atrace: make clock & bus bw tracing optional

This change makes enabling clock tracing and bus bandwidth tracing depend on
whether the device's kernel supports these features.  If it's not supported it
will be skipped.

Change-Id: I51d57299693635b0ecebb75de5dccd5b62d47be3

1 files changed, 23 insertions, 18 deletions

diff --git a/atrace/atrace.c b/atrace/atrace.c
index 381a4ed9..5edc47b3 100644
--- a/atrace/atrace.c
+++ b/atrace/atrace.c
@@ -93,6 +93,11 @@ static const char* k_tracePath =
 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;
+}
+
 // Write a string to a file, returning true if the write was successful.
 bool writeStr(const char* filename, const char* str)
 {
@@ -151,11 +156,14 @@ static bool setSchedSwitchTracingEnable(bool enable)
 // Enable or disable tracing of the Bus utilization.
 static bool setBusUtilizationTracingEnable(bool enable)
 {
-    bool ok = false;
+    bool ok = true, oneSet = false;
     // these can be platform specific so make sure that at least
     // one succeeds.
-    ok |= setKernelOptionEnable(k_memoryBusEnablePath, enable);
-    return ok;
+    if (fileExists(k_memoryBusEnablePath)) {
+        ok &= setKernelOptionEnable(k_memoryBusEnablePath, enable);
+        oneSet |= ok;
+    }
+    return ok && (oneSet || !enable);
 }
 
 // Enable or disable tracing of the CPU clock frequency.
@@ -163,7 +171,9 @@ static bool setFrequencyTracingEnable(bool enable)
 {
     bool ok = true;
     ok &= setKernelOptionEnable(k_cpuFreqEnablePath, enable);
-    ok &= setKernelOptionEnable(k_clockSetRateEnablePath, enable);
+    if (fileExists(k_clockSetRateEnablePath)) {
+        ok &= setKernelOptionEnable(k_clockSetRateEnablePath, enable);
+    }
     return ok;
 }
 
@@ -177,7 +187,11 @@ static bool setCpuIdleTracingEnable(bool enable)
 // the CPU load.
 static bool setGovernorLoadTracingEnable(bool enable)
 {
-    return setKernelOptionEnable(k_governorLoadEnablePath, enable);
+    bool ok = true;
+    if (fileExists(k_governorLoadEnablePath) || enable) {
+        ok &= setKernelOptionEnable(k_governorLoadEnablePath, enable);
+    }
+    return ok;
 }
 
 // Enable or disable tracing of the kernel workqueues.
@@ -232,11 +246,6 @@ 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)
 {
@@ -245,12 +254,9 @@ static bool startTrace(bool isRoot)
     // 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 &= setGovernorLoadTracingEnable(g_traceGovernorLoad);
     ok &= setTraceBufferSizeKB(g_traceBufferSizeKB);
     ok &= setGlobalClockEnable(true);
 
@@ -258,6 +264,7 @@ static bool startTrace(bool isRoot)
     // require root should have errored out earlier if we're not running as
     // root.
     if (isRoot) {
+        ok &= setBusUtilizationTracingEnable(g_traceBusUtilization);
         ok &= setWorkqueueTracingEnabled(g_traceWorkqueue);
         ok &= setDiskTracingEnabled(g_traceDisk);
     }
@@ -281,14 +288,12 @@ static void stopTrace(bool isRoot)
     // Set the options back to their defaults.
     setTraceOverwriteEnable(true);
     setSchedSwitchTracingEnable(false);
-    setBusUtilizationTracingEnable(false);
     setFrequencyTracingEnable(false);
-    if (fileExists(k_governorLoadEnablePath)) {
-        setGovernorLoadTracingEnable(false);
-    }
+    setGovernorLoadTracingEnable(false);
     setGlobalClockEnable(false);
 
     if (isRoot) {
+        setBusUtilizationTracingEnable(false);
         setWorkqueueTracingEnabled(false);
         setDiskTracingEnabled(false);
     }