logd守护进程

• 1、adb logcat命令
• 2、logd守护进程启动
• • 2.1 logd文件目录
  • 2.2 main方法启动
• 3、LogBuffer缓存大小
• • 3.1 缓存大小优先级设置
  • 3.2 缓存大小相关代码位置

1、adb logcat命令

Usage: logcat [options] [filterspecs]General options:-b, --buffer=       Request alternate ring buffer(s):main system radio events crash default allAdditionally, 'kernel' for userdebug and eng builds, and'security' for Device Owner installations.Multiple -b parameters or comma separated list of buffers areallowed. Buffers are interleaved.Default -b main,system,crash,kernel.-L, --last                  Dump logs from prior to last reboot from pstore.-c, --clear                 Clear (flush) the entire log and exit.if -f is specified, clear the specified file and its related rotatedlog files instead.if -L is specified, clear pstore log instead.-d                          Dump the log and then exit (don't block).--pid=                 Only print logs from the given pid.--wrap                      Sleep for 2 hours or when buffer about to wrap whichevercomes first. Improves efficiency of polling by providingan about-to-wrap wakeup.Formatting:-v, --format=       Sets log print format verb and adverbs, where  is one of:brief help long process raw tag thread threadtime timeModifying adverbs can be added:color descriptive epoch monotonic printable uid usec UTC year zoneMultiple -v parameters or comma separated list of format and formatmodifiers are allowed.-D, --dividers              Print dividers between each log buffer.-B, --binary                Output the log in binary.Outfile files:-f, --file=           Log to file instead of stdout.-r, --rotate-kbytes=     Rotate log every  kbytes. Requires -f option.-n, --rotate-count=  Sets max number of rotated logs to , default 4.--id=                   If the signature  for logging to file changes, then clear theassociated files and continue.Logd control:These options send a control message to the logd daemon on device, print its return message ifapplicable, then exit. They are incompatible with -L, as these attributes do not apply to pstore.-g, --buffer-size           Get the size of the ring buffers within logd.-G, --buffer-size=    Set size of a ring buffer in logd. May suffix with K or M.This can individually control each buffer's size with -b.-S, --statistics            Output statistics.--pid can be used to provide pid specific stats.-p, --prune                 Print prune rules. Each rule is specified as UID, UID/PID or /PID. A'~' prefix indicates that elements matching the rule should be prunedwith higher priority otherwise they're pruned with lower priority. Allother pruning activity is oldest first. Special case ~! represents anautomatic pruning for the noisiest UID as determined by the currentstatistics.  Special case ~1000/! represents pruning of the worst PIDwithin AID_SYSTEM when AID_SYSTEM is the noisiest UID.-P, --prune=' ...'    Set prune rules, using same format as listed above. Must be quoted.Filtering:-s                          Set default filter to silent. Equivalent to filterspec '*:S'-e, --regex=          Only print lines where the log message matches  where  isan ECMAScript regular expression.-m, --max-count=     Quit after printing  lines. This is meant to be paired with--regex, but will work on its own.--print                     This option is only applicable when --regex is set and only useful if--max-count is also provided.With --print, logcat will print all messages even if they do notmatch the regex. Logcat will quit after printing the max-count numberof lines that match the regex.-t                   Print only the most recent  lines (implies -d).-t ''                 Print the lines since specified time (implies -d).-T                   Print only the most recent  lines (does not imply -d).-T ''                 Print the lines since specified time (not imply -d).count is pure numerical, time is 'MM-DD hh:mm:ss.mmm...''YYYY-MM-DD hh:mm:ss.mmm...' or 'sssss.mmm...' format.--uid=                Only display log messages from UIDs present in the comma separate list. No name look-up is performed, so UIDs must be provided asnumeric values. This option is only useful for the 'root', 'log', and'system' users since only those users can view logs from other users.filterspecs are a series of[:priority]where  is a log component tag (or * for all) and priority is:V    Verbose (default for )D    Debug (default for '*')I    InfoW    WarnE    ErrorF    FatalS    Silent (suppress all output)'*' by itself means '*:D' and  by itself means :V.
If no '*' filterspec or -s on command line, all filter defaults to '*:V'.
eg: '*:S ' prints only , ':S' suppresses all  log messages.If not specified on the command line, filterspec is set from ANDROID_LOG_TAGS.If not specified with -v on command line, format is set from ANDROID_PRINTF_LOG
or defaults to "threadtime"-v , --format= options:Sets log print format verb and adverbs, where  is:brief long process raw tag thread threadtime timeand individually flagged modifying adverbs can be added:color descriptive epoch monotonic printable uid usec UTC year zoneSingle format verbs:brief      — Display priority/tag and PID of the process issuing the message.long       — Display all metadata fields, separate messages with blank lines.process    — Display PID only.raw        — Display the raw log message, with no other metadata fields.tag        — Display the priority/tag only.thread     — Display priority, PID and TID of process issuing the message.threadtime — Display the date, invocation time, priority, tag, and the PIDand TID of the thread issuing the message. (the default format).time       — Display the date, invocation time, priority/tag, and PID of theprocess issuing the message.Adverb modifiers can be used in combination:color       — Display in highlighted color to match priority. i.e. VERBOSEDEBUG INFO WARNING ERROR FATALdescriptive — events logs only, descriptions from event-log-tags database.epoch       — Display time as seconds since Jan 1 1970.monotonic   — Display time as cpu seconds since last boot.printable   — Ensure that any binary logging content is escaped.uid         — If permitted, display the UID or Android ID of logged process.usec        — Display time down the microsecond precision.UTC         — Display time as UTC.year        — Add the year to the displayed time.zone        — Add the local timezone to the displayed time.""    — Print using this public named timezone (experimental).

