dumpsys原理 - 安卓R

dumpsys在frameworks/native/cmds/dumpsys/dumpsys.cpp、dumpsys.h和main.cpp中实现，是一个可执行程序。

$ dumpsys -l 可以列出所有的服务。

$ dumpsys 可以对相应的服务执行dump方法。

$ dumpsys 可以对所有服务执行dump方法。

main.cpp中程序的main函数：

#include "dumpsys.h"

#include <binder/IServiceManager.h>

#include <iostream>
#include <signal.h>

using namespace android;

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

    Dumpsys dumpsys(sm.get());
    return dumpsys.main(argc, argv);
}

拿到ServiceManager，然后执行Dumpsys的main方法：

int Dumpsys::main(int argc, char* const argv[]) {
    Vector<String16> services;
    Vector<String16> args;
    String16 priorityType;
    Vector<String16> skippedServices;
    Vector<String16> protoServices;
    bool showListOnly = false;
    bool skipServices = false;
    bool asProto = false;
    Type type = Type::DUMP;
    int timeoutArgMs = 10000;
    int priorityFlags = IServiceManager::DUMP_FLAG_PRIORITY_ALL;
    static struct option longOptions[] = {{"pid", no_argument, 0, 0},
                                          {"priority", required_argument, 0, 0},
                                          {"proto", no_argument, 0, 0},
                                          {"skip", no_argument, 0, 0},
                                          {"help", no_argument, 0, 0},
                                          {0, 0, 0, 0}};

    // Must reset optind, otherwise subsequent calls will fail (wouldn't happen on main.cpp, but
    // happens on test cases).
    optind = 1;
    while (1) {
        int c;
        int optionIndex = 0;

        c = getopt_long(argc, argv, "+t:T:l", longOptions, &optionIndex);

        if (c == -1) {
            break;
        }

        switch (c) {
        case 0:
            if (!strcmp(longOptions[optionIndex].name, "skip")) {
                skipServices = true;
            } else if (!strcmp(longOptions[optionIndex].name, "proto")) {
                asProto = true;
            } else if (!strcmp(longOptions[optionIndex].name, "help")) {
                usage();
                return 0;
            } else if (!strcmp(longOptions[optionIndex].name, "priority")) {
                priorityType = String16(String8(optarg));
                if (!ConvertPriorityTypeToBitmask(priorityType, priorityFlags)) {
                    fprintf(stderr, "\n");
                    usage();
                    return -1;
                }
            } else if (!strcmp(longOptions[optionIndex].name, "pid")) {
                type = Type::PID;
            }
            break;

        case 't':
            {
                char* endptr;
                timeoutArgMs = strtol(optarg, &endptr, 10);
                timeoutArgMs = timeoutArgMs * 1000;
                if (*endptr != '\0' || timeoutArgMs <= 0) {
                    fprintf(stderr, "Error: invalid timeout(seconds) number: '%s'\n", optarg);
                    return -1;
                }
            }
            break;

        case 'T':
            {
                char* endptr;
                timeoutArgMs = strtol(optarg, &endptr, 10);
                if (*endptr != '\0' || timeoutArgMs <= 0) {
                    fprintf(stderr, "Error: invalid timeout(milliseconds) number: '%s'\n", optarg);
                    return -1;
                }
            }
            break;

        case 'l':
            showListOnly = true;
            break;

        default:
            fprintf(stderr, "\n");
            usage();
            return -1;
        }
    }

    for (int i = optind; i < argc; i++) {
        if (skipServices) {
            skippedServices.add(String16(argv[i]));
        } else {
            if (i == optind) {
                services.add(String16(argv[i]));
            } else {
                const String16 arg(argv[i]);
                args.add(arg);
                // For backward compatible, if the proto argument is passed to the service, the
                // dump request is also considered to use proto.
                if (!asProto && !arg.compare(String16(PriorityDumper::PROTO_ARG))) {
                    asProto = true;
                }
            }
        }
    }

    if ((skipServices && skippedServices.empty()) ||
            (showListOnly && (!services.empty() || !skippedServices.empty()))) {
        usage();
        return -1;
    }

    if (services.empty() || showListOnly) {
        services = listServices(priorityFlags, asProto);
        setServiceArgs(args, asProto, priorityFlags);
    }

    const size_t N = services.size();
    if (N > 1) {
        // first print a list of the current services
        std::cout << "Currently running services:" << std::endl;

        for (size_t i=0; i<N; i++) {
            sp<IBinder> service = sm_->checkService(services[i]);

            if (service != nullptr) {
                bool skipped = IsSkipped(skippedServices, services[i]);
                std::cout << "  " << services[i] << (skipped ? " (skipped)" : "") << std::endl;
            }
        }
    }

    if (showListOnly) {
        return 0;
    }

    for (size_t i = 0; i < N; i++) {
        const String16& serviceName = services[i];
        if (IsSkipped(skippedServices, serviceName)) continue;

