1.. SPDX-License-Identifier: CC-BY-2.5 2 3==================== 4Syntax and Operators 5==================== 6 7| 8 9BitBake files have their own syntax. The syntax has similarities to 10several other languages but also has some unique features. This section 11describes the available syntax and operators as well as provides 12examples. 13 14Basic Syntax 15============ 16 17This section provides some basic syntax examples. 18 19Basic Variable Setting 20---------------------- 21 22The following example sets ``VARIABLE`` to "value". This assignment 23occurs immediately as the statement is parsed. It is a "hard" 24assignment. :: 25 26 VARIABLE = "value" 27 28As expected, if you include leading or 29trailing spaces as part of an assignment, the spaces are retained:: 30 31 VARIABLE = " value" 32 VARIABLE = "value " 33 34Setting ``VARIABLE`` to "" sets 35it to an empty string, while setting the variable to " " sets it to a 36blank space (i.e. these are not the same values). :: 37 38 VARIABLE = "" 39 VARIABLE = " " 40 41You can use single quotes instead of double quotes when setting a 42variable's value. Doing so allows you to use values that contain the 43double quote character:: 44 45 VARIABLE = 'I have a " in my value' 46 47.. note:: 48 49 Unlike in Bourne shells, single quotes work identically to double 50 quotes in all other ways. They do not suppress variable expansions. 51 52Modifying Existing Variables 53---------------------------- 54 55Sometimes you need to modify existing variables. Following are some 56cases where you might find you want to modify an existing variable: 57 58- Customize a recipe that uses the variable. 59 60- Change a variable's default value used in a ``*.bbclass`` file. 61 62- Change the variable in a ``*.bbappend`` file to override the variable 63 in the original recipe. 64 65- Change the variable in a configuration file so that the value 66 overrides an existing configuration. 67 68Changing a variable value can sometimes depend on how the value was 69originally assigned and also on the desired intent of the change. In 70particular, when you append a value to a variable that has a default 71value, the resulting value might not be what you expect. In this case, 72the value you provide might replace the value rather than append to the 73default value. 74 75If after you have changed a variable's value and something unexplained 76occurs, you can use BitBake to check the actual value of the suspect 77variable. You can make these checks for both configuration and recipe 78level changes: 79 80- For configuration changes, use the following:: 81 82 $ bitbake -e 83 84 This 85 command displays variable values after the configuration files (i.e. 86 ``local.conf``, ``bblayers.conf``, ``bitbake.conf`` and so forth) 87 have been parsed. 88 89 .. note:: 90 91 Variables that are exported to the environment are preceded by the 92 string "export" in the command's output. 93 94- To find changes to a given variable in a specific recipe, use the 95 following:: 96 97 $ bitbake recipename -e | grep VARIABLENAME=\" 98 99 This command checks to see if the variable actually makes 100 it into a specific recipe. 101 102Line Joining 103------------ 104 105Outside of :ref:`functions <bitbake-user-manual/bitbake-user-manual-metadata:functions>`, 106BitBake joins any line ending in 107a backslash character ("\") with the following line before parsing 108statements. The most common use for the "\" character is to split 109variable assignments over multiple lines, as in the following example:: 110 111 FOO = "bar \ 112 baz \ 113 qaz" 114 115Both the "\" character and the newline 116character that follow it are removed when joining lines. Thus, no 117newline characters end up in the value of ``FOO``. 118 119Consider this additional example where the two assignments both assign 120"barbaz" to ``FOO``:: 121 122 FOO = "barbaz" 123 FOO = "bar\ 124 baz" 125 126.. note:: 127 128 BitBake does not interpret escape sequences like "\n" in variable 129 values. For these to have an effect, the value must be passed to some 130 utility that interprets escape sequences, such as 131 ``printf`` or ``echo -n``. 132 133Variable Expansion 134------------------ 135 136Variables can reference the contents of other variables using a syntax 137that is similar to variable expansion in Bourne shells. The following 138assignments result in A containing "aval" and B evaluating to 139"preavalpost". :: 140 141 A = "aval" 142 B = "pre${A}post" 143 144.. note:: 145 146 Unlike in Bourne shells, the curly braces are mandatory: Only ``${FOO}`` and not 147 ``$FOO`` is recognized as an expansion of ``FOO``. 148 149The "=" operator does not immediately expand variable references in the 150right-hand side. Instead, expansion is deferred until the variable 151assigned to is actually used. The result depends on the current values 152of the referenced variables. The following example should clarify this 153behavior:: 154 155 A = "${B} baz" 156 B = "${C} bar" 157 C = "foo" 158 *At this point, ${A} equals "foo bar baz"* 159 C = "qux" 160 *At this point, ${A} equals "qux bar baz"* 161 B = "norf" 162 *At this point, ${A} equals "norf baz"\* 163 164Contrast this behavior with the 165:ref:`bitbake-user-manual/bitbake-user-manual-metadata:immediate variable 166expansion (:=)` operator. 167 168If the variable expansion syntax is used on a variable that does not 169exist, the string is kept as is. For example, given the following 170assignment, ``BAR`` expands to the literal string "${FOO}" as long as 171``FOO`` does not exist. :: 172 173 BAR = "${FOO}" 174 175Setting a default value (?=) 176---------------------------- 177 178You can use the "?=" operator to achieve a "softer" assignment for a 179variable. This type of assignment allows you to define a variable if it 180is undefined when the statement is parsed, but to leave the value alone 181if the variable has a value. Here is an example:: 182 183 A ?= "aval" 184 185If ``A`` is 186set at the time this statement is parsed, the variable retains its 187value. However, if ``A`` is not set, the variable is set to "aval". 188 189.. note:: 190 191 This assignment is immediate. Consequently, if multiple "?=" 192 assignments to a single variable exist, the first of those ends up 193 getting used. 194 195Setting a weak default value (??=) 196---------------------------------- 197 198It is possible to use a "weaker" assignment than in the previous section 199by using the "??=" operator. This assignment behaves identical to "?=" 200except that the assignment is made at the end of the parsing process 201rather than immediately. Consequently, when multiple "??=" assignments 202exist, the last one is used. Also, any "=" or "?=" assignment will 203override the value set with "??=". Here is an example:: 204 205 A ??= "somevalue" 206 A ??= "someothervalue" 207 208If ``A`` is set before the above statements are 209parsed, the variable retains its value. If ``A`` is not set, the 210variable is set to "someothervalue". 211 212Again, this assignment is a "lazy" or "weak" assignment because it does 213not occur until the end of the parsing process. 214 215Immediate variable expansion (:=) 216--------------------------------- 217 218The ":=" operator results in a variable's contents being expanded 219immediately, rather than when the variable is actually used:: 220 221 T = "123" 222 A := "test ${T}" 223 T = "456" 224 B := "${T} ${C}" 225 C = "cval" 226 C := "${C}append" 227 228In this example, ``A`` contains "test 123", even though the final value 229of :term:`T` is "456". The variable :term:`B` will end up containing "456 230cvalappend". This is because references to undefined variables are 231preserved as is during (immediate)expansion. This is in contrast to GNU 232Make, where undefined variables expand to nothing. The variable ``C`` 233contains "cvalappend" since ``${C}`` immediately expands to "cval". 234 235.. _appending-and-prepending: 236 237Appending (+=) and prepending (=+) With Spaces 238---------------------------------------------- 239 240Appending and prepending values is common and can be accomplished using 241the "+=" and "=+" operators. These operators insert a space between the 242current value and prepended or appended value. 243 244These operators take immediate effect during parsing. Here are some 245examples:: 246 247 B = "bval" 248 B += "additionaldata" 249 C = "cval" 250 C =+ "test" 251 252The variable :term:`B` contains "bval additionaldata" and ``C`` contains "test 253cval". 254 255.. _appending-and-prepending-without-spaces: 256 257Appending (.=) and Prepending (=.) Without Spaces 258------------------------------------------------- 259 260If you want to append or prepend values without an inserted space, use 261the ".=" and "=." operators. 262 263These operators take immediate effect during parsing. Here are some 264examples:: 265 266 B = "bval" 267 B .= "additionaldata" 268 C = "cval" 269 C =. "test" 270 271The variable :term:`B` contains "bvaladditionaldata" and ``C`` contains 272"testcval". 273 274Appending and Prepending (Override Style Syntax) 275------------------------------------------------ 276 277You can also append and prepend a variable's value using an override 278style syntax. When you use this syntax, no spaces are inserted. 279 280These operators differ from the ":=", ".=", "=.", "+=", and "=+" 281operators in that their effects are applied at variable expansion time 282rather than being immediately applied. Here are some examples:: 283 284 B = "bval" 285 B:append = " additional data" 286 C = "cval" 287 C:prepend = "additional data " 288 D = "dval" 289 D:append = "additional data" 290 291The variable :term:`B` 292becomes "bval additional data" and ``C`` becomes "additional data cval". 293The variable ``D`` becomes "dvaladditional data". 