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diff --git a/en/devices/tech/ota/index.html b/en/devices/tech/ota/index.html index 234ff2de..58737b5c 100644 --- a/en/devices/tech/ota/index.html +++ b/en/devices/tech/ota/index.html @@ -23,138 +23,42 @@ -<p>Android devices in the field can receive and install over-the-air (OTA) -updates to the system and application software. Devices have a special -recovery partition with the software needed to unpack a downloaded update -package and apply it to the rest of the system.</p> -<p>This section describes the structure of these packages and the tools -provided to build them. It is intended for developers who want to -make the OTA update system work on new Android devices and those who are -building update packages for use with released devices. OTA updates are -designed to upgrade the underlying operating system and the read-only apps -installed on the system partition; these updates do <i>not</i> affect -applications installed by the user from Google Play. -</p> -<p>This section describes the OTA system as of the Android 5.x release. For -help porting OTA-related code from older releases, see <a href="#migrating"> -Migrating from previous releases</a>. -</p> + <p> + Android devices in the field can receive and install over-the-air (OTA) + updates to the system and application software. This section describes + the structure of the update packages and the tools provided to build + them. It is intended for developers who want to make the OTA update + system work on new Android devices and those who are building update + packages for use with released devices. OTA updates are designed to + upgrade the underlying operating system and the read-only apps installed + on the system partition; these updates do <em>not</em> affect + applications installed by the user from Google Play. + </p> -<h2 id="android-device-layout">Android device layout</h2> -<p>The flash space on an Android device typically contains the following -partitions.</p> + <h2 id="ab_updates">A/B updates</h2> -<dl> -<dt>boot</dt> -<dd>Contains the Linux kernel and a minimal root filesystem (loaded into a RAM -disk). It mounts system and other partitions and starts the runtime located on -the system partition.</dd> -<dt>system</dt> -<dd>Contains system applications and libraries that have source code available -on Android Open Source Project (AOSP). During normal operation, this partition -is mounted read-only; its contents change only during an OTA update.</dd> -<dt>vendor</dt> -<dd>Contains system applications and libraries that do <em>not</em> have -source code available on Android Open Source Project (AOSP). During normal -operation, this partition is mounted read-only; its contents change only -during an OTA update.</dd> -<dt>userdata</dt> -<dd>Stores the data saved by applications installed by the user, etc. This -partition is not normally touched by the OTA update process.</dd> -<dt>cache</dt> -<dd>Temporary holding area used by a few applications (accessing this -partition requires special app permissions) and for storage of downloaded OTA -update packages. Other programs use this space with the expectation that files -can disappear at any time. Some OTA package installations may result in this -partition being wiped completely.</dd> -<dt>recovery</dt> -<dd>Contains a second complete Linux system, including a kernel and the -special recovery binary that reads a package and uses its contents to update -the other partitions.</dd> -<dt>misc</dt> -<dd>Tiny partition used by recovery to stash some information away about what -it's doing in case the device is restarted while the OTA package is being -applied.</dd></dl> + <p> + Modern A/B devices have two copies of each partition, A and B. Devices + apply the update to the currently unused partition while the system is + running but idle. A/B devices do not need space to download the update + package because they can apply the update as they read it from the + network. This is called <em>streaming A/B</em>. A/B updates are also + know as <em>seamless updates</em>. For more information about OTA + updates for A/B devices, see + <a href="/devices/tech/ota/ab_updates.html">A/B (Seamless) System + Update + </a>. + </p> -<h2 id="life-ota-update">Life of an OTA update</h2> -<p>A typical OTA update contains the following steps:</p> -<ol> -<li>Device performs regular check in with OTA servers and is notified of the -availability of an update, including the URL of the update package and a -description string to show the user.</li> -<li>Update downloads to a cache or data partition, and its cryptographic -signature is verified against the certificates in -<code>/system/etc/security/otacerts.zip</code>. User is prompted to install the -update.</li> -<li>Device reboots into recovery mode, in which the kernel and system in the -recovery partition are booted instead of the kernel in the boot partition.</li> -<li>Recovery binary is started by init. It finds command-line arguments in -<code>/cache/recovery/command</code> that point it to the downloaded package. -</li> -<li>Recovery verifies the cryptographic signature of the package against the -public keys in <code>/res/keys</code> (part of the RAM disk contained in the -recovery partition).</li> -<li>Data is pulled from the package and used to update the boot, system, -and/or vendor partitions as necessary. One of the new files left on the system -partition contains the contents of the new recovery partition.</li> -<li>Device reboots normally. <ol style="list-style-type:lower-alpha"> -<li>The newly updated boot partition is loaded, and it mounts and starts -executing binaries in the newly updated system partition.</li> -<li>As part of normal startup, the system checks the contents of the recovery -partition against the desired contents (which were previously stored as a file -in <code>/system</code>). They are different, so the recovery partition is -reflashed with the desired contents. (On subsequent boots, the recovery -partition already contains the new contents, so no reflash is necessary.)</li> -</ol></li> -</ol> -<p>The system update is complete!</p> + <h2 id="nonab_updates">Non-A/B updates</h2> -<h2 id="migrating">Migrating from previous releases</h2> - -<p>When migrating from Android 2.3/3.0/4.0 release, the major change is the -conversion of all the device-specific functionality from a set of C functions -with predefined names to C++ objects. The following table lists the old -functions and the new methods that serve a roughly equivalent purpose:</p> - -<table> -<tbody> -<tr> -<th>C function</th> -<th>C++ method</th> -</tr> -<tr> -<td>device_recovery_start()</td> -<td>Device::RecoveryStart()</td> -</tr> -<tr> -<td>device_toggle_display()<br> -device_reboot_now()<br> -</td> -<td>RecoveryUI::CheckKey()<br> -(also RecoveryUI::IsKeyPressed())<br> -</td> -</tr> -<tr> -<td>device_handle_key()</td> -<td>Device::HandleMenuKey()</td> -</tr> -<tr> -<td>device_perform_action()</td> -<td>Device::InvokeMenuItem()</td> -</tr> -<tr> -<td>device_wipe_data()</td> -<td>Device::WipeData()</td> -</tr> -<tr> -<td>device_ui_init()</td> -<td>ScreenRecoveryUI::Init()</td> -</tr> -</tbody> -</table> - -<p>Conversion of old functions to new methods should be reasonably -straightforward. Don't forget to add the new <code>make_device()</code> -function to create and return an instance of your new Device subclass.</p> + <p> + Older devices have a special recovery partition containing the software + needed to unpack a downloaded update package and apply the update to + the other partitions. For more information, see + <a href="/devices/tech/ota/nonab_updates.html">Non-A/B System Updates + </a>. + </p> + </body> </html> |