liblog/fake_log_device.c - platform/system/logging - Gitiles

 /*
  * Copyright (C) 2008 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 /*
  * Intercepts log messages intended for the Android log device.
  * When running in the context of the simulator, the messages are
  * passed on to the underlying (fake) log device.  When not in the
  * simulator, messages are printed to stderr.
  */
 #include "cutils/logd.h"

 #include <stdlib.h>
 #include <string.h>
 #include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>

 #ifdef HAVE_PTHREADS
 #include <pthread.h>
 #endif

 #define kMaxTagLen  16      /* from the long-dead utils/Log.cpp */

 #define kTagSetSize 16      /* arbitrary */

 #if 0
 #define TRACE(...) printf("fake_log_device: " __VA_ARGS__)
 #else
 #define TRACE(...) ((void)0)
 #endif

 /* from the long-dead utils/Log.cpp */
 typedef enum {
     FORMAT_OFF = 0,
     FORMAT_BRIEF,
     FORMAT_PROCESS,
     FORMAT_TAG,
     FORMAT_THREAD,
     FORMAT_RAW,
     FORMAT_TIME,
     FORMAT_THREADTIME,
     FORMAT_LONG
 } LogFormat;


 /*
  * Log driver state.
  */
 typedef struct LogState {
     /* the fake fd that's seen by the user */
     int     fakeFd;

     /* a printable name for this fake device */
     char   *debugName;

     /* nonzero if this is a binary log */
     int     isBinary;

     /* global minimum priority */
     int     globalMinPriority;

     /* output format */
     LogFormat outputFormat;

     /* tags and priorities */
     struct {
         char    tag[kMaxTagLen];
         int     minPriority;
     } tagSet[kTagSetSize];
 } LogState;


 #ifdef HAVE_PTHREADS
 /*
  * Locking.  Since we're emulating a device, we need to be prepared
  * to have multiple callers at the same time.  This lock is used
  * to both protect the fd list and to prevent LogStates from being
  * freed out from under a user.
  */
 static pthread_mutex_t fakeLogDeviceLock = PTHREAD_MUTEX_INITIALIZER;

 static void lock()
 {
     pthread_mutex_lock(&fakeLogDeviceLock);
 }

 static void unlock()
 {
     pthread_mutex_unlock(&fakeLogDeviceLock);
 }
 #else   // !HAVE_PTHREADS
 #define lock() ((void)0)
 #define unlock() ((void)0)
 #endif  // !HAVE_PTHREADS


 /*
  * File descriptor management.
  */
 #define FAKE_FD_BASE 10000
 #define MAX_OPEN_LOGS 16
 static LogState *openLogTable[MAX_OPEN_LOGS];

 /*
  * Allocate an fd and associate a new LogState with it.
  * The fd is available via the fakeFd field of the return value.
  */
 static LogState *createLogState()
 {
     size_t i;

     for (i = 0; i < sizeof(openLogTable); i++) {
         if (openLogTable[i] == NULL) {
             openLogTable[i] = calloc(1, sizeof(LogState));
             openLogTable[i]->fakeFd = FAKE_FD_BASE + i;
             return openLogTable[i];
         }
     }
     return NULL;
 }

 /*
  * Translate an fd to a LogState.
  */
 static LogState *fdToLogState(int fd)
 {
     if (fd >= FAKE_FD_BASE && fd < FAKE_FD_BASE + MAX_OPEN_LOGS) {
         return openLogTable[fd - FAKE_FD_BASE];
     }
     return NULL;
 }

 /*
  * Unregister the fake fd and free the memory it pointed to.
  */
 static void deleteFakeFd(int fd)
 {
     LogState *ls;

     lock();

     ls = fdToLogState(fd);
     if (ls != NULL) {
         openLogTable[fd - FAKE_FD_BASE] = NULL;
         free(ls->debugName);
         free(ls);
     }

     unlock();
 }

 /*
  * Configure logging based on ANDROID_LOG_TAGS environment variable.  We
  * need to parse a string that looks like
  *
  *   *:v jdwp:d dalvikvm:d dalvikvm-gc:i dalvikvmi:i
  *
  * The tag (or '*' for the global level) comes first, followed by a colon
  * and a letter indicating the minimum priority level we're expected to log.
  * This can be used to reveal or conceal logs with specific tags.
  *
  * We also want to check ANDROID_PRINTF_LOG to determine how the output
  * will look.
  */
 static void configureInitialState(const char* pathName, LogState* logState)
 {
     static const int kDevLogLen = sizeof("/dev/log/") - 1;

     logState->debugName = strdup(pathName);

     /* identify binary logs */
     if (strcmp(pathName + kDevLogLen, "events") == 0) {
         logState->isBinary = 1;
     }

     /* global min priority defaults to "info" level */
     logState->globalMinPriority = ANDROID_LOG_INFO;

