失眠网 > Android logd日志原理

Android logd日志原理

时间：2019-08-03 21:00:27

相关推荐

Android logd日志原理

一. 概述

无论是Android系统开发，还是应用开发，都离不开log，Androd上层采用logcat输出log。

1.1 logcat命令说明

可通过adb命令直接输出指定的log:

logcat -b events // 输出指定buffer的loglogcat -s "ActivityManager"logcat -L //上次重启时的loglogcat -f [filename] //将log保存到指定文件logcat -g //缓冲区大小logcat -S //统计log信息

-b 默认是指-b main -b system -b crash, 当然一可以指定其他参数, 或者直接指定all.

二. log函数使用

2.1 Java层

默认定义了5个Buffer缓冲区,如下:

log级别:

2.2 Kernel层

Linux Kernel最常使用的是printk，用法如下：

//第一个参数是级别，第二个是具体log内容printk(KERN_INFO x);

日志级别的定义位于kernel/include/linux/printk.h文件，如下：

日志输出到文件/proc/kmsg，可通过cat /proc/kmsg来获取内核log信息。

cat /proc/sys/kernel/printk

2.4 buffer大小

LogBuffer.cpp

可知 radio = 4M, 其他都为2M.

三. 原理分析

3.1 Log.i

[-> android/util/Log.java]

public static int i(String tag, String msg) {// [见小节3.2]return println_native(LOG_ID_MAIN, INFO, tag, msg);}

Log.java中的方法都是输出到main buffer, 其中println_native是Native方法，通过JNI调用如下方法。

3.2 println_native

[-> android_util_Log.cpp]

static jint android_util_Log_println_native(JNIEnv* env, jobject clazz,jint bufID, jint priority, jstring tagObj, jstring msgObj){const char* tag = NULL;const char* msg = NULL;...//获取log标签和内容if (tagObj != NULL)tag = env->GetStringUTFChars(tagObj, NULL);msg = env->GetStringUTFChars(msgObj, NULL);// [见小节3.3]int res = __android_log_buf_write(bufID, (android_LogPriority)priority, tag, msg);if (tag != NULL)env->ReleaseStringUTFChars(tagObj, tag);env->ReleaseStringUTFChars(msgObj, msg);return res;}

3.3 __android_log_buf_write

[-> logd_write.c]

int __android_log_buf_write(int bufID, int prio, const char *tag, const char *msg){struct iovec vec[3];char tmp_tag[32];...if ((bufID != LOG_ID_RADIO) &&(!strcmp(tag, "HTC_RIL") ||!strncmp(tag, "RIL", 3) || // RIL为前缀!strncmp(tag, "IMS", 3) || // IMS为前缀!strcmp(tag, "AT") ||!strcmp(tag, "GSM") ||!strcmp(tag, "STK") ||!strcmp(tag, "CDMA") ||!strcmp(tag, "PHONE") ||!strcmp(tag, "SMS"))) {bufID = LOG_ID_RADIO;//满足以上条件的tag，则默认输出到radio缓冲区，并修改相应的tagssnprintf(tmp_tag, sizeof(tmp_tag), "use-Rlog/RLOG-%s", tag);tag = tmp_tag;}...vec[0].iov_base = (unsigned char *) &prio;vec[0].iov_len = 1;vec[1].iov_base = (void *) tag;vec[1].iov_len = strlen(tag) + 1;vec[2].iov_base = (void *) msg;vec[2].iov_len = strlen(msg) + 1;// [见小节3.4]return write_to_log(bufID, vec, 3);}

对于满足特殊条件的tag，则会输出到LOG_ID_RADIO缓冲区；vec数组依次记录着log的级别，tag, msg.

其中write_to_log函数指针指向__write_to_log_init

static int (*write_to_log)(log_id_t, struct iovec *vec, size_t nr) = __write_to_log_init;

3.4 write_to_log

[-> logd_write.c]

static int __write_to_log_init(log_id_t log_id, struct iovec *vec, size_t nr){...if (write_to_log == __write_to_log_init) {int ret;ret = __write_to_log_initialize(); //执行log初始化【见小节3.4.1】if (ret < 0) {if (pstore_fd >= 0) {__write_to_log_daemon(log_id, vec, nr); //【见小节3.5】}return ret;}write_to_log = __write_to_log_daemon;}...return write_to_log(log_id, vec, nr);}

