简介

系统服务dropbox以文件形式记录了系统各种异常信息，例如app crash、native crash、anr、kernel panic等等

adb查询

adb shell dumpsys dropbox

app接口

源码
10.0

1.DropBoxManager dropbox = (DropBoxManager) getSystemService(Context.DROPBOX_SERVICE)
例如，dropbox.addText 可实现把需要记录的数据丢给dropbox进行存储

2.监听广播android.intent.action.DROPBOX_ENTRY_ADDED，可知系统发生了异常
注意权限：android.permission.READ_LOGS  -- 平台签名或priv-app

dropbox启动

1.SystemServer:run。SystemServer启动服务
private void startOtherServices() {
    ···
    mSystemServiceManager.startService(DropBoxManagerService.class);
    ···
}

2.DropBoxManagerService继承SystemService，启动顺序:构造方法 -->onStart
    a)构造方法
    public DropBoxManagerService(final Context context, File path) {
        super(context);
        mDropBoxDir = path;//dropbox路径/data/system/dropbox
        mContentResolver = getContext().getContentResolver();
        mHandler = new Handler() {
            @Override
            public void handleMessage(Message msg) {
                if (msg.what == MSG_SEND_BROADCAST) {
                    getContext().sendBroadcastAsUser((Intent)msg.obj, UserHandle.SYSTEM,
                            android.Manifest.permission.READ_LOGS);
                }
            }
        };
    }

    b)onStart启动
    public void onStart() {
        // 监听低内存，保证dropbox不占用更多空间
        IntentFilter filter = new IntentFilter();
        filter.addAction(Intent.ACTION_DEVICE_STORAGE_LOW);
        getContext().registerReceiver(mReceiver, filter);

        mContentResolver.registerContentObserver(
            Settings.Global.CONTENT_URI, true,
            new ContentObserver(new Handler()) {
                @Override
                public void onChange(boolean selfChange) {
                    mReceiver.onReceive(getContext(), (Intent) null);
                }
            });

        //注册dropbox服务
        publishBinderService(Context.DROPBOX_SERVICE, mStub);
    }

3.接口运用，发送广播DropBoxManager.ACTION_DROPBOX_ENTRY_ADDED
dropbox.add

     public void add(DropBoxManager.Entry entry) {
        ···
        try {
            ···
            final Intent dropboxIntent = new Intent(DropBoxManager.ACTION_DROPBOX_ENTRY_ADDED);
            dropboxIntent.putExtra(DropBoxManager.EXTRA_TAG, tag);
            dropboxIntent.putExtra(DropBoxManager.EXTRA_TIME, time);
            if (!mBooted) {
                dropboxIntent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY);
            }
            ···
            mHandler.sendMessage(mHandler.obtainMessage(MSG_SEND_BROADCAST, dropboxIntent));
        } catch (IOException e) {
            Slog.e(TAG, "Can't write: " + tag, e);
        } finally {
            IoUtils.closeQuietly(output);
            IoUtils.closeQuietly(input);
            entry.close();
            if (temp != null) temp.delete();
        }
    }  

dropbox日志路径：/data/system/dropbox

C:\Users\99418>adb shell ls -al /data/system/dropbox
total 432
drwx------  2 system system  4096 2021-12-23 06:02 .
drwxrwxr-x 16 system system  4096 2021-12-23 06:01 ..
-rw-------  1 system system   335 2022-01-25 14:40 SYSTEM_BOOT@1640210494810.txt
-rw-------  1 system system   334 2022-01-25 15:05 SYSTEM_BOOT@1640210494823.txt
-rw-------  1 system system   334 2021-12-23 06:01 SYSTEM_BOOT@1640210496077.txt
-rw-------  1 system system 19264 2022-01-25 14:40 SYSTEM_RECOVERY_KMSG@1640210494811.txt.gz
-rw-------  1 system system 19191 2022-01-25 15:05 SYSTEM_RECOVERY_KMSG@1640210494824.txt.gz
-rw-------  1 system system  5661 2022-01-25 14:40 SYSTEM_RECOVERY_LOG@1640210494809.txt.gz
-rw-------  1 system system  5076 2022-01-25 15:05 SYSTEM_RECOVERY_LOG@1640210494822.txt.gz
-rw-------  1 system system    30 2022-01-25 14:40 storage_trim@1640210494803.txt
-rw-------  1 system system  4192 2022-01-25 14:40 system_app_strictmode@1640210494804.txt.gz

