当标签以“IMS“开头时，为什么Logcat不打印日志?

当标签以“IMS"开头时，为什么Logcat不打印日志?

一、 问题描述

为什么Logcat以IMS"开头时Logcat不打印日志?

@Override
public void onClick(View v) {
    switch (v.getId()) {
        case R.id.btnOne:
            System.out.println("Button One log by sout");
            Log.e("IMSfsadfasdfasdf", "log by Log.e()");
            break;
        case R.id.btnTwo:
            System.out.println("Button Two log by sout");
            Log.e("MService", "log by Log.e()");
            break;
    }
}

日志:

04-07 15:05:48.838 4363-4363/com.licheedev.myapplication I/System.out:
Button One log by sout 04-07 15:05:49.916
4363-4363/com.licheedev.myapplication I/System.out: Button Two log by
sout 04-07 15:05:49.916 4363-4363/com.licheedev.myapplication
E/MService: log by Log.e() 04-07 15:05:54.109
4363-4363/com.licheedev.myapplication I/System.out: Button Two log by
sout 04-07 15:05:54.109 4363-4363/com.licheedev.myapplication
E/MService: log by Log.e() 04-07 15:05:54.822
4363-4363/com.licheedev.myapplication I/System.out: Button One log by
sout 04-07 15:05:55.638 4363-4363/com.licheedev.myapplication
I/System.out: Button One log by sout

二、分析

Android 的日志机制中的这行代码有关.这是在函数 __android_log_write(prio, tag, buf);

/* XXX: This needs to go! */
if (!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")) {
        log_id = LOG_ID_RADIO;
        // 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;
}

函数判断了传入参数的合法合理性，进行处理后，将参数打包传递给结构体iovec，同时将bugID，以及打包好的iovec作为参数传递给write_to_log。

要稍微注意下，如果tag包含HTC_RIL, RIL, IMS, AT, GSM, STK, CDMA, PHONE, SMS, （这些都是涉及到radio），就将bugID设置为LOG_ID_RADIO。将不同的类型归属到不同的缓冲区中。

三、解决办法：

方法一：
app中更改打印log的TAG，避免这些字符：HTC_RIL, RIL, IMS, AT, GSM, STK, CDMA, PHONE, SMS

方法二：
使用radio log可以看到对应的log：

抓取Android RIL层 log，在调试Android通信方面的代码时，这个Log非常关键。抓取命令如下：

adb logcat -b radio >e://radio.log