atrace: clean up tracing option enabling

This change switches atrace to use a table-driven approach to enabling and
disabling options.  It unifies how framework and kernel tracing are enabled,
and causes userland tracing options to be picked up by currently running
processes.

Change-Id: Iba2a3012ca0a67c4defdd076bce597db26e9f539

cmds/atrace/Android.mk

@@ -3,15 +3,18 @@
 LOCAL_PATH:= $(call my-dir)
 include $(CLEAR_VARS)
 
-LOCAL_SRC_FILES:= atrace.c
+LOCAL_SRC_FILES:= atrace.cpp
 
 LOCAL_C_INCLUDES += external/zlib
-LOCAL_CFLAGS += -std=c99
 
 LOCAL_MODULE:= atrace
 
 LOCAL_MODULE_TAGS:= optional
 
-LOCAL_SHARED_LIBRARIES := libz
+LOCAL_SHARED_LIBRARIES := \
+    libbinder \
+    libcutils \
+    libutils \
+    libz \
 
 include $(BUILD_EXECUTABLE)

cmds/atrace/atrace.cpp

@@ -26,18 +26,90 @@
 #include <time.h>
 #include <zlib.h>
 
+#include <binder/IBinder.h>
+#include <binder/IServiceManager.h>
+#include <binder/Parcel.h>
+
+#include <cutils/properties.h>
+
+#include <utils/String8.h>
+#include <utils/Trace.h>
+
+using namespace android;
+
 #define NELEM(x) ((int) (sizeof(x) / sizeof((x)[0])))
 
+enum { MAX_SYS_FILES = 8 };
+
+const char* k_traceTagsProperty = "debug.atrace.tags.enableflags";
+
+typedef enum { OPT, REQ } requiredness  ;
+
+struct TracingCategory {
+    // The name identifying the category.
+    const char* name;
+
+    // A longer description of the category.
+    const char* longname;
+
+    // The userland tracing tags that the category enables.
+    uint64_t tags;
+
+    // The fname==NULL terminated list of /sys/ files that the category
+    // enables.
+    struct {
+        // Whether the file must be writable in order to enable the tracing
+        // category.
+        requiredness required;
+
+        // The path to the enable file.
+        const char* path;
+    } sysfiles[MAX_SYS_FILES];
+};
+
+/* Tracing categories */
+static const TracingCategory k_categories[] = {
+    { "gfx",    "Graphics",         ATRACE_TAG_GRAPHICS, { } },
+    { "input",  "Input",            ATRACE_TAG_INPUT, { } },
+    { "view",   "View System",      ATRACE_TAG_VIEW, { } },
+    { "wm",     "Window Manager",   ATRACE_TAG_WINDOW_MANAGER, { } },
+    { "am",     "Activity Manager", ATRACE_TAG_ACTIVITY_MANAGER, { } },
+    { "audio",  "Audio",            ATRACE_TAG_AUDIO, { } },
+    { "video",  "Video",            ATRACE_TAG_VIDEO, { } },
+    { "camera", "Camera",           ATRACE_TAG_CAMERA, { } },
+    { "sched",  "CPU Scheduling",   0, {
+        { REQ,  "/sys/kernel/debug/tracing/events/sched/sched_switch/enable" },
+        { REQ,  "/sys/kernel/debug/tracing/events/sched/sched_wakeup/enable" },
+    } },
+    { "freq",   "CPU Frequency",    0, {
+        { REQ,  "/sys/kernel/debug/tracing/events/power/cpu_frequency/enable" },
+        { OPT, "/sys/kernel/debug/tracing/events/power/clock_set_rate/enable" },
+    } },
+    { "membus", "Memory Bus Utilization", 0, {
+        { REQ,  "/sys/kernel/debug/tracing/events/memory_bus/enable" },
+    } },
+    { "idle",   "CPU Idle",         0, {
+        { REQ,  "/sys/kernel/debug/tracing/events/power/cpu_idle/enable" },
+    } },
+    { "disk",   "Disk I/O",         0, {
+        { REQ,  "/sys/kernel/debug/tracing/events/ext4/ext4_sync_file_enter/enable" },
+        { REQ,  "/sys/kernel/debug/tracing/events/ext4/ext4_sync_file_exit/enable" },
+        { REQ,  "/sys/kernel/debug/tracing/events/block/block_rq_issue/enable" },
+        { REQ,  "/sys/kernel/debug/tracing/events/block/block_rq_complete/enable" },
+    } },
+    { "load",   "CPU Load",         0, {
+        { REQ,  "/sys/kernel/debug/tracing/events/cpufreq_interactive/enable" },
+    } },
+    { "sync",   "Synchronization",  0, {
+        { REQ,  "/sys/kernel/debug/tracing/events/sync/enable" },
+    } },
+    { "workq",  "Kernel Workqueues", 0, {
+        { REQ,  "/sys/kernel/debug/tracing/events/workqueue/enable" },
+    } },
+};
+
 /* 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_traceSync = false;
-static bool g_traceWorkqueue = false;
 static bool g_traceOverwrite = false;
 static int g_traceBufferSizeKB = 2048;
 static bool g_compress = false;
@@ -46,6 +118,7 @@ static int g_initialSleepSecs = 0;
 