记录的系统错误
1.系统正常启动后的自检工作
1)SYSTEM_BOOT
开机一次，记录一次

2)SYSTEM_RESTART
如果system_server在设备运行过程中异常，则会有记录

3)SYSTEM_LAST_KMSG
kernel异常。
pstore是persistent storage的缩写，内核发生异常通过此把异常日志记录下来，方便定位问题。
ramoops指的是采用ram保存oops信息(kernel 异常信息)的一个功能，利用pstore技术实现。

kernel异常信息保存地：
panic
/proc/last_kmsg

oops
/sys/fs/pstore/console-ramoops
/sys/fs/pstore/console-ramoops-0

4)SYSTEM_TOMBSTONE
TOMBSTONE 是 Android 用来记录 native 进程崩溃的 core dump 日志, 系统服务在启动完成后会增加一个 Observer 来侦测 tombstone 日志文件的变化, 每当生成新的 tombstone 文件, 就会增加一条 SYSTEM_TOMBSTONE 记录到 DropBoxManager 中.

5)SYSTEM_RECOVERY_LOG/SYSTEM_RECOVERY_KMSG
SYSTEM_RECOVERY_KMSG：recovery kerenl日志
SYSTEM_RECOVERY_LOG：recovery 升级或恢复出厂设置等等日志

6)SYSTEM_FSCK
文件系统完整性校验日志

7)SYSTEM_AUDIT
kernel 异常信息的查漏补缺日志

BootReceiver.java
    private void logBootEvents(Context ctx) throws IOException {
        final DropBoxManager db = (DropBoxManager) ctx.getSystemService(Context.DROPBOX_SERVICE);
        final String headers = getBootHeadersToLogAndUpdate();
        final String bootReason = SystemProperties.get("ro.boot.bootreason", null);

        String recovery = RecoverySystem.handleAftermath(ctx);
        if (recovery != null && db != null) {
            db.addText("SYSTEM_RECOVERY_LOG", headers + recovery);
        }

        String lastKmsgFooter = "";
        if (bootReason != null) {
            lastKmsgFooter = new StringBuilder(512)
                .append("\n")
                .append("Boot info:\n")
                .append("Last boot reason: ").append(bootReason).append("\n")
                .toString();
        }

        HashMap<String, Long> timestamps = readTimestamps();

        if (SystemProperties.getLong("ro.runtime.firstboot", 0) == 0) {
            if (StorageManager.inCryptKeeperBounce()) {
                // Encrypted, first boot to get PIN/pattern/password so data is tmpfs
                // Don't set ro.runtime.firstboot so that we will do this again
                // when data is properly mounted
            } else {
                String now = Long.toString(System.currentTimeMillis());
                SystemProperties.set("ro.runtime.firstboot", now);
            }
            if (db != null) db.addText("SYSTEM_BOOT", headers);

            // Negative sizes mean to take the *tail* of the file (see FileUtils.readTextFile())
            // kernel panic日志，例如异常重启
            addFileWithFootersToDropBox(db, timestamps, headers, lastKmsgFooter,
                    "/proc/last_kmsg", -LOG_SIZE, "SYSTEM_LAST_KMSG");
            addFileWithFootersToDropBox(db, timestamps, headers, lastKmsgFooter,
                    "/sys/fs/pstore/console-ramoops", -LOG_SIZE, "SYSTEM_LAST_KMSG");
            addFileWithFootersToDropBox(db, timestamps, headers, lastKmsgFooter,
                    "/sys/fs/pstore/console-ramoops-0", -LOG_SIZE, "SYSTEM_LAST_KMSG");
            
