atrace/atrace.c - platform/system/extras - Git at Google

 /*
  * Copyright (C) 2012 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.
  */

 #include <errno.h>
 #include <fcntl.h>
 #include <signal.h>
 #include <stdarg.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/sendfile.h>
 #include <time.h>
 #include <zlib.h>

 #define NELEM(x) ((int) (sizeof(x) / sizeof((x)[0])))

 /* Command line options */
 static int g_traceDurationSeconds = 5;
 static bool g_traceSchedSwitch = false;
 static bool g_traceFrequency = false;
 static bool g_traceBusUtilization = false;
 static bool g_traceCpuIdle = false;
 static bool g_traceDisk = false;
 static bool g_traceGovernorLoad = false;
 static bool g_traceWorkqueue = false;
 static bool g_traceOverwrite = false;
 static int g_traceBufferSizeKB = 2048;
 static bool g_compress = false;

 /* Global state */
 static bool g_traceAborted = false;

 /* Sys file paths */
 static const char* k_traceClockPath =
     "/sys/kernel/debug/tracing/trace_clock";

 static const char* k_traceBufferSizePath =
     "/sys/kernel/debug/tracing/buffer_size_kb";

 static const char* k_tracingOverwriteEnablePath =
     "/sys/kernel/debug/tracing/options/overwrite";

 static const char* k_schedSwitchEnablePath =
     "/sys/kernel/debug/tracing/events/sched/sched_switch/enable";

 static const char* k_schedWakeupEnablePath =
     "/sys/kernel/debug/tracing/events/sched/sched_wakeup/enable";

 static const char* k_memoryBusEnablePath =
     "/sys/kernel/debug/tracing/events/memory_bus/enable";

 static const char* k_cpuFreqEnablePath =
     "/sys/kernel/debug/tracing/events/power/cpu_frequency/enable";

 static const char *k_clockSetRateEnablePath =
     "/sys/kernel/debug/tracing/events/power/clock_set_rate/enable";

 static const char* k_cpuIdleEnablePath =
     "/sys/kernel/debug/tracing/events/power/cpu_idle/enable";

 static const char* k_governorLoadEnablePath =
     "/sys/kernel/debug/tracing/events/cpufreq_interactive/enable";

 static const char* k_workqueueEnablePath =
     "/sys/kernel/debug/tracing/events/workqueue/enable";

 static const char* k_diskEnablePaths[] = {
         "/sys/kernel/debug/tracing/events/ext4/ext4_sync_file_enter/enable",
         "/sys/kernel/debug/tracing/events/ext4/ext4_sync_file_exit/enable",
         "/sys/kernel/debug/tracing/events/block/block_rq_issue/enable",
         "/sys/kernel/debug/tracing/events/block/block_rq_complete/enable",
 };

 static const char* k_tracingOnPath =
     "/sys/kernel/debug/tracing/tracing_on";

 static const char* k_tracePath =
     "/sys/kernel/debug/tracing/trace";

 static const char* k_traceMarkerPath =
     "/sys/kernel/debug/tracing/trace_marker";

 // Write a string to a file, returning true if the write was successful.
 bool writeStr(const char* filename, const char* str)
 {
     int fd = open(filename, O_WRONLY);
     if (fd == -1) {
         fprintf(stderr, "error opening %s: %s (%d)\n", filename,
                 strerror(errno), errno);
         return false;
     }

     bool ok = true;
     ssize_t len = strlen(str);
     if (write(fd, str, len) != len) {
         fprintf(stderr, "error writing to %s: %s (%d)\n", filename,
                 strerror(errno), errno);
         ok = false;
     }

     close(fd);

     return ok;
 }

 // Enable or disable a kernel option by writing a "1" or a "0" into a /sys file.
 static bool setKernelOptionEnable(const char* filename, bool enable)
 {
     return writeStr(filename, enable ? "1" : "0");
 }

 // Enable or disable a collection of kernel options by writing a "1" or a "0" into each /sys file.
 static bool setMultipleKernelOptionsEnable(const char** filenames, size_t count, bool enable)
 {
     bool result = true;
     for (size_t i = 0; i < count; i++) {
         result &= setKernelOptionEnable(filenames[i], enable);
     }
     return result;
 }