3.4.1 __write_to_log_initialize

static int __write_to_log_initialize(){int i, ret = 0;if (pstore_fd < 0) {//打开pstore文件, 用于panic时记录上次重启前的logpstore_fd = TEMP_FAILURE_RETRY(open("/dev/pmsg0", O_WRONLY));}if (logd_fd < 0) { //首次执行logd_fd = -1// 初始化socketi = TEMP_FAILURE_RETRY(socket(PF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC, 0));if (i < 0) {ret = -errno;//设置为非阻塞模式} else if (TEMP_FAILURE_RETRY(fcntl(i, F_SETFL, O_NONBLOCK)) < 0) {ret = -errno;close(i);} else {struct sockaddr_un un;memset(&un, 0, sizeof(struct sockaddr_un));un.sun_family = AF_UNIX;strcpy(un.sun_path, "/dev/socket/logdw"); // socket通道// 连接该socketif (TEMP_FAILURE_RETRY(connect(i, (struct sockaddr *)&un,sizeof(struct sockaddr_un))) < 0) {ret = -errno;close(i);} else {logd_fd = i; // 将新打开的socket的文件描述符赋予该logd_fd.}}}return ret;}

该方法主要功能:

打开pstore文件, 用于panic时记录上次重启前的log; (只打开一次);初始化并连接socket (“/dev/socket/logdw”), 设置为非阻塞模式;将socket的文件描述符赋予该logd_fd.

接下来进入真正写log的方法.

3.5 __write_to_log_daemon

static int __write_to_log_daemon(log_id_t log_id, struct iovec *vec, size_t nr){ssize_t ret;...static const unsigned header_length = 2;struct iovec newVec[nr + header_length];android_log_header_t header;android_pmsg_log_header_t pmsg_header;struct timespec ts;size_t i, payload_size;static uid_t last_uid = AID_ROOT;static pid_t last_pid = (pid_t) -1;static atomic_int_fast32_t dropped;...if (last_uid == AID_ROOT) {last_uid = getuid(); //获取uid}if (last_pid == (pid_t) -1) {last_pid = getpid(); //获取pid}clock_gettime(CLOCK_REALTIME, &ts); //获取realtimepmsg_header.magic = LOGGER_MAGIC;pmsg_header.len = sizeof(pmsg_header) + sizeof(header);pmsg_header.uid = last_uid;pmsg_header.pid = last_pid;header.tid = gettid(); //获取tidheader.realtime.tv_sec = ts.tv_sec;header.realtime.tv_nsec = ts.tv_nsec;newVec[0].iov_base = (unsigned char *) &pmsg_header;newVec[0].iov_len = sizeof(pmsg_header);newVec[1].iov_base = (unsigned char *) &header;newVec[1].iov_len = sizeof(header);if (logd_fd > 0) {int32_t snapshot = atomic_exchange_explicit(&dropped, 0, memory_order_relaxed);if (snapshot) {android_log_event_int_t buffer;header.id = LOG_ID_EVENTS;buffer.header.tag = htole32(LIBLOG_LOG_TAG);buffer.payload.type = EVENT_TYPE_INT;buffer.payload.data = htole32(snapshot);newVec[2].iov_base = &buffer;newVec[2].iov_len = sizeof(buffer);ret = TEMP_FAILURE_RETRY(writev(logd_fd, newVec + 1, 2));if (ret != (ssize_t)(sizeof(header) + sizeof(buffer))) {atomic_fetch_add_explicit(&dropped, snapshot, memory_order_relaxed);}}}header.id = log_id;for (payload_size = 0, i = header_length; i < nr + header_length; i++) {newVec[i].iov_base = vec[i - header_length].iov_base;payload_size += newVec[i].iov_len = vec[i - header_length].iov_len;// 限制每条log最大为4076bif (payload_size > LOGGER_ENTRY_MAX_PAYLOAD) {newVec[i].iov_len -= payload_size - LOGGER_ENTRY_MAX_PAYLOAD;if (newVec[i].iov_len) {++i;}payload_size = LOGGER_ENTRY_MAX_PAYLOAD;break;}}pmsg_header.len += payload_size;if (pstore_fd >= 0) {//写入pstoreTEMP_FAILURE_RETRY(writev(pstore_fd, newVec, i));}...// 写入logd[见小节3.6]ret = TEMP_FAILURE_RETRY(writev(logd_fd, newVec + 1, i - 1));...if (ret > (ssize_t)sizeof(header)) {ret -= sizeof(header);} else if (ret == -EAGAIN) {atomic_fetch_add_explicit(&dropped, 1, memory_order_relaxed);}return ret;}

