android 6.0 logcat机制（一）java层写log，logd接受log

第一篇博客，讲的主要是c++，java中打印log，然后通过socket传给logd，然后logd是如何处理接受log的。

一、logcat常用命令

 

logcat -c

清除已有log信息

 

logcat -b main 显示主缓冲区的log

logcat -b radio 显示无线缓冲区的log

logcat -b events 显示事件缓冲区的log 

logcat -f [filename] 将log保存到指定的文件中，例如logcat -b radio -f /data/radio.log

比较常用的是显示时间:logcat -v time &

logcat -g 查看缓冲区的大小

  logcat -g main

  logcat -g radio 

  logcat -g events 

logcat打印/dev/log设备下的三个文件radio, events, main数据

logcat默认是输出main、system缓冲区的log

二、java的Log打印

在android的java层的log有几种，比如Log Slog Rlog

我们先来看看其实现：

Slog

public final class Slog {

private Slog() {
}

public static int v(String tag, String msg) {
return Log.println_native(Log.LOG_ID_SYSTEM, Log.VERBOSE, tag, msg);
}

public static int v(String tag, String msg, Throwable tr) {
return Log.println_native(Log.LOG_ID_SYSTEM, Log.VERBOSE, tag,
msg + '\n' + Log.getStackTraceString(tr));
}

public static int d(String tag, String msg) {
return Log.println_native(Log.LOG_ID_SYSTEM, Log.DEBUG, tag, msg);
}


Rlog



public final class Rlog {

private Rlog() {
}

public static int v(String tag, String msg) {
return Log.println_native(Log.LOG_ID_RADIO, Log.VERBOSE, tag, msg);
}

public static int v(String tag, String msg, Throwable tr) {
return Log.println_native(Log.LOG_ID_RADIO, Log.VERBOSE, tag,
msg + '\n' + Log.getStackTraceString(tr));
}

public static int d(String tag, String msg) {
return Log.println_native(Log.LOG_ID_RADIO, Log.DEBUG, tag, msg);
}

Log

private Log() {
}

/**
* Send a {@link #VERBOSE} log message.
* @param tag Used to identify the source of a log message.  It usually identifies
*        the class or activity where the log call occurs.
* @param msg The message you would like logged.
*/
public static int v(String tag, String msg) {
return println_native(LOG_ID_MAIN, VERBOSE, tag, msg);
}

/**
* Send a {@link #VERBOSE} log message and log the exception.
* @param tag Used to identify the source of a log message.  It usually identifies
*        the class or activity where the log call occurs.
* @param msg The message you would like logged.
* @param tr An exception to log
*/
public static int v(String tag, String msg, Throwable tr) {
return println_native(LOG_ID_MAIN, VERBOSE, tag, msg + '\n' + getStackTraceString(tr));
}

最终都是调用了printIn_native只是id不同main，system，radio。

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;

if (msgObj == NULL) {
jniThrowNullPointerException(env, "println needs a message");
return -1;
}

if (bufID < 0 || bufID >= LOG_ID_MAX) {
jniThrowNullPointerException(env, "bad bufID");
return -1;
}

if (tagObj != NULL)
tag = env->GetStringUTFChars(tagObj, NULL);
msg = env->GetStringUTFChars(msgObj, NULL);

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;
}然后又调用了__android_log_buf_write函数，是在system/core/liblog/logd_write.c文件中

int __android_log_buf_write(int bufID, int prio, const char *tag, const char *msg)
{
struct iovec vec[3];
char tmp_tag[32];

if (!tag)
tag = "";

/* XXX: This needs to go! */
if ((bufID != LOG_ID_RADIO) &&
(!strcmp(tag, "HTC_RIL") ||
!strncmp(tag, "RIL", 3) || /* Any log tag with "RIL" as the prefix */
!strncmp(tag, "IMS", 3) || /* Any log tag with "IMS" as the prefix */
!strcmp(tag, "AT") ||
!strcmp(tag, "GSM") ||
!strcmp(tag, "STK") ||
!strcmp(tag, "CDMA") ||
!strcmp(tag, "PHONE") ||
!strcmp(tag, "SMS"))) {
bufID = LOG_ID_RADIO;//这些tag也归类到radio中
/* Inform third party apps/ril/radio.. to use Rlog or RLOG */
snprintf(tmp_tag, sizeof(tmp_tag), "use-Rlog/RLOG-%s", tag);
tag = tmp_tag;
}

#if __BIONIC__
if (prio == ANDROID_LOG_FATAL) {
android_set_abort_message(msg);
}
#endif