 // Enable or disable overwriting of the kernel trace buffers.  Disabling this
 // will cause tracing to stop once the trace buffers have filled up.
 static bool setTraceOverwriteEnable(bool enable)
 {
     return setKernelOptionEnable(k_tracingOverwriteEnablePath, enable);
 }

 // Enable or disable tracing of the kernel scheduler switching.
 static bool setSchedSwitchTracingEnable(bool enable)
 {
     bool ok = true;
     ok &= setKernelOptionEnable(k_schedSwitchEnablePath, enable);
     ok &= setKernelOptionEnable(k_schedWakeupEnablePath, enable);
     return ok;
 }

 // Enable or disable tracing of the Bus utilization.
 static bool setBusUtilizationTracingEnable(bool enable)
 {
     bool ok = false;
     // these can be platform specific so make sure that at least
     // one succeeds.
     ok |= setKernelOptionEnable(k_memoryBusEnablePath, enable);
     return ok;
 }

 // Enable or disable tracing of the CPU clock frequency.
 static bool setFrequencyTracingEnable(bool enable)
 {
     bool ok = true;
     ok &= setKernelOptionEnable(k_cpuFreqEnablePath, enable);
     ok &= setKernelOptionEnable(k_clockSetRateEnablePath, enable);
     return ok;
 }

 // Enable or disable tracing of CPU idle events.
 static bool setCpuIdleTracingEnable(bool enable)
 {
     return setKernelOptionEnable(k_cpuIdleEnablePath, enable);
 }

 // Enable or disable tracing of the interactive CPU frequency governor's idea of
 // the CPU load.
 static bool setGovernorLoadTracingEnable(bool enable)
 {
     return setKernelOptionEnable(k_governorLoadEnablePath, enable);
 }

 // Enable or disable tracing of the kernel workqueues.
 static bool setWorkqueueTracingEnabled(bool enable)
 {
     return setKernelOptionEnable(k_workqueueEnablePath, enable);
 }

 // Enable or disable tracing of disk I/O.
 static bool setDiskTracingEnabled(bool enable)
 {
     return setMultipleKernelOptionsEnable(k_diskEnablePaths, NELEM(k_diskEnablePaths), enable);
 }

 // Enable or disable kernel tracing.
 static bool setTracingEnabled(bool enable)
 {
     return setKernelOptionEnable(k_tracingOnPath, enable);
 }

 // Clear the contents of the kernel trace.
 static bool clearTrace()
 {
     int traceFD = creat(k_tracePath, 0);
     if (traceFD == -1) {
         fprintf(stderr, "error truncating %s: %s (%d)\n", k_tracePath,
                 strerror(errno), errno);
         return false;
     }

     close(traceFD);

     return true;
 }

 // Set the size of the kernel's trace buffer in kilobytes.
 static bool setTraceBufferSizeKB(int size)
 {
     char str[32] = "1";
     int len;
     if (size < 1) {
         size = 1;
     }
     snprintf(str, 32, "%d", size);
     return writeStr(k_traceBufferSizePath, str);
 }

 // Enable or disable the kernel's use of the global clock.  Disabling the global
 // clock will result in the kernel using a per-CPU local clock.
 static bool setGlobalClockEnable(bool enable)
 {
     return writeStr(k_traceClockPath, enable ? "global" : "local");
 }

 // Check whether a file exists.
 static bool fileExists(const char* filename) {
     return access(filename, F_OK) != -1;
 }

 // Enable tracing in the kernel.
 static bool startTrace(bool isRoot)
 {
     bool ok = true;

     // Set up the tracing options that don't require root.
     ok &= setTraceOverwriteEnable(g_traceOverwrite);
     ok &= setSchedSwitchTracingEnable(g_traceSchedSwitch);
     ok &= setBusUtilizationTracingEnable(g_traceBusUtilization);
     ok &= setFrequencyTracingEnable(g_traceFrequency);
     ok &= setCpuIdleTracingEnable(g_traceCpuIdle);
     if (fileExists(k_governorLoadEnablePath) || g_traceGovernorLoad) {
         ok &= setGovernorLoadTracingEnable(g_traceGovernorLoad);
     }
     ok &= setTraceBufferSizeKB(g_traceBufferSizeKB);
     ok &= setGlobalClockEnable(true);

