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<html devsite>
<head>
<title>Packages</title>
<meta name="project_path" value="/_project.yaml" />
<meta name="book_path" value="/_book.yaml" />
</head>
<body>
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<p class=note><strong>Note:</strong> This section uses sample <code>.hal</code>
files to illustrate how HIDL language constructs map to C++.</p>
<p>With few exceptions, HIDL interface packages are located in
<code>hardware/interfaces</code> or the <code>vendor/</code> directory. The
<code>hardware/interfaces</code> top-level maps directly to the
<code>android.hardware</code> package namespace; the version is a subdirectory
under the package (not interface) namespace.</p>
<p>The <code>hidl-gen</code> compiler compiles the <code>.hal</code> files into
a set of a <code>.h</code> and <code>.cpp</code> files. From these autogenerated
files a shared library that client/server implementations link against is built.
The <code>Android.bp</code> file that builds this shared library is
autogenerated by the <code>hardware/interfaces/update-makefiles.sh</code>
script. Every time you add a new package to <code>hardware/interfaces</code>, or
add/remove <code>.hal</code> files to/from an existing package, you must rerun
the script to ensure the generated shared library is up-to-date.</p>
<p>For example, the <code>IFoo.hal</code> sample file should be located in
<code>hardware/interfaces/samples/1.0</code>. The sample
<code><strong>IFoo.hal</code></strong> file creates an IFoo interface in the
<strong>samples</strong> package:</p>
<pre class="prettyprint">
package android.hardware.samples@1.0;
interface IFoo {
struct Foo {
int64_t someValue;
handle myHandle;
};
someMethod() generates (vec<uint32_t>);
anotherMethod(Foo foo) generates (int32_t ret);
};
</pre>
<h2 id=generated-files>Generated files</h2>
<p>Autogenerated files in a HIDL package are linked into a single shared
library with the same name as the package (for example,
<code>android.hardware.samples@1.0</code>). The shared library also exports a
single header, <code>IFoo.h</code>, which can be included by clients and
servers. Using the <code>hidl-gen</code> compiler with the <code>IFoo.hal</code>
interface file as an input, binderized mode has the following autogenerated
files:</p>
<p><img src="../images/treble_cpp_compiler_generated_files.png"></p>
<p><strong>Figure 1.</strong> Files generated by compiler.</p>
<ul>
<li><code><strong>IFoo.h</code></strong>. Describes the pure <code>IFoo</code>
interface in a C++ class; it contains the methods and types defined in the
<code>IFoo</code> interface in the <code>IFoo.hal</code> file, translated to C++
types where necessary. <strong>Does not contain</strong> details related to the
RPC mechanism (e.g., <code>HwBinder</code>) used to implement this interface.
The class is namespaced with the package and version, e.g.
<code>::android::hardware::samples::IFoo::V1_0</code>. Both clients and servers
include this header: Clients for calling methods on it and servers for
implementing those methods.</li>
<li><code><strong>IHwFoo.h</code></strong>. Header file that contains
declarations for functions that serialize data types used in the interface.
Developers should never include his header directly (it does not contain any
classes).</li>
<li><code><strong>BpFoo.h</code></strong>. A class that inherits from
<code>IFoo</code> and describes the <code>HwBinder</code> proxy (client-side)
implementation of the interface. Developers should never refer to this class
directly.</li>
<li><code><strong>BnFoo.h</code></strong>.<strong> </strong>A class that holds a
reference to an <code>IFoo</code> implementation and describes the
<code>HwBinder</code> stub (server-side) implementation of the interface.
Developers should never refer to this class directly.</li>
<li><code><strong>FooAll.cpp</code></strong>. A class that contains the
implementations for both the <code>HwBinder</code> proxy and the
<code>HwBinder</code> stub. When a client calls an interface method, the proxy
automatically marshals the arguments from the client and sends the transaction
to the binder kernel driver, which delivers the transaction to the stub on the
other side (which then calls the actual server implementation).</li>
</ul>
<p>The files are structured similarly to the files generated by
<code>aidl-cpp</code> (for details, see "Passthrough mode" in the
<a href="/devices/architecture/hidl/index.html">HIDL Overview</a>). The only
autogenerated file that is independent of the RPC mechanism used by HIDL is
<code>IFoo.h</code>; all other files are tied to the HwBinder RPC mechanism used
by HIDL. Therefore, client and server implementations <strong>should never
directly refer to anything other than <code>IFoo</code></strong>. To achieve
this, include only <code>IFoo.h</code> and link against the generated shared
library.</p>
<p class=note><strong>Note</strong>: HwBinder is only one possible transport;
new transports may be added in the future.</p>
<h2 id=link-libraries>Linking to shared libraries</h2>
<p>A client or server that uses any interface in a package must include the
shared library of that package in <strong>one (1)</strong> of the following
locations:</p>
<ul>
<li>In <strong>Android.mk</strong>:
<pre class="prettyprint">
LOCAL_SHARED_LIBRARIES += android.hardware.samples@1.0
</pre>
</li>
<li>In <strong>Android.bp</strong>:
<pre class="prettyprint">
shared_libs: [
/* ... */
"android.hardware.samples@1.0",
],
</pre>
</li>
</ul>
<p>For specific libraries:</p>
<table>
<tr>
<th><code>libhidlbase</code></th>
<td>Includes standard HIDL data-types. Unless your interface consists only of
primitives that map directly to C++ primitives, you must also link this library:
<pre class="prettyprint">
LOCAL_SHARED_LIBRARIES += libhidlbase
</pre>
</td>
</tr>
<tr>
<th><code>libhidltransport</code></th>
<td>Handles the transport of HIDL calls over different RPC/IPC mechanisms. You
must always link this library:
<pre class="prettyprint">
LOCAL_SHARED_LIBRARIES += libhidltransport
</pre>
</td>
</tr>
<tr>
<th><code>libhwbinder</code></th>
<td>You must also link to this library:
<pre class="prettyprint">
LOCAL_SHARED_LIBRARIES += libhwbinder
</pre>
</td>
</tr>
<tr>
<th><code>libfmq</code></th>
<td>To use Fast Message Queue IPC, you must also link to this library.
<pre class="prettyprint">
LOCAL_SHARED_LIBRARIES += libfmq
</pre>
</td>
</tr>
</tbody>
</table>
<h2 id=namespaces>Namespaces</h2>
<p>HIDL functions and types such as <code>Return<T></code> and
<code>Void()</code> are declared in namespace <code>::android::hardware</code>.
The C++ namespace of a package is determined by the package name and version.
For example, a package <strong>mypackage</strong> with version 1.2 under
<code>hardware/interfaces</code> has the following qualities:</p>
<ul>
<li><strong>C++ namespace</strong> is
<code>::android::hardware::mypackage::V1_2</code></li>
<li><strong>Fully qualified name </strong>of <code>IMyInterface</code> in that
package is: <code>::android::hardware::mypackage::V1_2::IMyInterface</code>.
(<code>IMyInterface</code> is an identifier, not part of the namespace).</li>
<li><strong>Types</strong> defined in the package's <code>types.hal</code> file
are identified as:
<code>::android::hardware::mypackage::V1_2::MyPackageType</code></li>
</ul>
</body>
</html>
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