该方法的主要功能, 准备log相关的信息:

piduidtidrealtimemsg

3.6 writev

[-> uio.c]

int writev( int fd, const struct iovec* vecs, int count ){int total = 0;for ( ; count > 0; count--, vecs++ ) {const char* buf = vecs->iov_base;intlen = vecs->iov_len;while (len > 0) {//将数据写入fdint ret = write( fd, buf, len );...total += ret;buf += ret;len -= ret;}}Exit:return total;}

3.7 小节

一句话总结就是Log.i()最终是通过调用write()向logd守护进程的socket(“/dev/socket/logdw”)端写入需要打印的日志信息。接下来再来看logd的工作过程。

四. logd守护进程

logd是由init进程所启动的守护进程

service logd /system/bin/logdclass coresocket logd stream 0666 logd logdsocket logdr seqpacket 0666 logd logdsocket logdw dgram 0222 logd logdgroup root system

创建3个socket通道,用于进程间通信.

4.1 main()

[-> /system/core/logd/main.cpp]

int main(int argc, char *argv[]) {int fdPmesg = -1;bool klogd = true;if (klogd) {//以只读方式打开内核log的/proc/kmsgfdPmesg = open("/proc/kmsg", O_RDONLY | O_NDELAY);}//以读写方式打开/dev/kmsgfdDmesg = open("/dev/kmsg", O_WRONLY);//处理reinit命令if ((argc > 1) && argv[1] && !strcmp(argv[1], "--reinit")) {int sock = TEMP_FAILURE_RETRY(socket_local_client("logd",ANDROID_SOCKET_NAMESPACE_RESERVED,SOCK_STREAM));...static const char reinit[] = "reinit";//写入"reinit"ssize_t ret = TEMP_FAILURE_RETRY(write(sock, reinit, sizeof(reinit)));...struct pollfd p;memset(&p, 0, sizeof(p));p.fd = sock;p.events = POLLIN;ret = TEMP_FAILURE_RETRY(poll(&p, 1, 100)); //进入poll轮询...static const char success[] = "success";char buffer[sizeof(success) - 1];memset(buffer, 0, sizeof(buffer));//读取数据,保存到bufferret = TEMP_FAILURE_RETRY(read(sock, buffer, sizeof(buffer)));...//比较读取的数据是否为"success"return strncmp(buffer, success, sizeof(success) - 1) != 0;}sem_init(&reinit, 0, 0);sem_init(&uidName, 0, 0);sem_init(&sem_name, 0, 1);pthread_attr_t attr;if (!pthread_attr_init(&attr)) {...if (!pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED)) {pthread_t thread;reinit_running = true;//创建线程"logd.daemon", 该线程入口函数reinit_thread_start()if (pthread_create(&thread, &attr, reinit_thread_start, NULL)) {reinit_running = false;}}pthread_attr_destroy(&attr);}...LastLogTimes *times = new LastLogTimes();//创建LogBuffer对象logBuf = new LogBuffer(times);signal(SIGHUP, reinit_signal_handler);if (property_get_bool_svelte("logd.statistics")) {logBuf->enableStatistics();}//监听/dev/socket/logdr, 当client连接上则将buffer信息写入client.LogReader *reader = new LogReader(logBuf);if (reader->startListener()) {exit(1);}//监听/dev/socket/logdw, 新日志添加到LogBuffer, 并且LogReader发送更新给已连接的clientLogListener *swl = new LogListener(logBuf, reader);if (swl->startListener(300)) {exit(1);}//监听/dev/socket/logd, 处理logd管理命令CommandListener *cl = new CommandListener(logBuf, reader, swl);if (cl->startListener()) {exit(1);}bool auditd = property_get_bool("logd.auditd", true);LogAudit *al = NULL;if (auditd) {bool dmesg = property_get_bool("logd.auditd.dmesg", true);al = new LogAudit(logBuf, reader, dmesg ? fdDmesg : -1);}LogKlog *kl = NULL;if (klogd) {kl = new LogKlog(logBuf, reader, fdDmesg, fdPmesg, al != NULL);}readDmesg(al, kl);if (kl && kl->startListener()) {delete kl;}if (al && al->startListener()) {delete al;}TEMP_FAILURE_RETRY(pause());exit(0);}