     // Set up the tracing options that do require root.  The options that
     // require root should have errored out earlier if we're not running as
     // root.
     if (isRoot) {
         ok &= setWorkqueueTracingEnabled(g_traceWorkqueue);
         ok &= setDiskTracingEnabled(g_traceDisk);
     }

     // Enable tracing.
     ok &= setTracingEnabled(true);

     if (!ok) {
         fprintf(stderr, "error: unable to start trace\n");
     }

     return ok;
 }

 // Disable tracing in the kernel.
 static void stopTrace(bool isRoot)
 {
     // Disable tracing.
     setTracingEnabled(false);

     // Set the options back to their defaults.
     setTraceOverwriteEnable(true);
     setSchedSwitchTracingEnable(false);
     setBusUtilizationTracingEnable(false);
     setFrequencyTracingEnable(false);
     if (fileExists(k_governorLoadEnablePath)) {
         setGovernorLoadTracingEnable(false);
     }
     setGlobalClockEnable(false);

     if (isRoot) {
         setWorkqueueTracingEnabled(false);
         setDiskTracingEnabled(false);
     }

     // Note that we can't reset the trace buffer size here because that would
     // clear the trace before we've read it.
 }

 // Read the current kernel trace and write it to stdout.
 static void dumpTrace()
 {
     int traceFD = open(k_tracePath, O_RDWR);
     if (traceFD == -1) {
         fprintf(stderr, "error opening %s: %s (%d)\n", k_tracePath,
                 strerror(errno), errno);
         return;
     }

     if (g_compress) {
         z_stream zs;
         uint8_t *in, *out;
         int result, flush;

         bzero(&zs, sizeof(zs));
         result = deflateInit(&zs, Z_DEFAULT_COMPRESSION);
         if (result != Z_OK) {
             fprintf(stderr, "error initializing zlib: %d\n", result);
             close(traceFD);
             return;
         }

         const size_t bufSize = 64*1024;
         in = (uint8_t*)malloc(bufSize);
         out = (uint8_t*)malloc(bufSize);
         flush = Z_NO_FLUSH;

         zs.next_out = out;
         zs.avail_out = bufSize;

         do {

             if (zs.avail_in == 0) {
                 // More input is needed.
                 result = read(traceFD, in, bufSize);
                 if (result < 0) {
                     fprintf(stderr, "error reading trace: %s (%d)\n",
                             strerror(errno), errno);
                     result = Z_STREAM_END;
                     break;
                 } else if (result == 0) {
                     flush = Z_FINISH;
                 } else {
                     zs.next_in = in;
                     zs.avail_in = result;
                 }
             }

             if (zs.avail_out == 0) {
                 // Need to write the output.
                 result = write(STDOUT_FILENO, out, bufSize);
                 if ((size_t)result < bufSize) {
                     fprintf(stderr, "error writing deflated trace: %s (%d)\n",
                             strerror(errno), errno);
                     result = Z_STREAM_END; // skip deflate error message
                     zs.avail_out = bufSize; // skip the final write
                     break;
                 }
                 zs.next_out = out;
                 zs.avail_out = bufSize;
             }

         } while ((result = deflate(&zs, flush)) == Z_OK);

         if (result != Z_STREAM_END) {
             fprintf(stderr, "error deflating trace: %s\n", zs.msg);
         }

         if (zs.avail_out < bufSize) {
             size_t bytes = bufSize - zs.avail_out;
             result = write(STDOUT_FILENO, out, bytes);
             if ((size_t)result < bytes) {
                 fprintf(stderr, "error writing deflated trace: %s (%d)\n",
                         strerror(errno), errno);
             }
         }

         result = deflateEnd(&zs);
         if (result != Z_OK) {
             fprintf(stderr, "error cleaning up zlib: %d\n", result);
         }

         free(in);
         free(out);
     } else {
         ssize_t sent = 0;
         while ((sent = sendfile(STDOUT_FILENO, traceFD, NULL, 64*1024*1024)) > 0);
         if (sent == -1) {
             fprintf(stderr, "error dumping trace: %s (%d)\n", strerror(errno),
                     errno);
         }
     }