294 295.. note:: 296 297 You must control all spacing when you use the override syntax. 298 299It is also possible to append and prepend to shell functions and 300BitBake-style Python functions. See the ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:shell functions`" and ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:bitbake-style python functions`" 301sections for examples. 302 303.. _removing-override-style-syntax: 304 305Removal (Override Style Syntax) 306------------------------------- 307 308You can remove values from lists using the removal override style 309syntax. Specifying a value for removal causes all occurrences of that 310value to be removed from the variable. 311 312When you use this syntax, BitBake expects one or more strings. 313Surrounding spaces and spacing are preserved. Here is an example:: 314 315 FOO = "123 456 789 123456 123 456 123 456" 316 FOO:remove = "123" 317 FOO:remove = "456" 318 FOO2 = " abc def ghi abcdef abc def abc def def" 319 FOO2:remove = "\ 320 def \ 321 abc \ 322 ghi \ 323 " 324 325The variable ``FOO`` becomes 326" 789 123456 " and ``FOO2`` becomes " abcdef ". 327 328Like ":append" and ":prepend", ":remove" is applied at variable 329expansion time. 330 331Override Style Operation Advantages 332----------------------------------- 333 334An advantage of the override style operations ":append", ":prepend", and 335":remove" as compared to the "+=" and "=+" operators is that the 336override style operators provide guaranteed operations. For example, 337consider a class ``foo.bbclass`` that needs to add the value "val" to 338the variable ``FOO``, and a recipe that uses ``foo.bbclass`` as follows:: 339 340 inherit foo 341 FOO = "initial" 342 343If ``foo.bbclass`` uses the "+=" operator, 344as follows, then the final value of ``FOO`` will be "initial", which is 345not what is desired:: 346 347 FOO += "val" 348 349If, on the other hand, ``foo.bbclass`` 350uses the ":append" operator, then the final value of ``FOO`` will be 351"initial val", as intended:: 352 353 FOO:append = " val" 354 355.. note:: 356 357 It is never necessary to use "+=" together with ":append". The following 358 sequence of assignments appends "barbaz" to FOO:: 359 360 FOO:append = "bar" 361 FOO:append = "baz" 362 363 364 The only effect of changing the second assignment in the previous 365 example to use "+=" would be to add a space before "baz" in the 366 appended value (due to how the "+=" operator works). 367 368Another advantage of the override style operations is that you can 369combine them with other overrides as described in the 370":ref:`bitbake-user-manual/bitbake-user-manual-metadata:conditional syntax (overrides)`" section. 371 372Variable Flag Syntax 373-------------------- 374 375Variable flags are BitBake's implementation of variable properties or 376attributes. It is a way of tagging extra information onto a variable. 377You can find more out about variable flags in general in the 378":ref:`bitbake-user-manual/bitbake-user-manual-metadata:variable flags`" section. 379 380You can define, append, and prepend values to variable flags. All the 381standard syntax operations previously mentioned work for variable flags 382except for override style syntax (i.e. ":prepend", ":append", and 383":remove"). 384 385Here are some examples showing how to set variable flags:: 386 387 FOO[a] = "abc" 388 FOO[b] = "123" 389 FOO[a] += "456" 390 391The variable ``FOO`` has two flags: 392``[a]`` and ``[b]``. The flags are immediately set to "abc" and "123", 393respectively. The ``[a]`` flag becomes "abc 456". 394 395No need exists to pre-define variable flags. You can simply start using 396them. One extremely common application is to attach some brief 397documentation to a BitBake variable as follows:: 398 399 CACHE[doc] = "The directory holding the cache of the metadata." 400 401Inline Python Variable Expansion 402-------------------------------- 403 404You can use inline Python variable expansion to set variables. Here is 405an example:: 406 407 DATE = "${@time.strftime('%Y%m%d',time.gmtime())}" 408 409This example results in the ``DATE`` variable being set to the current date. 410 411Probably the most common use of this feature is to extract the value of 412variables from BitBake's internal data dictionary, ``d``. The following 413lines select the values of a package name and its version number, 414respectively:: 415 416 PN = "${@bb.parse.vars_from_file(d.getVar('FILE', False),d)[0] or 'defaultpkgname'}" 417 PV = "${@bb.parse.vars_from_file(d.getVar('FILE', False),d)[1] or '1.0'}" 418 419.. note:: 420 421 Inline Python expressions work just like variable expansions insofar as the 422 "=" and ":=" operators are concerned. Given the following assignment, foo() 423 is called each time FOO is expanded:: 424 425 FOO = "${@foo()}" 426 427 Contrast this with the following immediate assignment, where foo() is only 428 called once, while the assignment is parsed:: 429 430 FOO := "${@foo()}" 431 432For a different way to set variables with Python code during parsing, 433see the 434":ref:`bitbake-user-manual/bitbake-user-manual-metadata:anonymous python functions`" section. 435 436Unsetting variables 437------------------- 438 439It is possible to completely remove a variable or a variable flag from 440BitBake's internal data dictionary by using the "unset" keyword. Here is 441an example:: 442 443 unset DATE 444 unset do_fetch[noexec] 445 446These two statements remove the ``DATE`` and the ``do_fetch[noexec]`` flag. 447 448Providing Pathnames 449------------------- 450 451When specifying pathnames for use with BitBake, do not use the tilde 452("~") character as a shortcut for your home directory. Doing so might 453cause BitBake to not recognize the path since BitBake does not expand 454this character in the same way a shell would. 455 456Instead, provide a fuller path as the following example illustrates:: 457 458 BBLAYERS ?= " \ 459 /home/scott-lenovo/LayerA \ 460 " 461 462Exporting Variables to the Environment 463====================================== 464 465You can export variables to the environment of running tasks by using 466the ``export`` keyword. For example, in the following example, the 467``do_foo`` task prints "value from the environment" when run:: 468 469 export ENV_VARIABLE 470 ENV_VARIABLE = "value from the environment" 471 472 do_foo() { 473 bbplain "$ENV_VARIABLE" 474 } 475 476.. note:: 477 478 BitBake does not expand ``$ENV_VARIABLE`` in this case because it lacks the 479 obligatory ``{}`` . Rather, ``$ENV_VARIABLE`` is expanded by the shell. 480 481It does not matter whether ``export ENV_VARIABLE`` appears before or 482after assignments to ``ENV_VARIABLE``. 483 484It is also possible to combine ``export`` with setting a value for the 485variable. Here is an example:: 486 487 export ENV_VARIABLE = "variable-value" 488 489In the output of ``bitbake -e``, variables that are exported to the 490environment are preceded by "export". 491 492Among the variables commonly exported to the environment are ``CC`` and 493``CFLAGS``, which are picked up by many build systems. 494 495Conditional Syntax (Overrides) 496============================== 497 498BitBake uses :term:`OVERRIDES` to control what 499variables are overridden after BitBake parses recipes and configuration 500files. This section describes how you can use :term:`OVERRIDES` as 501conditional metadata, talks about key expansion in relationship to 502:term:`OVERRIDES`, and provides some examples to help with understanding. 503 504Conditional Metadata 505-------------------- 506 507You can use :term:`OVERRIDES` to conditionally select a specific version of 508a variable and to conditionally append or prepend the value of a 509variable. 510 511.. note:: 512 513 Overrides can only use lower-case characters. Additionally, 514 underscores are not permitted in override names as they are used to 515 separate overrides from each other and from the variable name. 516 517- *Selecting a Variable:* The :term:`OVERRIDES` variable is a 518 colon-character-separated list that contains items for which you want 519 to satisfy conditions. Thus, if you have a variable that is 520 conditional on "arm", and "arm" is in :term:`OVERRIDES`, then the 521 "arm"-specific version of the variable is used rather than the 522 non-conditional version. Here is an example:: 523 524 OVERRIDES = "architecture:os:machine" 525 TEST = "default" 526 TEST_os = "osspecific" 527 TEST_nooverride = "othercondvalue" 528 529 In this example, the :term:`OVERRIDES` 530 variable lists three overrides: "architecture", "os", and "machine". 531 The variable ``TEST`` by itself has a default value of "default". You 532 select the os-specific version of the ``TEST`` variable by appending 533 the "os" override to the variable (i.e. ``TEST_os``). 534 535 To better understand this, consider a practical example that assumes 536 an OpenEmbedded metadata-based Linux kernel recipe file. The 537 following lines from the recipe file first set the kernel branch 538 variable ``KBRANCH`` to a default value, then conditionally override 539 that value based on the architecture of the build:: 540 541 KBRANCH = "standard/base" 542 KBRANCH:qemuarm = "standard/arm-versatile-926ejs" 543 KBRANCH:qemumips = "standard/mti-malta32" 544 KBRANCH:qemuppc = "standard/qemuppc" 545 KBRANCH:qemux86 = "standard/common-pc/base" 546 KBRANCH:qemux86-64 = "standard/common-pc-64/base" 547 KBRANCH:qemumips64 = "standard/mti-malta64" 548 549- *Appending and Prepending:* BitBake also supports append and prepend 550 operations to variable values based on whether a specific item is 551 listed in :term:`OVERRIDES`. Here is an example:: 552 553 DEPENDS = "glibc ncurses" 554 OVERRIDES = "machine:local" 555 DEPENDS:append:machine = "libmad" 556 557 In this example, :term:`DEPENDS` becomes "glibc ncurses libmad". 