     /*
      * This is based on the the long-dead utils/Log.cpp code.
      */
     const char* tags = getenv("ANDROID_LOG_TAGS");
     TRACE("Found ANDROID_LOG_TAGS='%s'\n", tags);
     if (tags != NULL) {
         int entry = 0;

         while (*tags != '\0') {
             char tagName[kMaxTagLen];
             int i, minPrio;

             while (isspace(*tags))
                 tags++;

             i = 0;
             while (*tags != '\0' && !isspace(*tags) && *tags != ':' &&
                 i < kMaxTagLen)
             {
                 tagName[i++] = *tags++;
             }
             if (i == kMaxTagLen) {
                 TRACE("ERROR: env tag too long (%d chars max)\n", kMaxTagLen-1);
                 return;
             }
             tagName[i] = '\0';

             /* default priority, if there's no ":" part; also zero out '*' */
             minPrio = ANDROID_LOG_VERBOSE;
             if (tagName[0] == '*' && tagName[1] == '\0') {
                 minPrio = ANDROID_LOG_DEBUG;
                 tagName[0] = '\0';
             }

             if (*tags == ':') {
                 tags++;
                 if (*tags >= '0' && *tags <= '9') {
                     if (*tags >= ('0' + ANDROID_LOG_SILENT))
                         minPrio = ANDROID_LOG_VERBOSE;
                     else
                         minPrio = *tags - '\0';
                 } else {
                     switch (*tags) {
                     case 'v':   minPrio = ANDROID_LOG_VERBOSE;  break;
                     case 'd':   minPrio = ANDROID_LOG_DEBUG;    break;
                     case 'i':   minPrio = ANDROID_LOG_INFO;     break;
                     case 'w':   minPrio = ANDROID_LOG_WARN;     break;
                     case 'e':   minPrio = ANDROID_LOG_ERROR;    break;
                     case 'f':   minPrio = ANDROID_LOG_FATAL;    break;
                     case 's':   minPrio = ANDROID_LOG_SILENT;   break;
                     default:    minPrio = ANDROID_LOG_DEFAULT;  break;
                     }
                 }

                 tags++;
                 if (*tags != '\0' && !isspace(*tags)) {
                     TRACE("ERROR: garbage in tag env; expected whitespace\n");
                     TRACE("       env='%s'\n", tags);
                     return;
                 }
             }

             if (tagName[0] == 0) {
                 logState->globalMinPriority = minPrio;
                 TRACE("+++ global min prio %d\n", logState->globalMinPriority);
             } else {
                 logState->tagSet[entry].minPriority = minPrio;
                 strcpy(logState->tagSet[entry].tag, tagName);
                 TRACE("+++ entry %d: %s:%d\n",
                     entry,
                     logState->tagSet[entry].tag,
                     logState->tagSet[entry].minPriority);
                 entry++;
             }
         }
     }


     /*
      * Taken from the long-dead utils/Log.cpp
      */
     const char* fstr = getenv("ANDROID_PRINTF_LOG");
     LogFormat format;
     if (fstr == NULL) {
         format = FORMAT_BRIEF;
     } else {
         if (strcmp(fstr, "brief") == 0)
             format = FORMAT_BRIEF;
         else if (strcmp(fstr, "process") == 0)
             format = FORMAT_PROCESS;
         else if (strcmp(fstr, "tag") == 0)
             format = FORMAT_PROCESS;
         else if (strcmp(fstr, "thread") == 0)
             format = FORMAT_PROCESS;
         else if (strcmp(fstr, "raw") == 0)
             format = FORMAT_PROCESS;
         else if (strcmp(fstr, "time") == 0)
             format = FORMAT_PROCESS;
         else if (strcmp(fstr, "long") == 0)
             format = FORMAT_PROCESS;
         else
             format = (LogFormat) atoi(fstr);        // really?!
     }

     logState->outputFormat = format;
 }

 /*
  * Return a human-readable string for the priority level.  Always returns
  * a valid string.
  */
 static const char* getPriorityString(int priority)
 {
     /* the first character of each string should be unique */
     static const char* priorityStrings[] = {
         "Verbose", "Debug", "Info", "Warn", "Error", "Assert"
     };
     int idx;

     idx = (int) priority - (int) ANDROID_LOG_VERBOSE;
     if (idx < 0 ||
         idx >= (int) (sizeof(priorityStrings) / sizeof(priorityStrings[0])))
         return "?unknown?";
     return priorityStrings[idx];
 }

 #ifndef HAVE_WRITEV
 /*
  * Some platforms like WIN32 do not have writev().
  * Make up something to replace it.
  */
 static ssize_t fake_writev(int fd, const struct iovec *iov, int iovcnt) {
     int result = 0;
     struct iovec* end = iov + iovcnt;
     for (; iov < end; iov++) {
         int w = write(fd, iov->iov_base, iov->iov_len);
         if (w != iov->iov_len) {
             if (w < 0)
                 return w;
             return result + w;
         }
         result += w;
     }
     return result;
 }

 #define writev fake_writev
 #endif


 /*
  * Write a filtered log message to stderr.
  *
  * Log format parsing taken from the long-dead utils/Log.cpp.
  */
 static void showLog(LogState *state,
         int logPrio, const char* tag, const char* msg)
 {
 #if defined(HAVE_LOCALTIME_R)
     struct tm tmBuf;
 #endif
     struct tm* ptm;
     char timeBuf[32];
     char prefixBuf[128], suffixBuf[128];
     char priChar;
     time_t when;
     pid_t pid, tid;

     TRACE("LOG %d: %s %s", logPrio, tag, msg);

     priChar = getPriorityString(logPrio)[0];
     when = time(NULL);
     pid = tid = getpid();       // find gettid()?