     close(traceFD);
 }

 // Print the command usage help to stderr.
 static void showHelp(const char *cmd)
 {
     fprintf(stderr, "usage: %s [options]\n", cmd);
     fprintf(stderr, "options include:\n"
                     "  -b N            use a trace buffer size of N KB\n"
                     "  -c              trace into a circular buffer\n"
                     "  -d              trace disk I/O\n"
                     "  -f              trace clock frequency changes\n"
                     "  -l              trace CPU frequency governor load\n"
                     "  -s              trace the kernel scheduler switches\n"
                     "  -t N            trace for N seconds [defualt 5]\n"
                     "  -u              trace bus utilization\n"
                     "  -w              trace the kernel workqueue\n"
                     "  -z              compress the trace dump\n");
 }

 static void handleSignal(int signo) {
     g_traceAborted = true;
 }

 static void registerSigHandler() {
     struct sigaction sa;
     sigemptyset(&sa.sa_mask);
     sa.sa_flags = 0;
     sa.sa_handler = handleSignal;
     sigaction(SIGHUP, &sa, NULL);
     sigaction(SIGINT, &sa, NULL);
     sigaction(SIGQUIT, &sa, NULL);
     sigaction(SIGTERM, &sa, NULL);
 }

 int main(int argc, char **argv)
 {
     bool isRoot = (getuid() == 0);

     if (argc == 2 && 0 == strcmp(argv[1], "--help")) {
         showHelp(argv[0]);
         exit(0);
     }

     for (;;) {
         int ret;

         ret = getopt(argc, argv, "b:cidflst:uwz");

         if (ret < 0) {
             break;
         }

         switch(ret) {
             case 'b':
                 g_traceBufferSizeKB = atoi(optarg);
             break;

             case 'c':
                 g_traceOverwrite = true;
             break;

             case 'i':
                 g_traceCpuIdle = true;
             break;

             case 'l':
                 g_traceGovernorLoad = true;
             break;

             case 'd':
                 if (!isRoot) {
                     fprintf(stderr, "error: tracing disk activity requires root privileges\n");
                     exit(1);
                 }
                 g_traceDisk = true;
             break;

             case 'f':
                 g_traceFrequency = true;
             break;

             case 's':
                 g_traceSchedSwitch = true;
             break;

             case 't':
                 g_traceDurationSeconds = atoi(optarg);
             break;

             case 'u':
                 if (!isRoot) {
                     fprintf(stderr, "error: tracing bus utilization requires root privileges\n");
                     exit(1);
                 }
                 g_traceBusUtilization = true;
             break;

             case 'w':
                 if (!isRoot) {
                     fprintf(stderr, "error: tracing kernel work queues requires root privileges\n");
                     exit(1);
                 }
                 g_traceWorkqueue = true;
             break;

             case 'z':
                 g_compress = true;
             break;

             default:
                 fprintf(stderr, "\n");
                 showHelp(argv[0]);
                 exit(-1);
             break;
         }
     }

     registerSigHandler();

     bool ok = startTrace(isRoot);

     if (ok) {
         printf("capturing trace...");
         fflush(stdout);

         // We clear the trace after starting it because tracing gets enabled for
         // each CPU individually in the kernel. Having the beginning of the trace
         // contain entries from only one CPU can cause "begin" entries without a
         // matching "end" entry to show up if a task gets migrated from one CPU to
         // another.
         ok = clearTrace();

         if (ok) {
             // Sleep to allow the trace to be captured.
             struct timespec timeLeft;
             timeLeft.tv_sec = g_traceDurationSeconds;
             timeLeft.tv_nsec = 0;
             do {
                 if (g_traceAborted) {
                     break;
                 }
             } while (nanosleep(&timeLeft, &timeLeft) == -1 && errno == EINTR);
         }
     }

     // Stop the trace and restore the default settings.
     stopTrace(isRoot);

     if (ok) {
         if (!g_traceAborted) {
             printf(" done\nTRACE:\n");
             fflush(stdout);
             dumpTrace();
         } else {
             printf("\ntrace aborted.\n");
             fflush(stdout);
         }
         clearTrace();
     } else {
         fprintf(stderr, "unable to start tracing\n");
     }