        if (startDumpThread(type, serviceName, args) == OK) {
            bool addSeparator = (N > 1);
            if (addSeparator) {
                writeDumpHeader(STDOUT_FILENO, serviceName, priorityFlags);
            }
            std::chrono::duration<double> elapsedDuration;
            size_t bytesWritten = 0;
            status_t status =
                writeDump(STDOUT_FILENO, serviceName, std::chrono::milliseconds(timeoutArgMs),
                          asProto, elapsedDuration, bytesWritten);

            if (status == TIMED_OUT) {
                std::cout << std::endl
                     << "*** SERVICE '" << serviceName << "' DUMP TIMEOUT (" << timeoutArgMs
                     << "ms) EXPIRED ***" << std::endl
                     << std::endl;
            }

            if (addSeparator) {
                writeDumpFooter(STDOUT_FILENO, serviceName, elapsedDuration);
            }
            bool dumpComplete = (status == OK);
            stopDumpThread(dumpComplete);
        }
    }

    return 0;
}

Dumpsys的startDumpThread方法：

status_t Dumpsys::startDumpThread(Type type, const String16& serviceName,
                                  const Vector<String16>& args) {
    sp<IBinder> service = sm_->checkService(serviceName);
    if (service == nullptr) {
        std::cerr << "Can't find service: " << serviceName << std::endl;
        return NAME_NOT_FOUND;
    }

    int sfd[2];
    if (pipe(sfd) != 0) {
        std::cerr << "Failed to create pipe to dump service info for " << serviceName << ": "
             << strerror(errno) << std::endl;
        return -errno;
    }

    redirectFd_ = unique_fd(sfd[0]);
    unique_fd remote_end(sfd[1]);
    sfd[0] = sfd[1] = -1;

    // dump blocks until completion, so spawn a thread..
    activeThread_ = std::thread([=, remote_end{std::move(remote_end)}]() mutable {
        status_t err = 0;

        switch (type) {
        case Type::DUMP:
            err = service->dump(remote_end.get(), args);
            break;
        case Type::PID:
            err = dumpPidToFd(service, remote_end);
            break;
        default:
            std::cerr << "Unknown dump type" << static_cast<int>(type) << std::endl;
            return;
        }

        if (err != OK) {
            std::cerr << "Error dumping service info status_t: " << statusToString(err) << " "
                 << serviceName << std::endl;
        }
    });
    return OK;
}

开启了线程去执行service的dump方法，并创建管道，线程将dump返回的信息写入管道的写入端，管道的读取端为redirectFd_。

Dumpsys的writeDump方法：

status_t Dumpsys::writeDump(int fd, const String16& serviceName, std::chrono::milliseconds timeout,
                            bool asProto, std::chrono::duration<double>& elapsedDuration,
                            size_t& bytesWritten) const {
    status_t status = OK;
    size_t totalBytes = 0;
    auto start = std::chrono::steady_clock::now();
    auto end = start + timeout;

    int serviceDumpFd = redirectFd_.get();
    if (serviceDumpFd == -1) {
        return INVALID_OPERATION;
    }

    struct pollfd pfd = {.fd = serviceDumpFd, .events = POLLIN};

    while (true) {
        // Wrap this in a lambda so that TEMP_FAILURE_RETRY recalculates the timeout.
        auto time_left_ms = [end]() {
            auto now = std::chrono::steady_clock::now();
            auto diff = std::chrono::duration_cast<std::chrono::milliseconds>(end - now);
            return std::max(diff.count(), 0LL);
        };

        int rc = TEMP_FAILURE_RETRY(poll(&pfd, 1, time_left_ms()));
        if (rc < 0) {
            std::cerr << "Error in poll while dumping service " << serviceName << " : "
                 << strerror(errno) << std::endl;
            status = -errno;
            break;
        } else if (rc == 0) {
            status = TIMED_OUT;
            break;
        }

        char buf[4096];
        rc = TEMP_FAILURE_RETRY(read(redirectFd_.get(), buf, sizeof(buf)));
        if (rc < 0) {
            std::cerr << "Failed to read while dumping service " << serviceName << ": "
                 << strerror(errno) << std::endl;
            status = -errno;
            break;
        } else if (rc == 0) {
            // EOF.
            break;
        }

        if (!WriteFully(fd, buf, rc)) {
            std::cerr << "Failed to write while dumping service " << serviceName << ": "
                 << strerror(errno) << std::endl;
            status = -errno;
            break;
        }
        totalBytes += rc;
    }

    if ((status == TIMED_OUT) && (!asProto)) {
        std::string msg = StringPrintf("\n*** SERVICE '%s' DUMP TIMEOUT (%llums) EXPIRED ***\n\n",
                                       String8(serviceName).string(), timeout.count());
        WriteStringToFd(msg, fd);
    }

    elapsedDuration = std::chrono::steady_clock::now() - start;
    bytesWritten = totalBytes;
    return status;
}

从管道的读取端redirectFd_读入dump的信息并输出，同时还有超时控制机制。