558 559 Again, using an OpenEmbedded metadata-based kernel recipe file as an 560 example, the following lines will conditionally append to the 561 ``KERNEL_FEATURES`` variable based on the architecture:: 562 563 KERNEL_FEATURES:append = " ${KERNEL_EXTRA_FEATURES}" 564 KERNEL_FEATURES:append:qemux86=" cfg/sound.scc cfg/paravirt_kvm.scc" 565 KERNEL_FEATURES:append:qemux86-64=" cfg/sound.scc cfg/paravirt_kvm.scc" 566 567- *Setting a Variable for a Single Task:* BitBake supports setting a 568 variable just for the duration of a single task. Here is an example:: 569 570 FOO_task-configure = "val 1" 571 FOO:task-compile = "val 2" 572 573 In the 574 previous example, ``FOO`` has the value "val 1" while the 575 ``do_configure`` task is executed, and the value "val 2" while the 576 ``do_compile`` task is executed. 577 578 Internally, this is implemented by prepending the task (e.g. 579 "task-compile:") to the value of 580 :term:`OVERRIDES` for the local datastore of the 581 ``do_compile`` task. 582 583 You can also use this syntax with other combinations (e.g. 584 "``:prepend``") as shown in the following example:: 585 586 EXTRA_OEMAKE:prepend:task-compile = "${PARALLEL_MAKE} " 587 588Key Expansion 589------------- 590 591Key expansion happens when the BitBake datastore is finalized. To better 592understand this, consider the following example:: 593 594 A${B} = "X" 595 B = "2" 596 A2 = "Y" 597 598In this case, after all the parsing is complete, BitBake expands 599``${B}`` into "2". This expansion causes ``A2``, which was set to "Y" 600before the expansion, to become "X". 601 602.. _variable-interaction-worked-examples: 603 604Examples 605-------- 606 607Despite the previous explanations that show the different forms of 608variable definitions, it can be hard to work out exactly what happens 609when variable operators, conditional overrides, and unconditional 610overrides are combined. This section presents some common scenarios 611along with explanations for variable interactions that typically confuse 612users. 613 614There is often confusion concerning the order in which overrides and 615various "append" operators take effect. Recall that an append or prepend 616operation using ":append" and ":prepend" does not result in an immediate 617assignment as would "+=", ".=", "=+", or "=.". Consider the following 618example:: 619 620 OVERRIDES = "foo" 621 A = "Z" 622 A:foo:append = "X" 623 624For this case, 625``A`` is unconditionally set to "Z" and "X" is unconditionally and 626immediately appended to the variable ``A:foo``. Because overrides have 627not been applied yet, ``A:foo`` is set to "X" due to the append and 628``A`` simply equals "Z". 629 630Applying overrides, however, changes things. Since "foo" is listed in 631:term:`OVERRIDES`, the conditional variable ``A`` is replaced with the "foo" 632version, which is equal to "X". So effectively, ``A:foo`` replaces 633``A``. 634 635This next example changes the order of the override and the append:: 636 637 OVERRIDES = "foo" 638 A = "Z" 639 A:append:foo = "X" 640 641For this case, before 642overrides are handled, ``A`` is set to "Z" and ``A:append:foo`` is set 643to "X". Once the override for "foo" is applied, however, ``A`` gets 644appended with "X". Consequently, ``A`` becomes "ZX". Notice that spaces 645are not appended. 646 647This next example has the order of the appends and overrides reversed 648back as in the first example:: 649 650 OVERRIDES = "foo" 651 A = "Y" 652 A:foo:append = "Z" 653 A:foo:append = "X" 654 655For this case, before any overrides are resolved, 656``A`` is set to "Y" using an immediate assignment. After this immediate 657assignment, ``A:foo`` is set to "Z", and then further appended with "X" 658leaving the variable set to "ZX". Finally, applying the override for 659"foo" results in the conditional variable ``A`` becoming "ZX" (i.e. 660``A`` is replaced with ``A:foo``). 661 662This final example mixes in some varying operators:: 663 664 A = "1" 665 A:append = "2" 666 A:append = "3" 667 A += "4" 668 A .= "5" 669 670For this case, the type of append 671operators are affecting the order of assignments as BitBake passes 672through the code multiple times. Initially, ``A`` is set to "1 45" 673because of the three statements that use immediate operators. After 674these assignments are made, BitBake applies the ":append" operations. 675Those operations result in ``A`` becoming "1 4523". 676 677Sharing Functionality 678===================== 679 680BitBake allows for metadata sharing through include files (``.inc``) and 681class files (``.bbclass``). For example, suppose you have a piece of 682common functionality such as a task definition that you want to share 683between more than one recipe. In this case, creating a ``.bbclass`` file 684that contains the common functionality and then using the ``inherit`` 685directive in your recipes to inherit the class would be a common way to 686share the task. 687 688This section presents the mechanisms BitBake provides to allow you to 689share functionality between recipes. Specifically, the mechanisms 690include ``include``, ``inherit``, :term:`INHERIT`, and ``require`` 691directives. 692 693Locating Include and Class Files 694-------------------------------- 695 696BitBake uses the :term:`BBPATH` variable to locate 697needed include and class files. Additionally, BitBake searches the 698current directory for ``include`` and ``require`` directives. 699 700.. note:: 701 702 The BBPATH variable is analogous to the environment variable PATH . 703 704In order for include and class files to be found by BitBake, they need 705to be located in a "classes" subdirectory that can be found in 706:term:`BBPATH`. 707 708``inherit`` Directive 709--------------------- 710 711When writing a recipe or class file, you can use the ``inherit`` 712directive to inherit the functionality of a class (``.bbclass``). 713BitBake only supports this directive when used within recipe and class 714files (i.e. ``.bb`` and ``.bbclass``). 715 716The ``inherit`` directive is a rudimentary means of specifying 717functionality contained in class files that your recipes require. For 718example, you can easily abstract out the tasks involved in building a 719package that uses Autoconf and Automake and put those tasks into a class 720file and then have your recipe inherit that class file. 721 722As an example, your recipes could use the following directive to inherit 723an ``autotools.bbclass`` file. The class file would contain common 724functionality for using Autotools that could be shared across recipes:: 725 726 inherit autotools 727 728In this case, BitBake would search for the directory 729``classes/autotools.bbclass`` in :term:`BBPATH`. 730 731.. note:: 732 733 You can override any values and functions of the inherited class 734 within your recipe by doing so after the "inherit" statement. 735 736If you want to use the directive to inherit multiple classes, separate 737them with spaces. The following example shows how to inherit both the 738``buildhistory`` and ``rm_work`` classes:: 739 740 inherit buildhistory rm_work 741 742An advantage with the inherit directive as compared to both the 743:ref:`include <bitbake-user-manual/bitbake-user-manual-metadata:\`\`include\`\` directive>` and :ref:`require <bitbake-user-manual/bitbake-user-manual-metadata:\`\`require\`\` directive>` 744directives is that you can inherit class files conditionally. You can 745accomplish this by using a variable expression after the ``inherit`` 746statement. Here is an example:: 747 748 inherit ${VARNAME} 749 750If ``VARNAME`` is 751going to be set, it needs to be set before the ``inherit`` statement is 752parsed. One way to achieve a conditional inherit in this case is to use 753overrides:: 754 755 VARIABLE = "" 756 VARIABLE:someoverride = "myclass" 757 758Another method is by using anonymous Python. Here is an example:: 759 760 python () { 761 if condition == value: 762 d.setVar('VARIABLE', 'myclass') 763 else: 764 d.setVar('VARIABLE', '') 765 } 766 767Alternatively, you could use an in-line Python expression in the 768following form:: 769 770 inherit ${@'classname' if condition else ''} 771 inherit ${@functionname(params)} 772 773In all cases, if the expression evaluates to an 774empty string, the statement does not trigger a syntax error because it 775becomes a no-op. 776 777``include`` Directive 778--------------------- 779 780BitBake understands the ``include`` directive. This directive causes 781BitBake to parse whatever file you specify, and to insert that file at 782that location. The directive is much like its equivalent in Make except 783that if the path specified on the include line is a relative path, 784BitBake locates the first file it can find within :term:`BBPATH`. 785 786The include directive is a more generic method of including 787functionality as compared to the :ref:`inherit <bitbake-user-manual/bitbake-user-manual-metadata:\`\`inherit\`\` directive>` 788directive, which is restricted to class (i.e. ``.bbclass``) files. The 789include directive is applicable for any other kind of shared or 790encapsulated functionality or configuration that does not suit a 791``.bbclass`` file. 792 793As an example, suppose you needed a recipe to include some self-test 794definitions:: 795 796 include test_defs.inc 797 798.. note:: 799 800 The include directive does not produce an error when the file cannot be 801 found. Consequently, it is recommended that if the file you are including is 802 expected to exist, you should use :ref:`require <require-inclusion>` instead 803 of include . Doing so makes sure that an error is produced if the file cannot 804 be found. 