[log] add Android log system support (#2614)

Developers can use the command `ot-ctl log level 5` to change the
default log level to DEBUG. Sometimes, the `ot-daemon` crashes before
developers can run the ot-ctl command on Android.

This commit add Android log system support, so that developers can
run the command `setprop log.tag.ot-daemon DEBUG` to change the log
level before the ot-daemon runs.

src/agent/main.cpp

@@ -55,6 +55,7 @@
 #include "ncp/thread_host.hpp"
 
 #ifdef OTBR_ENABLE_PLATFORM_ANDROID
+#include <log/log.h>
 #ifndef __ANDROID__
 #error "OTBR_ENABLE_PLATFORM_ANDROID can be enabled for only Android devices"
 #endif
@@ -177,16 +178,21 @@ static void OnAllocateFailed(void)
 
 static otbrLogLevel GetDefaultLogLevel(void)
 {
-    otbrLogLevel level = OTBR_LOG_INFO;
-
 #if OTBR_ENABLE_PLATFORM_ANDROID
-    char value[PROPERTY_VALUE_MAX];
+    // The log level is set to DEBUG by default, the final output log will be filtered by Android log system.
+    otbrLogLevel level = OTBR_LOG_DEBUG;
+    char         value[PROPERTY_VALUE_MAX];
+
+    // Set the Android log level to INFO by default.
+    __android_log_set_minimum_priority(ANDROID_LOG_INFO);
 
     property_get("ro.build.type", value, "user");
     if (!strcmp(value, "user"))
     {
         level = OTBR_LOG_WARNING;
     }
+#else
+    otbrLogLevel level = OTBR_LOG_INFO;
 #endif
 
     return level;

src/common/logging.cpp

@@ -44,6 +44,10 @@
 #include <sys/time.h>
 #include <syslog.h>
 
+#if OTBR_ENABLE_PLATFORM_ANDROID
+#include <log/log.h>
+#endif
+
 #include <sstream>
 
 #include "common/code_utils.hpp"
@@ -87,20 +91,25 @@ void otbrLogSyslogSetEnabled(bool aEnabled)
 /** Initialize logging */
 void otbrLogInit(const char *aProgramName, otbrLogLevel aLevel, bool aPrintStderr, bool aSyslogDisable)
 {
-    const char *ident;
-
-    assert(aProgramName != nullptr);
     assert(aLevel >= OTBR_LOG_EMERG && aLevel <= OTBR_LOG_DEBUG);
-
-    ident = strrchr(aProgramName, '/');
-    ident = (ident != nullptr) ? ident + 1 : aProgramName;
-
     otbrLogSyslogSetEnabled(!aSyslogDisable);
 
+#if OTBR_ENABLE_PLATFORM_ANDROID
+    OTBR_UNUSED_VARIABLE(aProgramName);
+#else
+    assert(aProgramName != nullptr);
+
     if (!sSyslogDisabled)
     {
+        const char *ident;
+
+        ident = strrchr(aProgramName, '/');
+        ident = (ident != nullptr) ? ident + 1 : aProgramName;
+
         openlog(ident, (LOG_CONS | LOG_PID) | (aPrintStderr ? LOG_PERROR : 0), OTBR_SYSLOG_FACILITY_ID);
     }
+#endif
+
     sLevel        = aLevel;
     sDefaultLevel = sLevel;
 }
@@ -130,6 +139,38 @@ static const char *GetPrefix(const char *aLogTag)
     return prefix;
 }
 
+#if OTBR_ENABLE_PLATFORM_ANDROID
+static android_LogPriority ConvertToAndroidLogPriority(otbrLogLevel aLevel)
+{
+    android_LogPriority priority;
+
+    switch (aLevel)
+    {
+    case OTBR_LOG_EMERG:
+    case OTBR_LOG_ALERT:
+    case OTBR_LOG_CRIT:
+        priority = ANDROID_LOG_FATAL;
+        break;
+    case OTBR_LOG_ERR:
+        priority = ANDROID_LOG_ERROR;
+        break;
+    case OTBR_LOG_WARNING:
+        priority = ANDROID_LOG_WARN;
+        break;
+    case OTBR_LOG_NOTICE:
+    case OTBR_LOG_INFO:
+        priority = ANDROID_LOG_INFO;
+        break;
+    case OTBR_LOG_DEBUG:
+    default:
+        priority = ANDROID_LOG_DEBUG;
+        break;
+    }
+
+    return priority;
+}
+#endif
+
 /** log to the syslog or standard out */
 void otbrLog(otbrLogLevel aLevel, const char *aLogTag, const char *aFormat, ...)
 {
@@ -147,7 +188,12 @@ void otbrLog(otbrLogLevel aLevel, const char *aLogTag, const char *aFormat, ...)
         }
         else
         {
+#if OTBR_ENABLE_PLATFORM_ANDROID
+            __android_log_print(ConvertToAndroidLogPriority(aLevel), LOG_TAG, "%s%s: %s", sLevelString[aLevel],
+                                GetPrefix(aLogTag), buffer);
+#else
             syslog(static_cast<int>(aLevel), "%s%s: %s", sLevelString[aLevel], GetPrefix(aLogTag), buffer);
+#endif
         }
     }
 
@@ -177,7 +223,11 @@ void otbrLogvNoFilter(otbrLogLevel aLevel, const char *aFormat, va_list aArgList
     }
     else
     {
+#if OTBR_ENABLE_PLATFORM_ANDROID
+        __android_log_vprint(ConvertToAndroidLogPriority(aLevel), LOG_TAG, aFormat, aArgList);
+#else
         vsyslog(static_cast<int>(aLevel), aFormat, aArgList);
+#endif
     }
 }