        <para>Note the use of the 
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERDIR'>LAYERDIR</ulink></filename> 
                        variable with the immediate expansion operator.
                        The <filename>LAYERDIR</filename> variable expands to the directory of the current layer and
                        requires the immediate expansion operator so that BitBake does not wait to expand the variable 
                        when it's parsing a different directory.</para>
                        <para>Through the use of the <filename>BBPATH</filename> variable,
                        BitBake locates <filename>.bbclass</filename> files, configuration
                        files, and files that are included with <filename>include</filename> 
                        and <filename>require</filename> statements. 
                        For these cases, BitBake uses the first file with the matching name found in 
                        <filename>BBPATH</filename>.
                        This is similar to the way the <filename>PATH</filename> variable is used for binaries. 
                        We recommend, therefore, that you use unique <filename>.bbclass</filename>
                        and configuration file names in your custom layer.</para></listitem>
                    <listitem><para><emphasis>Add Content:</emphasis> Depending on the type of layer, 
                        add the content.
                        If the layer adds support for a machine, add the machine configuration in 
                        a <filename>conf/machine/</filename> file within the layer.
                        If the layer adds distro policy, add the distro configuration in a
                        <filename>conf/distro/</filename> file with the layer.
                        If the layer introduces new recipes, put the recipes you need in 
                        <filename>recipes-*</filename> subdirectories within the layer.</para></listitem>
                </orderedlist>
            </para>

            <para>
                To create layers that are easier to maintain, you should consider the following:
                <itemizedlist>
                    <listitem><para>Avoid "overlaying" entire recipes from other layers in your 
                        configuration.
                        In other words, don't copy an entire recipe into your layer and then modify it.
                        Use <filename>.bbappend</filename> files to override the parts of the 
                        recipe you need to modify.</para></listitem>
                    <listitem><para>Avoid duplicating include files.
                        Use <filename>.bbappend</filename> files for each recipe that uses an include 
                        file.
                        Or, if you are introducing a new recipe that requires the inc file, use the 
                        path relative to the original layer directory to refer to the file.
                        For example, use <filename>require recipes-core/somepackage/somefile.inc</filename>
                        instead of <filename>require somefile.inc</filename>. 
                        If you're finding you have to overlay the include file, it could indicate a 
                        deficiency in the include file in the layer to which it originally belongs.
                        If this is the case, you need to address that deficiency instead of overlaying
                        the include file.
                        For example, consider how Qt 4 database support plugins are configured.
                        The Yocto Project does not have MySQL or PostgreSQL, however OpenEmbedded's
                        layer <filename>meta-oe</filename> does.
                        Consequently, <filename>meta-oe</filename> uses <filename>.bbappend</filename>
                        files to modify the <filename>QT_SQL_DRIVER_FLAGS</filename> variable to enable 
                        the appropriate plugins. 
                        This variable was added to the <filename>qt4.inc</filename> include file in 
                        The Yocto Project specifically to allow the <filename>meta-oe</filename> layer
                        to be able to control which plugins are built.</para></listitem>
                </itemizedlist> 
            </para>

            <para>
                We also recommend the following:
                <itemizedlist>
                    <listitem><para>Store custom layers in a Git repository that uses the 
                        <filename>meta-&lt;layer_name&gt;</filename> format.</para></listitem>
                    <listitem><para>Clone the repository alongside other <filename>meta</filename>
                        directories in the Yocto Project source files area.</para></listitem>
                 </itemizedlist>
                 Following these recommendations keeps your Yocto Project files area and 
                 its configuration entirely inside the Yocto Project's core base.
            </para>
        </section>

        <section id='enabling-your-layer'>
            <title>Enabling Your Layer</title>

            <para>
                Before the Yocto Project build system can use your new layer, you need to enable it.
                To enable your layer, simply add your layer's path to the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'>BBLAYERS</ulink></filename> 
                variable in your <filename>conf/bblayers.conf</filename> file, which is found in the 
                <link linkend='yocto-project-build-directory'>Yocto Project Build Directory</link>. 
                The following example shows how to enable a layer named <filename>meta-mylayer</filename>:
                <literallayout class='monospaced'>
     LCONF_VERSION = "1"

     BBFILES ?= ""
     BBLAYERS = " \
       /path/to/poky/meta \
       /path/to/poky/meta-yocto \
       /path/to/poky/meta-mylayer \
       "
                </literallayout>
            </para>

            <para>
                BitBake parses each <filename>conf/layer.conf</filename> file as specified in the 
                <filename>BBLAYERS</filename> variable within the <filename>conf/bblayers.conf</filename>
                file.
                During the processing of each <filename>conf/layer.conf</filename> file, BitBake adds the 
                recipes, classes and configurations contained within the particular layer to the Yocto 
                Project.
            </para>
        </section>

        <section id='using-bbappend-files'>
            <title>Using .bbappend Files</title>

            <para>
                Recipe append files (<filename>.bbappend</filename> type) allow your layer to make additions or 
                changes to the content of another layer's recipe without having to copy the other recipe into 
                your layer.
                Your <filename>.bbappend</filename> file resides in your layer, while the underlying recipe 
                to which you are appending resides in a different layer.
            </para>

            <para>
                Append files files must have the same name as the underlying recipe.
                For example, the append file <filename>someapp_1.1.bbappend</filename> must 
                apply to <filename>someapp_1.1.bb</filename>.
                This means the original recipe and append file names are version number specific.
                If the underlying recipe is renamed to update to a newer version, the 
                corresponding <filename>.bbappend</filename> file must be renamed as well.
                During the build process, BitBake displays an error on starting if it detects a 
                <filename>.bbappend</filename> file that does not have an underlying recipe 
                with a matching name.
            </para>

            <para>
                Being able to append information to an existing recipe not only avoids duplication, 
                but also automatically applies recipe changes in a different layer to your layer.
                If you were copying recipes, you would have to manually merge changes as they occur.
            </para>

            <para>
                As an example, consider the main formfactor recipe and a corresponding formfactor 
                append file both from the Yocto Project Files.
                Here is the main formfactor recipe, which is named <filename>formfactor_0.0.bb</filename> and  
                located in the meta layer at <filename>meta/bsp-recipes/formfactor</filename>:
                <literallayout class='monospaced'>
     DESCRIPTION = "Device formfactor information"
     SECTION = "base"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COREBASE}/LICENSE;md5=3f40d7994397109285ec7b81fdeb3b58 \
                    file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
     PR = "r19"

     SRC_URI = "file://config file://machconfig"
     S = "${WORKDIR}"

     PACKAGE_ARCH = "${MACHINE_ARCH}"
     INHIBIT_DEFAULT_DEPS = "1"

     do_install() {
     	# Only install file if it has a contents
             install -d ${D}${sysconfdir}/formfactor/
             install -m 0644 ${S}/config ${D}${sysconfdir}/formfactor/
     	if [ -s "${S}/machconfig" ]; then
     	        install -m 0644 ${S}/machconfig ${D}${sysconfdir}/formfactor/
	     fi
     }
                </literallayout>
                Here is the append file, which is named <filename>formfactor_0.0.bbappend</filename> and is from the 
                Crown Bay BSP Layer named <filename>meta-intel/meta-crownbay</filename>:
                <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
 
     PRINC = "1"
                </literallayout>
                This example adds or overrides files in 
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                within a bbappend by extending the path BitBake uses to search for files. 
                The most reliable way to do this is by prepending the 
                <filename>FILESEXTRAPATHS</filename> variable.
                For example, if you have your files in a directory that is named the same as your package 
                (<ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>),
                you can add this directory by adding the following to your bbappend file:
                <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
                </literallayout>
                Using the immediate expansion assignment operator <filename>:=</filename> is important because 
                of the reference to <filename>THISDIR</filename>.
                The trailing colon character is important as it ensures that items in the list remain 
                colon-separated.
                <note>BitBake automatically defines the <filename>THISDIR</filename> variable.
                    You should never set this variable yourself.
                    Using <filename>_prepend</filename> ensures your path will be searched prior to other 
                    paths in the final list.
                </note>
            </para>
        </section>

        <section id='prioritizing-your-layer'>
            <title>Prioritizing Your Layer</title>

            <para>
                Each layer is assigned a priority value.
                Priority values control which layer takes precedence if there are recipe files with 
                the same name in multiple layers.
                For these cases, the recipe file from the layer with a higher priority number taking precedence.
                Priority values also affect the order in which multiple <filename>.bbappend</filename> files 
                for the same recipe are applied. 
                You can either specify the priority manually, or allow the build system to calculate it
                based on the layer's dependencies.
            </para>