805 806.. _require-inclusion: 807 808``require`` Directive 809--------------------- 810 811BitBake understands the ``require`` directive. This directive behaves 812just like the ``include`` directive with the exception that BitBake 813raises a parsing error if the file to be included cannot be found. Thus, 814any file you require is inserted into the file that is being parsed at 815the location of the directive. 816 817The require directive, like the include directive previously described, 818is a more generic method of including functionality as compared to the 819:ref:`inherit <bitbake-user-manual/bitbake-user-manual-metadata:\`\`inherit\`\` directive>` directive, which is restricted to class 820(i.e. ``.bbclass``) files. The require directive is applicable for any 821other kind of shared or encapsulated functionality or configuration that 822does not suit a ``.bbclass`` file. 823 824Similar to how BitBake handles :ref:`include <bitbake-user-manual/bitbake-user-manual-metadata:\`\`include\`\` directive>`, if 825the path specified on the require line is a relative path, BitBake 826locates the first file it can find within :term:`BBPATH`. 827 828As an example, suppose you have two versions of a recipe (e.g. 829``foo_1.2.2.bb`` and ``foo_2.0.0.bb``) where each version contains some 830identical functionality that could be shared. You could create an 831include file named ``foo.inc`` that contains the common definitions 832needed to build "foo". You need to be sure ``foo.inc`` is located in the 833same directory as your two recipe files as well. Once these conditions 834are set up, you can share the functionality using a ``require`` 835directive from within each recipe:: 836 837 require foo.inc 838 839``INHERIT`` Configuration Directive 840----------------------------------- 841 842When creating a configuration file (``.conf``), you can use the 843:term:`INHERIT` configuration directive to inherit a 844class. BitBake only supports this directive when used within a 845configuration file. 846 847As an example, suppose you needed to inherit a class file called 848``abc.bbclass`` from a configuration file as follows:: 849 850 INHERIT += "abc" 851 852This configuration directive causes the named class to be inherited at 853the point of the directive during parsing. As with the ``inherit`` 854directive, the ``.bbclass`` file must be located in a "classes" 855subdirectory in one of the directories specified in :term:`BBPATH`. 856 857.. note:: 858 859 Because .conf files are parsed first during BitBake's execution, using 860 INHERIT to inherit a class effectively inherits the class globally (i.e. for 861 all recipes). 862 863If you want to use the directive to inherit multiple classes, you can 864provide them on the same line in the ``local.conf`` file. Use spaces to 865separate the classes. The following example shows how to inherit both 866the ``autotools`` and ``pkgconfig`` classes:: 867 868 INHERIT += "autotools pkgconfig" 869 870Functions 871========= 872 873As with most languages, functions are the building blocks that are used 874to build up operations into tasks. BitBake supports these types of 875functions: 876 877- *Shell Functions:* Functions written in shell script and executed 878 either directly as functions, tasks, or both. They can also be called 879 by other shell functions. 880 881- *BitBake-Style Python Functions:* Functions written in Python and 882 executed by BitBake or other Python functions using 883 ``bb.build.exec_func()``. 884 885- *Python Functions:* Functions written in Python and executed by 886 Python. 887 888- *Anonymous Python Functions:* Python functions executed automatically 889 during parsing. 890 891Regardless of the type of function, you can only define them in class 892(``.bbclass``) and recipe (``.bb`` or ``.inc``) files. 893 894Shell Functions 895--------------- 896 897Functions written in shell script and executed either directly as 898functions, tasks, or both. They can also be called by other shell 899functions. Here is an example shell function definition:: 900 901 some_function () { 902 echo "Hello World" 903 } 904 905When you create these types of functions in 906your recipe or class files, you need to follow the shell programming 907rules. The scripts are executed by ``/bin/sh``, which may not be a bash 908shell but might be something such as ``dash``. You should not use 909Bash-specific script (bashisms). 910 911Overrides and override-style operators like ``:append`` and ``:prepend`` 912can also be applied to shell functions. Most commonly, this application 913would be used in a ``.bbappend`` file to modify functions in the main 914recipe. It can also be used to modify functions inherited from classes. 915 916As an example, consider the following:: 917 918 do_foo() { 919 bbplain first 920 fn 921 } 922 923 fn:prepend() { 924 bbplain second 925 } 926 927 fn() { 928 bbplain third 929 } 930 931 do_foo:append() { 932 bbplain fourth 933 } 934 935Running ``do_foo`` prints the following:: 936 937 recipename do_foo: first 938 recipename do_foo: second 939 recipename do_foo: third 940 recipename do_foo: fourth 941 942.. note:: 943 944 Overrides and override-style operators can be applied to any shell 945 function, not just :ref:`tasks <bitbake-user-manual/bitbake-user-manual-metadata:tasks>`. 946 947You can use the ``bitbake -e`` recipename command to view the final 948assembled function after all overrides have been applied. 949 950BitBake-Style Python Functions 951------------------------------ 952 953These functions are written in Python and executed by BitBake or other 954Python functions using ``bb.build.exec_func()``. 955 956An example BitBake function is:: 957 958 python some_python_function () { 959 d.setVar("TEXT", "Hello World") 960 print d.getVar("TEXT") 961 } 962 963Because the 964Python "bb" and "os" modules are already imported, you do not need to 965import these modules. Also in these types of functions, the datastore 966("d") is a global variable and is always automatically available. 967 968.. note:: 969 970 Variable expressions (e.g. ``${X}`` ) are no longer expanded within Python 971 functions. This behavior is intentional in order to allow you to freely set 972 variable values to expandable expressions without having them expanded 973 prematurely. If you do wish to expand a variable within a Python function, 974 use ``d.getVar("X")`` . Or, for more complicated expressions, use ``d.expand()``. 975 976Similar to shell functions, you can also apply overrides and 977override-style operators to BitBake-style Python functions. 978 979As an example, consider the following:: 980 981 python do_foo:prepend() { 982 bb.plain("first") 983 } 984 985 python do_foo() { 986 bb.plain("second") 987 } 988 989 python do_foo:append() { 990 bb.plain("third") 991 } 992 993Running ``do_foo`` prints the following:: 994 995 recipename do_foo: first 996 recipename do_foo: second 997 recipename do_foo: third 998 999You can use the ``bitbake -e`` recipename command to view 1000the final assembled function after all overrides have been applied. 1001 1002Python Functions 1003---------------- 1004 1005These functions are written in Python and are executed by other Python 1006code. Examples of Python functions are utility functions that you intend 1007to call from in-line Python or from within other Python functions. Here 1008is an example:: 1009 1010 def get_depends(d): 1011 if d.getVar('SOMECONDITION'): 1012 return "dependencywithcond" 1013 else: 1014 return "dependency" 1015 1016 SOMECONDITION = "1" 1017 DEPENDS = "${@get_depends(d)}" 1018 1019This would result in :term:`DEPENDS` containing ``dependencywithcond``. 1020 1021Here are some things to know about Python functions: 1022 1023- Python functions can take parameters. 1024 1025- The BitBake datastore is not automatically available. Consequently, 1026 you must pass it in as a parameter to the function. 1027 1028- The "bb" and "os" Python modules are automatically available. You do 1029 not need to import them. 1030 1031BitBake-Style Python Functions Versus Python Functions 1032------------------------------------------------------ 1033 1034Following are some important differences between BitBake-style Python 1035functions and regular Python functions defined with "def": 1036 1037- Only BitBake-style Python functions can be :ref:`tasks <bitbake-user-manual/bitbake-user-manual-metadata:tasks>`. 1038 1039- Overrides and override-style operators can only be applied to 1040 BitBake-style Python functions. 1041 1042- Only regular Python functions can take arguments and return values. 1043 1044- :ref:`Variable flags <bitbake-user-manual/bitbake-user-manual-metadata:variable flags>` such as 1045 ``[dirs]``, ``[cleandirs]``, and ``[lockfiles]`` can be used on BitBake-style 1046 Python functions, but not on regular Python functions. 1047 1048- BitBake-style Python functions generate a separate 1049 ``${``\ :term:`T`\ ``}/run.``\ function-name\ ``.``\ pid 1050 script that is executed to run the function, and also generate a log 1051 file in ``${T}/log.``\ function-name\ ``.``\ pid if they are executed 1052 as tasks. 1053 1054 Regular Python functions execute "inline" and do not generate any 1055 files in ``${T}``. 1056 1057- Regular Python functions are called with the usual Python syntax. 1058 BitBake-style Python functions are usually tasks and are called 1059 directly by BitBake, but can also be called manually from Python code 1060 by using the ``bb.build.exec_func()`` function. Here is an example:: 1061 1062 bb.build.exec_func("my_bitbake_style_function", d) 1063 1064 .. note:: 1065 1066 ``bb.build.exec_func()`` can also be used to run shell functions from Python 1067 code. If you want to run a shell function before a Python function within 1068 the same task, then you can use a parent helper Python function that 1069 starts by running the shell function with ``bb.build.exec_func()`` and then 1070 runs the Python code. 1071 1072 To detect errors from functions executed with 1073 ``bb.build.exec_func()``, you can catch the ``bb.build.FuncFailed`` 1074 exception. 