Android：dumpsys

比如#dumpsys diskstats會打印系統中內部存儲設備的使用情況。
那這個dumpsys diskstats到底是從哪裡打印存儲設備的情況的呢？
先看一下dumpsys.cpp的main函數實現

int main(int argc, char* const argv[])
{
    signal(SIGPIPE, SIG_IGN);
    sp sm = defaultServiceManager();
    fflush(stdout);
    if (sm == NULL) {
        ALOGE("Unable to get default service manager!");
        aerr << "dumpsys: Unable to get default service manager!" << endl;
        return 20;
    }

    Vector services;
    Vector args;
    bool showListOnly = false;
    if ((argc == 2) && (strcmp(argv[1], "-l") == 0)) {
        showListOnly = true;
    }
    if ((argc == 1) || showListOnly) {
        services = sm->listServices();
        services.sort(sort_func);
        args.add(String16("-a"));
    } else {
        services.add(String16(argv[1]));
        for (int i=2; i 1) {
        // first print a list of the current services
        aout << "Currently running services:" << endl;

        for (size_t i=0; i service = sm->checkService(services[i]);
            if (service != NULL) {
                aout << "  " << services[i] << endl;
            }
        }
    }

    if (showListOnly) {
        return 0;
    }

    for (size_t i=0; i service = sm->checkService(services[i]);
        if (service != NULL) {
            if (N > 1) {
                aout << "------------------------------------------------------------"
                        "-------------------" << endl;
                aout << "DUMP OF SERVICE " << services[i] << ":" << endl;
            }
            int err = service->dump(STDOUT_FILENO, args);
            if (err != 0) {
                aerr << "Error dumping service info: (" << strerror(err)
                        << ") " << services[i] << endl;
            }
        } else {
            aerr << "Can't find service: " << services[i] << endl;
        }
    }
    return 0;
}

這裡#dumpsys diskstats命令會在dumpsys的main函數中，從所有注冊的service裡邊找到叫diskstats的，然後調用其dump()函數。那diskstats是否已經注冊了呢？
可以再SystemServer.java->startOtherServices()函數中找到

private void startOtherServices() {
    ...
    try {
        Slog.i(TAG, "DiskStats Service");
        ServiceManager.addService("diskstats", new 
            DiskStatsService(context));
        } catch (Throwable e) {
            reportWtf("starting DiskStats Service", e);
        }
    }
    ...
}

以下是DiskStatsService類的定義，可以看到已經定義了dump()函數。可以從dump()函數裡看到是怎麼打印disk信息的

public class DiskStatsService extends Binder {
    private static final String TAG = "DiskStatsService";

    private final Context mContext;

    public DiskStatsService(Context context) {
        mContext = context;
    }

    @Override
    protected void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.DUMP, TAG);

        // Run a quick-and-dirty performance test: write 512 bytes
        byte[] junk = new byte[512];
        for (int i = 0; i < junk.length; i++) junk[i] = (byte) i;  // Write nonzero bytes

        File tmp = new File(Environment.getDataDirectory(), "system/perftest.tmp");
        FileOutputStream fos = null;
        IOException error = null;

        long before = SystemClock.uptimeMillis();
        try {
            fos = new FileOutputStream(tmp);
            fos.write(junk);
        } catch (IOException e) {
            error = e;
        } finally {
            try { if (fos != null) fos.close(); } catch (IOException e) {}
        }

        long after = SystemClock.uptimeMillis();
        if (tmp.exists()) tmp.delete();

        if (error != null) {
            pw.print("Test-Error: ");
            pw.println(error.toString());
        } else {
            pw.print("Latency: ");
            pw.print(after - before);
            pw.println("ms [512B Data Write]");
        }

        reportFreeSpace(Environment.getDataDirectory(), "Data", pw);
        reportFreeSpace(Environment.getDownloadCacheDirectory(), "Cache", pw);
        reportFreeSpace(new File("/system"), "System", pw);

        // TODO: Read /proc/yaffs and report interesting values;
        // add configurable (through args) performance test parameters.
    }

    private void reportFreeSpace(File path, String name, PrintWriter pw) {
        try {
            StatFs statfs = new StatFs(path.getPath());
            long bsize = statfs.getBlockSize();
            long avail = statfs.getAvailableBlocks();
            long total = statfs.getBlockCount();
            if (bsize <= 0 || total <= 0) {
                throw new IllegalArgumentException(
                        "Invalid stat: bsize=" + bsize + " avail=" + avail + " total=" + total);
            }

            pw.print(name);
            pw.print("-Free: ");
            pw.print(avail * bsize / 1024);
            pw.print("K / ");
            pw.print(total * bsize / 1024);
            pw.print("K total = ");
            pw.print(avail * 100 / total);
            pw.println("% free");
        } catch (IllegalArgumentException e) {
            pw.print(name);
            pw.print("-Error: ");
            pw.println(e.toString());
            return;
        }
    }
}