 /* Global state */
 static bool g_traceAborted = false;
+static bool g_categoryEnables[NELEM(k_categories)] = {};
 
 /* Sys file paths */
 static const char* k_traceClockPath =
@@ -57,56 +130,24 @@ static const char* k_traceBufferSizePath =
 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_syncEnablePath =
-    "/sys/kernel/debug/tracing/events/sync/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";
-
 // Check whether a file exists.
 static bool fileExists(const char* filename) {
     return access(filename, F_OK) != -1;
 }
 
+// Check whether a file is writable.
+static bool fileIsWritable(const char* filename) {
+    return access(filename, W_OK) != -1;
+}
+
 // Write a string to a file, returning true if the write was successful.
-bool writeStr(const char* filename, const char* str)
+static bool writeStr(const char* filename, const char* str)
 {
     int fd = open(filename, O_WRONLY);
     if (fd == -1) {
@@ -128,20 +169,61 @@ bool writeStr(const char* filename, const char* str)
     return ok;
 }
 
-// Enable or disable a kernel option by writing a "1" or a "0" into a /sys file.
+// 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.
+// Check whether the category is supported on the device with the current
-static bool setMultipleKernelOptionsEnable(const char** filenames, size_t count, bool enable)
+// rootness.  A category is supported only if all its required /sys/ files are
+// writable and if enabling the category will enable one or more tracing tags
+// or /sys/ files.
+static bool isCategorySupported(const TracingCategory& category)
 {
-    bool result = true;
+    bool ok = category.tags != 0;
-    for (size_t i = 0; i < count; i++) {
+    for (int i = 0; i < MAX_SYS_FILES; i++) {
-        result &= setKernelOptionEnable(filenames[i], enable);
+        const char* path = category.sysfiles[i].path;
+        bool req = category.sysfiles[i].required == REQ;
+        if (path != NULL) {
+            if (req) {
+                if (!fileIsWritable(path)) {
+                    return false;
+                } else {
+                    ok = true;
+                }
+            } else {
+                ok |= fileIsWritable(path);
+            }
+        }
     }
-    return result;
+    return ok;
+}
+
+// Check whether the category would be supported on the device if the user
+// were root.  This function assumes that root is able to write to any file
+// that exists.  It performs the same logic as isCategorySupported, but it
+// uses file existance rather than writability in the /sys/ file checks.
+static bool isCategorySupportedForRoot(const TracingCategory& category)
+{
+    bool ok = category.tags != 0;
+    for (int i = 0; i < MAX_SYS_FILES; i++) {
+        const char* path = category.sysfiles[i].path;
+        bool req = category.sysfiles[i].required == REQ;
+        if (path != NULL) {
+            if (req) {
+                if (!fileExists(path)) {
+                    return false;
+                } else {
+                    ok = true;
+                }
+            } else {
+                ok |= fileExists(path);
+            }
+        }
+    }
+    return ok;
 }
 