1075 1076 .. note:: 1077 1078 Functions in metadata (recipes and classes) should not themselves raise 1079 ``bb.build.FuncFailed``. Rather, ``bb.build.FuncFailed`` should be viewed as a 1080 general indicator that the called function failed by raising an 1081 exception. For example, an exception raised by ``bb.fatal()`` will be caught 1082 inside ``bb.build.exec_func()``, and a ``bb.build.FuncFailed`` will be raised in 1083 response. 1084 1085Due to their simplicity, you should prefer regular Python functions over 1086BitBake-style Python functions unless you need a feature specific to 1087BitBake-style Python functions. Regular Python functions in metadata are 1088a more recent invention than BitBake-style Python functions, and older 1089code tends to use ``bb.build.exec_func()`` more often. 1090 1091Anonymous Python Functions 1092-------------------------- 1093 1094Sometimes it is useful to set variables or perform other operations 1095programmatically during parsing. To do this, you can define special 1096Python functions, called anonymous Python functions, that run at the end 1097of parsing. For example, the following conditionally sets a variable 1098based on the value of another variable:: 1099 1100 python () { 1101 if d.getVar('SOMEVAR') == 'value': 1102 d.setVar('ANOTHERVAR', 'value2') 1103 } 1104 1105An equivalent way to mark a function as an anonymous function is to give it 1106the name "__anonymous", rather than no name. 1107 1108Anonymous Python functions always run at the end of parsing, regardless 1109of where they are defined. If a recipe contains many anonymous 1110functions, they run in the same order as they are defined within the 1111recipe. As an example, consider the following snippet:: 1112 1113 python () { 1114 d.setVar('FOO', 'foo 2') 1115 } 1116 1117 FOO = "foo 1" 1118 1119 python () { 1120 d.appendVar('BAR',' bar 2') 1121 } 1122 1123 BAR = "bar 1" 1124 1125The previous example is conceptually 1126equivalent to the following snippet:: 1127 1128 FOO = "foo 1" 1129 BAR = "bar 1" 1130 FOO = "foo 2" 1131 BAR += "bar 2" 1132 1133``FOO`` ends up with the value "foo 2", and 1134``BAR`` with the value "bar 1 bar 2". Just as in the second snippet, the 1135values set for the variables within the anonymous functions become 1136available to tasks, which always run after parsing. 1137 1138Overrides and override-style operators such as "``:append``" are applied 1139before anonymous functions run. In the following example, ``FOO`` ends 1140up with the value "foo from anonymous":: 1141 1142 FOO = "foo" 1143 FOO:append = " from outside" 1144 1145 python () { 1146 d.setVar("FOO", "foo from anonymous") 1147 } 1148 1149For methods 1150you can use with anonymous Python functions, see the 1151":ref:`bitbake-user-manual/bitbake-user-manual-metadata:functions you can call from within python`" 1152section. For a different method to run Python code during parsing, see 1153the ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:inline python variable expansion`" section. 1154 1155Flexible Inheritance for Class Functions 1156---------------------------------------- 1157 1158Through coding techniques and the use of ``EXPORT_FUNCTIONS``, BitBake 1159supports exporting a function from a class such that the class function 1160appears as the default implementation of the function, but can still be 1161called if a recipe inheriting the class needs to define its own version 1162of the function. 1163 1164To understand the benefits of this feature, consider the basic scenario 1165where a class defines a task function and your recipe inherits the 1166class. In this basic scenario, your recipe inherits the task function as 1167defined in the class. If desired, your recipe can add to the start and 1168end of the function by using the ":prepend" or ":append" operations 1169respectively, or it can redefine the function completely. However, if it 1170redefines the function, there is no means for it to call the class 1171version of the function. ``EXPORT_FUNCTIONS`` provides a mechanism that 1172enables the recipe's version of the function to call the original 1173version of the function. 1174 1175To make use of this technique, you need the following things in place: 1176 1177- The class needs to define the function as follows:: 1178 1179 classname_functionname 1180 1181 For example, if you have a class file 1182 ``bar.bbclass`` and a function named ``do_foo``, the class must 1183 define the function as follows:: 1184 1185 bar_do_foo 1186 1187- The class needs to contain the ``EXPORT_FUNCTIONS`` statement as 1188 follows:: 1189 1190 EXPORT_FUNCTIONS functionname 1191 1192 For example, continuing with 1193 the same example, the statement in the ``bar.bbclass`` would be as 1194 follows:: 1195 1196 EXPORT_FUNCTIONS do_foo 1197 1198- You need to call the function appropriately from within your recipe. 1199 Continuing with the same example, if your recipe needs to call the 1200 class version of the function, it should call ``bar_do_foo``. 1201 Assuming ``do_foo`` was a shell function and ``EXPORT_FUNCTIONS`` was 1202 used as above, the recipe's function could conditionally call the 1203 class version of the function as follows:: 1204 1205 do_foo() { 1206 if [ somecondition ] ; then 1207 bar_do_foo 1208 else 1209 # Do something else 1210 fi 1211 } 1212 1213 To call your modified version of the function as defined in your recipe, 1214 call it as ``do_foo``. 1215 1216With these conditions met, your single recipe can freely choose between 1217the original function as defined in the class file and the modified 1218function in your recipe. If you do not set up these conditions, you are 1219limited to using one function or the other. 1220 1221Tasks 1222===== 1223 1224Tasks are BitBake execution units that make up the steps that BitBake 1225can run for a given recipe. Tasks are only supported in recipes and 1226classes (i.e. in ``.bb`` files and files included or inherited from 1227``.bb`` files). By convention, tasks have names that start with "do\_". 1228 1229Promoting a Function to a Task 1230------------------------------ 1231 1232Tasks are either :ref:`shell functions <bitbake-user-manual/bitbake-user-manual-metadata:shell functions>` or 1233:ref:`BitBake-style Python functions <bitbake-user-manual/bitbake-user-manual-metadata:bitbake-style python functions>` 1234that have been promoted to tasks by using the ``addtask`` command. The 1235``addtask`` command can also optionally describe dependencies between 1236the task and other tasks. Here is an example that shows how to define a 1237task and declare some dependencies:: 1238 1239 python do_printdate () { 1240 import time 1241 print time.strftime('%Y%m%d', time.gmtime()) 1242 } 1243 addtask printdate after do_fetch before do_build 1244 1245The first argument to ``addtask`` is the name 1246of the function to promote to a task. If the name does not start with 1247"do\_", "do\_" is implicitly added, which enforces the convention that all 1248task names start with "do\_". 1249 1250In the previous example, the ``do_printdate`` task becomes a dependency 1251of the ``do_build`` task, which is the default task (i.e. the task run 1252by the ``bitbake`` command unless another task is specified explicitly). 1253Additionally, the ``do_printdate`` task becomes dependent upon the 1254``do_fetch`` task. Running the ``do_build`` task results in the 1255``do_printdate`` task running first. 1256 1257.. note:: 1258 1259 If you try out the previous example, you might see that the 1260 ``do_printdate`` 1261 task is only run the first time you build the recipe with the 1262 ``bitbake`` 1263 command. This is because BitBake considers the task "up-to-date" 1264 after that initial run. If you want to force the task to always be 1265 rerun for experimentation purposes, you can make BitBake always 1266 consider the task "out-of-date" by using the 1267 :ref:`[nostamp] <bitbake-user-manual/bitbake-user-manual-metadata:Variable Flags>` 1268 variable flag, as follows:: 1269 1270 do_printdate[nostamp] = "1" 1271 1272 You can also explicitly run the task and provide the 1273 -f option as follows:: 1274 1275 $ bitbake recipe -c printdate -f 1276 1277 When manually selecting a task to run with the bitbake ``recipe 1278 -c task`` command, you can omit the "do\_" prefix as part of the task 1279 name. 1280 1281You might wonder about the practical effects of using ``addtask`` 1282without specifying any dependencies as is done in the following example:: 1283 1284 addtask printdate 1285 1286In this example, assuming dependencies have not been 1287added through some other means, the only way to run the task is by 1288explicitly selecting it with ``bitbake`` recipe ``-c printdate``. You 1289can use the ``do_listtasks`` task to list all tasks defined in a recipe 1290as shown in the following example:: 1291 1292 $ bitbake recipe -c listtasks 1293 1294For more information on task dependencies, see the 1295":ref:`bitbake-user-manual/bitbake-user-manual-execution:dependencies`" section. 1296 1297See the ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:variable flags`" section for information 1298on variable flags you can use with tasks. 1299 1300.. note:: 1301 1302 While it's infrequent, it's possible to define multiple tasks as 1303 dependencies when calling ``addtask``. For example, here's a snippet 1304 from the OpenEmbedded class file ``package_tar.bbclass``:: 1305 1306 addtask package_write_tar before do_build after do_packagedata do_package 1307 1308 Note how the ``package_write_tar`` task has to wait until both of 1309 ``do_packagedata`` and ``do_package`` complete. 