该方法功能:

LogReader: 监听/dev/socket/logdr, 当client连接上则将buffer信息写入client. 所对应线程名”logd.reader”LogListener: 监听/dev/socket/logdw, 新日志添加到LogBuffer, 并且LogReader发送更新给已连接的client. 所对应线程名”logd.writer”CommandListener: 监听/dev/socket/logd, 处理logd管理命令. 所对应线程名”logd.control”LogAudit: 所对应线程名”logd.auditd”LogKlog: 所对应线程名”logd.klogd”入口reinit_thread_start: 所对应线程名”logd.daemon”LogTimeEntry::threadStart: 所对应线程名”ogd.reader.per”

另外, ANDROID_SOCKET_NAMESPACE_RESERVED代表位于/dev/socket名字空间。通过adb命令, 可以看到logd进程有9个子线程。

logd381 121880 9132 sigsuspend 7f8301fdac S /system/bin/logdsystem 382 381 21880 9132 futex_wait 7f82fcf9c4 S logd.daemonlogd383 381 21880 9132 poll_sched 7f8301fd1c S logd.readerlogd384 381 21880 9132 poll_sched 7f8301fd1c S logd.writerlogd385 381 21880 9132 poll_sched 7f8301fd1c S logd.controllogd392 381 21880 9132 poll_sched 7f8301fd1c S logd.klogdlogd393 381 21880 9132 poll_sched 7f8301fd1c S logd.auditdlogd3716 381 21880 9132 futex_wait 7f82fcf9c4 S logd.reader.perlogd4329 381 21880 9132 futex_wait 7f82fcf9c4 S logd.reader.perlogd5224 381 21880 9132 futex_wait 7f82fcf9c4 S logd.reader.per

接下来, 继续回到前面log输出过程, 接下来进入logd的LogListener处理过程, 如下:

4.2 LogListener

[-> LogListener.cpp]

int main(int argc, char *argv[]) {...logBuf = new LogBuffer(times); //[见小节4.2.1]LogListener *swl = new LogListener(logBuf, reader); //[见小节4.2.2]if (swl->startListener(300)) { //[见小节4.3]exit(1);}...}

4.2.1 LogBuffer.init

[-> LogBuffer.cpp]

void LogBuffer::init() {static const char global_tuneable[] = "persist.logd.size";static const char global_default[] = "ro.logd.size";//获取buffer默认大小unsigned long default_size = property_get_size(global_tuneable);if (!default_size) {default_size = property_get_size(global_default);}log_id_for_each(i) {char key[PROP_NAME_MAX];snprintf(key, sizeof(key), "%s.%s",global_tuneable, android_log_id_to_name(i));unsigned long property_size = property_get_size(key);if (!property_size) {snprintf(key, sizeof(key), "%s.%s",global_default, android_log_id_to_name(i));//比如获取的是persist.logd.size.system所对应的值property_size = property_get_size(key);}if (!property_size) {property_size = default_size;}if (!property_size) {//此值为256kproperty_size = LOG_BUFFER_SIZE;}if (setSize(i, property_size)) {//此值为64ksetSize(i, LOG_BUFFER_MIN_SIZE);}}}

buffer大小设置的优先级顺序为:

persist.logd.size.xxx; 比如persist.logd.size.system;persist.logd.size;ro.logd.size;LOG_BUFFER_SIZE, 即256k;LOG_BUFFER_MIN_SIZE, 即64k。

4.2.2 LogListener

[-> LogListener.cpp]

LogListener::LogListener(LogBuffer *buf, LogReader *reader) :SocketListener(getLogSocket(), false),logbuf(buf),reader(reader) {}

此处getLogSocket()过程创建logdw的服务端,并监听客户端消息.