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;

return write_to_log(bufID, vec, 3);
}而write_to_log就是__write_to_log_init函数

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

因为这里log库是公用的代码，host target都是也就是有的是pc代码，有的是手机代码共有了

static int __write_to_log_init(log_id_t log_id, struct iovec *vec, size_t nr)
{
#if !defined(_WIN32)
pthread_mutex_lock(&log_init_lock);
#endif

if (write_to_log == __write_to_log_init) {
int ret;

ret = __write_to_log_initialize();//先调用了__write_to_log_initialize
if (ret < 0) {
#if !defined(_WIN32)
pthread_mutex_unlock(&log_init_lock);
#endif
#if (FAKE_LOG_DEVICE == 0)
if (pstore_fd >= 0) {
__write_to_log_daemon(log_id, vec, nr);//然后调用__write_to_log_daemon方法
}
#endif
return ret;
}

write_to_log = __write_to_log_daemon;
}

#if !defined(_WIN32)
pthread_mutex_unlock(&log_init_lock);
#endif

return write_to_log(log_id, vec, nr);
}

上面的函数我们先调用了__write_to_log_initialize函数，然后再调用了__write_to_log_daemon函数

static int __write_to_log_initialize()
{
int i, ret = 0;

#if FAKE_LOG_DEVICE//这个是host才有的
for (i = 0; i < LOG_ID_MAX; i++) {
char buf[sizeof("/dev/log_system")];
snprintf(buf, sizeof(buf), "/dev/log_%s", android_log_id_to_name(i));
log_fds[i] = fakeLogOpen(buf, O_WRONLY);
}
#else
if (pstore_fd < 0) {
pstore_fd = TEMP_FAILURE_RETRY(open("/dev/pmsg0", O_WRONLY));
}

if (logd_fd < 0) {
i = TEMP_FAILURE_RETRY(socket(PF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC, 0));
if (i < 0) {
ret = -errno;
} 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");// 我们的socket

if (TEMP_FAILURE_RETRY(connect(i, (struct sockaddr *)&un,
sizeof(struct sockaddr_un))) < 0) {
ret = -errno;
close(i);
} else {
logd_fd = i;//连接socket成功后，保存在log_fd这个全局变量中
}
}
}
#endif

return ret;
}

上面初始化，我们的socket是dev/socket/logdw，__write_to_log_daemon函数我们就不看了就是往socket写log，而用的就是log_fd这个fd。

三、logd接受socket传过来的log

往socket写之后，又会在哪里接受呢？

答案是logd

我们先看下logd的main函数

在logd的main函数中如下代码：

LogListener *swl = new LogListener(logBuf, reader);
// Backlog and /proc/sys/net/unix/max_dgram_qlen set to large value
if (swl->startListener(300)) {
exit(1);
}我们看下其构造函数，

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

int LogListener::getLogSocket() {
static const char socketName[] = "logdw";
int sock = android_get_control_socket(socketName);

if (sock < 0) {
sock = socket_local_server(socketName,
ANDROID_SOCKET_NAMESPACE_RESERVED,
SOCK_DGRAM);
}

int on = 1;
if (setsockopt(sock, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on)) < 0) {
return -1;
}
return sock;
}

监听的socket为logdw，当有socket数据来的会调用onDataAvailable函数，这个函数我们就不看了，在这个函数中调用了LogBuffer::log函数。

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) {
if ((log_id >= LOG_ID_MAX) || (log_id < 0)) {
return -EINVAL;
}

LogBufferElement *elem = new LogBufferElement(log_id, realtime,//新建一个LogBufferElement对象
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)) {
// Log traffic received to total
pthread_mutex_lock(&mLogElementsLock);
stats.add(elem);//统计信息
stats.subtract(elem);
pthread_mutex_unlock(&mLogElementsLock);
delete elem;
return -EACCES;
}

pthread_mutex_lock(&mLogElementsLock);

// Insert elements in time sorted order if possible
//  NB: if end is region locked, place element at end of list
LogBufferElementCollection::iterator it = mLogElements.end();
LogBufferElementCollection::iterator last = it;
while (last != mLogElements.begin()) {
--it;
if ((*it)->getRealTime() <= realtime) {
break;
}
last = it;
}

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);//将对象插入mLogElements
} else {
mLogElements.insert(last,elem);
}

LogTimeEntry::unlock();
}

stats.add(elem);
maybePrune(log_id);
pthread_mutex_unlock(&mLogElementsLock);

return len;
}

这个函数主要讲log的内容信息封装在LogBufferElement，然后放到mLogElements中，最后调用maybePrune函数。

// Prune at most 10% of the log entries or 256, whichever is less.
//
// mLogElementsLock must be held when this function is called.
void LogBuffer::maybePrune(log_id_t id) {
size_t sizes = stats.sizes(id);//某个id的log个数
unsigned long maxSize = log_buffer_size(id);
if (sizes > maxSize) {
size_t sizeOver = sizes - ((maxSize * 9) / 10);
size_t elements = stats.elements(id);
size_t minElements = elements / 10;
unsigned long pruneRows = elements * sizeOver / sizes;
if (pruneRows <= minElements) {
pruneRows = minElements;
}
if (pruneRows > 256) {
pruneRows = 256;
}
prune(id, pruneRows);
}
}