2、logd守护进程启动

2.1 logd文件目录

Android系统启动 查看 init 进程解析 rc 文件，其中解析 logd.rc，调用到logd/main.cpp主函数。
相关目录：
system/logging/logd/logd.rc
system/logging/logd/main.cpp

logd.rc文件：

service logd /system/bin/logdsocket logd stream 0666 logd logdsocket logdr seqpacket 0666 logd logdsocket logdw dgram+passcred 0222 logd logdfile /proc/kmsg rfile /dev/kmsg wuser logdgroup logd system package_info readproccapabilities SYSLOG AUDIT_CONTROLpriority 10writepid /dev/cpuset/system-background/tasksservice logd-reinit /system/bin/logd --reinitoneshotdisableduser logdgroup logdwritepid /dev/cpuset/system-background/tasks# Limit SELinux denial generation to 5/second
service logd-auditctl /system/bin/auditctl -r 5oneshotdisableduser logdgroup logdcapabilities AUDIT_CONTROLon fswrite /dev/event-log-tags "# content owned by logd
"chown logd logd /dev/event-log-tagschmod 0644 /dev/event-log-tagson property:sys.boot_completed=1start logd-auditctl

2.2 main方法启动

• 1. 使用 android::base::KernelLogger 调试logd内部的日志输出，这部分日志输出到kernel log中，通过dmesg获取/dev/kmsg
• 2. 处理“reinit”命令
• 3. ro.logd.kernel 属性控制获取/proc/kmsg的FD
• 4. log_buffer 有chatty、serialized、simple模式（默认serialized），通过属性logd.buffer_type获取；LogBuffer 是负责保存所有日志条目的对象。
• 5. 相关监听线程：
  • /dev/socket/logdr LogReader监听
  • /dev/socket/logdw LogListener监听
  • /dev/socket/logd CommandListener监听