1310 1311Deleting a Task 1312--------------- 1313 1314As well as being able to add tasks, you can delete them. Simply use the 1315``deltask`` command to delete a task. For example, to delete the example 1316task used in the previous sections, you would use:: 1317 1318 deltask printdate 1319 1320If you delete a task using the ``deltask`` command and the task has 1321dependencies, the dependencies are not reconnected. For example, suppose 1322you have three tasks named ``do_a``, ``do_b``, and ``do_c``. 1323Furthermore, ``do_c`` is dependent on ``do_b``, which in turn is 1324dependent on ``do_a``. Given this scenario, if you use ``deltask`` to 1325delete ``do_b``, the implicit dependency relationship between ``do_c`` 1326and ``do_a`` through ``do_b`` no longer exists, and ``do_c`` 1327dependencies are not updated to include ``do_a``. Thus, ``do_c`` is free 1328to run before ``do_a``. 1329 1330If you want dependencies such as these to remain intact, use the 1331``[noexec]`` varflag to disable the task instead of using the 1332``deltask`` command to delete it:: 1333 1334 do_b[noexec] = "1" 1335 1336Passing Information Into the Build Task Environment 1337--------------------------------------------------- 1338 1339When running a task, BitBake tightly controls the shell execution 1340environment of the build tasks to make sure unwanted contamination from 1341the build machine cannot influence the build. 1342 1343.. note:: 1344 1345 By default, BitBake cleans the environment to include only those 1346 things exported or listed in its whitelist to ensure that the build 1347 environment is reproducible and consistent. You can prevent this 1348 "cleaning" by setting the :term:`BB_PRESERVE_ENV` variable. 1349 1350Consequently, if you do want something to get passed into the build task 1351environment, you must take these two steps: 1352 1353#. Tell BitBake to load what you want from the environment into the 1354 datastore. You can do so through the 1355 :term:`BB_ENV_WHITELIST` and 1356 :term:`BB_ENV_EXTRAWHITE` variables. For 1357 example, assume you want to prevent the build system from accessing 1358 your ``$HOME/.ccache`` directory. The following command "whitelists" 1359 the environment variable ``CCACHE_DIR`` causing BitBake to allow that 1360 variable into the datastore:: 1361 1362 export BB_ENV_EXTRAWHITE="$BB_ENV_EXTRAWHITE CCACHE_DIR" 1363 1364#. Tell BitBake to export what you have loaded into the datastore to the 1365 task environment of every running task. Loading something from the 1366 environment into the datastore (previous step) only makes it 1367 available in the datastore. To export it to the task environment of 1368 every running task, use a command similar to the following in your 1369 local configuration file ``local.conf`` or your distribution 1370 configuration file:: 1371 1372 export CCACHE_DIR 1373 1374 .. note:: 1375 1376 A side effect of the previous steps is that BitBake records the 1377 variable as a dependency of the build process in things like the 1378 setscene checksums. If doing so results in unnecessary rebuilds of 1379 tasks, you can whitelist the variable so that the setscene code 1380 ignores the dependency when it creates checksums. 1381 1382Sometimes, it is useful to be able to obtain information from the 1383original execution environment. BitBake saves a copy of the original 1384environment into a special variable named :term:`BB_ORIGENV`. 1385 1386The :term:`BB_ORIGENV` variable returns a datastore object that can be 1387queried using the standard datastore operators such as 1388``getVar(, False)``. The datastore object is useful, for example, to 1389find the original ``DISPLAY`` variable. Here is an example:: 1390 1391 origenv = d.getVar("BB_ORIGENV", False) 1392 bar = origenv.getVar("BAR", False) 1393 1394The previous example returns ``BAR`` from the original execution 1395environment. 1396 1397Variable Flags 1398============== 1399 1400Variable flags (varflags) help control a task's functionality and 1401dependencies. BitBake reads and writes varflags to the datastore using 1402the following command forms:: 1403 1404 variable = d.getVarFlags("variable") 1405 self.d.setVarFlags("FOO", {"func": True}) 1406 1407When working with varflags, the same syntax, with the exception of 1408overrides, applies. In other words, you can set, append, and prepend 1409varflags just like variables. See the 1410":ref:`bitbake-user-manual/bitbake-user-manual-metadata:variable flag syntax`" section for details. 1411 1412BitBake has a defined set of varflags available for recipes and classes. 1413Tasks support a number of these flags which control various 1414functionality of the task: 1415 1416- ``[cleandirs]``: Empty directories that should be created before 1417 the task runs. Directories that already exist are removed and 1418 recreated to empty them. 1419 1420- ``[depends]``: Controls inter-task dependencies. See the 1421 :term:`DEPENDS` variable and the 1422 ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:inter-task 1423 dependencies`" section for more information. 1424 1425- ``[deptask]``: Controls task build-time dependencies. See the 1426 :term:`DEPENDS` variable and the ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:build dependencies`" section for more information. 1427 1428- ``[dirs]``: Directories that should be created before the task 1429 runs. Directories that already exist are left as is. The last 1430 directory listed is used as the current working directory for the 1431 task. 1432 1433- ``[lockfiles]``: Specifies one or more lockfiles to lock while the 1434 task executes. Only one task may hold a lockfile, and any task that 1435 attempts to lock an already locked file will block until the lock is 1436 released. You can use this variable flag to accomplish mutual 1437 exclusion. 1438 1439- ``[noexec]``: When set to "1", marks the task as being empty, with 1440 no execution required. You can use the ``[noexec]`` flag to set up 1441 tasks as dependency placeholders, or to disable tasks defined 1442 elsewhere that are not needed in a particular recipe. 1443 1444- ``[nostamp]``: When set to "1", tells BitBake to not generate a 1445 stamp file for a task, which implies the task should always be 1446 executed. 1447 1448 .. caution:: 1449 1450 Any task that depends (possibly indirectly) on a ``[nostamp]`` task will 1451 always be executed as well. This can cause unnecessary rebuilding if you 1452 are not careful. 1453 1454- ``[number_threads]``: Limits tasks to a specific number of 1455 simultaneous threads during execution. This varflag is useful when 1456 your build host has a large number of cores but certain tasks need to 1457 be rate-limited due to various kinds of resource constraints (e.g. to 1458 avoid network throttling). ``number_threads`` works similarly to the 1459 :term:`BB_NUMBER_THREADS` variable but is task-specific. 1460 1461 Set the value globally. For example, the following makes sure the 1462 ``do_fetch`` task uses no more than two simultaneous execution 1463 threads: do_fetch[number_threads] = "2" 1464 1465 .. warning:: 1466 1467 - Setting the varflag in individual recipes rather than globally 1468 can result in unpredictable behavior. 1469 1470 - Setting the varflag to a value greater than the value used in 1471 the :term:`BB_NUMBER_THREADS` variable causes ``number_threads`` to 1472 have no effect. 1473 1474- ``[postfuncs]``: List of functions to call after the completion of 1475 the task. 1476 1477- ``[prefuncs]``: List of functions to call before the task executes. 1478 1479- ``[rdepends]``: Controls inter-task runtime dependencies. See the 1480 :term:`RDEPENDS` variable, the 1481 :term:`RRECOMMENDS` variable, and the 1482 ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:inter-task dependencies`" section for 1483 more information. 1484 1485- ``[rdeptask]``: Controls task runtime dependencies. See the 1486 :term:`RDEPENDS` variable, the 1487 :term:`RRECOMMENDS` variable, and the 1488 ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:runtime dependencies`" section for more 1489 information. 1490 1491- ``[recideptask]``: When set in conjunction with ``recrdeptask``, 1492 specifies a task that should be inspected for additional 1493 dependencies. 1494 1495- ``[recrdeptask]``: Controls task recursive runtime dependencies. 1496 See the :term:`RDEPENDS` variable, the 1497 :term:`RRECOMMENDS` variable, and the 1498 ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:recursive dependencies`" section for 1499 more information. 1500 1501- ``[stamp-extra-info]``: Extra stamp information to append to the 1502 task's stamp. As an example, OpenEmbedded uses this flag to allow 1503 machine-specific tasks. 1504 1505- ``[umask]``: The umask to run the task under. 1506 1507Several varflags are useful for controlling how signatures are 1508calculated for variables. For more information on this process, see the 1509":ref:`bitbake-user-manual/bitbake-user-manual-execution:checksums (signatures)`" section. 1510 1511- ``[vardeps]``: Specifies a space-separated list of additional 1512 variables to add to a variable's dependencies for the purposes of 1513 calculating its signature. Adding variables to this list is useful, 1514 for example, when a function refers to a variable in a manner that 1515 does not allow BitBake to automatically determine that the variable 1516 is referred to. 1517 1518- ``[vardepsexclude]``: Specifies a space-separated list of variables 1519 that should be excluded from a variable's dependencies for the 1520 purposes of calculating its signature. 