我们首先看下这个英文注释，如果某个id的log超过了最大值，要删除256或者log总数的10%。

我们再来看看log_buffer_size这个函数，这个函数是某个id的log最大数。

int LogBuffer::setSize(log_id_t id, unsigned long size) {
// Reasonable limits ...
if (!valid_size(size)) {
return -1;
}
pthread_mutex_lock(&mLogElementsLock);
log_buffer_size(id) = size;
pthread_mutex_unlock(&mLogElementsLock);
return 0;
}在setSize函数中初始化，那我们再看看是谁调用了setSize函数

void LogBuffer::init() {
static const char global_tuneable[] = "persist.logd.size"; // Settings App
static const char global_default[] = "ro.logd.size";       // BoardConfig.mk

unsigned long default_size = property_get_size(global_tuneable);//从系统属性中获取默认大小
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);//从系统属性中获取某个log id的大小

if (!property_size) {
snprintf(key, sizeof(key), "%s.%s",
global_default, android_log_id_to_name(i));
property_size = property_get_size(key);
}

if (!property_size) {
property_size = default_size;
}

if (!property_size) {
property_size = LOG_BUFFER_SIZE;//没有设置属性就是这个值，是256k
}

if (setSize(i, property_size)) {
setSize(i, LOG_BUFFER_MIN_SIZE);
}
}
}

获取系统属性的话，是下面这个函数计算出来。系统属性persist.logd.size，或者persist.logd.size.radio等

static unsigned long property_get_size(const char *key) {
char property[PROPERTY_VALUE_MAX];
property_get(key, property, "");

char *cp;
unsigned long value = strtoul(property, &cp, 10);

switch(*cp) {
case 'm':
case 'M':
value *= 1024;
/* FALLTHRU */
case 'k':
case 'K':
value *= 1024;
/* FALLTHRU */
case '\0':
break;

default:
value = 0;
}

if (!valid_size(value)) {
value = 0;
}

return value;
}

最后我们每个log id的最大值都是256k，超过的话就要调用prune删除对应id的log了。

四、总结

最后我们可以通过设置系统属性persist.logd.size来设置每个log id的最大缓存值，或者persist.logd.size.radio设置每个id的最大缓存值。

步骤：

将手机连上电脑并且进入root

setproppersist.logd.size.radio 1024k

reboot 重启

另外可以用getprop | grep logd查看设置的属性是否生效

logcat -g 可以查看每个id 的缓存大小

当然这是通过属性的方法设置，我们还可以通过logcat的命令，logcat -G 10m是设置所有的id的大小，logcat -b radio -G 10m是设置radio的log的缓存大小

在logcat中有如下代码，处理设置缓存大小：

case 'G': {
char *cp;
if (strtoll(optarg, &cp, 0) > 0) {
setLogSize = strtoll(optarg, &cp, 0);
} else {
setLogSize = 0;
}

switch(*cp) {
case 'g':
case 'G':
setLogSize *= 1024;
/* FALLTHRU */
case 'm':
case 'M':
setLogSize *= 1024;
/* FALLTHRU */
case 'k':
case 'K':
setLogSize *= 1024;
/* FALLTHRU */
case '\0':
break;

default:
setLogSize = 0;
}

if (!setLogSize) {
fprintf(stderr, "ERROR: -G <num><multiplier>\n");
return EXIT_FAILURE;
}
}
break;

最终会设置到logd中去，在logcat中调用的是android_logger_set_log_size函数

if (setLogSize && android_logger_set_log_size(dev->logger, setLogSize)) {
logcat_panic(false, "failed to set the log size");
}

最终会调用到到logd中的runCommand中：

int CommandListener::SetBufSizeCmd::runCommand(SocketClient *cli,
int argc, char **argv) {
setname();
if (!clientHasLogCredentials(cli)) {
cli->sendMsg("Permission Denied");
return 0;
}

if (argc < 3) {
cli->sendMsg("Missing Argument");
return 0;
}

int id = atoi(argv[1]);
if ((id < LOG_ID_MIN) || (LOG_ID_MAX <= id)) {
cli->sendMsg("Range Error");
return 0;
}

unsigned long size = atol(argv[2]);
if (mBuf.setSize((log_id_t) id, size)) {
cli->sendMsg("Range Error");
return 0;
}

cli->sendMsg("success");
return 0;
}

最终也会调用到LogBuffer::setSize函数，只是写属性后是永久生效的。