     /*
      * Get the current date/time in pretty form
      *
      * It's often useful when examining a log with "less" to jump to
      * a specific point in the file by searching for the date/time stamp.
      * For this reason it's very annoying to have regexp meta characters
      * in the time stamp.  Don't use forward slashes, parenthesis,
      * brackets, asterisks, or other special chars here.
      */
 #if defined(HAVE_LOCALTIME_R)
     ptm = localtime_r(&when, &tmBuf);
 #else
     ptm = localtime(&when);
 #endif
     //strftime(timeBuf, sizeof(timeBuf), "%Y-%m-%d %H:%M:%S", ptm);
     strftime(timeBuf, sizeof(timeBuf), "%m-%d %H:%M:%S", ptm);

     /*
      * Construct a buffer containing the log header and log message.
      */
     size_t prefixLen, suffixLen;

     switch (state->outputFormat) {
     case FORMAT_TAG:
         prefixLen = snprintf(prefixBuf, sizeof(prefixBuf),
             "%c/%-8s: ", priChar, tag);
         strcpy(suffixBuf, "\n"); suffixLen = 1;
         break;
     case FORMAT_PROCESS:
         prefixLen = snprintf(prefixBuf, sizeof(prefixBuf),
             "%c(%5d) ", priChar, pid);
         suffixLen = snprintf(suffixBuf, sizeof(suffixBuf),
             "  (%s)\n", tag);
         break;
     case FORMAT_THREAD:
         prefixLen = snprintf(prefixBuf, sizeof(prefixBuf),
             "%c(%5d:%p) ", priChar, pid, (void*)tid);
         strcpy(suffixBuf, "\n"); suffixLen = 1;
         break;
     case FORMAT_RAW:
         prefixBuf[0] = 0; prefixLen = 0;
         strcpy(suffixBuf, "\n"); suffixLen = 1;
         break;
     case FORMAT_TIME:
         prefixLen = snprintf(prefixBuf, sizeof(prefixBuf),
             "%s %-8s\n\t", timeBuf, tag);
         strcpy(suffixBuf, "\n"); suffixLen = 1;
         break;
     case FORMAT_THREADTIME:
         prefixLen = snprintf(prefixBuf, sizeof(prefixBuf),
             "%s %5d %5d %c %-8s \n\t", timeBuf, pid, tid, priChar, tag);
         strcpy(suffixBuf, "\n"); suffixLen = 1;
         break;
     case FORMAT_LONG:
         prefixLen = snprintf(prefixBuf, sizeof(prefixBuf),
             "[ %s %5d:%p %c/%-8s ]\n",
             timeBuf, pid, (void*)tid, priChar, tag);
         strcpy(suffixBuf, "\n\n"); suffixLen = 2;
         break;
     default:
         prefixLen = snprintf(prefixBuf, sizeof(prefixBuf),
             "%c/%-8s(%5d): ", priChar, tag, pid);
         strcpy(suffixBuf, "\n"); suffixLen = 1;
         break;
      }

     /*
      * Figure out how many lines there will be.
      */
     const char* end = msg + strlen(msg);
     size_t numLines = 0;
     const char* p = msg;
     while (p < end) {
         if (*p++ == '\n') numLines++;
     }
     if (p > msg && *(p-1) != '\n') numLines++;

     /*
      * Create an array of iovecs large enough to write all of
      * the lines with a prefix and a suffix.
      */
     const size_t INLINE_VECS = 6;
     const size_t MAX_LINES   = ((size_t)~0)/(3*sizeof(struct iovec*));
     struct iovec stackVec[INLINE_VECS];
     struct iovec* vec = stackVec;
     size_t numVecs;

     if (numLines > MAX_LINES)
         numLines = MAX_LINES;

     numVecs = numLines*3;  // 3 iovecs per line.
     if (numVecs > INLINE_VECS) {
         vec = (struct iovec*)malloc(sizeof(struct iovec)*numLines);
         if (vec == NULL) {
             msg = "LOG: write failed, no memory";
             numVecs = 3;
             numLines = 1;
             vec = stackVec;
         }
     }

     /*
      * Fill in the iovec pointers.
      */
     p = msg;
     struct iovec* v = vec;
     int totalLen = 0;
     while (numLines > 0 && p < end) {
         if (prefixLen > 0) {
             v->iov_base = prefixBuf;
             v->iov_len = prefixLen;
             totalLen += prefixLen;
             v++;
         }
         const char* start = p;
         while (p < end && *p != '\n') p++;
         if ((p-start) > 0) {
             v->iov_base = (void*)start;
             v->iov_len = p-start;
             totalLen += p-start;
             v++;
         }
         if (*p == '\n') p++;
         if (suffixLen > 0) {
             v->iov_base = suffixBuf;
             v->iov_len = suffixLen;
             totalLen += suffixLen;
             v++;
         }
         numLines -= 1;
     }