4.2.3 SocketListener

SocketListener::SocketListener(int socketFd, bool listen) {init(NULL, socketFd, listen, false);}void SocketListener::init(const char *socketName, int socketFd, bool listen, bool useCmdNum) {mListen = listen; // mListen=falsemSocketName = socketName;mSock = socketFd;mUseCmdNum = useCmdNum;pthread_mutex_init(&mClientsLock, NULL);mClients = new SocketClientCollection();}

SocketListener对象创建完成，则开始执行SocketListener来监听socket请求。

4.3 startListener

[-> SocketListener.cpp]

int SocketListener::startListener() {return startListener(4);}int SocketListener::startListener(int backlog) {if (!mSocketName && mSock == -1) {...} else if (mSocketName) {if ((mSock = android_get_control_socket(mSocketName)) < 0) {...}fcntl(mSock, F_SETFD, FD_CLOEXEC);}if (mListen && listen(mSock, backlog) < 0) {return -1;} else if (!mListen)mClients->push_back(new SocketClient(mSock, false, mUseCmdNum));if (pipe(mCtrlPipe)) {return -1;}//创建线程[见小节4.4]if (pthread_create(&mThread, NULL, SocketListener::threadStart, this)) {return -1;}return 0;}

通过调用pthread_create创建完线程，在新创建的线程中执行threadStart()过程。

4.4 threadStart

[-> SocketListener.cpp]

void *SocketListener::threadStart(void *obj) {SocketListener *me = reinterpret_cast<SocketListener *>(obj);me->runListener(); //[见小节4.5]pthread_exit(NULL);return NULL;}

4.5 runListener

[-> SocketListener.cpp]

void SocketListener::runListener() {SocketClientCollection pendingList;while(1) {...while (!pendingList.empty()) {it = pendingList.begin(); //找到第一个即将要处理的客户端SocketClient* c = *it;pendingList.erase(it);if (!onDataAvailable(c)) { //处理该消息[见小节4.6]release(c, false);}c->decRef();}}}

4.6 onDataAvailable

[-> LogListener.cpp]

bool LogListener::onDataAvailable(SocketClient *cli) {static bool name_set;if (!name_set) {prctl(PR_SET_NAME, "logd.writer");name_set = true;}char buffer[sizeof_log_id_t + sizeof(uint16_t) + sizeof(log_time)+ LOGGER_ENTRY_MAX_PAYLOAD];struct iovec iov = { buffer, sizeof(buffer) };memset(buffer, 0, sizeof(buffer));char control[CMSG_SPACE(sizeof(struct ucred))];struct msghdr hdr = {NULL,0,&iov, //记录buffer地址指针1,control,sizeof(control),0,};int socket = cli->getSocket();//通过socket接收消息,保存到hdr,其n代表消息长度ssize_t n = recvmsg(socket, &hdr, 0);...struct ucred *cred = NULL;struct cmsghdr *cmsg = CMSG_FIRSTHDR(&hdr);//获取ucred信息while (cmsg != NULL) {if (cmsg->cmsg_level == SOL_SOCKET&& cmsg->cmsg_type == SCM_CREDENTIALS) {cred = (struct ucred *)CMSG_DATA(cmsg);break;}cmsg = CMSG_NXTHDR(&hdr, cmsg);}if (cred == NULL) {return false;}...//获取android_log_header_t结构体指针android_log_header_t *header = reinterpret_cast<android_log_header_t *>(buffer);if (header->id >= LOG_ID_MAX || header->id == LOG_ID_KERNEL) {return false;}char *msg = ((char *)buffer) + sizeof(android_log_header_t);n -= sizeof(android_log_header_t);//[见小节4.7]if (logbuf->log((log_id_t)header->id, header->realtime,cred->uid, cred->pid, header->tid, msg,((size_t) n <= USHRT_MAX) ? (unsigned short) n : USHRT_MAX) >= 0) {//[见小节4.8]reader->notifyNewLog();}return true;}

LogBuffer.log()的参数说明:

android_log_header_t提供 log_id, realtime, tiducred提供 uid, pid.msghdr提供 msg

4.7 LogBuffer.log

[-> LogBuffer.cpp]

