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1<html>
2<head>
3<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
4<title>6.1. Parsing</title>
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7<link rel="home" href="index.html" title="The Yocto Project Reference Manual">
8<link rel="up" href="ref-bitbake.html" title="Chapter 6. BitBake">
9<link rel="prev" href="ref-bitbake.html" title="Chapter 6. BitBake">
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11</head>
12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="section" title="6.1. Parsing">
13<div class="titlepage"><div><div><h2 class="title" style="clear: both">
14<a name="ref-bitbake-parsing"></a>6.1. Parsing</h2></div></div></div>
15<p>
16 BitBake parses configuration files, classes, and <code class="filename">.bb</code> files.
17 </p>
18<p>
19 The first thing BitBake does is look for the <code class="filename">bitbake.conf</code> file.
20 This file resides in the
21 <a class="link" href="../dev-manual/source-directory.html" target="_self">Source Directory</a>
22 within the <code class="filename">meta/conf/</code> directory.
23 BitBake finds it by examining its
24 <a class="link" href="ref-variables-glos.html#var-BBPATH" title="BBPATH"><code class="filename">BBPATH</code></a> environment
25 variable and looking for the <code class="filename">meta/conf/</code>
26 directory.
27 </p>
28<p>
29 The <code class="filename">bitbake.conf</code> file lists other configuration
30 files to include from a <code class="filename">conf/</code>
31 directory below the directories listed in <code class="filename">BBPATH</code>.
32 In general, the most important configuration file from a user's perspective
33 is <code class="filename">local.conf</code>, which contains a user's customized
34 settings for the OpenEmbedded build environment.
35 Other notable configuration files are the distribution
36 configuration file (set by the
37 <code class="filename"><a class="link" href="ref-variables-glos.html#var-DISTRO" title="DISTRO">DISTRO</a></code> variable)
38 and the machine configuration file
39 (set by the
40 <code class="filename"><a class="link" href="ref-variables-glos.html#var-MACHINE" title="MACHINE">MACHINE</a></code> variable).
41 The <code class="filename">DISTRO</code> and <code class="filename">MACHINE</code> BitBake environment
42 variables are both usually set in
43 the <code class="filename">local.conf</code> file.
44 Valid distribution
45 configuration files are available in the <code class="filename">meta/conf/distro/</code> directory
46 and valid machine configuration
47 files in the <code class="filename">meta/conf/machine/</code> directory.
48 Within the <code class="filename">meta/conf/machine/include/</code>
49 directory are various <code class="filename">tune-*.inc</code> configuration files that provide common
50 "tuning" settings specific to and shared between particular architectures and machines.
51 </p>
52<p>
53 After the parsing of the configuration files, some standard classes are included.
54 The <code class="filename">base.bbclass</code> file is always included.
55 Other classes that are specified in the configuration using the
56 <code class="filename"><a class="link" href="ref-variables-glos.html#var-INHERIT" title="INHERIT">INHERIT</a></code>
57 variable are also included.
58 Class files are searched for in a <code class="filename">classes</code> subdirectory
59 under the paths in <code class="filename">BBPATH</code> in the same way as
60 configuration files.
61 </p>
62<p>
63 After classes are included, the variable
64 <code class="filename"><a class="link" href="ref-variables-glos.html#var-BBFILES" title="BBFILES">BBFILES</a></code>
65 is set, usually in
66 <code class="filename">local.conf</code>, and defines the list of places to search for
67 <code class="filename">.bb</code> files.
68 By default, the <code class="filename">BBFILES</code> variable specifies the
69 <code class="filename">meta/recipes-*/</code> directory within Poky.
70 Adding extra content to <code class="filename">BBFILES</code> is best achieved through the use of
71 BitBake layers as described in the
72 "<a class="link" href="../dev-manual/understanding-and-creating-layers.html" target="_self">Understanding and
73 Creating Layers</a>" section of the Yocto Project Development Manual.
74 </p>
75<p>
76 BitBake parses each <code class="filename">.bb</code> file in <code class="filename">BBFILES</code> and
77 stores the values of various variables.
78 In summary, for each <code class="filename">.bb</code>
79 file the configuration plus the base class of variables are set, followed
80 by the data in the <code class="filename">.bb</code> file
81 itself, followed by any inherit commands that
82 <code class="filename">.bb</code> file might contain.
83 </p>
84<p>
85 Because parsing <code class="filename">.bb</code> files is a time
86 consuming process, a cache is kept to speed up subsequent parsing.
87 This cache is invalid if the timestamp of the <code class="filename">.bb</code>
88 file itself changes, or if the timestamps of any of the include,
89 configuration or class files the <code class="filename">.bb</code>
90 file depends on changes.
91 </p>
92</div></body>
93</html>
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