            //recovery日志。例如OTA升级或恢复出厂设置的时候
            addFileToDropBox(db, timestamps, headers, "/cache/recovery/log", -LOG_SIZE,
                    "SYSTEM_RECOVERY_LOG");
            addFileToDropBox(db, timestamps, headers, "/cache/recovery/last_kmsg",
                    -LOG_SIZE, "SYSTEM_RECOVERY_KMSG");
            
            //kernel日志的查漏补缺备份
            addAuditErrorsToDropBox(db, timestamps, headers, -LOG_SIZE, "SYSTEM_AUDIT");
        } else {
            if (db != null) db.addText("SYSTEM_RESTART", headers);
        }
        // log always available fs_stat last so that logcat collecting tools can wait until
        // fs_stat to get all file system metrics.
        logFsShutdownTime();
        logFsMountTime();
        //fsck文件系统校验日志收集
        //fsck（file system consistency check）是Unix和类Unix系统上用于检查文件系统完整性的工具
        addFsckErrorsToDropBoxAndLogFsStat(db, timestamps, headers, -LOG_SIZE, "SYSTEM_FSCK");
        logSystemServerShutdownTimeMetrics();

        // Scan existing tombstones (in case any new ones appeared)
        //native进程崩溃日志收集
        File[] tombstoneFiles = TOMBSTONE_DIR.listFiles();
        for (int i = 0; tombstoneFiles != null && i < tombstoneFiles.length; i++) {
            if (tombstoneFiles[i].isFile()) {
                addFileToDropBox(db, timestamps, headers, tombstoneFiles[i].getPath(),
                        LOG_SIZE, "SYSTEM_TOMBSTONE");
            }
        }

        writeTimestamps(timestamps);

        // Start watching for new tombstone files; will record them as they occur.
        // This gets registered with the singleton file observer thread.
        // /data/tombstones目录监听收集
        sTombstoneObserver = new FileObserver(TOMBSTONE_DIR.getPath(), FileObserver.CREATE) {
            @Override
            public void onEvent(int event, String path) {
                HashMap<String, Long> timestamps = readTimestamps();
                try {
                    File file = new File(TOMBSTONE_DIR, path);
                    if (file.isFile() && file.getName().startsWith("tombstone_")) {
                        addFileToDropBox(db, timestamps, headers, file.getPath(), LOG_SIZE,
                                TAG_TOMBSTONE);
                    }
                } catch (IOException e) {
                    Slog.e(TAG, "Can't log tombstone", e);
                }
                writeTimestamps(timestamps);
            }
        };

        sTombstoneObserver.startWatching();
    }

2.java/native crash。-- crash/native_crash
java/native层异常的区分在于eventType:crash/native_crash

ActivityManagerService
    void handleApplicationCrashInner(String eventType, ProcessRecord r, String processName,
            ApplicationErrorReport.CrashInfo crashInfo) {
        //event事件的日志记录：EventLogTags.AM_CRASH --> am_crash
        EventLog.writeEvent(EventLogTags.AM_CRASH, Binder.getCallingPid(),
                UserHandle.getUserId(Binder.getCallingUid()), processName,
                r == null ? -1 : r.info.flags,
                crashInfo.exceptionClassName,
                crashInfo.exceptionMessage,
                crashInfo.throwFileName,
                crashInfo.throwLineNumber);

        ···
        //加入到dropbox
        addErrorToDropBox(
                eventType, r, processName, null, null, null, null, null, null, crashInfo);
        //其他业务处理
        mAppErrors.crashApplication(r, crashInfo);
    }

java层：handleApplicationCrashInner("crash", r, processName, crashInfo);
native层： mAm.handleApplicationCrashInner("native_crash", mApp, mApp.processName, ci);