     // Reset the trace buffer size to 1.
     setTraceBufferSizeKB(1);

     return g_traceAborted ? 1 : 0;
 }
	/*
	* Copyright (C) 2012 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.
	*/

	#include <errno.h>
	#include <fcntl.h>
	#include <signal.h>
	#include <stdarg.h>
	#include <stdbool.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <sys/sendfile.h>
	#include <time.h>
	#include <zlib.h>

	#define NELEM(x) ((int) (sizeof(x) / sizeof((x)[0])))

	/* Command line options */
	static int g_traceDurationSeconds = 5;
	static bool g_traceSchedSwitch = false;
	static bool g_traceFrequency = false;
	static bool g_traceBusUtilization = false;
	static bool g_traceCpuIdle = false;
	static bool g_traceDisk = false;
	static bool g_traceGovernorLoad = false;
	static bool g_traceWorkqueue = false;
	static bool g_traceOverwrite = false;
	static int g_traceBufferSizeKB = 2048;
	static bool g_compress = false;

	/* Global state */
	static bool g_traceAborted = false;

	/* Sys file paths */
	static const char* k_traceClockPath =
	"/sys/kernel/debug/tracing/trace_clock";

	static const char* k_traceBufferSizePath =
	"/sys/kernel/debug/tracing/buffer_size_kb";

	static const char* k_tracingOverwriteEnablePath =
	"/sys/kernel/debug/tracing/options/overwrite";

	static const char* k_schedSwitchEnablePath =
	"/sys/kernel/debug/tracing/events/sched/sched_switch/enable";

	static const char* k_schedWakeupEnablePath =
	"/sys/kernel/debug/tracing/events/sched/sched_wakeup/enable";

	static const char* k_memoryBusEnablePath =
	"/sys/kernel/debug/tracing/events/memory_bus/enable";

	static const char* k_cpuFreqEnablePath =
	"/sys/kernel/debug/tracing/events/power/cpu_frequency/enable";

	static const char *k_clockSetRateEnablePath =
	"/sys/kernel/debug/tracing/events/power/clock_set_rate/enable";

	static const char* k_cpuIdleEnablePath =
	"/sys/kernel/debug/tracing/events/power/cpu_idle/enable";

	static const char* k_governorLoadEnablePath =
	"/sys/kernel/debug/tracing/events/cpufreq_interactive/enable";

	static const char* k_workqueueEnablePath =
	"/sys/kernel/debug/tracing/events/workqueue/enable";

	static const char* k_diskEnablePaths[] = {
	"/sys/kernel/debug/tracing/events/ext4/ext4_sync_file_enter/enable",
	"/sys/kernel/debug/tracing/events/ext4/ext4_sync_file_exit/enable",
	"/sys/kernel/debug/tracing/events/block/block_rq_issue/enable",
	"/sys/kernel/debug/tracing/events/block/block_rq_complete/enable",
	};

	static const char* k_tracingOnPath =
	"/sys/kernel/debug/tracing/tracing_on";

	static const char* k_tracePath =
	"/sys/kernel/debug/tracing/trace";

	static const char* k_traceMarkerPath =
	"/sys/kernel/debug/tracing/trace_marker";

	// Write a string to a file, returning true if the write was successful.
	bool writeStr(const char* filename, const char* str)
	{
	int fd = open(filename, O_WRONLY);
	if (fd == -1) {
	fprintf(stderr, "error opening %s: %s (%d)\n", filename,
	strerror(errno), errno);
	return false;
	}

	bool ok = true;
	ssize_t len = strlen(str);
	if (write(fd, str, len) != len) {
	fprintf(stderr, "error writing to %s: %s (%d)\n", filename,
	strerror(errno), errno);
	ok = false;
	}

	close(fd);

	return ok;
	}

	// Enable or disable a kernel option by writing a "1" or a "0" into a /sys file.
	static bool setKernelOptionEnable(const char* filename, bool enable)
	{
	return writeStr(filename, enable ? "1" : "0");
	}

	// Enable or disable a collection of kernel options by writing a "1" or a "0" into each /sys file.
	static bool setMultipleKernelOptionsEnable(const char** filenames, size_t count, bool enable)
	{
	bool result = true;
	for (size_t i = 0; i < count; i++) {
	result &= setKernelOptionEnable(filenames[i], enable);
	}
	return result;
	}