            <para>
                To specify the layer's priority manually, use the 
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PRIORITY'><filename>BBFILE_PRIORITY</filename></ulink>
                variable.
                For example:
                <literallayout class='monospaced'>
     BBFILE_PRIORITY := "1"
                </literallayout>
            </para>

            <note>
                <para>It is possible for a recipe with a lower version number 
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                in a layer that has a higher priority to take precedence.</para>
                <para>Also, the layer priority does not currently affect the precedence order of 
                <filename>.conf</filename> or <filename>.bbclass</filename> files.
                Future versions of BitBake might address this.</para>
            </note>
        </section>

        <section id='managing-layers'>
            <title>Managing Layers</title>

            <para>
                You can use the BitBake layer management tool to provide a view into the structure of 
                recipes across a multi-layer project.
                Being able to generate output that reports on configured layers with their paths and 
                priorities and on <filename>.bbappend</filename> files and their applicable recipes
                can help to reveal potential problems.
            </para>

            <para>
                Use the following form when running the layer management tool.
                <literallayout class='monospaced'>
     $ bitbake-layers &lt;command&gt; [arguments]
                </literallayout>
                The following list describes the available commands:
                <itemizedlist>
                    <listitem><para><filename><emphasis>help:</emphasis></filename>
                        Displays general help or help on a specified command.</para></listitem>
                    <listitem><para><filename><emphasis>show-layers:</emphasis></filename>
                        Show the current configured layers.</para></listitem>
                    <listitem><para><filename><emphasis>show-recipes:</emphasis></filename>
                        Lists available recipes and the layers that provide them.  
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-overlayed:</emphasis></filename>
                        Lists overlayed recipes.  
                        A recipe is overlayed when a recipe with the same name exists in another layer 
                        that has a higher layer priority.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-appends:</emphasis></filename>
                        Lists <filename>.bbappend</filename> files and the recipe files to which
                        they apply.</para></listitem>
                    <listitem><para><filename><emphasis>flatten:</emphasis></filename>
                        Flattens the layer configuration into a separate output directory.
                        Flattening your layer configuration builds a "flattened" directory that contains
                        the contents of all layers, with any overlayed recipes removed and any
                        recipe append files (<filename>.bbappend</filename>) appended to the corresponding recipes.
                        You might have to perform some manual cleanup of the flattened layer as follows:
                        <itemizedlist>
                            <listitem><para>Non-recipe files (such as patches) are overwritten.
                                The flatten command shows a warning for these files.</para></listitem>
                            <listitem><para>Anything beyond the normal layer setup has been added to 
                                the <filename>layer.conf</filename> file.
                                Only the lowest priority layer's <filename>layer.conf</filename> is used.
                                </para></listitem>
                            <listitem><para>Overridden and appended items from <filename>.bbappend</filename>
                                files need to be cleaned up.
                                The contents of each <filename>.bbappend</filename> end up in the 
                                flattened recipe.
                                However, if there are appended or changed variable values, you need to tidy 
                                these up yourself.
                                Consider the following example.
                                Here, the <filename>bitbake-layers</filename> command adds the line
                                <filename>#### bbappended ...</filename> so that you know where the following
                                lines originate:
                                <literallayout class='monospaced'>
     ...
     DESCRIPTION = "A useful utility"
     ...
     EXTRA_OECONF = "--enable-something"
     ...

     #### bbappended from meta-anotherlayer ####

     DESCRIPTION = "Customized utility"
     EXTRA_OECONF += "--enable-somethingelse"
                                </literallayout>
                                Ideally, you would tidy up these utilities as follows:
                                <literallayout class='monospaced'>
     ...
     DESCRIPTION = "Customized utility"
     ...
     EXTRA_OECONF = "--enable-something --enable-somethingelse"
     ...
                                </literallayout></para></listitem>
                        </itemizedlist></para></listitem>
                </itemizedlist>
            </para>
        </section>
    </section>

    <section id='usingpoky-extend-addpkg'>
        <title>Adding a Package</title>

        <para>
            To add a package into the Yocto Project you need to write a recipe for it. 
            Writing a recipe means creating a <filename>.bb</filename> file that sets some
            variables.
            For information on variables that are useful for recipes and for information about recipe naming
            issues, see the 
            "<ulink url='&YOCTO_DOCS_REF_URL;#ref-varlocality-recipe-required'>Required</ulink>" 
            section of the Yocto Project Reference Manual.
        </para>

        <para>
            Before writing a recipe from scratch, it is often useful to check
            whether someone else has written one already. 
            OpenEmbedded is a good place to look as it has a wider scope and range of packages.
            Because the Yocto Project aims to be compatible with OpenEmbedded, most recipes 
            you find there should work in Yocto Project.
        </para>

        <para>
            For new packages, the simplest way to add a recipe is to base it on a similar
            pre-existing recipe. 
            The sections that follow provide some examples that show how to add standard 
            types of packages.
        </para>

        <section id='usingpoky-extend-addpkg-singlec'>
            <title>Single .c File Package (Hello World!)</title>

            <para>
                Building an application from a single file that is stored locally (e.g. under 
                <filename>files/</filename>) requires a recipe that has the file listed in 
                the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>
                variable. 
                Additionally, you need to manually write the <filename>do_compile</filename> and
                <filename>do_install</filename> tasks.
                The <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename> 
                variable defines the 
                directory containing the source code, which is set to 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'>
                WORKDIR</ulink></filename> in this case - the directory BitBake uses for the build.
                <literallayout class='monospaced'>
     DESCRIPTION = "Simple helloworld application"
     SECTION = "examples"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"
     PR = "r0"

     SRC_URI = "file://helloworld.c"

     S = "${WORKDIR}"

     do_compile() {
     	${CC} helloworld.c -o helloworld
     }

     do_install() {
     	install -d ${D}${bindir}
     	install -m 0755 helloworld ${D}${bindir}
     }
                </literallayout>
            </para>

            <para>
                By default, the <filename>helloworld</filename>, <filename>helloworld-dbg</filename>,
                and <filename>helloworld-dev</filename> packages are built. 
                For information on how to customize the packaging process, see the
                "<link linkend='splitting-an-application-into-multiple-packages'>Splitting an Application
                into Multiple Packages</link>" section.
            </para>
        </section>

        <section id='usingpoky-extend-addpkg-autotools'>
            <title>Autotooled Package</title>
            <para>
                Applications that use Autotools such as <filename>autoconf</filename> and 
                <filename>automake</filename> require a recipe that has a source archive listed in 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename> and 
                also inherits Autotools, which instructs BitBake to use the
                <filename>autotools.bbclass</filename> file, which contains the definitions of all the steps
                needed to build an Autotool-based application.
                The result of the build is automatically packaged. 
                And, if the application uses NLS for localization, packages with local information are 
                generated (one package per language). 
                Following is one example: (<filename>hello_2.3.bb</filename>)
                <literallayout class='monospaced'>
     DESCRIPTION = "GNU Helloworld application"
     SECTION = "examples"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe"
     PR = "r0"

     SRC_URI = "${GNU_MIRROR}/hello/hello-${PV}.tar.gz"

     inherit autotools gettext
                 </literallayout>
            </para>

            <para>
                The variable 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'>LIC_FILES_CHKSUM</ulink></filename> 
                is used to track source license changes as described in the
                "<ulink url='&YOCTO_DOCS_REF_URL;#usingpoky-configuring-LIC_FILES_CHKSUM'>Track License Change</ulink>" section. 
                You can quickly create Autotool-based recipes in a manner similar to the previous example.
            </para>
        </section>

        <section id='usingpoky-extend-addpkg-makefile'>
            <title>Makefile-Based Package</title>

            <para>
                Applications that use GNU <filename>make</filename> also require a recipe that has
                the source archive listed in 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>. 
                You do not need to add a <filename>do_compile</filename> step since by default BitBake 
                starts the <filename>make</filename> command to compile the application. 
                If you need additional <filename>make</filename> options you should store them in the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OEMAKE'>EXTRA_OEMAKE</ulink></filename>
                variable.
                BitBake passes these options into the <filename>make</filename> GNU invocation. 
                Note that a <filename>do_install</filename> task is still required.
                Otherwise BitBake runs an empty <filename>do_install</filename> task by default. 
            </para>

            <para>
                Some applications might require extra parameters to be passed to the compiler.
                For example, the application might need an additional header path. 
                You can accomplish this by adding to the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-CFLAGS'>CFLAGS</ulink></filename> variable.
                The following example shows this:
                <literallayout class='monospaced'>
     CFLAGS_prepend = "-I ${S}/include "
                </literallayout>
            </para>