     /*
      * Write the entire message to the log file with a single writev() call.
      * We need to use this rather than a collection of printf()s on a FILE*
      * because of multi-threading and multi-process issues.
      *
      * If the file was not opened with O_APPEND, this will produce interleaved
      * output when called on the same file from multiple processes.
      *
      * If the file descriptor is actually a network socket, the writev()
      * call may return with a partial write.  Putting the writev() call in
      * a loop can result in interleaved data.  This can be alleviated
      * somewhat by wrapping the writev call in the Mutex.
      */

     for(;;) {
         int cc = writev(fileno(stderr), vec, v-vec);

         if (cc == totalLen) break;

         if (cc < 0) {
             if(errno == EINTR) continue;

                 /* can't really log the failure; for now, throw out a stderr */
             fprintf(stderr, "+++ LOG: write failed (errno=%d)\n", errno);
             break;
         } else {
                 /* shouldn't happen when writing to file or tty */
             fprintf(stderr, "+++ LOG: write partial (%d of %d)\n", cc, totalLen);
             break;
         }
     }

     /* if we allocated storage for the iovecs, free it */
     if (vec != stackVec)
         free(vec);
 }


 /*
  * Receive a log message.  We happen to know that "vector" has three parts:
  *
  *  priority (1 byte)
  *  tag (N bytes -- null-terminated ASCII string)
  *  message (N bytes -- null-terminated ASCII string)
  */
 static ssize_t logWritev(int fd, const struct iovec* vector, int count)
 {
     LogState* state;

     /* Make sure that no-one frees the LogState while we're using it.
      * Also guarantees that only one thread is in showLog() at a given
      * time (if it matters).
      */
     lock();

     state = fdToLogState(fd);
     if (state == NULL) {
         errno = EBADF;
         goto error;
     }

     if (state->isBinary) {
         TRACE("%s: ignoring binary log\n", state->debugName);
         goto bail;
     }

     if (count != 3) {
         TRACE("%s: writevLog with count=%d not expected\n",
             state->debugName, count);
         goto error;
     }

     /* pull out the three fields */
     int logPrio = *(const char*)vector[0].iov_base;
     const char* tag = (const char*) vector[1].iov_base;
     const char* msg = (const char*) vector[2].iov_base;

     /* see if this log tag is configured */
     int i;
     int minPrio = state->globalMinPriority;
     for (i = 0; i < kTagSetSize; i++) {
         if (state->tagSet[i].minPriority == ANDROID_LOG_UNKNOWN)
             break;      /* reached end of configured values */

         if (strcmp(state->tagSet[i].tag, tag) == 0) {
             //TRACE("MATCH tag '%s'\n", tag);
             minPrio = state->tagSet[i].minPriority;
             break;
         }
     }

     if (logPrio >= minPrio) {
         showLog(state, logPrio, tag, msg);
     } else {
         //TRACE("+++ NOLOG(%d): %s %s", logPrio, tag, msg);
     }

 bail:
     unlock();
     return vector[0].iov_len + vector[1].iov_len + vector[2].iov_len;
 error:
     unlock();
     return -1;
 }

 /*
  * Free up our state and close the fake descriptor.
  */
 static int logClose(int fd)
 {
     deleteFakeFd(fd);
     return 0;
 }

 /*
  * Open a log output device and return a fake fd.
  */
 static int logOpen(const char* pathName, int flags)
 {
     LogState *logState;
     int fd = -1;

     lock();

     logState = createLogState();
     if (logState != NULL) {
         configureInitialState(pathName, logState);
         fd = logState->fakeFd;
     } else  {
         errno = ENFILE;
     }

     unlock();

     return fd;
 }


 /*
  * Runtime redirection.  If this binary is running in the simulator,
  * just pass log messages to the emulated device.  If it's running
  * outside of the simulator, write the log messages to stderr.
  */

 static int (*redirectOpen)(const char *pathName, int flags) = NULL;
 static int (*redirectClose)(int fd) = NULL;
 static ssize_t (*redirectWritev)(int fd, const struct iovec* vector, int count)
         = NULL;

 static void setRedirects()
 {
     const char *ws;

     /* Wrapsim sets this environment variable on children that it's
      * created using its LD_PRELOAD wrapper.
      */
     ws = getenv("ANDROID_WRAPSIM");
     if (ws != NULL && strcmp(ws, "1") == 0) {
         /* We're running inside wrapsim, so we can just write to the device. */
         redirectOpen = (int (*)(const char *pathName, int flags))open;
         redirectClose = close;
         redirectWritev = writev;
     } else {
         /* There's no device to delegate to; handle the logging ourselves. */
         redirectOpen = logOpen;
         redirectClose = logClose;
         redirectWritev = logWritev;
     }
 }

 int fakeLogOpen(const char *pathName, int flags)
 {
     if (redirectOpen == NULL) {
         setRedirects();
     }
     return redirectOpen(pathName, flags);
 }

 int fakeLogClose(int fd)
 {
     /* Assume that open() was called first. */
     return redirectClose(fd);
 }

 ssize_t fakeLogWritev(int fd, const struct iovec* vector, int count)
 {
     /* Assume that open() was called first. */
     return redirectWritev(fd, vector, count);
 }
	/*
	* Copyright (C) 2008 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/
	/*
	* Intercepts log messages intended for the Android log device.
	* When running in the context of the simulator, the messages are
	* passed on to the underlying (fake) log device. When not in the
	* simulator, messages are printed to stderr.
	*/
	#include "cutils/logd.h"

