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4<title>3.4. Automatically Added Runtime Dependencies</title>
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12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="section" title="3.4. Automatically Added Runtime Dependencies">
13<div class="titlepage"><div><div><h2 class="title" style="clear: both">
14<a name="automatically-added-runtime-dependencies"></a>3.4. Automatically Added Runtime Dependencies</h2></div></div></div>
15<p>
16 The OpenEmbedded build system automatically adds common types of
17 runtime dependencies between packages, which means that you do not
18 need to explicitly declare the packages using
19 <a class="link" href="../ref-manual/var-RDEPENDS.html" target="_self"><code class="filename">RDEPENDS</code></a>.
20 Three automatic mechanisms exist (<code class="filename">shlibdeps</code>,
21 <code class="filename">pcdeps</code>, and <code class="filename">depchains</code>)
22 that handle shared libraries, package configuration (pkg-config)
23 modules, and <code class="filename">-dev</code> and
24 <code class="filename">-dbg</code> packages, respectively.
25 For other types of runtime dependencies, you must manually declare
26 the dependencies.
27 </p>
28<div class="itemizedlist"><ul class="itemizedlist" type="disc">
29<li class="listitem">
30<p>
31 <code class="filename">shlibdeps</code>:
32 During the
33 <a class="link" href="../ref-manual/ref-tasks-package.html" target="_self"><code class="filename">do_package</code></a>
34 task of each recipe, all shared libraries installed by the
35 recipe are located.
36 For each shared library, the package that contains the
37 shared library is registered as providing the shared
38 library.
39 More specifically, the package is registered as providing
40 the
41 <a class="ulink" href="https://en.wikipedia.org/wiki/Soname" target="_self">soname</a>
42 of the library.
43 The resulting shared-library-to-package mapping
44 is saved globally in
45 <a class="link" href="../ref-manual/var-PKGDATA_DIR.html" target="_self"><code class="filename">PKGDATA_DIR</code></a>
46 by the
47 <a class="link" href="../ref-manual/ref-tasks-packagedata.html" target="_self"><code class="filename">do_packagedata</code></a>
48 task.</p>
49<p>Simultaneously, all executables and shared libraries
50 installed by the recipe are inspected to see what shared
51 libraries they link against.
52 For each shared library dependency that is found,
53 <code class="filename">PKGDATA_DIR</code> is queried to
54 see if some package (likely from a different recipe)
55 contains the shared library.
56 If such a package is found, a runtime dependency is added
57 from the package that depends on the shared library to the
58 package that contains the library.</p>
59<p>The automatically added runtime dependency also
60 includes a version restriction.
61 This version restriction specifies that at least the
62 current version of the package that provides the shared
63 library must be used, as if
64 "<em class="replaceable"><code>package</code></em> (&gt;= <em class="replaceable"><code>version</code></em>)"
65 had been added to
66 <a class="link" href="../ref-manual/var-RDEPENDS.html" target="_self"><code class="filename">RDEPENDS</code></a>.
67 This forces an upgrade of the package containing the shared
68 library when installing the package that depends on the
69 library, if needed.</p>
70<p>If you want to avoid a package being registered as
71 providing a particular shared library (e.g. because the library
72 is for internal use only), then add the library to
73 <a class="link" href="../ref-manual/var-PRIVATE_LIBS.html" target="_self"><code class="filename">PRIVATE_LIBS</code></a>
74 inside the package's recipe.
75 </p>
76</li>
77<li class="listitem">
78<p>
79 <code class="filename">pcdeps</code>:
80 During the
81 <a class="link" href="../ref-manual/ref-tasks-package.html" target="_self"><code class="filename">do_package</code></a>
82 task of each recipe, all pkg-config modules
83 (<code class="filename">*.pc</code> files) installed by the recipe
84 are located.
85 For each module, the package that contains the module is
86 registered as providing the module.
87 The resulting module-to-package mapping is saved globally in
88 <a class="link" href="../ref-manual/var-PKGDATA_DIR.html" target="_self"><code class="filename">PKGDATA_DIR</code></a>
89 by the
90 <a class="link" href="../ref-manual/ref-tasks-packagedata.html" target="_self"><code class="filename">do_packagedata</code></a>
91 task.</p>
92<p>Simultaneously, all pkg-config modules installed by
93 the recipe are inspected to see what other pkg-config
94 modules they depend on.
95 A module is seen as depending on another module if it
96 contains a "Requires:" line that specifies the other module.
97 For each module dependency,
98 <code class="filename">PKGDATA_DIR</code> is queried to see if some
99 package contains the module.
100 If such a package is found, a runtime dependency is added
101 from the package that depends on the module to the package
102 that contains the module.
103 </p>
104<div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;">
105<h3 class="title">Note</h3>
106 The <code class="filename">pcdeps</code> mechanism most often
107 infers dependencies between <code class="filename">-dev</code>
108 packages.
109 </div>
110<p>
111 </p>
112</li>
113<li class="listitem">
114<p>
115 <code class="filename">depchains</code>:
116 If a package <code class="filename">foo</code> depends on a package
117 <code class="filename">bar</code>, then <code class="filename">foo-dev</code>
118 and <code class="filename">foo-dbg</code> are also made to depend on
119 <code class="filename">bar-dev</code> and
120 <code class="filename">bar-dbg</code>, respectively.
121 Taking the <code class="filename">-dev</code> packages as an
122 example, the <code class="filename">bar-dev</code> package might
123 provide headers and shared library symlinks needed by
124 <code class="filename">foo-dev</code>, which shows the need
125 for a dependency between the packages.</p>
126<p>The dependencies added by
127 <code class="filename">depchains</code> are in the form of
128 <a class="link" href="../ref-manual/var-RRECOMMENDS.html" target="_self"><code class="filename">RRECOMMENDS</code></a>.
129 </p>
130<div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;">
131<h3 class="title">Note</h3>
132 By default, <code class="filename">foo-dev</code> also has an
133 <code class="filename">RDEPENDS</code>-style dependency on
134 <code class="filename">foo</code>, because the default value of
135 <code class="filename">RDEPENDS_${PN}-dev</code> (set in
136 <code class="filename">bitbake.conf</code>) includes
137 "${PN}".
138 </div>
139<p>To ensure that the dependency chain is never broken,
140 <code class="filename">-dev</code> and <code class="filename">-dbg</code>
141 packages are always generated by default, even if the
142 packages turn out to be empty.
143 See the
144 <a class="link" href="../ref-manual/var-ALLOW_EMPTY.html" target="_self"><code class="filename">ALLOW_EMPTY</code></a>
145 variable for more information.
146 </p>
147</li>
148</ul></div>
149<p>
150 </p>
151<p>
152 The <code class="filename">do_package</code> task depends on the
153 <a class="link" href="../ref-manual/ref-tasks-packagedata.html" target="_self"><code class="filename">do_packagedata</code></a>
154 task of each recipe in
155 <a class="link" href="../ref-manual/var-DEPENDS.html" target="_self"><code class="filename">DEPENDS</code></a>
156 through use of a
157 <code class="filename">[</code><a class="link" href="../bitbake-user-manual/variable-flags.html" target="_self"><code class="filename">deptask</code></a><code class="filename">]</code>
158 declaration, which guarantees that the required
159 shared-library/module-to-package mapping information will be available
160 when needed as long as <code class="filename">DEPENDS</code> has been
161 correctly set.
162 </p>
163</div></body>
164</html>
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