            <para>
            In the following example, <filename>mtd-utils</filename> is a makefile-based package:
                <literallayout class='monospaced'>
     DESCRIPTION = "Tools for managing memory technology devices."
     SECTION = "base"
     DEPENDS = "zlib lzo e2fsprogs util-linux"
     HOMEPAGE = "http://www.linux-mtd.infradead.org/"
     LICENSE = "GPLv2"
     LIC_FILES_CHKSUM = "file://COPYING;md5=0636e73ff0215e8d672dc4c32c317bb3 \
                         file://include/common.h;beginline=1;endline=17;md5=ba05b07912a44ea2bf81ce409380049c"

     SRC_URI = "git://git.infradead.org/mtd-utils.git;protocol=git;tag=v${PV}"

     S = "${WORKDIR}/git/"

     EXTRA_OEMAKE = "'CC=${CC}' 'CFLAGS=${CFLAGS} -I${S}/include -DWITHOUT_XATTR' \
                     'BUILDDIR=${S}'"

     do_install () {
             oe_runmake install DESTDIR=${D} SBINDIR=${sbindir} MANDIR=${mandir} \
                                INCLUDEDIR=${includedir}
             install -d ${D}${includedir}/mtd/
             for f in ${S}/include/mtd/*.h; do
                     install -m 0644 $f ${D}${includedir}/mtd/
             done
     }
                </literallayout>
            </para>
        </section>

        <section id='splitting-an-application-into-multiple-packages'>
            <title>Splitting an Application into Multiple Packages</title>

            <para>                        
                You can use the variables 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink></filename> and 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'>FILES</ulink></filename> 
                to split an application into multiple packages.
            </para>

            <para>
                Following is an example that uses the <filename>libXpm</filename> recipe. 
                By default, this recipe generates a single package that contains the library along 
                with a few binaries.  
                You can modify the recipe to split the binaries into separate packages:
                <literallayout class='monospaced'>
     require xorg-lib-common.inc

     DESCRIPTION = "X11 Pixmap library"
     LICENSE = "X-BSD"
     LIC_FILES_CHKSUM = "file://COPYING;md5=3e07763d16963c3af12db271a31abaa5"
     DEPENDS += "libxext libsm libxt"
     PR = "r3"
     PE = "1"

     XORG_PN = "libXpm"

     PACKAGES =+ "sxpm cxpm"
     FILES_cxpm = "${bindir}/cxpm"
     FILES_sxpm = "${bindir}/sxpm"
                </literallayout>
            </para>

            <para>
                In the previous example, we want to ship the <filename>sxpm</filename>
                and <filename>cxpm</filename> binaries in separate packages. 
                Since <filename>bindir</filename> would be packaged into the main 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'>PN</ulink></filename> 
                package by default, we prepend the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink>
                </filename> variable so additional package names are added to the start of list. 
                This results in the extra 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'>FILES</ulink>_*</filename>
                variables then containing information that define which files and
                directories go into which packages. 
                Files included by earlier packages are skipped by latter packages.
                Thus, the main 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'>PN</ulink></filename> package 
                does not include the above listed files.
            </para>
        </section>

        <section id='including-static-library-files'>
            <title>Including Static Library Files</title>

            <para>                        
                If you are building a library and the library offers static linking, you can control
                which static library files (<filename>*.a</filename> files) get included in the 
                built library.  
            </para>

            <para>
                The <filename>PACKAGES</filename> and <filename>FILES_*</filename> variables in the 
                <filename>meta/conf/bitbake.conf</filename> configuration file define how files installed
                by the <filename>do_install</filename> task are packaged.
                By default, the <filename>PACKAGES</filename> variable contains 
                <filename>${PN}-staticdev</filename>, which includes all static library files.
                <note>
                    Previously released versions of the Yocto Project defined the static library files 
                    through <filename>${PN}-dev</filename>.
                </note>
                Following, is part of the BitBake configuration file. 
                You can see where the static library files are defined:
                <literallayout class='monospaced'>
     PACKAGES = "${PN}-dbg ${PN} ${PN}-doc ${PN}-dev ${PN}-staticdev ${PN}-locale"
     PACKAGES_DYNAMIC = "${PN}-locale-*"
     FILES = ""

     FILES_${PN} = "${bindir}/* ${sbindir}/* ${libexecdir}/* ${libdir}/lib*${SOLIBS} \
                 ${sysconfdir} ${sharedstatedir} ${localstatedir} \
                 ${base_bindir}/* ${base_sbindir}/* \
                 ${base_libdir}/*${SOLIBS} \
                 ${datadir}/${BPN} ${libdir}/${BPN}/* \
                 ${datadir}/pixmaps ${datadir}/applications \
                 ${datadir}/idl ${datadir}/omf ${datadir}/sounds \
                 ${libdir}/bonobo/servers"

     FILES_${PN}-doc = "${docdir} ${mandir} ${infodir} ${datadir}/gtk-doc \
                 ${datadir}/gnome/help"
     SECTION_${PN}-doc = "doc"
     
     FILES_${PN}-dev = "${includedir} ${libdir}/lib*${SOLIBSDEV} ${libdir}/*.la \
                     ${libdir}/*.o ${libdir}/pkgconfig ${datadir}/pkgconfig \
                     ${datadir}/aclocal ${base_libdir}/*.o"
     SECTION_${PN}-dev = "devel"
     ALLOW_EMPTY_${PN}-dev = "1"
     RDEPENDS_${PN}-dev = "${PN} (= ${EXTENDPKGV})"
     
     FILES_${PN}-staticdev = "${libdir}/*.a ${base_libdir}/*.a"
     SECTION_${PN}-staticdev = "devel"
     RDEPENDS_${PN}-staticdev = "${PN}-dev (= ${EXTENDPKGV})"
                </literallayout>
            </para>
        </section>

        <section id='usingpoky-extend-addpkg-postinstalls'>
            <title>Post Install Scripts</title>

            <para>
                To add a post-installation script to a package, add a <filename>pkg_postinst_PACKAGENAME()
                </filename> function to the <filename>.bb</filename> file and use 
                <filename>PACKAGENAME</filename> as the name of the package you want to attach to the 
                <filename>postinst</filename> script.
                Normally 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'>PN</ulink></filename>
                can be used, which automatically expands to PACKAGENAME.
                A post-installation function has the following structure:
                <literallayout class='monospaced'>
     pkg_postinst_PACKAGENAME () {
     #!/bin/sh -e
     # Commands to carry out
     }
                </literallayout>
            </para>

            <para>
                The script defined in the post-installation function is called when the 
                root filesystem is created. 
                If the script succeeds, the package is marked as installed. 
                If the script fails, the package is marked as unpacked and the script is
                executed when the image boots again.
            </para>

            <para>
                Sometimes it is necessary for the execution of a post-installation
                script to be delayed until the first boot.  
                For example, the script might need to be executed on the device itself. 
                To delay script execution until boot time, use the following structure in the 
                post-installation script:
                <literallayout class='monospaced'>
     pkg_postinst_PACKAGENAME () {
     #!/bin/sh -e
     if [ x"$D" = "x" ]; then
          # Actions to carry out on the device go here
     else
          exit 1
     fi
     }
                </literallayout>
            </para>

            <para>
                The previous example delays execution until the image boots again because the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'>D</ulink></filename> 
                variable points
                to the directory containing the image when the root filesystem is created at build time but
                is unset when executed on the first boot. 
            </para>
        </section>
    </section>

    <section id='usingpoky-extend-customimage'>
        <title>Customizing Images</title>

        <para>
            You can customize Yocto Project images to satisfy particular requirements. 
            This section describes several methods and provides guidelines for each.
        </para>

        <section id='usingpoky-extend-customimage-custombb'>
            <title>Customizing Images Using Custom .bb Files</title>

            <para>
                One way to get additional software into an image is to create a custom image. 
                The following example shows the form for the two lines you need:
                <literallayout class='monospaced'>
     IMAGE_INSTALL = "task-core-x11-base package1 package2"

     inherit core-image
                </literallayout>
            </para>

            <para>
                By creating a custom image, a developer has total control
                over the contents of the image. 
                It is important to use the correct names of packages in the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename> 
                variable. 
                You must use the OpenEmbedded notation and not the Debian notation for the names 
                (e.g. <filename>eglibc-dev</filename> instead of <filename>libc6-dev</filename>).
            </para>