1521 1522- ``[vardepvalue]``: If set, instructs BitBake to ignore the actual 1523 value of the variable and instead use the specified value when 1524 calculating the variable's signature. 1525 1526- ``[vardepvalueexclude]``: Specifies a pipe-separated list of 1527 strings to exclude from the variable's value when calculating the 1528 variable's signature. 1529 1530Events 1531====== 1532 1533BitBake allows installation of event handlers within recipe and class 1534files. Events are triggered at certain points during operation, such as 1535the beginning of operation against a given recipe (i.e. ``*.bb``), the 1536start of a given task, a task failure, a task success, and so forth. The 1537intent is to make it easy to do things like email notification on build 1538failures. 1539 1540Following is an example event handler that prints the name of the event 1541and the content of the :term:`FILE` variable:: 1542 1543 addhandler myclass_eventhandler 1544 python myclass_eventhandler() { 1545 from bb.event import getName 1546 print("The name of the Event is %s" % getName(e)) 1547 print("The file we run for is %s" % d.getVar('FILE')) 1548 } 1549 myclass_eventhandler[eventmask] = "bb.event.BuildStarted 1550 bb.event.BuildCompleted" 1551 1552In the previous example, an eventmask has been 1553set so that the handler only sees the "BuildStarted" and 1554"BuildCompleted" events. This event handler gets called every time an 1555event matching the eventmask is triggered. A global variable "e" is 1556defined, which represents the current event. With the ``getName(e)`` 1557method, you can get the name of the triggered event. The global 1558datastore is available as "d". In legacy code, you might see "e.data" 1559used to get the datastore. However, realize that "e.data" is deprecated 1560and you should use "d" going forward. 1561 1562The context of the datastore is appropriate to the event in question. 1563For example, "BuildStarted" and "BuildCompleted" events run before any 1564tasks are executed so would be in the global configuration datastore 1565namespace. No recipe-specific metadata exists in that namespace. The 1566"BuildStarted" and "BuildCompleted" events also run in the main 1567cooker/server process rather than any worker context. Thus, any changes 1568made to the datastore would be seen by other cooker/server events within 1569the current build but not seen outside of that build or in any worker 1570context. Task events run in the actual tasks in question consequently 1571have recipe-specific and task-specific contents. These events run in the 1572worker context and are discarded at the end of task execution. 1573 1574During a standard build, the following common events might occur. The 1575following events are the most common kinds of events that most metadata 1576might have an interest in viewing: 1577 1578- ``bb.event.ConfigParsed()``: Fired when the base configuration; which 1579 consists of ``bitbake.conf``, ``base.bbclass`` and any global 1580 :term:`INHERIT` statements; has been parsed. You can see multiple such 1581 events when each of the workers parse the base configuration or if 1582 the server changes configuration and reparses. Any given datastore 1583 only has one such event executed against it, however. If 1584 :term:`BB_INVALIDCONF` is set in the datastore by the event 1585 handler, the configuration is reparsed and a new event triggered, 1586 allowing the metadata to update configuration. 1587 1588- ``bb.event.HeartbeatEvent()``: Fires at regular time intervals of one 1589 second. You can configure the interval time using the 1590 ``BB_HEARTBEAT_EVENT`` variable. The event's "time" attribute is the 1591 ``time.time()`` value when the event is triggered. This event is 1592 useful for activities such as system state monitoring. 1593 1594- ``bb.event.ParseStarted()``: Fired when BitBake is about to start 1595 parsing recipes. This event's "total" attribute represents the number 1596 of recipes BitBake plans to parse. 1597 1598- ``bb.event.ParseProgress()``: Fired as parsing progresses. This 1599 event's "current" attribute is the number of recipes parsed as well 1600 as the "total" attribute. 1601 1602- ``bb.event.ParseCompleted()``: Fired when parsing is complete. This 1603 event's "cached", "parsed", "skipped", "virtuals", "masked", and 1604 "errors" attributes provide statistics for the parsing results. 1605 1606- ``bb.event.BuildStarted()``: Fired when a new build starts. BitBake 1607 fires multiple "BuildStarted" events (one per configuration) when 1608 multiple configuration (multiconfig) is enabled. 1609 1610- ``bb.build.TaskStarted()``: Fired when a task starts. This event's 1611 "taskfile" attribute points to the recipe from which the task 1612 originates. The "taskname" attribute, which is the task's name, 1613 includes the ``do_`` prefix, and the "logfile" attribute point to 1614 where the task's output is stored. Finally, the "time" attribute is 1615 the task's execution start time. 1616 1617- ``bb.build.TaskInvalid()``: Fired if BitBake tries to execute a task 1618 that does not exist. 1619 1620- ``bb.build.TaskFailedSilent()``: Fired for setscene tasks that fail 1621 and should not be presented to the user verbosely. 1622 1623- ``bb.build.TaskFailed()``: Fired for normal tasks that fail. 1624 1625- ``bb.build.TaskSucceeded()``: Fired when a task successfully 1626 completes. 1627 1628- ``bb.event.BuildCompleted()``: Fired when a build finishes. 1629 1630- ``bb.cooker.CookerExit()``: Fired when the BitBake server/cooker 1631 shuts down. This event is usually only seen by the UIs as a sign they 1632 should also shutdown. 1633 1634This next list of example events occur based on specific requests to the 1635server. These events are often used to communicate larger pieces of 1636information from the BitBake server to other parts of BitBake such as 1637user interfaces: 1638 1639- ``bb.event.TreeDataPreparationStarted()`` 1640- ``bb.event.TreeDataPreparationProgress()`` 1641- ``bb.event.TreeDataPreparationCompleted()`` 1642- ``bb.event.DepTreeGenerated()`` 1643- ``bb.event.CoreBaseFilesFound()`` 1644- ``bb.event.ConfigFilePathFound()`` 1645- ``bb.event.FilesMatchingFound()`` 1646- ``bb.event.ConfigFilesFound()`` 1647- ``bb.event.TargetsTreeGenerated()`` 1648 1649.. _variants-class-extension-mechanism: 1650 1651Variants - Class Extension Mechanism 1652==================================== 1653 1654BitBake supports multiple incarnations of a recipe file via the 1655:term:`BBCLASSEXTEND` variable. 1656 1657The :term:`BBCLASSEXTEND` variable is a space separated list of classes used 1658to "extend" the recipe for each variant. Here is an example that results in a 1659second incarnation of the current recipe being available. This second 1660incarnation will have the "native" class inherited. :: 1661 1662 BBCLASSEXTEND = "native" 1663 1664.. note:: 1665 1666 The mechanism for this class extension is extremely specific to the 1667 implementation. Usually, the recipe's :term:`PROVIDES` , :term:`PN` , and 1668 :term:`DEPENDS` variables would need to be modified by the extension 1669 class. For specific examples, see the OE-Core native , nativesdk , and 1670 multilib classes. 1671 1672Dependencies 1673============ 1674 1675To allow for efficient parallel processing, BitBake handles dependencies 1676at the task level. Dependencies can exist both between tasks within a 1677single recipe and between tasks in different recipes. Following are 1678examples of each: 1679 1680- For tasks within a single recipe, a recipe's ``do_configure`` task 1681 might need to complete before its ``do_compile`` task can run. 1682 1683- For tasks in different recipes, one recipe's ``do_configure`` task 1684 might require another recipe's ``do_populate_sysroot`` task to finish 1685 first such that the libraries and headers provided by the other 1686 recipe are available. 1687 1688This section describes several ways to declare dependencies. Remember, 1689even though dependencies are declared in different ways, they are all 1690simply dependencies between tasks. 1691 1692.. _dependencies-internal-to-the-bb-file: 1693 1694Dependencies Internal to the ``.bb`` File 1695----------------------------------------- 1696 1697BitBake uses the ``addtask`` directive to manage dependencies that are 1698internal to a given recipe file. You can use the ``addtask`` directive 1699to indicate when a task is dependent on other tasks or when other tasks 1700depend on that recipe. Here is an example:: 1701 1702 addtask printdate after do_fetch before do_build 1703 1704In this example, the ``do_printdate`` task 1705depends on the completion of the ``do_fetch`` task, and the ``do_build`` 1706task depends on the completion of the ``do_printdate`` task. 1707 1708.. note:: 1709 1710 For a task to run, it must be a direct or indirect dependency of some 1711 other task that is scheduled to run. 1712 1713 For illustration, here are some examples: 1714 1715 - The directive ``addtask mytask before do_configure`` causes 1716 ``do_mytask`` to run before ``do_configure`` runs. Be aware that 1717 ``do_mytask`` still only runs if its :ref:`input 1718 checksum <bitbake-user-manual/bitbake-user-manual-execution:checksums (signatures)>` has changed since the last time it was 1719 run. Changes to the input checksum of ``do_mytask`` also 1720 indirectly cause ``do_configure`` to run. 1721 1722 - The directive ``addtask mytask after do_configure`` by itself 1723 never causes ``do_mytask`` to run. ``do_mytask`` can still be run 1724 manually as follows:: 1725 1726 $ bitbake recipe -c mytask 1727 1728 Declaring ``do_mytask`` as a dependency of some other task that is 1729 scheduled to run also causes it to run. Regardless, the task runs after 1730 ``do_configure``. 