int main(int argc, char* argv[]) {// We want EPIPE when a reader disconnects, not to terminate logd.signal(SIGPIPE, SIG_IGN);// logd is written under the assumption that the timezone is UTC.// If TZ is not set, persist.sys.timezone is looked up in some time utility// libc functions, including mktime. It confuses the logd time handling,// so here explicitly set TZ to UTC, which overrides the property.setenv("TZ", "UTC", 1);// issue reinit command. KISS argument parsing.if ((argc > 1) && argv[1] && !strcmp(argv[1], "--reinit")) {return issueReinit();}android::base::InitLogging(argv, [](android::base::LogId log_id, android::base::LogSeverity severity,const char* tag, const char* file, unsigned int line, const char* message) {if (tag && strcmp(tag, "logd") != 0) {auto prefixed_message = android::base::StringPrintf("%s: %s", tag, message);android::base::KernelLogger(log_id, severity, "logd", file, line,prefixed_message.c_str());} else {android::base::KernelLogger(log_id, severity, "logd", file, line, message);}});static const char dev_kmsg[] = "/dev/kmsg";int fdDmesg = android_get_control_file(dev_kmsg);if (fdDmesg < 0) {fdDmesg = TEMP_FAILURE_RETRY(open(dev_kmsg, O_WRONLY | O_CLOEXEC));}int fdPmesg = -1;bool klogd = GetBoolPropertyEngSvelteDefault("ro.logd.kernel");if (klogd) {SetProperty("ro.logd.kernel", "true");static const char proc_kmsg[] = "/proc/kmsg";fdPmesg = android_get_control_file(proc_kmsg);if (fdPmesg < 0) {fdPmesg = TEMP_FAILURE_RETRY(open(proc_kmsg, O_RDONLY | O_NDELAY | O_CLOEXEC));}if (fdPmesg < 0) PLOG(ERROR) << "Failed to open " << proc_kmsg;}bool auditd = GetBoolProperty("ro.logd.auditd", true);DropPrivs(klogd, auditd);// A cache of event log tagsLogTags log_tags;// Pruning configuration.PruneList prune_list;std::string buffer_type = GetProperty("logd.buffer_type", "serialized");// Partial (required for chatty) or full logging statistics.LogStatistics log_statistics(GetBoolPropertyEngSvelteDefault("logd.statistics"),buffer_type == "serialized");// Serves the purpose of managing the last logs times read on a socket connection, and as a// reader lock on a range of log entries.LogReaderList reader_list;// LogBuffer is the object which is responsible for holding all log entries.LogBuffer* log_buffer = nullptr;if (buffer_type == "chatty") {log_buffer = new ChattyLogBuffer(&reader_list, &log_tags, &prune_list, &log_statistics);} else if (buffer_type == "serialized") {log_buffer = new SerializedLogBuffer(&reader_list, &log_tags, &log_statistics);} else if (buffer_type == "simple") {log_buffer = new SimpleLogBuffer(&reader_list, &log_tags, &log_statistics);} else {LOG(FATAL) << "buffer_type must be one of 'chatty', 'serialized', or 'simple'";}// LogReader listens on /dev/socket/logdr. When a client// connects, log entries in the LogBuffer are written to the client.LogReader* reader = new LogReader(log_buffer, &reader_list);if (reader->startListener()) {return EXIT_FAILURE;}// LogListener listens on /dev/socket/logdw for client// initiated log messages. New log entries are added to LogBuffer// and LogReader is notified to send updates to connected clients.LogListener* swl = new LogListener(log_buffer);if (!swl->StartListener()) {return EXIT_FAILURE;}// Command listener listens on /dev/socket/logd for incoming logd// administrative commands.CommandListener* cl = new CommandListener(log_buffer, &log_tags, &prune_list, &log_statistics);if (cl->startListener()) {return EXIT_FAILURE;}// LogAudit listens on NETLINK_AUDIT socket for selinux// initiated log messages. New log entries are added to LogBuffer// and LogReader is notified to send updates to connected clients.LogAudit* al = nullptr;if (auditd) {int dmesg_fd = GetBoolProperty("ro.logd.auditd.dmesg", true) ? fdDmesg : -1;al = new LogAudit(log_buffer, dmesg_fd, &log_statistics);}LogKlog* kl = nullptr;if (klogd) {kl = new LogKlog(log_buffer, fdDmesg, fdPmesg, al != nullptr, &log_statistics);}readDmesg(al, kl);// failure is an option ... messages are in dmesg (required by standard)if (kl && kl->startListener()) {delete kl;}if (al && al->startListener()) {delete al;}TEMP_FAILURE_RETRY(pause());return EXIT_SUCCESS;
}

3、LogBuffer缓存大小

3.1 缓存大小优先级设置

1、persist.logd.size.[buffer_name]; 比如buffer_name为main、system、events、crash;
2、ro.logd.size.[buffer_name]
3、persist.logd.size 开发模式中可以设置大小
4、ro.logd.size
5、kLogBufferMinSize = 64 * 1024 默认64k

3.2 缓存大小相关代码位置

system/logging/logd/SerializedLogBuffer.cpp

system/logging/logd/SimpleLogBuffer.cpp

system/logging/logd/ChattyLogBuffer.cpp

system/logging/logd/LogBuffer.h
system/logging/logd/LogSize.cpp

system/logging/liblog/logger_name.cpp