            <para>
                The other method for creating a custom image is to modify an existing image. 
                For example, if a developer wants to add <filename>strace</filename> into 
                the <filename>core-image-sato</filename> image, they can use the following recipe:
                <literallayout class='monospaced'>
     require core-image-sato.bb

     IMAGE_INSTALL += "strace"
                </literallayout>
            </para>
        </section>

        <section id='usingpoky-extend-customimage-customtasks'>
            <title>Customizing Images Using Custom Tasks</title>

            <para>
                For complex custom images, the best approach is to create a custom task package
                that is used to build the image or images. 
                A good example of a tasks package is 
                <filename>meta/recipes-sato/tasks/task-poky.bb</filename>. 
                The 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink></filename> 
                variable lists the task packages to build along with the complementary
                <filename>-dbg</filename> and <filename>-dev</filename> packages. 
                For each package added, you can use 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'>RDEPENDS</ulink></filename>
                and 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'>RRECOMMENDS</ulink></filename> 
                entries to provide a list of packages the parent task package should contain. 
                Following is an example:
                <literallayout class='monospaced'>
     DESCRIPTION = "My Custom Tasks"

     PACKAGES = "\
         task-custom-apps \
         task-custom-apps-dbg \
         task-custom-apps-dev \
         task-custom-tools \
         task-custom-tools-dbg \
         task-custom-tools-dev \
         "

     RDEPENDS_task-custom-apps = "\
         dropbear \
         portmap \
         psplash"

     RDEPENDS_task-custom-tools = "\
         oprofile \
         oprofileui-server \
         lttng-control \
         lttng-viewer"

     RRECOMMENDS_task-custom-tools = "\
         kernel-module-oprofile"
                </literallayout>
            </para>

            <para>
                In the previous example, two task packages are created with their dependencies and their
                recommended package dependencies listed: <filename>task-custom-apps</filename>, and 
                <filename>task-custom-tools</filename>. 
                To build an image using these task packages, you need to add 
                <filename>task-custom-apps</filename> and/or 
                <filename>task-custom-tools</filename> to 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>.
                For other forms of image dependencies see the other areas of this section.
            </para>
        </section>

        <section id='usingpoky-extend-customimage-imagefeatures'>
            <title>Customizing Images Using Custom <filename>IMAGE_FEATURES</filename> and 
                <filename>EXTRA_IMAGE_FEATURES</filename></title>

            <para>
                Ultimately users might want to add extra image features to the set used by 
                Yocto Project with the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'>IMAGE_FEATURES</ulink></filename>
                variable. 
                To create these features, the best reference is 
                <filename>meta/classes/core-image.bbclass</filename>, which shows how the 
                Yocto Project achieves this. 
                In summary, the file looks at the contents of the 
                <filename>IMAGE_FEATURES</filename>
                variable and then maps that into a set of tasks or packages. 
                Based on this information the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'> IMAGE_INSTALL</ulink></filename> 
                variable is generated automatically. 
                Users can add extra features by extending the class or creating a custom class for use 
                with specialized image <filename>.bb</filename> files.
                You can also add more features by configuring the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'>EXTRA_IMAGE_FEATURES</ulink></filename>
                variable in the <filename>local.conf</filename> file found in the Yocto Project
                files located in the build directory.
            </para>

            <para>
                The Yocto Project ships with two SSH servers you can use in your images: 
                Dropbear and OpenSSH. 
                Dropbear is a minimal SSH server appropriate for resource-constrained environments,
                while OpenSSH is a well-known standard SSH server implementation.
                By default, the <filename>core-image-sato</filename> image is configured to use Dropbear.
                The <filename>core-image-basic</filename> and <filename>core-image-lsb</filename>
                images both include OpenSSH.
                To change these defaults, edit the <filename>IMAGE_FEATURES</filename> variable
                so that it sets the image you are working with to include 
                <filename>ssh-server-dropbear</filename> or <filename>ssh-server-openssh</filename>.
            </para>
        </section>

        <section id='usingpoky-extend-customimage-localconf'>
            <title>Customizing Images Using <filename>local.conf</filename></title>

            <para>
                It is possible to customize image contents by using variables from your
                local configuration in your <filename>conf/local.conf</filename> file. 
                Because it is limited to local use, this method generally only allows you to 
                add packages and is not as flexible as creating your own customized image.
                When you add packages using local variables this way, you need to realize that 
                these variable changes affect all images at the same time and might not be
                what you require.
            </para>

            <section id='adding-packages'>
                <title>Adding Packages</title>

                <para>
                    The simplest way to add extra packages to all images is by using the 
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>
                    variable with the <filename>_append</filename> operator:
                    <literallayout class='monospaced'>
     IMAGE_INSTALL_append = " strace"
                    </literallayout>
                    Use of the syntax is important.
                    Specifically, the space between the quote and the package name, which is
                    <filename>strace</filename> in this example.
                    This space is required since the <filename>_append</filename>
                    operator does not add the space.
                </para>

                <para>
                    Furthermore, you must use <filename>_append</filename> instead of the <filename>+=</filename> 
                    operator if you want to avoid ordering issues. 
                    The reason for this is because doing so uncondtionally appends to the variable and 
                    avoids ordering problems due to the variable being set in image recipes and 
                    <filename>.bbclass</filename> files with operators like <filename>?=</filename>.
                    Using <filename>_append</filename> ensures the operation takes affect.
                </para>

                <para>
                    As shown in its simplest use, <filename>IMAGE_INSTALL_append</filename> affects
                    all images.
                    It is possible to extend the syntax so that the variable applies to a specific image only.
                    Here is an example:
                    <literallayout class='monospaced'>
     IMAGE_INSTALL_append_pn-core-image-minimal = " strace"
                    </literallayout>
                    This example adds <filename>strace</filename> to <filename>core-image-minimal</filename>
                    only.
                </para>

                <para>
                    You can add packages using a similar approach through the  
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-POKY_EXTRA_INSTALL'>POKY_EXTRA_INSTALL</ulink></filename> 
                    variable.
                    If you use this variable, only <filename>core-image-*</filename> images are affected.
                </para>
            </section>

            <section id='excluding-packages'>
                <title>Excluding Packages</title>

                <para>
                    It is possible to filter or mask out recipe and recipe append files such that 
                    BitBake ignores them.  
                    You can do this by providing an expression with the 
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBMASK'>BBMASK</ulink></filename> 
                    variable. 
                    Here is an example:
                    <literallayout class='monospaced'>
     BBMASK = ".*/meta-mymachine/recipes-maybe/"
                    </literallayout>
                    Here, all <filename>.bb</filename> and <filename>.bbappend</filename> files
                    in the directory that matches the expression are ignored during the build
                    process.
                </para>
            </section>
        </section>
    </section>

    <section id="platdev-newmachine">
        <title>Porting the Yocto Project to a New Machine</title>

<!--
WRITER NOTES:

I had this chat with Richard:

scottrif: Terminology question:  We speak of "New Machines" or "Adding a New Machine" 
          in YP.  Are "Machines" restricted to architectures? In poky/meta/conf/machine we have .conf 
          files for the five architectures.  What exactly does the term "Machine" mean?

      RP: no, each architecture has multiple different machines. A "machine" can correspond 
          to a particular reference board or hardware product
          we just have one reference machine per architecture
          We're  a little vague sometimes as "machine" can refer to either an individual platform,
          or in some cases a set of different platforms with common structure
          (e.g. netbooks)

scottrif: So our reference machines we supply are the five qemu* machines? 

      RP: in oe-core, plus one "real" target in meta-yocto
          (per arch)

scottrif: I see four in meta-yocto/conf/machine.  Shouldn't there be five if there is one 
          "real" target per architecture?

      RP: yes, we don't have one for x86_64 :/

scottrif: I think it is a bit difficult to map our four poky/meta-yocto/conf/machines to one of our 
          five architectures.  Some have key words in there that identify the architecture but 
          beagleboard and atom-pc don't.
          We have a section that describes adding a Machine Configuration file to Yocto and 
          it states that TARGET_ARCH is one of the most important variables that need to be 
          set in the .conf file.  The four I am looking at don't have that variable.

      RP: That has changed a little now. You need to include the appropriate tune file
          which will set it for you
          People had a tendency not to set all the right pieces so it got abstracted

scottrif: Got it.  I see them in poky/meta/conf/machine/include.

SOME CONCLUSIONS:

I need to define the term machine.  It is confusing.  Then, this section needs to be cleared up
so that there are some definite steps on how to do this.  I need more detail here.