int LogBuffer::log(log_id_t log_id, log_time realtime,uid_t uid, pid_t pid, pid_t tid,const char *msg, unsigned short len) {...//创建一条log信息LogBufferElement *elem = new LogBufferElement(log_id, realtime,uid, pid, tid, msg, len);int prio = ANDROID_LOG_INFO;const char *tag = NULL;if (log_id == LOG_ID_EVENTS) {tag = android::tagToName(elem->getTag());} else {prio = *msg;tag = msg + 1;}if (!__android_log_is_loggable(prio, tag, ANDROID_LOG_VERBOSE)) {pthread_mutex_lock(&mLogElementsLock);stats.add(elem); //对于不运行输出log的状态下, 只统计log信息, 记录log本身stats.subtract(elem);pthread_mutex_unlock(&mLogElementsLock);delete elem;return -EACCES;}pthread_mutex_lock(&mLogElementsLock);LogBufferElementCollection::iterator it = mLogElements.end();LogBufferElementCollection::iterator last = it;//根据时间排序,找到应该插入的点while (last != mLogElements.begin()) {--it;if ((*it)->getRealTime() <= realtime) {break;}last = it;}//将log信息插入合适的位置if (last == mLogElements.end()) {mLogElements.push_back(elem);} else {uint64_t end = 1;bool end_set = false;bool end_always = false;LogTimeEntry::lock();LastLogTimes::iterator t = mTimes.begin();while(t != mTimes.end()) {LogTimeEntry *entry = (*t);if (entry->owned_Locked()) {if (!entry->mNonBlock) {end_always = true;break;}if (!end_set || (end <= entry->mEnd)) {end = entry->mEnd;end_set = true;}}t++;}if (end_always|| (end_set && (end >= (*last)->getSequence()))) {mLogElements.push_back(elem);} else {mLogElements.insert(last,elem);}LogTimeEntry::unlock();}stats.add(elem); //[4.7.1]maybePrune(log_id); //[4.7.2]pthread_mutex_unlock(&mLogElementsLock);return len;}

4.7.1 stats.add

[-> LogStatistics.cpp]

void LogStatistics::add(LogBufferElement *e) {log_id_t log_id = e->getLogId();unsigned short size = e->getMsgLen();mSizes[log_id] += size; //对应的buffer所使用大小增加++mElements[log_id]; //对应的buffer中log记录加1;mSizesTotal[log_id] += size;++mElementsTotal[log_id];if (log_id == LOG_ID_KERNEL) {return;}//以uid为单位, 添加到uidTable表格uidTable[log_id].add(e->getUid(), e);if (!enable) {return;}pidTable.add(e->getPid(), e);tidTable.add(e->getTid(), e);uint32_t tag = e->getTag();if (tag) {tagTable.add(tag, e);}}

将log信息分别记录到uidTable, pidTable, tidTable, tagTable.

4.7.2 maybePrune

[-> LogBuffer.cpp]

void LogBuffer::maybePrune(log_id_t id) {size_t sizes = stats.sizes(id); //log占用内存大小unsigned long maxSize = log_buffer_size(id); //最大上限,比如2Mif (sizes > maxSize) {size_t sizeOver = sizes - ((maxSize * 9) / 10); //超出90%的部分大小size_t elements = stats.realElements(id); // 真实的log行数size_t minElements = elements / 100; // 真实的log行数的1%行//minPrune = 4, 保证1%的log行数>=4if (minElements < minPrune) {minElements = minPrune;}unsigned long pruneRows = elements * sizeOver / sizes;if (pruneRows < minElements) { //保证>= 1%的log行数pruneRows = minElements;}//maxPrune = 256, 保证pruneRows<=256;if (pruneRows > maxPrune) {pruneRows = maxPrune;}prune(id, pruneRows); //[见小节4.7.3]}}

假设某个buffer的大小为2M:

pruneRows = elements * sizeOver / sizes= elements * (1 - 0.9*(maxSize/sizes))= elements * (1 - 1.8/sizes);

其中elements代表的是当前buffer的log总行数;sizes代表对的是当前buffer的log总大小。

这就意味着某个buffer中的log行数越多，或者log占用内存越大，则需要裁剪的日志行数越多。每次裁剪日志行数等于总行数的10%，并且需要大于等于4行，且不超过256行。

4.7.3 prune

[-> LogBuffer.cpp]