1731 1732Build Dependencies 1733------------------ 1734 1735BitBake uses the :term:`DEPENDS` variable to manage 1736build time dependencies. The ``[deptask]`` varflag for tasks signifies 1737the task of each item listed in :term:`DEPENDS` that must complete before 1738that task can be executed. Here is an example:: 1739 1740 do_configure[deptask] = "do_populate_sysroot" 1741 1742In this example, the ``do_populate_sysroot`` task 1743of each item in :term:`DEPENDS` must complete before ``do_configure`` can 1744execute. 1745 1746Runtime Dependencies 1747-------------------- 1748 1749BitBake uses the :term:`PACKAGES`, :term:`RDEPENDS`, and :term:`RRECOMMENDS` 1750variables to manage runtime dependencies. 1751 1752The :term:`PACKAGES` variable lists runtime packages. Each of those packages 1753can have :term:`RDEPENDS` and :term:`RRECOMMENDS` runtime dependencies. The 1754``[rdeptask]`` flag for tasks is used to signify the task of each item 1755runtime dependency which must have completed before that task can be 1756executed. :: 1757 1758 do_package_qa[rdeptask] = "do_packagedata" 1759 1760In the previous 1761example, the ``do_packagedata`` task of each item in :term:`RDEPENDS` must 1762have completed before ``do_package_qa`` can execute. 1763Although :term:`RDEPENDS` contains entries from the 1764runtime dependency namespace, BitBake knows how to map them back 1765to the build-time dependency namespace, in which the tasks are defined. 1766 1767Recursive Dependencies 1768---------------------- 1769 1770BitBake uses the ``[recrdeptask]`` flag to manage recursive task 1771dependencies. BitBake looks through the build-time and runtime 1772dependencies of the current recipe, looks through the task's inter-task 1773dependencies, and then adds dependencies for the listed task. Once 1774BitBake has accomplished this, it recursively works through the 1775dependencies of those tasks. Iterative passes continue until all 1776dependencies are discovered and added. 1777 1778The ``[recrdeptask]`` flag is most commonly used in high-level recipes 1779that need to wait for some task to finish "globally". For example, 1780``image.bbclass`` has the following:: 1781 1782 do_rootfs[recrdeptask] += "do_packagedata" 1783 1784This statement says that the ``do_packagedata`` task of 1785the current recipe and all recipes reachable (by way of dependencies) 1786from the image recipe must run before the ``do_rootfs`` task can run. 1787 1788BitBake allows a task to recursively depend on itself by 1789referencing itself in the task list:: 1790 1791 do_a[recrdeptask] = "do_a do_b" 1792 1793In the same way as before, this means that the ``do_a`` 1794and ``do_b`` tasks of the current recipe and all 1795recipes reachable (by way of dependencies) from the recipe 1796must run before the ``do_a`` task can run. In this 1797case BitBake will ignore the current recipe's ``do_a`` 1798task circular dependency on itself. 1799 1800Inter-Task Dependencies 1801----------------------- 1802 1803BitBake uses the ``[depends]`` flag in a more generic form to manage 1804inter-task dependencies. This more generic form allows for 1805inter-dependency checks for specific tasks rather than checks for the 1806data in :term:`DEPENDS`. Here is an example:: 1807 1808 do_patch[depends] = "quilt-native:do_populate_sysroot" 1809 1810In this example, the ``do_populate_sysroot`` task of the target ``quilt-native`` 1811must have completed before the ``do_patch`` task can execute. 1812 1813The ``[rdepends]`` flag works in a similar way but takes targets in the 1814runtime namespace instead of the build-time dependency namespace. 1815 1816Functions You Can Call From Within Python 1817========================================= 1818 1819BitBake provides many functions you can call from within Python 1820functions. This section lists the most commonly used functions, and 1821mentions where to find others. 1822 1823Functions for Accessing Datastore Variables 1824------------------------------------------- 1825 1826It is often necessary to access variables in the BitBake datastore using 1827Python functions. The BitBake datastore has an API that allows you this 1828access. Here is a list of available operations: 1829 1830.. list-table:: 1831 :widths: auto 1832 :header-rows: 1 1833 1834 * - *Operation* 1835 - *Description* 1836 * - ``d.getVar("X", expand)`` 1837 - Returns the value of variable "X". Using "expand=True" expands the 1838 value. Returns "None" if the variable "X" does not exist. 1839 * - ``d.setVar("X", "value")`` 1840 - Sets the variable "X" to "value" 1841 * - ``d.appendVar("X", "value")`` 1842 - Adds "value" to the end of the variable "X". Acts like ``d.setVar("X", 1843 "value")`` if the variable "X" does not exist. 1844 * - ``d.prependVar("X", "value")`` 1845 - Adds "value" to the start of the variable "X". Acts like 1846 ``d.setVar("X","value")`` if the variable "X" does not exist. 1847 * - ``d.delVar("X")`` 1848 - Deletes the variable "X" from the datastore. Does nothing if the variable 1849 "X" does not exist. 1850 * - ``d.renameVar("X", "Y")`` 1851 - Renames the variable "X" to "Y". Does nothing if the variable "X" does 1852 not exist. 1853 * - ``d.getVarFlag("X", flag, expand)`` 1854 - Returns the value of variable "X". Using "expand=True" expands the 1855 value. Returns "None" if either the variable "X" or the named flag does 1856 not exist. 1857 * - ``d.setVarFlag("X", flag, "value")`` 1858 - Sets the named flag for variable "X" to "value". 1859 * - ``d.appendVarFlag("X", flag, "value")`` 1860 - Appends "value" to the named flag on the variable "X". Acts like 1861 ``d.setVarFlag("X", flag, "value")`` if the named flag does not exist. 1862 * - ``d.prependVarFlag("X", flag, "value")`` 1863 - Prepends "value" to the named flag on the variable "X". Acts like 1864 ``d.setVarFlag("X", flag, "value")`` if the named flag does not exist. 1865 * - ``d.delVarFlag("X", flag)`` 1866 - Deletes the named flag on the variable "X" from the datastore. 1867 * - ``d.setVarFlags("X", flagsdict)`` 1868 - Sets the flags specified in the ``flagsdict()`` 1869 parameter. ``setVarFlags`` does not clear previous flags. Think of this 1870 operation as ``addVarFlags``. 1871 * - ``d.getVarFlags("X")`` 1872 - Returns a ``flagsdict`` of the flags for the variable "X". Returns "None" 1873 if the variable "X" does not exist. 1874 * - ``d.delVarFlags("X")`` 1875 - Deletes all the flags for the variable "X". Does nothing if the variable 1876 "X" does not exist. 1877 * - ``d.expand(expression)`` 1878 - Expands variable references in the specified string 1879 expression. References to variables that do not exist are left as is. For 1880 example, ``d.expand("foo ${X}")`` expands to the literal string "foo 1881 ${X}" if the variable "X" does not exist. 1882 1883Other Functions 1884--------------- 1885 1886You can find many other functions that can be called from Python by 1887looking at the source code of the ``bb`` module, which is in 1888``bitbake/lib/bb``. For example, ``bitbake/lib/bb/utils.py`` includes 1889the commonly used functions ``bb.utils.contains()`` and 1890``bb.utils.mkdirhier()``, which come with docstrings. 1891 1892Task Checksums and Setscene 1893=========================== 1894 1895BitBake uses checksums (or signatures) along with the setscene to 1896determine if a task needs to be run. This section describes the process. 1897To help understand how BitBake does this, the section assumes an 1898OpenEmbedded metadata-based example. 1899 1900These checksums are stored in :term:`STAMP`. You can 1901examine the checksums using the following BitBake command:: 1902 1903 $ bitbake-dumpsigs 1904 1905This command returns the signature data in a readable 1906format that allows you to examine the inputs used when the OpenEmbedded 1907build system generates signatures. For example, using 1908``bitbake-dumpsigs`` allows you to examine the ``do_compile`` task's 1909"sigdata" for a C application (e.g. ``bash``). Running the command also 1910reveals that the "CC" variable is part of the inputs that are hashed. 1911Any changes to this variable would invalidate the stamp and cause the 1912``do_compile`` task to run. 1913 1914The following list describes related variables: 1915 1916- :term:`BB_HASHCHECK_FUNCTION`: 1917 Specifies the name of the function to call during the "setscene" part 1918 of the task's execution in order to validate the list of task hashes. 1919 1920- :term:`BB_SETSCENE_DEPVALID`: 1921 Specifies a function BitBake calls that determines whether BitBake 1922 requires a setscene dependency to be met. 1923 1924- :term:`BB_STAMP_POLICY`: Defines the mode 1925 for comparing timestamps of stamp files. 1926 1927- :term:`BB_STAMP_WHITELIST`: Lists stamp 1928 files that are looked at when the stamp policy is "whitelist". 1929 1930- :term:`BB_TASKHASH`: Within an executing task, 1931 this variable holds the hash of the task as returned by the currently 1932 enabled signature generator. 1933 1934- :term:`STAMP`: The base path to create stamp files. 1935 1936- :term:`STAMPCLEAN`: Again, the base path to 1937 create stamp files but can use wildcards for matching a range of 1938 files for clean operations. 1939 1940Wildcard Support in Variables 1941============================= 1942 1943Support for wildcard use in variables varies depending on the context in 1944which it is used. For example, some variables and filenames allow 1945limited use of wildcards through the "``%``" and "``*``" characters. 1946Other variables or names support Python's 1947`glob <https://docs.python.org/3/library/glob.html>`_ syntax, 1948`fnmatch <https://docs.python.org/3/library/fnmatch.html#module-fnmatch>`_ 1949syntax, or 1950`Regular Expression (re) <https://docs.python.org/3/library/re.html>`_ 1951syntax. 1952 1953For variables that have wildcard suport, the documentation describes 1954which form of wildcard, its use, and its limitations. 1955