-->

        <para>
            Adding a new machine to the Yocto Project is a straightforward process. 
            This section provides information that gives you an idea of the changes you must make.
            The information covers adding machines similar to those the Yocto Project already supports. 
            Although well within the capabilities of the Yocto Project, adding a totally new architecture 
            might require 
            changes to <filename>gcc/eglibc</filename> and to the site information, which is 
            beyond the scope of this manual.
        </para>

        <para>
            For a complete example that shows how to add a new machine to the Yocto Project, 
            see the 
            "<ulink url='&YOCTO_DOCS_DEV_URL;#dev-manual-bsp-appendix'>BSP Development Example</ulink>" 
            in Appendix A.
        </para>

        <section id="platdev-newmachine-conffile">
            <title>Adding the Machine Configuration File</title>

            <para>
                To add a machine configuration you need to add a <filename>.conf</filename> file
                with details of the device being added to the <filename>conf/machine/</filename> file.
                The name of the file determines the name the Yocto Project uses to reference the new machine.
            </para>

            <para>
                The most important variables to set in this file are as follows:
                <itemizedlist>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-TARGET_ARCH'>
                        TARGET_ARCH</ulink></filename> (e.g. "arm")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PREFERRED_PROVIDER'>
                        PREFERRED_PROVIDER</ulink></filename>_virtual/kernel (see below)</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES'>
                        MACHINE_FEATURES</ulink></filename> (e.g. "kernel26 apm screen wifi")</para></listitem>
                </itemizedlist>
            </para>

            <para> 
                You might also need these variables:
                <itemizedlist>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SERIAL_CONSOLE'>
                        SERIAL_CONSOLE</ulink></filename> (e.g. "115200 ttyS0")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_IMAGETYPE'>
                        KERNEL_IMAGETYPE</ulink></filename> (e.g. "zImage")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FSTYPES'>
                        IMAGE_FSTYPES</ulink></filename> (e.g. "tar.gz jffs2")</para></listitem>
                </itemizedlist>
            </para>

            <para> 
                You can find full details on these variables in the reference section. 
                You can leverage many existing machine <filename>.conf</filename> files from 
                <filename>meta/conf/machine/</filename>.
            </para>
        </section>

        <section id="platdev-newmachine-kernel">
            <title>Adding a Kernel for the Machine</title>

            <para>
                The Yocto Project needs to be able to build a kernel for the machine. 
                You need to either create a new kernel recipe for this machine, or extend an 
                existing recipe. 
                You can find several kernel examples in the 
                Yocto Project file's <filename>meta/recipes-kernel/linux</filename>
                directory that you can use as references.
            </para>

            <para>
                If you are creating a new recipe, normal recipe-writing rules apply for setting 
                up a 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>. 
                Thus, you need to specify any necessary patches and set 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename> to point at the source code. 
                You need to create a <filename>configure</filename> task that configures the 
                unpacked kernel with a defconfig.
                You can do this by using a <filename>make defconfig</filename> command or,
                more commonly, by copying in a suitable <filename>defconfig</filename> file and and then running 
                <filename>make oldconfig</filename>. 
                By making use of <filename>inherit kernel</filename> and potentially some of the 
                <filename>linux-*.inc</filename> files, most other functionality is 
                centralized and the the defaults of the class normally work well.
            </para>

            <para>
                If you are extending an existing kernel, it is usually a matter of adding a 
                suitable defconfig file.
                The file needs to be added into a location similar to defconfig files
                used for other machines in a given kernel. 
                A possible way to do this is by listing the file in the 
                <filename>SRC_URI</filename> and adding the machine to the expression in 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-COMPATIBLE_MACHINE'>COMPATIBLE_MACHINE</ulink></filename>:
                <literallayout class='monospaced'>
     COMPATIBLE_MACHINE = '(qemux86|qemumips)'
                </literallayout>
            </para>
        </section>

        <section id="platdev-newmachine-formfactor">
            <title>Adding a Formfactor Configuration File</title>

            <para>
                A formfactor configuration file provides information about the 
                target hardware for which the Yocto Project is building and information that 
                the Yocto Project cannot obtain from other sources such as the kernel.  
                Some examples of information contained in a formfactor configuration file include 
                framebuffer orientation, whether or not the system has a keyboard, 
                the positioning of the keyboard in relation to the screen, and 
                the screen resolution.
            </para>

            <para>
                The Yocto Project uses reasonable defaults in most cases, but if customization is 
                necessary you need to create a <filename>machconfig</filename> file 
                in the Yocto Project file's <filename>meta/recipes-bsp/formfactor/files</filename>
                directory.
                This directory contains directories for specific machines such as 
                <filename>qemuarm</filename> and <filename>qemux86</filename>.
                For information about the settings available and the defaults, see the 
                <filename>meta/recipes-bsp/formfactor/files/config</filename> file found in the
                same area. 
                Following is an example for qemuarm:
                <literallayout class='monospaced'>
     HAVE_TOUCHSCREEN=1
     HAVE_KEYBOARD=1

     DISPLAY_CAN_ROTATE=0
     DISPLAY_ORIENTATION=0
     #DISPLAY_WIDTH_PIXELS=640
     #DISPLAY_HEIGHT_PIXELS=480
     #DISPLAY_BPP=16
     DISPLAY_DPI=150
     DISPLAY_SUBPIXEL_ORDER=vrgb
                </literallayout>
            </para>
        </section>
    </section>

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

        <para>
            Although the Yocto Project is typically used to build software, 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 
            <link linkend='yocto-project-build-directory'>Yocto Project's Build Directory</link>, 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.
            You can accomplish these steps all within either a 
            <ulink url='http://savannah.nongnu.org/projects/quilt'>Quilt</ulink> or 
            <link linkend='git'>Git</link> workflow.
        </para>

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

            <para>
                During a build, the unpacked temporary source code used by recipes 
                to build packages is available in the Yocto Project 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 
                <link linkend='yocto-project-files'>Yocto Project Files</link>:
                <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>
                    <filename>BP</filename> represents the "Base Package", which is the base package
                    name and the package 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>) depends
                on the package name and the architecture of the target device.
                For example, here is the work directory for packages whose targets are not device-dependent:
                <literallayout class='monospaced'>
     ${TMPDIR}/work/${PACKAGE_ARCH}-poky-${TARGET_OS}/${PN}-${PV}-${PR}
                </literallayout>
                Let's look at an example without variables.
                Assuming a Yocto Project Files top-level directory named <filename>poky</filename>
                and a default Yocto Project Build Directory of <filename>poky/build</filename>, 
                the following is the work directory for the <filename>acl</filename> package:
                <literallayout class='monospaced'>
     ~/poky/build/tmp/work/i586-poky-linux/acl-2.2.51-r3
                </literallayout>
            </para>

            <para>
                If your package is dependent on the target device, the work directory varies slightly:
                <literallayout class='monospaced'>
     ${TMPDIR}/work/${MACHINE}-poky-${TARGET_OS}/${PN}-${PV}-${PR}
                </literallayout>
                Again, assuming a Yocto Project Files top-level directory named <filename>poky</filename>
                and a default Yocto Project Build Directory of <filename>poky/build</filename>, the 
                following is the work directory for the <filename>acl</filename> package that is being 
                built for a MIPS-based device:
                <literallayout class='monospaced'>
     ~/poky/build/tmp/work/mips-poky-linux/acl-2.2.51-r2
                </literallayout>
            </para>

            <note>
                To better understand how the Yocto Project build system resolves directories during the 
                build process, see the glossary entries for the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>,
                <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>,
                <ulink url='&YOCTO_DOCS_REF_URL;#var-TOPDIR'><filename>TOPDIR</filename></ulink>,
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></ulink>,
                <ulink url='&YOCTO_DOCS_REF_URL;#var-TARGET_OS'><filename>TARGET_OS</filename></ulink>,
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>,
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>,
                and
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
                variables in the Yocto Project Reference Manual.
            </note>

            <para>
                Now that you know where to locate the directory that has the temporary source code, you can use a 
                Quilt or Git workflow to make your edits, test the changes, and preserve the 
                changes in the form of patches.
            </para>
        </section>

        <section id="using-a-quilt-workflow">
            <title>Using a Quilt 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 temporary source code, 
                test changes, and then preserve the changes in the form of a patch all using Quilt.
            </para>

