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| |
| <p>Android O adds support for <code>storaged</code>, an Android native daemon that |
| collects and publishes storage metrics on Android devices.</p> |
| |
| <ul> |
| <li>For daily diskstats, <code>storaged</code> periodically parses |
| <code>/sys/block/mmcblk0/stat</code> (eMMC storage devices) or |
| <code>/sys/block/sda/stat</code> (non-eMMC devices).</li> |
| |
| <li>For eMMC lifetime, <code>storaged</code> parses <code>/d/mmc0/mmc0:001/ext_csd</code> (if |
| available).</li> |
| |
| <li>For application I/O blaming, <code>storaged</code> periodically traverses |
| <code>/proc/uid_io/stats</code> and maintains parsed data, which includes data |
| from all applications (not just running applications). <code>dumpsys</code> can |
| call <code>storaged</code> to log the application I/O usage in a bug report.</li> |
| </ul> |
| |
| <p>Diskstat (including stalled diskstats) and eMMC information is logged to the |
| Android event log, where a platform checkin service collects the logs.</p> |
| |
| <p><code>storaged</code> operations occur automatically and are handled entirely by the Android |
| framework, so you don't need to do any implementation work. This page |
| describes the design of <code>storaged</code> (including new interfaces) and how to use it to |
| get I/O status from the kernel.</p> |
| |
| <h2 id="storaged-design">storaged design</h2> |
| |
| <p>For accounting and permission flexibility, <code>storaged</code> is implemented as a kernel |
| module that returns per-uid I/O information (instead of using standard |
| <code>proc/PID/io</code>). Raw I/O data for each I/O request continues to be |
| stored and updated in kernel <code>task_struct</code>, and the kernel keeps |
| track of when a process exits so it doesn't miss I/O usage that occurs from the |
| last <code>storaged</code> polling event.</p> |
| |
| <p>The module reads raw data and processes it only when the framework notifies it |
| of a uid foreground/background switch or when the <code>storaged</code> daemon requests a |
| report. At that time, the module exports a file node from kernel for |
| communication with framework and <code>storaged</code> daemon.</p> |
| |
| <p><code>storaged</code> introduces the <code>/proc/uid_io/stats</code> interface, which returns |
| a list of I/O stats for each UID in the system. The format is:</p> |
| |
| <pre><uid>: <foreground read bytes> <foreground write bytes> <foreground read chars> <foreground write chars> <background read bytes> <background write bytes> <background read chars> <background write chars> |
| </pre> |
| |
| <ul> |
| <li>read/write bytes are I/O events from a storage device.</li> |
| <li>read/write chars (also in bytes) are data requested by read/write |
| syscalls.</li> |
| </ul> |
| |
| <h2 id="getting-i-o-status-from-the-kernel">Getting I/O status from the |
| kernel</h2> |
| |
| <p>To dump I/O usage from the kernel, use the <code>storaged</code> command with |
| the <strong><code>-u</code></strong> option.</p> |
| |
| <p>Command: <code>storaged -u</code></p> |
| |
| <p>Command output format: <code>name/uid fg_rchar fg_wchar fg_rbytes fg_wbytes |
| bg_rchar bg_wchar bg_rbytes bg_wbytes fg_fsync bg_fsync</code></p> |
| |
| <p class="note"><strong>Note: </strong>This output is similar to the output for |
| <code>proc/uid_io/stats</code>. This is because <code>storaged</code> processes data from |
| <code>/proc/uid_io/stats</code> and generates its own data.</p> |
| |
| <p>Example output:</p> |
| |
| <pre>com.google.android.backuptransport 2269 60 0 0 1719845663 143912573 149065728 184180736 |
| com.android.vending 2170 60 0 0 219904796 38693092 174436352 18944000</pre> |
| |
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