	#include <stdlib.h>
	#include <string.h>
	#include <ctype.h>
	#include <errno.h>
	#include <fcntl.h>

	#ifdef HAVE_PTHREADS
	#include <pthread.h>
	#endif

	#define kMaxTagLen 16 /* from the long-dead utils/Log.cpp */

	#define kTagSetSize 16 /* arbitrary */

	#if 0
	#define TRACE(...) printf("fake_log_device: " __VA_ARGS__)
	#else
	#define TRACE(...) ((void)0)
	#endif

	/* from the long-dead utils/Log.cpp */
	typedef enum {
	FORMAT_OFF = 0,
	FORMAT_BRIEF,
	FORMAT_PROCESS,
	FORMAT_TAG,
	FORMAT_THREAD,
	FORMAT_RAW,
	FORMAT_TIME,
	FORMAT_THREADTIME,
	FORMAT_LONG
	} LogFormat;


	/*
	* Log driver state.
	*/
	typedef struct LogState {
	/* the fake fd that's seen by the user */
	int fakeFd;

	/* a printable name for this fake device */
	char *debugName;

	/* nonzero if this is a binary log */
	int isBinary;

	/* global minimum priority */
	int globalMinPriority;

	/* output format */
	LogFormat outputFormat;

	/* tags and priorities */
	struct {
	char tag[kMaxTagLen];
	int minPriority;
	} tagSet[kTagSetSize];
	} LogState;


	#ifdef HAVE_PTHREADS
	/*
	* Locking. Since we're emulating a device, we need to be prepared
	* to have multiple callers at the same time. This lock is used
	* to both protect the fd list and to prevent LogStates from being
	* freed out from under a user.
	*/
	static pthread_mutex_t fakeLogDeviceLock = PTHREAD_MUTEX_INITIALIZER;

	static void lock()
	{
	pthread_mutex_lock(&fakeLogDeviceLock);
	}

	static void unlock()
	{
	pthread_mutex_unlock(&fakeLogDeviceLock);
	}
	#else // !HAVE_PTHREADS
	#define lock() ((void)0)
	#define unlock() ((void)0)
	#endif // !HAVE_PTHREADS


	/*
	* File descriptor management.
	*/
	#define FAKE_FD_BASE 10000
	#define MAX_OPEN_LOGS 16
	static LogState *openLogTable[MAX_OPEN_LOGS];

	/*
	* Allocate an fd and associate a new LogState with it.
	* The fd is available via the fakeFd field of the return value.
	*/
	static LogState *createLogState()
	{
	size_t i;

	for (i = 0; i < sizeof(openLogTable); i++) {
	if (openLogTable[i] == NULL) {
	openLogTable[i] = calloc(1, sizeof(LogState));
	openLogTable[i]->fakeFd = FAKE_FD_BASE + i;
	return openLogTable[i];
	}
	}
	return NULL;
	}

	/*
	* Translate an fd to a LogState.
	*/
	static LogState *fdToLogState(int fd)
	{
	if (fd >= FAKE_FD_BASE && fd < FAKE_FD_BASE + MAX_OPEN_LOGS) {
	return openLogTable[fd - FAKE_FD_BASE];
	}
	return NULL;
	}

	/*
	* Unregister the fake fd and free the memory it pointed to.
	*/
	static void deleteFakeFd(int fd)
	{
	LogState *ls;

	lock();

	ls = fdToLogState(fd);
	if (ls != NULL) {
	openLogTable[fd - FAKE_FD_BASE] = NULL;
	free(ls->debugName);
	free(ls);
	}

	unlock();
	}

	/*
	* Configure logging based on ANDROID_LOG_TAGS environment variable. We
	* need to parse a string that looks like
	*
	* *:v jdwp:d dalvikvm:d dalvikvm-gc:i dalvikvmi:i
	*
	* The tag (or '*' for the global level) comes first, followed by a colon
	* and a letter indicating the minimum priority level we're expected to log.
	* This can be used to reveal or conceal logs with specific tags.
	*
	* We also want to check ANDROID_PRINTF_LOG to determine how the output
	* will look.
	*/
	static void configureInitialState(const char* pathName, LogState* logState)
	{
	static const int kDevLogLen = sizeof("/dev/log/") - 1;

	logState->debugName = strdup(pathName);

	/* identify binary logs */
	if (strcmp(pathName + kDevLogLen, "events") == 0) {
	logState->isBinary = 1;
	}

	/* global min priority defaults to "info" level */
	logState->globalMinPriority = ANDROID_LOG_INFO;

