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<html devsite>
<head>
<title>Enabling the VNDK</title>
<meta name="project_path" value="/_project.yaml" />
<meta name="book_path" value="/_book.yaml" />
</head>
<body>
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<p>The VNDK requires several changes to a codebase to separate concerns between
vendor and system. Use the following guide to enable VNDK in a vendor/OEM
codebase.</p>
<h2 id=build-system-libraries>Build system libraries</h2>
<p>The build system contains several types of objects including libraries
(shared, static, or header) and binaries:</p>
<img src="../images/treble_vndk_build_system_libraries.png">
<figcaption><strong>Figure 1.</strong> Build system libraries.</figcaption>
<ul>
<li><strong>core</strong>. Used by the system image, on the system image. These
libraries cannot be used by <code>vendor</code>, <code>vendor_available</code>,
<code>vndk</code>, or <code>vndk-sp</code> libraries.
<pre class="prettyprint">
cc_library {
name: "libThatIsCore",
...
}
</pre>
</li>
<li><strong>vendor-only</strong> (or <code>proprietary</code>). Used by the
vendor image, on the vendor image.
<pre class="prettyprint">
cc_library {
name: "libThatIsVendorOnly",
proprietary: true,
# or: vendor: true, # (for things in AOSP)
...
}
</dpre>
</li>
<li><strong>vendor_available</strong>. Used by the vendor image, on the vendor
image (may contain duplicates of <code>core</code>).
<pre class="prettyprint">
cc_library {
name: "libThatIsVendorAvailable",
vendor_available: true,
...
}
</pre>
</li>
<li><strong>vndk</strong>. Used by the vendor image, on the system image (a
subset of <code>vendor_available</code>).
<pre class="prettyprint">
cc_library {
name: "libThatIsVndk",
vendor_available: true,
vndk: {
enabled: true,
}
...
}
</pre>
</li>
<li><strong>vndk-sp</strong>. Used by the system image indirectly, on the
system image (subset of <code>core</code>).
<pre class="prettyprint">
cc_library {
name: "libThatIsVndkSp",
vendor_available: true,
vndk: {
enabled: true,
support_system_process: true,
}
...
}
</pre>
</li>
<li><strong>llndk</strong>. Used by both the system and vendor images.
<pre class="prettyprint">
llndk_library {
name: "libThasIsLlndk",
}
</pre>
</li>
</ul>
<p>When a lib is marked as <code>vendor_available:true</code>, it is built
twice:</p>
<ul>
<li>Once for platform (and thus installed to <code>/system/lib</code>).</li>
<li>Once for vendor (and thus installed to <code>/vendor/lib</code>,
<code>/system/lib/vndk</code>, or <code>/system/lib/vndk-sp</code>).</li>
</ul>
<p>The vendor versions of libs are built with <code>-D__ANDROID_VNDK__</code>.
Private system components that may change significantly in future versions of
Android are disabled with this flag. In addition, different libraries export a
different set of headers (such as <code>liblog</code>). Options specific to a
vendor variant of a target can be specified in an <code>Android.bp</code> file
in:</p>
<pre class="prettyprint">target: { vendor: { … } }</pre>
<h2 id=enabling>Enabling VNDK for a codebase</h2>
<p>To enable the VNDK for a codebase:</p>
<ol>
<li>Determine eligibility by calculating the required sizes of
<code>vendor.img</code> and <code>system.img</code> partitions.</li>
<li>Enable <code>BOARD_VNDK_VERSION=current</code>. You can add to
<code>BoardConfig.mk</code> or build components with it directly (i.e.
<code>m -j BOARD_VNDK_VERSION=current <var>MY-LIB</var></code>).</li>
</ol>
<p>After enabling <code>BOARD_VNDK_VERSION=current</code>, the build system
enforces the following dependency and header requirements.</p>
<h3 id=managing-dependencies>Managing dependencies</h3>
<p>A <code>vendor</code> object that depends on a <code>core</code> component
that doesn't exist in the <code>vndk</code> or as a <code>vendor</code> object
must be resolved using one of the following options:</p>
<ul>
<li>The dependency can be removed.</li>
<li>If the <code>core</code> component is owned by <code>vendor</code>, it can
be marked as <code>vendor_available</code> or <code>vendor</code>.</li>
<li>A change making the core object part of the <code>vndk</code> may be
upstreamed to Google.</li>
</ul>
<p>In addition, if a <code>core</code> component has dependencies on a
<code>vendor</code> component, the <code>vendor</code> component must be made
into a <code>core</code> component <strong>or</strong> the dependency must be
removed in another way (for example, by removing the dependency or by moving the
dependency into a <code>vendor</code> component).</p>
<h3 id=managing-headers>Managing headers</h3>
<p>Global header dependencies must be removed to enable the build system to know
whether to build the headers with or without <code>-D__ANDROID_VNDK__</code>.
For example, libutils headers such as <code>utils/StrongPointer.h</code> can
still be accessed using the header library
<a href="https://android.googlesource.com/platform/system/core/+/master/libutils/include/utils" class="external"><code>libutils_headers</code></a>.
</p>
<p>Some headers (such as <code>unistd.h</code>) can no longer be transitively
included but can be included locally.</p>
<p>Finally, the public part of <code>private/android_filesystem_config.h</code>
has been moved to <code>cutils/android_filesystem_config.h</code>. To manage
these headers, do one of the following:</p>
<ul>
<li>Remove the dependency to
<code>private/android_filesystem_config.h</code> by replacing all
<code>AID_*</code> macros with
<code><a href="http://man7.org/linux/man-pages/man3/getgrnam.3.html" class="external">getgrnam</code></a>/<code><a href="http://man7.org/linux/man-pages/man3/getpwnam.3.html" class="external">getpwnam</code></a>
calls if possible. For example:
<ul>
<li><code>(uid_t)AID_WIFI</code> becomes
<code>getpwnam("wifi")->pw_uid</code>.</li>
<li><code>(gid_t)AID_SDCARD_R</code> becomes
<code>getgrnam("sdcard_r")->gr_gid</code>.</li>
</ul>
For details, refer to
<code><a href="https://android.googlesource.com/platform/system/core/+/master/libcutils/include/private/android_filesystem_config.h" class="external">private/android_filesystem_config.h</code></a>.
</li>
<li>For hard-coded AIS, include
<code>cutils/android_filesystem_config.h</code>.</li>
</ul>
</body>
</html>
|