bool LogBuffer::prune(log_id_t id, unsigned long pruneRows, uid_t caller_uid) {LogTimeEntry *oldest = NULL;bool busy = false;bool clearAll = pruneRows == ULONG_MAX;LogTimeEntry::lock();LastLogTimes::iterator times = mTimes.begin();while(times != mTimes.end()) {LogTimeEntry *entry = (*times);if (entry->owned_Locked() && entry->isWatching(id)&& (!oldest ||(oldest->mStart > entry->mStart) ||((oldest->mStart == entry->mStart) &&(entry->mTimeout.tv_sec || entry->mTimeout.tv_nsec)))) {oldest = entry;}times++;}LogBufferElementCollection::iterator it;if (caller_uid != AID_ROOT) {it = mLastSet[id] ? mLast[id] : mLogElements.begin();while (it != mLogElements.end()) {LogBufferElement *element = *it;if ((element->getLogId() != id) || (element->getUid() != caller_uid)) {++it;continue;}if (!mLastSet[id] || ((*mLast[id])->getLogId() != id)) {mLast[id] = it;mLastSet[id] = true;}if (oldest && (oldest->mStart <= element->getSequence())) {busy = true;if (oldest->mTimeout.tv_sec || oldest->mTimeout.tv_nsec) {oldest->triggerReader_Locked();} else {oldest->triggerSkip_Locked(id, pruneRows);}break;}it = erase(it);pruneRows--;}LogTimeEntry::unlock();return busy;}//修剪 log最多的内容: 黑名单, uid, system uid的pidbool hasBlacklist = (id != LOG_ID_SECURITY) && mPrune.naughty();while (!clearAll && (pruneRows > 0)) {uid_t worst = (uid_t) -1;size_t worst_sizes = 0;size_t second_worst_sizes = 0;pid_t worstPid = 0;if (worstUidEnabledForLogid(id) && mPrune.worstUidEnabled()) {{ std::unique_ptr<const UidEntry *[]> sorted = stats.sort(AID_ROOT, (pid_t)0, 2, id);if (sorted.get() && sorted[0] && sorted[1]) {worst_sizes = sorted[0]->getSizes();//buffer总大小的1/8为阈值size_t threshold = log_buffer_size(id) / 8;if ((worst_sizes > threshold)&& (worst_sizes > (10 * sorted[0]->getDropped()))) {worst = sorted[0]->getKey();second_worst_sizes = sorted[1]->getSizes();if (second_worst_sizes < threshold) {second_worst_sizes = threshold;}}}}if ((worst == AID_SYSTEM) && mPrune.worstPidOfSystemEnabled()) {// 对于system_server进程,根据pid来决策std::unique_ptr<const PidEntry *[]> sorted = stats.sort(worst, (pid_t)0, 2, id, worst);if (sorted.get() && sorted[0] && sorted[1]) {worstPid = sorted[0]->getKey(); //最糟糕的pidsecond_worst_sizes = worst_sizes- sorted[0]->getSizes()+ sorted[1]->getSizes();}}}if ((worst == (uid_t) -1) && !hasBlacklist) {break;}bool kick = false;bool leading = true;it = mLastSet[id] ? mLast[id] : mLogElements.begin();bool gc = pruneRows <= 1;if (!gc && (worst != (uid_t) -1)) {{ LogBufferIteratorMap::iterator found = mLastWorstUid[id].find(worst);if ((found != mLastWorstUid[id].end())&& (found->second != mLogElements.end())) {leading = false;it = found->second;}}if (worstPid) {// begin scope for pid worst found iteratorLogBufferPidIteratorMap::iterator found= mLastWorstPidOfSystem[id].find(worstPid);if ((found != mLastWorstPidOfSystem[id].end())&& (found->second != mLogElements.end())) {leading = false;it = found->second;}}}static const timespec too_old = {EXPIRE_HOUR_THRESHOLD * 60 * 60, 0};LogBufferElementCollection::iterator lastt;lastt = mLogElements.end();--lastt;LogBufferElementLast last;while (it != mLogElements.end()) {LogBufferElement *element = *it;if (oldest && (oldest->mStart <= element->getSequence())) {busy = true;if (oldest->mTimeout.tv_sec || oldest->mTimeout.tv_nsec) {oldest->triggerReader_Locked();}break;}if (element->getLogId() != id) {++it;continue;}if (leading && (!mLastSet[id] || ((*mLast[id])->getLogId() != id))) {mLast[id] = it;mLastSet[id] = true;}unsigned short dropped = element->getDropped();// remove any leading dropsif (leading && dropped) {it = erase(it);continue;}if (dropped && last.coalesce(element, dropped)) {it = erase(it, true);continue;}if (hasBlacklist && mPrune.naughty(element)) {last.clear(element);it = erase(it);if (dropped) {continue;}pruneRows--;if (pruneRows == 0) {break;}if (element->getUid() == worst) {kick = true;if (worst_sizes < second_worst_sizes) {break;}worst_sizes -= element->getMsgLen();}continue;}if ((element->getRealTime() < ((*lastt)->getRealTime() - too_old))|| (element->getRealTime() > (*lastt)->getRealTime())) {break;}if (dropped) {last.add(element);if (worstPid&& ((!gc && (element->getPid() == worstPid))|| (mLastWorstPidOfSystem[id].find(element->getPid())== mLastWorstPidOfSystem[id].end()))) {mLastWorstPidOfSystem[id][element->getUid()] = it;}if ((!gc && !worstPid && (element->getUid() == worst))|| (mLastWorstUid[id].find(element->getUid())== mLastWorstUid[id].end())) {mLastWorstUid[id][element->getUid()] = it;}++it;continue;}if ((element->getUid() != worst)|| (worstPid && (element->getPid() != worstPid))) {leading = false;last.clear(element);++it;continue;}pruneRows--;if (pruneRows == 0) {break;}kick = true;unsigned short len = element->getMsgLen();// do not create any leading dropsif (leading) {it = erase(it);} else {stats.drop(element);element->setDropped(1);if (last.coalesce(element, 1)) {it = erase(it, true);} else {last.add(element);if (worstPid && (!gc|| (mLastWorstPidOfSystem[id].find(worstPid)== mLastWorstPidOfSystem[id].end()))) {mLastWorstPidOfSystem[id][worstPid] = it;}if ((!gc && !worstPid) || (mLastWorstUid[id].find(worst)== mLastWorstUid[id].end())) {mLastWorstUid[id][worst] = it;}++it;}}if (worst_sizes < second_worst_sizes) {break;}worst_sizes -= len;}last.clear();if (!kick || !mPrune.worstUidEnabled()) {break; // the following loop will ask bad clients to skip/drop}}bool whitelist = false;bool hasWhitelist = (id != LOG_ID_SECURITY) && mPrune.nice() && !clearAll;it = mLastSet[id] ? mLast[id] : mLogElements.begin();while((pruneRows > 0) && (it != mLogElements.end())) {LogBufferElement *element = *it;if (element->getLogId() != id) {it++;continue;}if (!mLastSet[id] || ((*mLast[id])->getLogId() != id)) {mLast[id] = it;mLastSet[id] = true;}if (oldest && (oldest->mStart <= element->getSequence())) {busy = true;if (whitelist) {break;}if (stats.sizes(id) > (2 * log_buffer_size(id))) {// kick a misbehaving log reader client off the islandoldest->release_Locked();} else if (oldest->mTimeout.tv_sec || oldest->mTimeout.tv_nsec) {oldest->triggerReader_Locked();} else {oldest->triggerSkip_Locked(id, pruneRows);}break;}if (hasWhitelist && !element->getDropped() && mPrune.nice(element)) {// WhiteListedwhitelist = true;it++;continue;}it = erase(it);pruneRows--;}// Do not save the whitelist if we are reader range limitedif (whitelist && (pruneRows > 0)) {it = mLastSet[id] ? mLast[id] : mLogElements.begin();while((it != mLogElements.end()) && (pruneRows > 0)) {LogBufferElement *element = *it;if (element->getLogId() != id) {++it;continue;}if (!mLastSet[id] || ((*mLast[id])->getLogId() != id)) {mLast[id] = it;mLastSet[id] = true;}if (oldest && (oldest->mStart <= element->getSequence())) {busy = true;if (stats.sizes(id) > (2 * log_buffer_size(id))) {// kick a misbehaving log reader client off the islandoldest->release_Locked();} else if (oldest->mTimeout.tv_sec || oldest->mTimeout.tv_nsec) {oldest->triggerReader_Locked();} else {oldest->triggerSkip_Locked(id, pruneRows);}break;}it = erase(it);pruneRows--;}}LogTimeEntry::unlock();return (pruneRows > 0) && busy;}

在PruneList::init()过程会完成黑白名单.

日志裁剪功能说明：

裁剪黑名单以及log打印最多的那个uid, 以及system uid中打印日志最多的pid进程中的日志;白名单的不删除

4.8 小节

每一行log记录为LogBufferElement，logd的执行调用链如下

SocketListener::runListener()LogListener.onDataAvailableLogBuffer::logLogBuffer::maybePruneLogReader::notifyNewLogSocketListener::runOnEachSocketFlushCommand::runSocketCommand