            <para>
                Follow these general steps:
                <orderedlist>
                    <listitem><para><emphasis>Find the Source Code:</emphasis>
                        The temporary source code used by the Yocto Project build system is kept in the 
                        Yocto Project Build Directory.  
                        See the 
                        "<link linkend='finding-the-temporary-source-code'>Finding the 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'>S</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 will 
                        be changing.
                        Add the files you will be modifying into 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 the changes to the temporary source code.</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>compile</filename> task as shown in the following example:
                        <literallayout class='monospaced'>
     $ bitbake -c compile -f &lt;name_of_package&gt;
                        </literallayout>
                        The <filename>-f</filename> or <filename>--force</filename>
                        option forces re-execution of the specified task.
                        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 <filename>-c clean</filename> or 
                        <filename>-c cleanall</filename> with BitBake for the package.
                        Modifications will also disappear if you use the <filename>rm_work</filename>
                        feature as described in the
                        "<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</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 as the recipe.
                        Placing the patch here guarantees that the Yocto Project 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>
                    <listitem><para><emphasis>Increment the Package Revision Number:</emphasis>
                        Finally, don't forget to 'bump' the 
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PR'>PR</ulink></filename>
                        value in the same recipe since the resulting packages have changed.</para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='using-a-git-workflow'>
            <title>Using a Git Workflow</title>
            <para>
                Git is an even more 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 temporary source code, 
                test changes, and then preserve the changes in the form of a patch all using Git.
                For general information on Git as it is used in the Yocto Project, see the 
                "<link linkend='git'>Git</link>" section.
            </para>

            <note>
                This workflow uses Git only for its ability to manage local changes to the source code 
                and produce patches independent of any version control used on the Yocto Project 
                Files.
            </note>

            <para>
                Follow these general steps:
                <orderedlist>
                    <listitem><para><emphasis>Find the Source Code:</emphasis>
                        The temporary source code used by the Yocto Project build system is kept in the 
                        Yocto Project Build Directory.  
                        See the 
                        "<link linkend='finding-the-temporary-source-code'>Finding the 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'>S</ulink>
                        variable.</para></listitem>
                    <listitem><para><emphasis>Initialize a Git Repository:</emphasis>
                        Use the <filename>git init</filename> command to initialize a new local repository
                        that is based on the work directory:
                        <literallayout class='monospaced'>
     $ git init
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Stage all the files:</emphasis>
                        Use the <filename>git add *</filename> command to stage all the files in the source
                        code directory so that they can be committed:
                        <literallayout class='monospaced'>
     $ git add *
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Commit the Source Files:</emphasis>
                        Use the <filename>git commit</filename> command to initially commit all the files in 
                        the work directory:
                        <literallayout class='monospaced'>
     $ git commit
                        </literallayout>
                        At this point, your Git repository is aware of all the source code files.
                        Any edits you now make to files will be tracked by Git.</para></listitem>
                    <listitem><para><emphasis>Edit the Files:</emphasis>
                        Make the changes to the temporary source code.</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>compile</filename> task as shown in the following example:
                        <literallayout class='monospaced'>
     $ bitbake -c compile -f &lt;name_of_package&gt;
                        </literallayout>
                        The <filename>-f</filename> or <filename>--force</filename>
                        option forces re-execution of the specified task.
                        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 <filename>-c clean</filename> or 
                        <filename>-c cleanall</filename> with BitBake for the package.
                        Modifications will also disappear if you use the <filename>rm_work</filename>
                        feature as described in the
                        "<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</ulink>" 
                        section of the Yocto Project Quick Start.
                        </note></para></listitem>
                    <listitem><para><emphasis>See the List of Files You Changed:</emphasis>
                        Use the <filename>git status</filename> command to see what files you have actually edited. 
                        The ability to have Git track the files you have changed is an advantage that this
                        workflow has over the Quilt workflow.
                        Here is the Git command to list your changed files:
                        <literallayout class='monospaced'>
     $ git status
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Stage the Modified Files:</emphasis>
                        Use the <filename>git add</filename> command to stage the changed files so they
                        can be committed as follows:
                        <literallayout class='monospaced'>
     $ git add file1.c file2.c file3.c
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Commit the Staged Files and View Your Changes:</emphasis>
                        Use the <filename>git commit</filename> command to commit the changes to the 
                        local repository.  
                        Once you have committed the files, you can use the <filename>git log</filename>
                        command to see your changes:
                        <literallayout class='monospaced'>
     $ git commit
     $ git log
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Generate the Patch:</emphasis>
                        Once the changes are committed, use the <filename>git format-patch</filename>
                        command to generate a patch file:
                        <literallayout class='monospaced'>
     $ git format-patch HEAD~1
                        </literallayout>
                        The <filename>HEAD~1</filename> part of the command causes Git to generate the 
                        patch file for the most recent commit.</para>
                        <para>At this point, the patch file has all your edits made 
                        to the <filename>file1.c</filename>, <filename>file2.c</filename>, and 
                        <filename>file3.c</filename> files.
                        You can find the resulting patch file in the current directory.
                        The patch file ends with <filename>.patch</filename>.</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 as the recipe.
                        Placing the patch here guarantees that the Yocto Project 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>
                    <listitem><para><emphasis>Increment the Package Revision Number:</emphasis>
                        Finally, don't forget to 'bump' the 
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PR'>PR</ulink></filename>
                        value in the same recipe since the resulting packages have changed.</para></listitem>
                </orderedlist>
            </para>
        </section>
    </section>

    <section id="building-multiple-architecture-libraries-into-one-image">
        <title>Combining Multiple Versions of Library Files into One Image</title>

        <para>
            The build system offers the ability to build libraries with different
            target optimizations or architecture formats and combine these together
            into one system image. 
            You can link different binaries in the image 
            against the different libraries as needed for specific use cases.
            This feature is called "Multilib."
        </para>

        <para>
            An example would be where you have most of a system compiled in 32-bit
            mode using 32-bit libraries, but you have something large, like a database
            engine, that needs to be a 64-bit application and use 64-bit libraries.
            Multilib allows you to get the best of both 32-bit and 64-bit libraries.
        </para>

        <para>
            While the Multilib feature is most commonly used for 32 and 64-bit differences,
            the approach the build system uses facilitates different target optimizations. 
            You could compile some binaries to use one set of libraries and other binaries
            to use other different sets of libraries.
            The libraries could differ in architecture, compiler options, or other 
            optimizations.
        </para>

        <para>
            This section overviews the Multilib process only. 
            For more details on how to implement Multilib, see the 
            <ulink url='&YOCTO_WIKI_URL;/wiki/Multilib'>Multilib</ulink> wiki 
            page.
        </para>

        <section id='preparing-to-use-multilib'>
            <title>Preparing to use Multilib</title>

            <para>
                User-specific requirements drive the Multilib feature,
                Consequently, there is no one "out-of-the-box" configuration that likely
                exists to meet your needs.
            </para>

            <para>
                In order to enable Multilib, you first need to ensure your recipe is
                extended to support multiple libraries. 
                Many standard recipes are already extended and support multiple libraries.
                You can check in the <filename>meta/conf/multilib.conf</filename>
                configuration file in the Yocto Project files directory to see how this is 
                done using the <filename>BBCLASSEXTEND</filename> variable.
                Eventually, all recipes will be covered and this list will be unneeded.
            </para>
  
            <para>
                For the most part, the Multilib class extension works automatically to
                extend the package name from <filename>${PN}</filename> to
                <filename>${MLPREFIX}${PN}</filename>, where <filename>MLPREFIX</filename>
                is the particular multilib (e.g. "lib32-" or "lib64-"). 
                Standard variables such as <filename>DEPENDS</filename>, 
                <filename>RDEPENDS</filename>, <filename>RPROVIDES</filename>, 
                <filename>RRECOMMENDS</filename>, <filename>PACKAGES</filename>, and 
                <filename>PACKAGES_DYNAMIC</filename> are automatically extended by the system.
                If you are extending any manual code in the recipe, you can use the 
                <filename>${MLPREFIX}</filename> variable to ensure those names are extended 
                correctly. 
                This automatic extension code resides in <filename>multilib.bbclass</filename>.
            </para>
        </section>

        <section id='using-multilib'>
            <title>Using Multilib</title>

            <para>
                After you have set up the recipes, you need to define the actual
                combination of multiple libraries you want to build. 
                You accomplish this through your <filename>local.conf</filename>
                configuration file in the 
                <link linkend='yocto-project-build-directory'>Yocto Project Build Directory</link>. 
                An example configuration would be as follows:
                <literallayout class='monospaced'>
     MACHINE = "qemux86-64"
     require conf/multilib.conf
     MULTILIBS = "multilib:lib32"
     DEFAULTTUNE_virtclass-multilib-lib32 = "x86"
     MULTILIB_IMAGE_INSTALL = "lib32-connman"
                </literallayout>
                This example enables an
                additional library named <filename>lib32</filename> alongside the 
                normal target packages.
                When combining these "lib32" alternatives, the example uses "x86" for tuning.
                For information on this particular tuning, see
                <filename>meta/conf/machine/include/ia32/arch-ia32.inc</filename>.
            </para>