 // Enable or disable overwriting of the kernel trace buffers.  Disabling this
@@ -151,78 +233,6 @@ 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 = true, oneSet = false;
-    // these can be platform specific so make sure that at least
-    // one succeeds.
-    if (fileExists(k_memoryBusEnablePath)) {
-        ok &= setKernelOptionEnable(k_memoryBusEnablePath, enable);
-        oneSet |= ok;
-    }
-    return ok && (oneSet || !enable);
-}
-
-// Enable or disable tracing of the CPU clock frequency.
-static bool setFrequencyTracingEnable(bool enable)
-{
-    bool ok = true;
-    ok &= setKernelOptionEnable(k_cpuFreqEnablePath, enable);
-    if (fileExists(k_clockSetRateEnablePath)) {
-        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)
-{
-    bool ok = true;
-    if (fileExists(k_governorLoadEnablePath) || enable) {
-        ok &= setKernelOptionEnable(k_governorLoadEnablePath, enable);
-    }
-    return ok;
-}
-
-// Enable or disable tracing of sync timelines and waits.
-static bool setSyncTracingEnabled(bool enable)
-{
-    bool ok = true;
-    if (fileExists(k_syncEnablePath) || enable) {
-        ok &= setKernelOptionEnable(k_syncEnablePath, enable);
-    }
-    return ok;
-}
-
-// 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)
 {
@@ -263,60 +273,126 @@ static bool setGlobalClockEnable(bool enable)
     return writeStr(k_traceClockPath, enable ? "global" : "local");
 }
 
+// Poke all the binder-enabled processes in the system to get them to re-read
+// their system properties.
+static bool pokeBinderServices()
+{
+    sp<IServiceManager> sm = defaultServiceManager();
+    Vector<String16> services = sm->listServices();
+    for (size_t i = 0; i < services.size(); i++) {
+        sp<IBinder> obj = sm->checkService(services[i]);
+        if (obj != NULL) {
+            Parcel data;
+            if (obj->transact(IBinder::SYSPROPS_TRANSACTION, data,
+                    NULL, 0) != OK) {
+                if (false) {
+                    // XXX: For some reason this fails on tablets trying to
+                    // poke the "phone" service.  It's not clear whether some
+                    // are expected to fail.
+                    String8 svc(services[i]);
+                    fprintf(stderr, "error poking binder service %s\n",
+                        svc.string());
+                    return false;
+                }
+            }
+        }
+    }
+    return true;
+}
+
+// Set the trace tags that userland tracing uses, and poke the running
+// processes to pick up the new value.
+static bool setTagsProperty(uint64_t tags)
+{
+    char buf[64];
+    snprintf(buf, 64, "%#llx", tags);
+    if (property_set(k_traceTagsProperty, buf) < 0) {
+        fprintf(stderr, "error setting trace tags system property\n");
+        return false;
+    }
+    return pokeBinderServices();
+}
+
+// Disable all /sys/ enable files.
+static bool disableKernelTraceEvents() {
+    bool ok = true;
+    for (int i = 0; i < NELEM(k_categories); i++) {
+        const TracingCategory &c = k_categories[i];
+        for (int j = 0; j < MAX_SYS_FILES; j++) {
+            const char* path = c.sysfiles[j].path;
+            if (path != NULL && fileIsWritable(path)) {
+                ok &= setKernelOptionEnable(path, false);
+            }
+        }
+    }
+    return ok;
+}
+
 // Enable tracing in the kernel.
-static bool startTrace(bool isRoot)
+static bool startTrace()
 {
     bool ok = true;
 