3.anr 异常。-- anr
这里涉及广播、Service、Provider等组件的anr以及触摸按键事件的anr

ProcessRecord
    void appNotResponding(String activityShortComponentName, ApplicationInfo aInfo,
            String parentShortComponentName, WindowProcessController parentProcess,
            boolean aboveSystem, String annotation) {
        ···
        //event事件的日志记录：EventLogTags.AM_ANR --> am_anr
        EventLog.writeEvent(EventLogTags.AM_ANR, userId, pid, processName, info.flags,
                    annotation);
        ···
        //加入到dropbox
        mService.addErrorToDropBox("anr", this, processName, activityShortComponentName,
                parentShortComponentName, parentPr, annotation, cpuInfo, tracesFile, null);
        ···
    }

4.wtf(What a Terrible Failure)。--- wtf
android.util.Log.wtf(String, String)，应用可调用布局异常点

ActivityManagerService

    ProcessRecord handleApplicationWtfInner(int callingUid, int callingPid, IBinder app, String tag,
            final ApplicationErrorReport.CrashInfo crashInfo) {
        final ProcessRecord r = findAppProcess(app, "WTF");
        final String processName = app == null ? "system_server"
                : (r == null ? "unknown" : r.processName);
        //event事件的日志记录：EventLogTags.AM_WTF --> am_wtf
        EventLog.writeEvent(EventLogTags.AM_WTF, UserHandle.getUserId(callingUid), callingPid,
                processName, r == null ? -1 : r.info.flags, tag, crashInfo.exceptionMessage);
        ···
        //加入到dropbox
        addErrorToDropBox("wtf", r, processName, null, null, null, tag, null, null, crashInfo);

        return r;
    }
注意：
当系统设置Settings.Global.WTF_IS_FATAL为1时，发送wtf可kill应用

5.strict mode。---**_strictmode
严格模式，主要为性能监测使用
StrictMode (严格模式), 顾名思义, 就是在比正常模式检测得更严格, 通常用来监测不应当在主线程执行的网络, 文件等操作. 任何 StrictMode 违例都会被 ActivityManagerService 在 DropBoxManager 中记录为一次 strict_mode 违例.

ActivityManagerService

    public void handleApplicationStrictModeViolation(
            IBinder app,
            int penaltyMask,
            StrictMode.ViolationInfo info) {
        ···
        //需要满足触发dropbox的条件
        if ((penaltyMask & StrictMode.PENALTY_DROPBOX) != 0) {
            Integer stackFingerprint = info.hashCode();
            boolean logIt = true;
            ···
            if (logIt) {//执行dropbox业务
                logStrictModeViolationToDropBox(r, info);
            }
        }

        ···
    }
    
    private void logStrictModeViolationToDropBox(
            ProcessRecord process,
            StrictMode.ViolationInfo info) {
        if (info == null) {
            return;
        }
        //收集信息，tag：***_strictmode
        ···省略···
        
        //加入到dropbox
        IoThread.getHandler().post(() -> {
            dbox.addText(dropboxTag, res);
        });
    } 

6.lowmem。低内存报告

ActivityManagerService
    final void doLowMemReportIfNeededLocked(ProcessRecord dyingProc) {
        // If there are no longer any background processes running,
        // and the app that died was not running instrumentation,
        // then tell everyone we are now low on memory.
        if (!mProcessList.haveBackgroundProcessLocked()) {
            ···
            //event事件的日志记录：EventLogTags.AM_LOW_MEMORY --> am_low_memory
            EventLog.writeEvent(EventLogTags.AM_LOW_MEMORY, mProcessList.getLruSizeLocked());
            ···
            if (doReport) {//如果报告，最后调入reportMemUsage
                Message msg = mHandler.obtainMessage(REPORT_MEM_USAGE_MSG, memInfos);
                mHandler.sendMessage(msg);
            }
            ···
        }
    }
    
    void reportMemUsage(ArrayList<ProcessMemInfo> memInfos) {
        ···
        addErrorToDropBox("lowmem", null, "system_server", null,
                null, null, tag.toString(), dropBuilder.toString(), null, null);
        ···
    }

7.watchdog
如果 WatchDog 监测到系统进程(system_server)出现问题, 会增加一条 watchdog 记录到 DropBoxManager 中, 并终止系统进程的执行.