	/*
	* This is based on the the long-dead utils/Log.cpp code.
	*/
	const char* tags = getenv("ANDROID_LOG_TAGS");
	TRACE("Found ANDROID_LOG_TAGS='%s'\n", tags);
	if (tags != NULL) {
	int entry = 0;

	while (*tags != '\0') {
	char tagName[kMaxTagLen];
	int i, minPrio;

	while (isspace(*tags))
	tags++;

	i = 0;
	while (tags != '\0' && !isspace(tags) && *tags != ':' &&
	i < kMaxTagLen)
	{
	tagName[i++] = *tags++;
	}
	if (i == kMaxTagLen) {
	TRACE("ERROR: env tag too long (%d chars max)\n", kMaxTagLen-1);
	return;
	}
	tagName[i] = '\0';

	/* default priority, if there's no ":" part; also zero out '' /
	minPrio = ANDROID_LOG_VERBOSE;
	if (tagName[0] == '*' && tagName[1] == '\0') {
	minPrio = ANDROID_LOG_DEBUG;
	tagName[0] = '\0';
	}

	if (*tags == ':') {
	tags++;
	if (tags >= '0' && tags <= '9') {
	if (*tags >= ('0' + ANDROID_LOG_SILENT))
	minPrio = ANDROID_LOG_VERBOSE;
	else
	minPrio = *tags - '\0';
	} else {
	switch (*tags) {
	case 'v': minPrio = ANDROID_LOG_VERBOSE; break;
	case 'd': minPrio = ANDROID_LOG_DEBUG; break;
	case 'i': minPrio = ANDROID_LOG_INFO; break;
	case 'w': minPrio = ANDROID_LOG_WARN; break;
	case 'e': minPrio = ANDROID_LOG_ERROR; break;
	case 'f': minPrio = ANDROID_LOG_FATAL; break;
	case 's': minPrio = ANDROID_LOG_SILENT; break;
	default: minPrio = ANDROID_LOG_DEFAULT; break;
	}
	}

	tags++;
	if (tags != '\0' && !isspace(tags)) {
	TRACE("ERROR: garbage in tag env; expected whitespace\n");
	TRACE(" env='%s'\n", tags);
	return;
	}
	}

	if (tagName[0] == 0) {
	logState->globalMinPriority = minPrio;
	TRACE("+++ global min prio %d\n", logState->globalMinPriority);
	} else {
	logState->tagSet[entry].minPriority = minPrio;
	strcpy(logState->tagSet[entry].tag, tagName);
	TRACE("+++ entry %d: %s:%d\n",
	entry,
	logState->tagSet[entry].tag,
	logState->tagSet[entry].minPriority);
	entry++;
	}
	}
	}


	/*
	* Taken from the long-dead utils/Log.cpp
	*/
	const char* fstr = getenv("ANDROID_PRINTF_LOG");
	LogFormat format;
	if (fstr == NULL) {
	format = FORMAT_BRIEF;
	} else {
	if (strcmp(fstr, "brief") == 0)
	format = FORMAT_BRIEF;
	else if (strcmp(fstr, "process") == 0)
	format = FORMAT_PROCESS;
	else if (strcmp(fstr, "tag") == 0)
	format = FORMAT_PROCESS;
	else if (strcmp(fstr, "thread") == 0)
	format = FORMAT_PROCESS;
	else if (strcmp(fstr, "raw") == 0)
	format = FORMAT_PROCESS;
	else if (strcmp(fstr, "time") == 0)
	format = FORMAT_PROCESS;
	else if (strcmp(fstr, "long") == 0)
	format = FORMAT_PROCESS;
	else
	format = (LogFormat) atoi(fstr); // really?!
	}

	logState->outputFormat = format;
	}

	/*
	* Return a human-readable string for the priority level. Always returns
	* a valid string.
	*/
	static const char* getPriorityString(int priority)
	{
	/* the first character of each string should be unique */
	static const char* priorityStrings[] = {
	"Verbose", "Debug", "Info", "Warn", "Error", "Assert"
	};
	int idx;

	idx = (int) priority - (int) ANDROID_LOG_VERBOSE;
	if (idx < 0 \|\|
	idx >= (int) (sizeof(priorityStrings) / sizeof(priorityStrings[0])))
	return "?unknown?";
	return priorityStrings[idx];
	}

	#ifndef HAVE_WRITEV
	/*
	* Some platforms like WIN32 do not have writev().
	* Make up something to replace it.
	*/
	static ssize_t fake_writev(int fd, const struct iovec *iov, int iovcnt) {
	int result = 0;
	struct iovec* end = iov + iovcnt;
	for (; iov < end; iov++) {
	int w = write(fd, iov->iov_base, iov->iov_len);
	if (w != iov->iov_len) {
	if (w < 0)
	return w;
	return result + w;
	}
	result += w;
	}
	return result;
	}

	#define writev fake_writev
	#endif


	/*
	* Write a filtered log message to stderr.
	*
	* Log format parsing taken from the long-dead utils/Log.cpp.
	*/
	static void showLog(LogState *state,
	int logPrio, const char* tag, const char* msg)
	{
	#if defined(HAVE_LOCALTIME_R)
	struct tm tmBuf;
	#endif
	struct tm* ptm;
	char timeBuf[32];
	char prefixBuf[128], suffixBuf[128];
	char priChar;
	time_t when;
	pid_t pid, tid;

	TRACE("LOG %d: %s %s", logPrio, tag, msg);

	priChar = getPriorityString(logPrio)[0];
	when = time(NULL);
	pid = tid = getpid(); // find gettid()?