	// Enable or disable overwriting of the kernel trace buffers. Disabling this
	// will cause tracing to stop once the trace buffers have filled up.
	static bool setTraceOverwriteEnable(bool enable)
	{
	return setKernelOptionEnable(k_tracingOverwriteEnablePath, enable);
	}

	// Enable or disable tracing of the kernel scheduler switching.
	static bool setSchedSwitchTracingEnable(bool enable)
	{
	bool ok = true;
	ok &= setKernelOptionEnable(k_schedSwitchEnablePath, enable);
	ok &= setKernelOptionEnable(k_schedWakeupEnablePath, enable);
	return ok;
	}

	// Enable or disable tracing of the Bus utilization.
	static bool setBusUtilizationTracingEnable(bool enable)
	{
	bool ok = false;
	// these can be platform specific so make sure that at least
	// one succeeds.
	ok \|= setKernelOptionEnable(k_memoryBusEnablePath, enable);
	return ok;
	}

	// Enable or disable tracing of the CPU clock frequency.
	static bool setFrequencyTracingEnable(bool enable)
	{
	bool ok = true;
	ok &= setKernelOptionEnable(k_cpuFreqEnablePath, enable);
	ok &= setKernelOptionEnable(k_clockSetRateEnablePath, enable);
	return ok;
	}

	// Enable or disable tracing of CPU idle events.
	static bool setCpuIdleTracingEnable(bool enable)
	{
	return setKernelOptionEnable(k_cpuIdleEnablePath, enable);
	}

	// Enable or disable tracing of the interactive CPU frequency governor's idea of
	// the CPU load.
	static bool setGovernorLoadTracingEnable(bool enable)
	{
	return setKernelOptionEnable(k_governorLoadEnablePath, enable);
	}

	// Enable or disable tracing of the kernel workqueues.
	static bool setWorkqueueTracingEnabled(bool enable)
	{
	return setKernelOptionEnable(k_workqueueEnablePath, enable);
	}

	// Enable or disable tracing of disk I/O.
	static bool setDiskTracingEnabled(bool enable)
	{
	return setMultipleKernelOptionsEnable(k_diskEnablePaths, NELEM(k_diskEnablePaths), enable);
	}

	// Enable or disable kernel tracing.
	static bool setTracingEnabled(bool enable)
	{
	return setKernelOptionEnable(k_tracingOnPath, enable);
	}

	// Clear the contents of the kernel trace.
	static bool clearTrace()
	{
	int traceFD = creat(k_tracePath, 0);
	if (traceFD == -1) {
	fprintf(stderr, "error truncating %s: %s (%d)\n", k_tracePath,
	strerror(errno), errno);
	return false;
	}

	close(traceFD);

	return true;
	}

	// Set the size of the kernel's trace buffer in kilobytes.
	static bool setTraceBufferSizeKB(int size)
	{
	char str[32] = "1";
	int len;
	if (size < 1) {
	size = 1;
	}
	snprintf(str, 32, "%d", size);
	return writeStr(k_traceBufferSizePath, str);
	}

	// Enable or disable the kernel's use of the global clock. Disabling the global
	// clock will result in the kernel using a per-CPU local clock.
	static bool setGlobalClockEnable(bool enable)
	{
	return writeStr(k_traceClockPath, enable ? "global" : "local");
	}

	// Check whether a file exists.
	static bool fileExists(const char* filename) {
	return access(filename, F_OK) != -1;
	}

	// Enable tracing in the kernel.
	static bool startTrace(bool isRoot)
	{
	bool ok = true;

	// Set up the tracing options that don't require root.
	ok &= setTraceOverwriteEnable(g_traceOverwrite);
	ok &= setSchedSwitchTracingEnable(g_traceSchedSwitch);
	ok &= setBusUtilizationTracingEnable(g_traceBusUtilization);
	ok &= setFrequencyTracingEnable(g_traceFrequency);
	ok &= setCpuIdleTracingEnable(g_traceCpuIdle);
	if (fileExists(k_governorLoadEnablePath) \|\| g_traceGovernorLoad) {
	ok &= setGovernorLoadTracingEnable(g_traceGovernorLoad);
	}
	ok &= setTraceBufferSizeKB(g_traceBufferSizeKB);
	ok &= setGlobalClockEnable(true);