WatchDog
    public void run() {
        ···
        while (true) {
            ···
            //event事件的日志记录：EventLogTags.WATCHDOG --> watchdog
            EventLog.writeEvent(EventLogTags.WATCHDOG, name.isEmpty() ? subject : name);
            ···
            /// M: WDT debug enhancement
            /// need to wait the AEE dumps all info, then kill system server @{
            // Try to add the error to the dropbox, but assuming that the ActivityManager
            // itself may be deadlocked.  (which has happened, causing this statement to
            // deadlock and the watchdog as a whole to be ineffective)
            Thread dropboxThread = new Thread("watchdogWriteToDropbox") {
                    public void run() {
                        //加入到dropbox
                        if (mActivity != null) {
                            mActivity.addErrorToDropBox(
                                    "watchdog", null, "system_server", null, null, null,
                                    name.isEmpty() ? subject : name, cpuInfo, stack, null);
                        }
                        StatsLog.write(StatsLog.SYSTEM_SERVER_WATCHDOG_OCCURRED, subject);
                    }
                };
            dropboxThread.start();
            try {
                dropboxThread.join(2000);  // wait up to 2 seconds for it to return.
            } catch (InterruptedException ignored) {}

            ···
        }
    }

8.其他
1)netstats_error/netstats_dump
NetworkStatsService 负责收集并持久化存储网络状态的统计数据, 当遇到明显的网络状态错误时, 它会增加一条 netstats_error 记录到 DropBoxManager.

NetworkStatsService
    private static final String TAG_NETSTATS_ERROR = "netstats_error";

    private class DropBoxNonMonotonicObserver implements NonMonotonicObserver<String> {
        @Override
        public void foundNonMonotonic(NetworkStats left, int leftIndex, NetworkStats right,
                int rightIndex, String cookie) {
            Log.w(TAG, "Found non-monotonic values; saving to dropbox");

            // record error for debugging
            final StringBuilder builder = new StringBuilder();
            builder.append("found non-monotonic " + cookie + " values at left[" + leftIndex
                    + "] - right[" + rightIndex + "]\n");
            builder.append("left=").append(left).append('\n');
            builder.append("right=").append(right).append('\n');

            mContext.getSystemService(DropBoxManager.class).addText(TAG_NETSTATS_ERROR,
                    builder.toString());
        }

        @Override
        public void foundNonMonotonic(
                NetworkStats stats, int statsIndex, String cookie) {
            Log.w(TAG, "Found non-monotonic values; saving to dropbox");

            final StringBuilder builder = new StringBuilder();
            builder.append("Found non-monotonic " + cookie + " values at [" + statsIndex + "]\n");
            builder.append("stats=").append(stats).append('\n');

            mContext.getSystemService(DropBoxManager.class).addText(TAG_NETSTATS_ERROR,
                    builder.toString());
        }
    }
    
NetworkStatsRecorder
    private static final String TAG_NETSTATS_DUMP = "netstats_dump";

    private void recoverFromWtf() {
        if (DUMP_BEFORE_DELETE) {
            ···
            mDropBox.addData(TAG_NETSTATS_DUMP, os.toByteArray(), 0);
        }
        ···
    }

2)BATTERY_DISCHARGE_INFO
BatteryService 负责检测充电状态, 并更新手机电池信息. 当遇到明显的 discharge 事件, 它会增加一条 BATTERY_DISCHARGE_INFO 记录到 DropBoxManager.