	/*
	* Get the current date/time in pretty form
	*
	* It's often useful when examining a log with "less" to jump to
	* a specific point in the file by searching for the date/time stamp.
	* For this reason it's very annoying to have regexp meta characters
	* in the time stamp. Don't use forward slashes, parenthesis,
	* brackets, asterisks, or other special chars here.
	*/
	#if defined(HAVE_LOCALTIME_R)
	ptm = localtime_r(&when, &tmBuf);
	#else
	ptm = localtime(&when);
	#endif
	//strftime(timeBuf, sizeof(timeBuf), "%Y-%m-%d %H:%M:%S", ptm);
	strftime(timeBuf, sizeof(timeBuf), "%m-%d %H:%M:%S", ptm);

	/*
	* Construct a buffer containing the log header and log message.
	*/
	size_t prefixLen, suffixLen;

	switch (state->outputFormat) {
	case FORMAT_TAG:
	prefixLen = snprintf(prefixBuf, sizeof(prefixBuf),
	"%c/%-8s: ", priChar, tag);
	strcpy(suffixBuf, "\n"); suffixLen = 1;
	break;
	case FORMAT_PROCESS:
	prefixLen = snprintf(prefixBuf, sizeof(prefixBuf),
	"%c(%5d) ", priChar, pid);
	suffixLen = snprintf(suffixBuf, sizeof(suffixBuf),
	" (%s)\n", tag);
	break;
	case FORMAT_THREAD:
	prefixLen = snprintf(prefixBuf, sizeof(prefixBuf),
	"%c(%5d:%p) ", priChar, pid, (void*)tid);
	strcpy(suffixBuf, "\n"); suffixLen = 1;
	break;
	case FORMAT_RAW:
	prefixBuf[0] = 0; prefixLen = 0;
	strcpy(suffixBuf, "\n"); suffixLen = 1;
	break;
	case FORMAT_TIME:
	prefixLen = snprintf(prefixBuf, sizeof(prefixBuf),
	"%s %-8s\n\t", timeBuf, tag);
	strcpy(suffixBuf, "\n"); suffixLen = 1;
	break;
	case FORMAT_THREADTIME:
	prefixLen = snprintf(prefixBuf, sizeof(prefixBuf),
	"%s %5d %5d %c %-8s \n\t", timeBuf, pid, tid, priChar, tag);
	strcpy(suffixBuf, "\n"); suffixLen = 1;
	break;
	case FORMAT_LONG:
	prefixLen = snprintf(prefixBuf, sizeof(prefixBuf),
	"[ %s %5d:%p %c/%-8s ]\n",
	timeBuf, pid, (void*)tid, priChar, tag);
	strcpy(suffixBuf, "\n\n"); suffixLen = 2;
	break;
	default:
	prefixLen = snprintf(prefixBuf, sizeof(prefixBuf),
	"%c/%-8s(%5d): ", priChar, tag, pid);
	strcpy(suffixBuf, "\n"); suffixLen = 1;
	break;
	}

	/*
	* Figure out how many lines there will be.
	*/
	const char* end = msg + strlen(msg);
	size_t numLines = 0;
	const char* p = msg;
	while (p < end) {
	if (*p++ == '\n') numLines++;
	}
	if (p > msg && *(p-1) != '\n') numLines++;

	/*
	* Create an array of iovecs large enough to write all of
	* the lines with a prefix and a suffix.
	*/
	const size_t INLINE_VECS = 6;
	const size_t MAX_LINES = ((size_t)~0)/(3sizeof(struct iovec));
	struct iovec stackVec[INLINE_VECS];
	struct iovec* vec = stackVec;
	size_t numVecs;

	if (numLines > MAX_LINES)
	numLines = MAX_LINES;

	numVecs = numLines*3; // 3 iovecs per line.
	if (numVecs > INLINE_VECS) {
	vec = (struct iovec)malloc(sizeof(struct iovec)numLines);
	if (vec == NULL) {
	msg = "LOG: write failed, no memory";
	numVecs = 3;
	numLines = 1;
	vec = stackVec;
	}
	}

	/*
	* Fill in the iovec pointers.
	*/
	p = msg;
	struct iovec* v = vec;
	int totalLen = 0;
	while (numLines > 0 && p < end) {
	if (prefixLen > 0) {
	v->iov_base = prefixBuf;
	v->iov_len = prefixLen;
	totalLen += prefixLen;
	v++;
	}
	const char* start = p;
	while (p < end && *p != '\n') p++;
	if ((p-start) > 0) {
	v->iov_base = (void*)start;
	v->iov_len = p-start;
	totalLen += p-start;
	v++;
	}
	if (*p == '\n') p++;
	if (suffixLen > 0) {
	v->iov_base = suffixBuf;
	v->iov_len = suffixLen;
	totalLen += suffixLen;
	v++;
	}
	numLines -= 1;
	}