	// Set up the tracing options that do require root. The options that
	// require root should have errored out earlier if we're not running as
	// root.
	if (isRoot) {
	ok &= setWorkqueueTracingEnabled(g_traceWorkqueue);
	ok &= setDiskTracingEnabled(g_traceDisk);
	}

	// Enable tracing.
	ok &= setTracingEnabled(true);

	if (!ok) {
	fprintf(stderr, "error: unable to start trace\n");
	}

	return ok;
	}

	// Disable tracing in the kernel.
	static void stopTrace(bool isRoot)
	{
	// Disable tracing.
	setTracingEnabled(false);

	// Set the options back to their defaults.
	setTraceOverwriteEnable(true);
	setSchedSwitchTracingEnable(false);
	setBusUtilizationTracingEnable(false);
	setFrequencyTracingEnable(false);
	if (fileExists(k_governorLoadEnablePath)) {
	setGovernorLoadTracingEnable(false);
	}
	setGlobalClockEnable(false);

	if (isRoot) {
	setWorkqueueTracingEnabled(false);
	setDiskTracingEnabled(false);
	}

	// Note that we can't reset the trace buffer size here because that would
	// clear the trace before we've read it.
	}

	// Read the current kernel trace and write it to stdout.
	static void dumpTrace()
	{
	int traceFD = open(k_tracePath, O_RDWR);
	if (traceFD == -1) {
	fprintf(stderr, "error opening %s: %s (%d)\n", k_tracePath,
	strerror(errno), errno);
	return;
	}

	if (g_compress) {
	z_stream zs;
	uint8_t in, out;
	int result, flush;

	bzero(&zs, sizeof(zs));
	result = deflateInit(&zs, Z_DEFAULT_COMPRESSION);
	if (result != Z_OK) {
	fprintf(stderr, "error initializing zlib: %d\n", result);
	close(traceFD);
	return;
	}

	const size_t bufSize = 64*1024;
	in = (uint8_t*)malloc(bufSize);
	out = (uint8_t*)malloc(bufSize);
	flush = Z_NO_FLUSH;

	zs.next_out = out;
	zs.avail_out = bufSize;

	do {

	if (zs.avail_in == 0) {
	// More input is needed.
	result = read(traceFD, in, bufSize);
	if (result < 0) {
	fprintf(stderr, "error reading trace: %s (%d)\n",
	strerror(errno), errno);
	result = Z_STREAM_END;
	break;
	} else if (result == 0) {
	flush = Z_FINISH;
	} else {
	zs.next_in = in;
	zs.avail_in = result;
	}
	}

	if (zs.avail_out == 0) {
	// Need to write the output.
	result = write(STDOUT_FILENO, out, bufSize);
	if ((size_t)result < bufSize) {
	fprintf(stderr, "error writing deflated trace: %s (%d)\n",
	strerror(errno), errno);
	result = Z_STREAM_END; // skip deflate error message
	zs.avail_out = bufSize; // skip the final write
	break;
	}
	zs.next_out = out;
	zs.avail_out = bufSize;
	}

	} while ((result = deflate(&zs, flush)) == Z_OK);

	if (result != Z_STREAM_END) {
	fprintf(stderr, "error deflating trace: %s\n", zs.msg);
	}

	if (zs.avail_out < bufSize) {
	size_t bytes = bufSize - zs.avail_out;
	result = write(STDOUT_FILENO, out, bytes);
	if ((size_t)result < bytes) {
	fprintf(stderr, "error writing deflated trace: %s (%d)\n",
	strerror(errno), errno);
	}
	}

	result = deflateEnd(&zs);
	if (result != Z_OK) {
	fprintf(stderr, "error cleaning up zlib: %d\n", result);
	}

	free(in);
	free(out);
	} else {
	ssize_t sent = 0;
	while ((sent = sendfile(STDOUT_FILENO, traceFD, NULL, 6410241024)) > 0);
	if (sent == -1) {
	fprintf(stderr, "error dumping trace: %s (%d)\n", strerror(errno),
	errno);
	}
	}