            <para>
                The example then includes <filename>lib32-connman</filename>
                in all the images, which illustrates one method of including a 
                multiple library dependency. 
                You can use a normal image build to include this dependency,
                for example:
                <literallayout class='monospaced'>
     $ bitbake core-image-sato
                </literallayout>
                You can also build Multilib packages specifically with a command like this:
                <literallayout class='monospaced'>
     $  bitbake lib32-connman
                </literallayout>
            </para>
        </section>

        <section id='additional-implementation-details'>
            <title>Additional Implementation Details</title>

            <para>
                Different packaging systems have different levels of native Multilib
                support. 
                For the RPM Package Management System, the following implementation details 
                exist:
                <itemizedlist>
                    <listitem><para>A unique architecture is defined for the Multilib packages,
                        along with creating a unique deploy folder under 
                        <filename>tmp/deploy/rpm</filename> in the 
                        <link linkend='yocto-project-build-directory'>Yocto Project Build Directory</link>. 
                        For example, consider <filename>lib32</filename> in a 
                        <filename>qemux86-64</filename> image. 
                        The possible architectures in the system are "all", "qemux86_64",
                        "lib32_qemux86_64", and "lib32_x86".</para></listitem>
                    <listitem><para>The <filename>${MLPREFIX}</filename> variable is stripped from 
                        <filename>${PN}</filename> during RPM packaging.
                        The naming for a normal RPM package and a Multilib RPM package in a
                        <filename>qemux86-64</filename> system resolves to something similar to
                        <filename>bash-4.1-r2.x86_64.rpm</filename> and 
                        <filename>bash-4.1.r2.lib32_x86.rpm</filename>, respectively.
                        </para></listitem>
                    <listitem><para>When installing a Multilib image, the RPM backend first 
                        installs the base image and then installs the Multilib libraries.
                        </para></listitem>
                    <listitem><para>The build system relies on RPM to resolve the identical files in the 
                        two (or more) Multilib packages.</para></listitem>
                </itemizedlist>
            </para>

            <para>
                For the IPK Package Management System, the following implementation details exist:
                <itemizedlist>
                    <listitem><para>The <filename>${MLPREFIX}</filename> is not stripped from 
                        <filename>${PN}</filename> during IPK packaging.
                        The naming for a normal RPM package and a Multilib IPK package in a
                        <filename>qemux86-64</filename> system resolves to something like 
                        <filename>bash_4.1-r2.x86_64.ipk</filename> and
                        <filename>lib32-bash_4.1-rw_x86.ipk</filename>, respectively.
                        </para></listitem>
                    <listitem><para>The IPK deploy folder is not modified with 
                        <filename>${MLPREFIX}</filename> because packages with and without 
                        the Multilib feature can exist in the same folder due to the 
                        <filename>${PN}</filename> differences.</para></listitem>
                    <listitem><para>IPK defines a sanity check for Multilib installation 
                        using certain rules for file comparison, overridden, etc.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section> 
    </section>

    <section id='configuring-the-kernel'>
        <title>Configuring the Kernel</title>

        <para>
            Configuring the Linux Yocto kernel consists of making sure the <filename>.config</filename>
            file has all the right information in it for the image you are building.
            You can use the <filename>menuconfig</filename> tool and configuration fragments to 
            make sure your <filename>.config</filename> file is just how you need it. 
            This section describes how to use <filename>menuconfig</filename>, create and use 
            configuration fragments, and how to interatively tweak your <filename>.config</filename>
            file to create the leanest kernel configuration file possible.
        </para>

        <para>
            For concepts on kernel configuration, see the
            "<ulink url='&YOCTO_DOCS_KERNEL_URL;#kernel-configuration'>Kernel Configuration</ulink>"
            section in the Yocto Project Kernel Architecture and Use Manual.
        </para>

        <section id='using-menuconfig'>
            <title>Using&nbsp;&nbsp;<filename>menuconfig</filename></title>
 
            <para>
                The easiest way to define kernel configurations is to set them through the
                <filename>menuconfig</filename> tool.
                For general information on <filename>menuconfig</filename>, see
                <ulink url='http://en.wikipedia.org/wiki/Menuconfig'></ulink>.
            </para>

            <para>
                To use the <filename>menuconfig</filename> tool in the Yocto Project development
                environment, you must build the tool using BitBake.
                The following commands build and invoke <filename>menuconfig</filename> assuming the 
                Yocto Project files top-level directory is <filename>~/poky</filename>:
                <literallayout class='monospaced'>
     $ cd ~/poky
     $ source oe-init-build-env
     $ bitbake linux-yocto -c menuconfig
                </literallayout>
                Once <filename>menuconfig</filename> comes up, its standard interface allows you to 
                examine and configure all the kernel configuration parameters.
                Once you have made your changes, simply exit the tool and save your changes to 
                create an updated version of the <filename>.config</filename> configuration file.
            </para>

            <para>
                For an example that shows how to change the <filename>SMP_CONFIG</filename> parameter
                using <filename>menuconfig</filename>, see the 
                "<link linkend='changing-the-config-smp-configuration-using-menuconfig'>Changing
                the <filename>CONFIG_SMP</filename> Configuration Using <filename>menuconfig</filename></link>" 
                section.
            </para>
        </section>

        <section id='creating-config-fragments'>
            <title>Creating Config Fragments</title>

            <para>
                Configuration fragments are simply kernel options that appear in a file.
                Syntactically, the configuration statement is identical to what would appear
                in the <filename>.config</filename>.
                For example, issuing the following from the shell would create a config fragment
                file named <filename>my_smp.cfg</filename> that enables multi-processor support
                within the kernel:
                <literallayout class='monospaced'>
     $ echo "CONFIG_SMP=y" >> my_smp.cfg
                </literallayout>
            </para>

            <para>
                Where do you put your configuration files?
                You can place these configuration files in the same area pointed to by  
                <filename>SRC_URI</filename>.
                The Yocto Project build process will pick up the configuration and add it to the 
                kernel's configuration.
                For example, assume you add the following to your 
                <filename>linux-yocto_3.0.bbappend</filename> file:
                <literallayout class='monospaced'>
     file://my_smp.cfg
                </literallayout>
                You would put the config fragment file <filename>my_smp.cfg</filename> in a 
                sub-directory with the same root name (<filename>linux-yocto</filename>)
                beneath the directory that contains your <filename>linux-yocto_3.0.bbappend</filename> 
                file and the build system will pick up and apply the fragment.
            </para>
        </section>

        <section id='fine-tuning-the-kernel-configuration-file'>
            <title>Fine-tuning the Kernel Configuration File</title>

            <para>
                You can make sure the <filename>.config</filename> is as lean or efficient as 
                possible by reading the output of the kernel configuration fragment audit,
                noting any issues, making changes to correct the issues, and then repeating.
            </para>

            <para>
                As part of the Linux Yocto kernel build process, the 
                <filename>kernel_configcheck</filename> task runs.
                This task validates the kernel configuration by checking the final 
                <filename>.config</filename> file against the input files.
                During the check, the task produces warning messages for the following 
                issues:
                <itemizedlist>
                    <listitem><para>Requested options that did not make the final 
                        <filename>.config</filename> file.</para></listitem>
                    <listitem><para>Configuration items that appear twice in the same 
                        configuration fragment.</para></listitem>
                    <listitem><para>Configuration items tagged as 'required' were overridden.
                        </para></listitem>
                    <listitem><para>A board overrides a non-board specific option.</para></listitem>
                    <listitem><para>Listed options not valid for the kernel being processed. 
                        In other words, the option does not appear anywhere.</para></listitem>
                </itemizedlist>
                <note>
                    The <filename>kernel_configcheck</filename> task can also optionally report
                    if an option is overridden during processing.
                </note>
            </para>

            <para>
                For each output warning, a message points to the file
                that contains a list of the options and a pointer to the config
                fragment that defines them.
                Collectively, the files are the key to streamlining the configiguration.
            </para>