	/*
	* Write the entire message to the log file with a single writev() call.
	* We need to use this rather than a collection of printf()s on a FILE*
	* because of multi-threading and multi-process issues.
	*
	* If the file was not opened with O_APPEND, this will produce interleaved
	* output when called on the same file from multiple processes.
	*
	* If the file descriptor is actually a network socket, the writev()
	* call may return with a partial write. Putting the writev() call in
	* a loop can result in interleaved data. This can be alleviated
	* somewhat by wrapping the writev call in the Mutex.
	*/

	for(;;) {
	int cc = writev(fileno(stderr), vec, v-vec);

	if (cc == totalLen) break;

	if (cc < 0) {
	if(errno == EINTR) continue;

	/* can't really log the failure; for now, throw out a stderr */
	fprintf(stderr, "+++ LOG: write failed (errno=%d)\n", errno);
	break;
	} else {
	/* shouldn't happen when writing to file or tty */
	fprintf(stderr, "+++ LOG: write partial (%d of %d)\n", cc, totalLen);
	break;
	}
	}

	/* if we allocated storage for the iovecs, free it */
	if (vec != stackVec)
	free(vec);
	}


	/*
	* Receive a log message. We happen to know that "vector" has three parts:
	*
	* priority (1 byte)
	* tag (N bytes -- null-terminated ASCII string)
	* message (N bytes -- null-terminated ASCII string)
	*/
	static ssize_t logWritev(int fd, const struct iovec* vector, int count)
	{
	LogState* state;

	/* Make sure that no-one frees the LogState while we're using it.
	* Also guarantees that only one thread is in showLog() at a given
	* time (if it matters).
	*/
	lock();

	state = fdToLogState(fd);
	if (state == NULL) {
	errno = EBADF;
	goto error;
	}

	if (state->isBinary) {
	TRACE("%s: ignoring binary log\n", state->debugName);
	goto bail;
	}

	if (count != 3) {
	TRACE("%s: writevLog with count=%d not expected\n",
	state->debugName, count);
	goto error;
	}

	/* pull out the three fields */
	int logPrio = (const char)vector[0].iov_base;
	const char* tag = (const char*) vector[1].iov_base;
	const char* msg = (const char*) vector[2].iov_base;

	/* see if this log tag is configured */
	int i;
	int minPrio = state->globalMinPriority;
	for (i = 0; i < kTagSetSize; i++) {
	if (state->tagSet[i].minPriority == ANDROID_LOG_UNKNOWN)
	break; /* reached end of configured values */

	if (strcmp(state->tagSet[i].tag, tag) == 0) {
	//TRACE("MATCH tag '%s'\n", tag);
	minPrio = state->tagSet[i].minPriority;
	break;
	}
	}

	if (logPrio >= minPrio) {
	showLog(state, logPrio, tag, msg);
	} else {
	//TRACE("+++ NOLOG(%d): %s %s", logPrio, tag, msg);
	}

	bail:
	unlock();
	return vector[0].iov_len + vector[1].iov_len + vector[2].iov_len;
	error:
	unlock();
	return -1;
	}

	/*
	* Free up our state and close the fake descriptor.
	*/
	static int logClose(int fd)
	{
	deleteFakeFd(fd);
	return 0;
	}

	/*
	* Open a log output device and return a fake fd.
	*/
	static int logOpen(const char* pathName, int flags)
	{
	LogState *logState;
	int fd = -1;

	lock();

	logState = createLogState();
	if (logState != NULL) {
	configureInitialState(pathName, logState);
	fd = logState->fakeFd;
	} else {
	errno = ENFILE;
	}

	unlock();

	return fd;
	}


	/*
	* Runtime redirection. If this binary is running in the simulator,
	* just pass log messages to the emulated device. If it's running
	* outside of the simulator, write the log messages to stderr.
	*/

	static int (redirectOpen)(const char pathName, int flags) = NULL;
	static int (*redirectClose)(int fd) = NULL;
	static ssize_t (redirectWritev)(int fd, const struct iovec vector, int count)
	= NULL;

	static void setRedirects()
	{
	const char *ws;

	/* Wrapsim sets this environment variable on children that it's
	* created using its LD_PRELOAD wrapper.
	*/
	ws = getenv("ANDROID_WRAPSIM");
	if (ws != NULL && strcmp(ws, "1") == 0) {
	/* We're running inside wrapsim, so we can just write to the device. */
	redirectOpen = (int ()(const char pathName, int flags))open;
	redirectClose = close;
	redirectWritev = writev;
	} else {
	/* There's no device to delegate to; handle the logging ourselves. */
	redirectOpen = logOpen;
	redirectClose = logClose;
	redirectWritev = logWritev;
	}
	}

	int fakeLogOpen(const char *pathName, int flags)
	{
	if (redirectOpen == NULL) {
	setRedirects();
	}
	return redirectOpen(pathName, flags);
	}

	int fakeLogClose(int fd)
	{
	/* Assume that open() was called first. */
	return redirectClose(fd);
	}

	ssize_t fakeLogWritev(int fd, const struct iovec* vector, int count)
	{
	/* Assume that open() was called first. */
	return redirectWritev(fd, vector, count);
	}