-    // Set up the tracing options that don't require root.
+    // Set up the tracing options.
     ok &= setTraceOverwriteEnable(g_traceOverwrite);
-    ok &= setSchedSwitchTracingEnable(g_traceSchedSwitch);
-    ok &= setFrequencyTracingEnable(g_traceFrequency);
-    ok &= setCpuIdleTracingEnable(g_traceCpuIdle);
-    ok &= setGovernorLoadTracingEnable(g_traceGovernorLoad);
     ok &= setTraceBufferSizeKB(g_traceBufferSizeKB);
     ok &= setGlobalClockEnable(true);
 
-    // Set up the tracing options that do require root.  The options that
+    // Set up the tags property.
-    // require root should have errored out earlier if we're not running as
+    uint64_t tags = 0;
-    // root.
+    for (int i = 0; i < NELEM(k_categories); i++) {
-    if (isRoot) {
+        if (g_categoryEnables[i]) {
-        ok &= setBusUtilizationTracingEnable(g_traceBusUtilization);
+            const TracingCategory &c = k_categories[i];
-        ok &= setSyncTracingEnabled(g_traceSync);
+            tags |= c.tags;
-        ok &= setWorkqueueTracingEnabled(g_traceWorkqueue);
+        }
-        ok &= setDiskTracingEnabled(g_traceDisk);
+    }
+    ok &= setTagsProperty(tags);
+
+    // Disable all the sysfs enables.  This is done as a separate loop from
+    // the enables to allow the same enable to exist in multiple categories.
+    ok &= disableKernelTraceEvents();
+
+    // Enable all the sysfs enables that are in an enabled category.
+    for (int i = 0; i < NELEM(k_categories); i++) {
+        if (g_categoryEnables[i]) {
+            const TracingCategory &c = k_categories[i];
+            for (int j = 0; j < MAX_SYS_FILES; j++) {
+                const char* path = c.sysfiles[j].path;
+                bool required = c.sysfiles[j].required == REQ;
+                if (path != NULL) {
+                    if (fileIsWritable(path)) {
+                        ok &= setKernelOptionEnable(path, true);
+                    } else if (required) {
+                        fprintf(stderr, "error writing file %s\n", path);
+                        ok = false;
+                    }
+                }
+            }
+        }
     }
 
     // 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)
+static void stopTrace()
 {
     // Disable tracing.
     setTracingEnabled(false);
 
+    // Disable all tracing that we're able to.
+    disableKernelTraceEvents();
+
+    // Disable all the trace tags.
+    setTagsProperty(0);
+
     // Set the options back to their defaults.
     setTraceOverwriteEnable(true);
-    setSchedSwitchTracingEnable(false);
-    setFrequencyTracingEnable(false);
-    setGovernorLoadTracingEnable(false);
     setGlobalClockEnable(false);
 
-    if (isRoot) {
-        setBusUtilizationTracingEnable(false);
-        setSyncTracingEnabled(false);
-        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.
 }
@@ -418,36 +494,15 @@ static void dumpTrace()
     close(traceFD);
 }
 
-// Print the command usage help to stderr.
+static void handleSignal(int signo)
-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"
-                    "  -y              trace sync timelines and waits\n"
-                    "  -z              compress the trace dump\n"
-                    "  --async_start   start circular trace and return immediatly\n"
-                    "  --async_dump    dump the current contents of circular trace buffer\n"
-                    "  --async_stop    stop tracing and dump the current contents of circular\n"
-                    "                    trace buffer\n"
-            );
-}
-
-static void handleSignal(int signo) {
     if (!g_nohup) {
         g_traceAborted = true;
     }
 }
 
-static void registerSigHandler() {
+static void registerSigHandler()
+{
     struct sigaction sa;
     sigemptyset(&sa.sa_mask);
     sa.sa_flags = 0;
@@ -458,9 +513,60 @@ static void registerSigHandler() {
     sigaction(SIGTERM, &sa, NULL);
 }
 
