框架
源码
基于Android源码7.1，解读logd的日志记录过程
frameworks/base/core/java/android/util/
- Log.java
- Slog.java
- EventLog.java
frameworks/base/core/jni/android_util_Log.cpp
/system/core/logcat/logcat.cpp
/system/core/liblog/logd_write.c
/system/core/liblog/uio.c
/system/core/logd/
- main.cpp
- LogBuffer.cpp
- LogStatistics.cpp
/system/core/libsysutils/src/SocketListener.cpp
Java
public final class Log {
public static native int println_native(int bufID,
int priority, String tag, String msg);
public static int d(String tag, String msg) {
return println_native(LOG_ID_MAIN, DEBUG, tag, msg);
}
}
Jni
/*
* In class android.util.Log:
* public static native int println_native(int buffer, int priority, String tag, String msg)
*/
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;
}
/*
* JNI registration.
*/
static const JNINativeMethod gMethods[] = {
/* name, signature, funcPtr */
{ "isLoggable", "(Ljava/lang/String;I)Z", (void*) android_util_Log_isLoggable },
{ "println_native", "(IILjava/lang/String;Ljava/lang/String;)I", (void*) android_util_Log_println_native },
{ "logger_entry_max_payload_native", "()I", (void*) android_util_Log_logger_entry_max_payload_native },
};
liblog
logger_write.c
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;
LIBLOG_ABI_PUBLIC int __android_log_buf_write(int bufID, int prio,
const char *tag, const char *msg)
{
---------------------------------------------------------------------------------
return write_to_log(bufID, vec, 3);
}
static int __write_to_log_init(log_id_t log_id, struct iovec *vec, size_t nr)
{
__android_log_lock();
if (write_to_log == __write_to_log_init) {
int ret;
ret = __write_to_log_initialize();
if (ret < 0) {
__android_log_unlock();
if (!list_empty(&__android_log_persist_write)) {
__write_to_log_daemon(log_id, vec, nr);
}
return ret;
}
write_to_log = __write_to_log_daemon;
}
__android_log_unlock();
return write_to_log(log_id, vec, nr);
}
/* log_init_lock assumed */
static int __write_to_log_initialize()
{
}
static int __write_to_log_daemon(log_id_t log_id, struct iovec *vec, size_t nr)
{
}
config_write.c
LIBLOG_HIDDEN void __android_log_config_write() {
#if (FAKE_LOG_DEVICE == 0)
extern struct android_log_transport_write logdLoggerWrite;
extern struct android_log_transport_write pmsgLoggerWrite;
__android_log_add_transport(&__android_log_transport_write, &logdLoggerWrite);
__android_log_add_transport(&__android_log_persist_write, &pmsgLoggerWrite);
#else
extern struct android_log_transport_write fakeLoggerWrite;
__android_log_add_transport(&__android_log_transport_write, &fakeLoggerWrite);
#endif
}
log_write.c
static int logdAvailable(log_id_t LogId);
static int logdOpen();
static void logdClose();
static int logdWrite(log_id_t logId, struct timespec *ts,
struct iovec *vec, size_t nr);
LIBLOG_HIDDEN struct android_log_transport_write logdLoggerWrite = {
.node = { &logdLoggerWrite.node, &logdLoggerWrite.node },
.context.sock = -1,
.name = "logd",
.available = logdAvailable,
.open = logdOpen,
.close = logdClose,
.write = logdWrite,
};
logd
logd.rc
service logd /system/bin/logd
socket logd stream 0666 logd logd
socket logdr seqpacket 0666 logd logd
socket logdw dgram 0222 logd logd
group root system readproc
writepid /dev/cpuset/system-background/tasks
service logd-reinit /system/bin/logd --reinit
oneshot
disabled
writepid /dev/cpuset/system-background/tasks
logcat
总结