    // TODO: Current code doesn't work since "--unplugged" flag in BSS was purposefully removed.
    private void logBatteryStatsLocked() {
        ···
        DropBoxManager db = (DropBoxManager) mContext.getSystemService(Context.DROPBOX_SERVICE);
        ···
        try {
            ··· 
            // add dump file to drop box
            db.addFile("BATTERY_DISCHARGE_INFO", dumpFile, DropBoxManager.IS_TEXT);
        }
        ···
    }

3)storage_benchmark/storage_trim
StorageManagerService 负责存储设备管理，例如sdcard或usb mass storage
fstrim提升磁盘性能，缓解Android卡顿

private static final String TAG_STORAGE_BENCHMARK = "storage_benchmark";
private static final String TAG_STORAGE_TRIM = "storage_trim";
    
public void benchmark(String volId, IVoldTaskListener listener) {
    ···
    mVold.benchmark(volId, new IVoldTaskListener.Stub() {
        ···
        final DropBoxManager dropBox = mContext.getSystemService(DropBoxManager.class);
        dropBox.addText(TAG_STORAGE_BENCHMARK, scrubPath(path)
                    + " " + ident + " " + create + " " + run + " " + destroy);
    ···
        
    });
}

public void fstrim(int flags, IVoldTaskListener listener) {
    ···
    mVold.fstrim(flags, new IVoldTaskListener.Stub() {
        @Override
        public void onStatus(int status, PersistableBundle extras) {
            ···
            final DropBoxManager dropBox = mContext.getSystemService(DropBoxManager.class);
                dropBox.addText(TAG_STORAGE_TRIM, scrubPath(path) + " " + bytes + " " + time);
            ···
            }
            ···
        });
    ···
}

4)network_watchlist_report
NetworkWatchlistService

WatchlistLoggingHandler

    private static final String DROPBOX_TAG = "network_watchlist_report";

    private void tryAggregateRecords(long lastRecordTime) {
        try {
            ···
            if (mDropBoxManager != null && mDropBoxManager.isTagEnabled(DROPBOX_TAG)) {
                ···
                if (encodedResult != null) {
                    addEncodedReportToDropBox(encodedResult);
                }
            } else {
                ···
            }
            ···
        } finally {
            ···
        }
    }
    
    private void addEncodedReportToDropBox(byte[] encodedReport) {
        mDropBoxManager.addData(DROPBOX_TAG, encodedReport, 0);
    }

5)incident
frameworks/base/cmds/incidentd

Broadcaster.cpp
Status status = dropbox->addFile(String16("incident"), readFd, 0);

6)keymaster
system/security/keystore

operation_proto_handler.cpp
    android::sp<android::os::DropBoxManager> dropbox(new android::os::DropBoxManager);
    size_t size = opConfigEvents.ByteSize();
    auto data = std::make_unique<uint8_t[]>(size);
    opConfigEvents.SerializeWithCachedSizesToArray(data.get());
    dropbox->addData(android::String16("keymaster"), data.get(), size, 0);

key_proto_handler.cpp
    android::sp<android::os::DropBoxManager> dropbox(new android::os::DropBoxManager());
    keyConfig.set_was_creation_successful(wasCreationSuccessful);
    size_t size = keyConfig.ByteSize();
    auto data = std::make_unique<uint8_t[]>(size);
    keyConfig.SerializeWithCachedSizesToArray(data.get());
    dropbox->addData(android::String16("keymaster"), data.get(), size, 0);

参考学习

http://xiaocong.github.io/blog/2012/11/21/to-introduce-android-dropboxmanager-service/
http://huaqianlee.github.io/2020/11/13/Android/pstore/
http://tjtech.me/analyze-pstore-ramoops-in-android-kernel.html
https://blog.csdn.net/zangdongming/article/details/37729315
https://skytoby.github.io/2019/fstrim/