+static bool setCategoryEnable(const char* name, bool enable)
+{
+    for (int i = 0; i < NELEM(k_categories); i++) {
+        const TracingCategory& c = k_categories[i];
+        if (strcmp(name, c.name) == 0) {
+            if (isCategorySupported(c)) {
+                g_categoryEnables[i] = enable;
+                return true;
+            } else {
+                if (isCategorySupportedForRoot(c)) {
+                    fprintf(stderr, "error: category \"%s\" requires root "
+                            "privileges.\n", name);
+                } else {
+                    fprintf(stderr, "error: category \"%s\" is not supported "
+                            "on this device.\n", name);
+                }
+                return false;
+            }
+        }
+    }
+    fprintf(stderr, "error: unknown tracing category \"%s\"\n", name);
+    return false;
+}
+
+static void listSupportedCategories()
+{
+    for (int i = 0; i < NELEM(k_categories); i++) {
+        const TracingCategory& c = k_categories[i];
+        if (isCategorySupported(c)) {
+            printf("  %10s - %s\n", c.name, c.longname);
+        }
+    }
+}
+
+// Print the command usage help to stderr.
+static void showHelp(const char *cmd)
+{
+    fprintf(stderr, "usage: %s [options] [categories...]\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"
+                    "  -n              ignore signals\n"
+                    "  -s N            sleep for N seconds before tracing [default 0]\n"
+                    "  -t N            trace for N seconds [defualt 5]\n"
+                    "  -z              compress the trace dump\n"
+                    "  --async_start   start circular trace and return immediatly\n"
+                    "  --async_dump    dump the current contents of circular trace buffer\n"
+                    "  --async_stop    stop tracing and dump the current contents of circular\n"
+                    "                    trace buffer\n"
+            );
+}
+
 int main(int argc, char **argv)
 {
-    bool isRoot = (getuid() == 0);
     bool async = false;
     bool traceStart = true;
     bool traceStop = true;
@@ -478,13 +584,20 @@ int main(int argc, char **argv)
             {"async_start",     no_argument, 0,  0 },
             {"async_stop",      no_argument, 0,  0 },
             {"async_dump",      no_argument, 0,  0 },
-            {0,         0,                 0,  0 }
+            {"list_categories", no_argument, 0,  0 },
+            {           0,                0, 0,  0 }
         };
 
-        ret = getopt_long(argc, argv, "b:cidflst:uwyznS:",
+        ret = getopt_long(argc, argv, "b:cns:t:z",
                           long_options, &option_index);
 
         if (ret < 0) {
+            for (int i = optind; i < argc; i++) {
+                if (!setCategoryEnable(argv[i], true)) {
+                    fprintf(stderr, "error enabling tracing category \"%s\"\n", argv[i]);
+                    exit(1);
+                }
+            }
             break;
         }
 
@@ -497,35 +610,11 @@ int main(int argc, char **argv)
                 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 'n':
                 g_nohup = true;
                 break;
 
             case 's':
-                g_traceSchedSwitch = true;
-            break;
-
-            case 'S':
                 g_initialSleepSecs = atoi(optarg);
             break;
 
@@ -533,30 +622,6 @@ int main(int argc, char **argv)
                 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 'y':
-                if (!isRoot) {
-                    fprintf(stderr, "error: tracing sync requires root privileges\n");
-                    exit(1);
-                }
-                g_traceSync = true;
-            break;
-
             case 'z':
                 g_compress = true;
             break;
@@ -574,6 +639,9 @@ int main(int argc, char **argv)
                     async = true;
                     traceStart = false;
                     traceStop = false;
+                } else if (!strcmp(long_options[option_index].name, "list_categories")) {
+                    listSupportedCategories();
+                    exit(0);
                 }
                 break;
 
@@ -591,7 +659,7 @@ int main(int argc, char **argv)
         sleep(g_initialSleepSecs);
     }
 
-    bool ok = startTrace(isRoot);
+    bool ok = startTrace();
 
     if (ok && traceStart) {
         printf("capturing trace...");
@@ -619,7 +687,7 @@ int main(int argc, char **argv)
 
     // Stop the trace and restore the default settings.
     if (traceStop)
-        stopTrace(isRoot);
+        stopTrace();
 
     if (ok && traceDump) {
         if (!g_traceAborted) {