	close(traceFD);
	}

	// Print the command usage help to stderr.
	static void showHelp(const char *cmd)
	{
	fprintf(stderr, "usage: %s [options]\n", cmd);
	fprintf(stderr, "options include:\n"
	" -b N use a trace buffer size of N KB\n"
	" -c trace into a circular buffer\n"
	" -d trace disk I/O\n"
	" -f trace clock frequency changes\n"
	" -l trace CPU frequency governor load\n"
	" -s trace the kernel scheduler switches\n"
	" -t N trace for N seconds [defualt 5]\n"
	" -u trace bus utilization\n"
	" -w trace the kernel workqueue\n"
	" -z compress the trace dump\n");
	}

	static void handleSignal(int signo) {
	g_traceAborted = true;
	}

	static void registerSigHandler() {
	struct sigaction sa;
	sigemptyset(&sa.sa_mask);
	sa.sa_flags = 0;
	sa.sa_handler = handleSignal;
	sigaction(SIGHUP, &sa, NULL);
	sigaction(SIGINT, &sa, NULL);
	sigaction(SIGQUIT, &sa, NULL);
	sigaction(SIGTERM, &sa, NULL);
	}

	int main(int argc, char **argv)
	{
	bool isRoot = (getuid() == 0);

	if (argc == 2 && 0 == strcmp(argv[1], "--help")) {
	showHelp(argv[0]);
	exit(0);
	}

	for (;;) {
	int ret;

	ret = getopt(argc, argv, "b:cidflst:uwz");

	if (ret < 0) {
	break;
	}

	switch(ret) {
	case 'b':
	g_traceBufferSizeKB = atoi(optarg);
	break;

	case 'c':
	g_traceOverwrite = true;
	break;

	case 'i':
	g_traceCpuIdle = true;
	break;

	case 'l':
	g_traceGovernorLoad = true;
	break;

	case 'd':
	if (!isRoot) {
	fprintf(stderr, "error: tracing disk activity requires root privileges\n");
	exit(1);
	}
	g_traceDisk = true;
	break;

	case 'f':
	g_traceFrequency = true;
	break;

	case 's':
	g_traceSchedSwitch = true;
	break;

	case 't':
	g_traceDurationSeconds = atoi(optarg);
	break;

	case 'u':
	if (!isRoot) {
	fprintf(stderr, "error: tracing bus utilization requires root privileges\n");
	exit(1);
	}
	g_traceBusUtilization = true;
	break;

	case 'w':
	if (!isRoot) {
	fprintf(stderr, "error: tracing kernel work queues requires root privileges\n");
	exit(1);
	}
	g_traceWorkqueue = true;
	break;

	case 'z':
	g_compress = true;
	break;

	default:
	fprintf(stderr, "\n");
	showHelp(argv[0]);
	exit(-1);
	break;
	}
	}

	registerSigHandler();

	bool ok = startTrace(isRoot);

	if (ok) {
	printf("capturing trace...");
	fflush(stdout);

	// We clear the trace after starting it because tracing gets enabled for
	// each CPU individually in the kernel. Having the beginning of the trace
	// contain entries from only one CPU can cause "begin" entries without a
	// matching "end" entry to show up if a task gets migrated from one CPU to
	// another.
	ok = clearTrace();

	if (ok) {
	// Sleep to allow the trace to be captured.
	struct timespec timeLeft;
	timeLeft.tv_sec = g_traceDurationSeconds;
	timeLeft.tv_nsec = 0;
	do {
	if (g_traceAborted) {
	break;
	}
	} while (nanosleep(&timeLeft, &timeLeft) == -1 && errno == EINTR);
	}
	}

	// Stop the trace and restore the default settings.
	stopTrace(isRoot);

	if (ok) {
	if (!g_traceAborted) {
	printf(" done\nTRACE:\n");
	fflush(stdout);
	dumpTrace();
	} else {
	printf("\ntrace aborted.\n");
	fflush(stdout);
	}
	clearTrace();
	} else {
	fprintf(stderr, "unable to start tracing\n");
	}

	// Reset the trace buffer size to 1.
	setTraceBufferSizeKB(1);

	return g_traceAborted ? 1 : 0;
	}