            <para>
                To streamline the configuration, do the following:
                <orderedlist>
                    <listitem><para>Start with a full configuration that you know
                        works - it builds and boots successfully.
                        This configuration file will be your baseline.</para></listitem>
                    <listitem><para>Separately run the <filename>configme</filename> and 
                        <filename>kernel_configcheck</filename> tasks.</para></listitem>
                    <listitem><para>Take the resulting list of files from the 
                        <filename>kernel_configcheck</filename> task warnings and do the following:
                        <itemizedlist>
                            <listitem><para>Drop values that are redefined in the fragment but do not
                                change the final <filename>.config</filename> file.</para></listitem>
                            <listitem><para>Analyze and potentially drop values from the 
                                <filename>.config</filename> file that override required 
                                configurations.</para></listitem>
                            <listitem><para>Analyze and potentially remove non-board specific options.
                                </para></listitem>
                            <listitem><para>Remove repeated and invalid options.</para></listitem>
                        </itemizedlist></para></listitem>
                    <listitem><para>After you have worked through the output of the kernel configuration 
                        audit, you can re-run the <filename>configme</filename> 
                        and <filename>kernel_configcheck</filename> tasks to see the results of your 
                        changes. 
                        If you have more issues, you can deal with them as described in the 
                        previous step.</para></listitem>
                </orderedlist> 
            </para>

            <para>
                Iteratively working through steps two through four eventually yields 
                a minimal, streamlined configuration file.
                Once you have the best <filename>.config</filename>, you can build the Linux
                Yocto kernel.
            </para>
        </section>
    </section>

    <section id="usingpoky-changes-updatingimages">
        <title>Updating Existing Images</title>

        <para>
            Often, rather than re-flashing a new image, you might wish to install updated 
            packages into an existing running system. 
            You can do this by first sharing the <filename>tmp/deploy/ipk/</filename> directory
            through a web server and then by changing <filename>/etc/opkg/base-feeds.conf</filename> 
            to point at the shared server.
            Following is an example:
            <literallayout class='monospaced'>
     $ src/gz all http://www.mysite.com/somedir/deploy/ipk/all
     $ src/gz armv7a http://www.mysite.com/somedir/deploy/ipk/armv7a
     $ src/gz beagleboard http://www.mysite.com/somedir/deploy/ipk/beagleboard
            </literallayout>
        </para>
    </section>

    <section id="usingpoky-changes-prbump">
        <title>Incrementing a Package Revision Number</title>

        <para>
            If a committed change results in changing the package output,
            then the value of the 
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PR'>PR</ulink></filename> 
            variable needs to be increased 
            (or "bumped") as part of that commit. 
            This means that for new recipes you must be sure to add the <filename>PR</filename>
            variable and set its initial value equal to "r0".  
            Failing to define <filename>PR</filename> makes it easy to miss when you bump a package.
            Note that you can only use integer values following the "r" in the 
            <filename>PR</filename> variable.
        </para>

        <para>
            If you are sharing a common <filename>.inc</filename> file with multiple recipes, 
            you can also use the 
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-INC_PR'>INC_PR</ulink></filename> 
            variable to ensure that 
            the recipes sharing the <filename>.inc</filename> file are rebuilt when the 
            <filename>.inc</filename> file itself is changed. 
            The <filename>.inc</filename> file must set <filename>INC_PR</filename>
            (initially to "r0"), and all recipes referring to it should set <filename>PR</filename>
            to "$(INC_PR).0" initially, incrementing the last number when the recipe is changed.
            If the <filename>.inc</filename> file is changed then its 
            <filename>INC_PR</filename> should be incremented.
        </para>

        <para> 
            When upgrading the version of a package, assuming the 
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'>PV</ulink></filename> 
            changes, the <filename>PR</filename> variable should be reset to "r0"
            (or "$(INC_PR).0" if you are using <filename>INC_PR</filename>).
        </para>

        <para>
            Usually, version increases occur only to packages.
            However, if for some reason <filename>PV</filename> changes but does not 
            increase, you can increase the 
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PE'>PE</ulink></filename> 
            variable (Package Epoch).
            The <filename>PE</filename> variable defaults to "0".
        </para>

        <para>
            Version numbering strives to follow the 
            <ulink url='http://www.debian.org/doc/debian-policy/ch-controlfields.html'>
            Debian Version Field Policy Guidelines</ulink>.
            These guidelines define how versions are compared and what "increasing" a version means.
        </para>

        <para>
            There are two reasons for following the previously mentioned guidelines.
            First, to ensure that when a developer updates and rebuilds, they get all the changes to
            the repository and do not have to remember to rebuild any sections.
            Second, to ensure that target users are able to upgrade their
            devices using package manager commands such as <filename>opkg upgrade</filename> 
            (or similar commands for dpkg/apt or rpm-based systems). 
        </para>

        <para>
            The goal is to ensure the Yocto Project has packages that can be upgraded in all cases.
        </para>
    </section>

    <section id="usingpoky-configuring-DISTRO_PN_ALIAS">
        <title>Handling a Package Name Alias</title>
        <para>
            Sometimes a package name you are using might exist under an alias or as a similarly named
            package in a different distribution.
            The Yocto Project implements a <filename>distro_check</filename>
            task that automatically connects to major distributions
            and checks for these situations. 
            If the package exists under a different name in a different distribution, you get a 
            <filename>distro_check</filename> mismatch.  
            You can resolve this problem by defining a per-distro recipe name alias using the 
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_PN_ALIAS'>DISTRO_PN_ALIAS</ulink></filename> 
            variable.
        </para>

        <para>
            Following is an example that shows how you specify the <filename>DISTRO_PN_ALIAS</filename>
            variable:
            <literallayout class='monospaced'>
     DISTRO_PN_ALIAS_pn-PACKAGENAME = "distro1=package_name_alias1 \
                                       distro2=package_name_alias2 \
                                       distro3=package_name_alias3 \
                                       ..."
            </literallayout>
        </para>
        
        <para>
            If you have more than one distribution alias, separate them with a space.
            Note that the Yocto Project currently automatically checks the 
            Fedora, OpenSuSE, Debian, Ubuntu, 
            and Mandriva distributions for source package recipes without having to specify them 
            using the <filename>DISTRO_PN_ALIAS</filename> variable.
            For example, the following command generates a report that lists the Linux distributions
            that include the sources for each of the Yocto Project recipes.
            <literallayout class='monospaced'>
     $ bitbake world -f -c distro_check
            </literallayout>
            The results are stored in the <filename>build/tmp/log/distro_check-${DATETIME}.results</filename> 
            file found in the Yocto Project files area.
        </para>
    </section>

    <section id="building-software-from-an-external-source">
        <title>Building Software from an External Source</title>

        <para>
            By default, the Yocto Project build system does its work from within the 
            <link linkend='yocto-project-build-directory'>Yocto Project Build Directory</link>.  
            The build process involves fetching the source files, unpacking them, and then patching them
            if necessary before the build takes place.
        </para>

        <para>
            Situations exist where you might want to build software from source files that are external to 
            and thus outside of the <link linkend='yocto-project-files'>Yocto Project Files</link>.
            For example, suppose you have a project that includes a new BSP with a heavily customized 
            kernel, a very minimal image, and some new user-space recipes.
            And, you want to minimize the exposure to the Yocto Project build system to the 
            development team so that they can focus on their project and maintain everyone's workflow
            as much as possible.
            In this case, you want a kernel source directory on the development machine where the 
            development occurs.
            You want the recipe's 
            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
            variable to point to the external directory and use it as is, not copy it.  
        </para>

        <para>
            To build from software that comes from an external source, all you need to do is
            change your recipe so that it inherits the 
            <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-externalsrc'><filename>externalsrc.bbclass</filename></ulink> 
            class and then sets the 
            <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>
            variable to point to your external source code.
            Here are the statements to put in your recipe:
            <literallayout class='monospaced'>
     inherit externalsrc
     S = "/some/path/to/your/package/source"
            </literallayout>
        </para>

        <para>
            It is important to know that the <filename>externalsrc.bbclass</filename> assumes that the 
            source directory <filename>S</filename> and the build directory 
            <ulink url='&YOCTO_DOCS_REF_URL;#var-B'><filename>B</filename></ulink>
            are different even though by default these directories are the same.
            This assumption is important because it supports building different variants of the recipe
            by using the 
            <ulink url='&YOCTO_DOCS_REF_URL;#var-BBCLASSEXTEND'><filename>BBCLASSEXTEND</filename></ulink>
            variable.
            You could allow the build directory to be the same as the source directory but you would 
            not be able to build more than one variant of the recipe.
            Consequently, if you are building multiple variants of the recipe, you need to establish a 
            build directory that is different than the source directory.
        </para>
    </section>
</chapter>

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