Find device-dependent disk stats file, and skip disk stats if not available.

Change-Id: I03afb85e3357dd4c2cf5effd98b194c71d77c71d

BUG=12171
TEST=unit tested

Review URL: http://codereview.chromium.org/6541007

metrics/Makefile

@@ -38,7 +38,8 @@ TESTLIB_OBJS = \
 	metrics_library_test.o
 
 TESTCOUNTER_LIBS = -lgmock -lgtest -lbase -lrt -lpthread -lglib-2.0
-DAEMON_LDFLAGS = $(LDFLAGS) $(LDCONFIG) -lrt -lbase -lpthread -lgflags -lglib-2.0
+DAEMON_LDFLAGS = $(LDFLAGS) $(LDCONFIG) -lrt -lbase -lpthread -lgflags \
+		 -lglib-2.0 -lrootdev
 TESTDAEMON_LIBS = -lgmock -lgtest
 TESTLIB_LIBS = -lgtest -lbase -lrt -lpthread -lglib-2.0
 

metrics/metrics_daemon.cc

@@ -146,8 +146,7 @@ MetricsDaemon::MetricsDaemon()
       session_state_(kUnknownSessionState),
       user_active_(false),
       usemon_interval_(0),
-      usemon_source_(NULL),
-      diskstats_path_(NULL) {}
+      usemon_source_(NULL) {}
 
 MetricsDaemon::~MetricsDaemon() {
   DeleteFrequencyCounters();
@@ -215,7 +214,7 @@ void MetricsDaemon::ConfigureCrashFrequencyReporter(
 }
 
 void MetricsDaemon::Init(bool testing, MetricsLibraryInterface* metrics_lib,
-                         const char* diskstats_path) {
+                         string diskstats_path) {
   testing_ = testing;
   DCHECK(metrics_lib != NULL);
   metrics_lib_ = metrics_lib;
@@ -243,8 +242,11 @@ void MetricsDaemon::Init(bool testing, MetricsLibraryInterface* metrics_lib,
   ConfigureCrashFrequencyReporter(kMetricUserCrashesDailyName);
   ConfigureCrashFrequencyReporter(kMetricUserCrashesWeeklyName);
 
-  diskstats_path_ = diskstats_path;
-  DiskStatsReporterInit();
+  // Don't attempt to collect disk stats if there is no disk stats file.
+  if (!diskstats_path.empty()) {
+    diskstats_path_ = diskstats_path;
+    DiskStatsReporterInit();
+  }
 
   // Don't setup D-Bus and GLib in test mode.
   if (testing)
@@ -541,7 +543,7 @@ void MetricsDaemon::DiskStatsReadStats(long int* read_sectors,
   int nchars;
   int nitems;
   char line[200];
-  int file = HANDLE_EINTR(open(diskstats_path_, O_RDONLY));
+  int file = HANDLE_EINTR(open(diskstats_path_.c_str(), O_RDONLY));
   if (file < 0) {
     PLOG(WARNING) << "cannot open " << diskstats_path_;
     return;

metrics/metrics_daemon.h

@@ -30,7 +30,7 @@ class MetricsDaemon {
 
   // Initializes.
   void Init(bool testing, MetricsLibraryInterface* metrics_lib,
-            const char* diskstats_path);
+            std::string diskstats_path);
 
   // Does all the work. If |run_as_daemon| is true, daemonizes by
   // forking.
@@ -304,7 +304,7 @@ class MetricsDaemon {
   long int write_sectors_;
 
   DiskStatsState diskstats_state_;
-  const char* diskstats_path_;
+  std::string diskstats_path_;
 };
 
 #endif  // METRICS_DAEMON_H_

metrics/metrics_daemon_main.cc

@@ -3,20 +3,44 @@
 // found in the LICENSE file.
 
 
+#include <base/logging.h>
+#include <base/string_util.h>
 #include <gflags/gflags.h>
+#include <rootdev/rootdev.h>
 
 #include "metrics_daemon.h"
 
 DEFINE_bool(daemon, true, "run as daemon (use -nodaemon for debugging)");
 
-// Path to disk stats.  This may be system dependent.
-const char kMetricsMainDiskStatsPath[] = "/sys/class/block/sda/stat";
+// Return the path to the disk stats in the sysfs.
+static
+const std::string MetricsMainDiskStatsPath() {
+  char dev_path_cstr[PATH_MAX];
+  std::string dev_prefix = "/dev/";
+  std::string dev_path;
+  std::string dev_name;
+
+  int ret = rootdev(dev_path_cstr, sizeof(dev_path_cstr), true, true);
+  if (ret != 0) {
+    LOG(WARNING) << "error " << ret << " determining root device";
+    return "";
+  }
+  dev_path = dev_path_cstr;
+  // Check that rootdev begins with "/dev/".
+  if (!StartsWithASCII(dev_path, dev_prefix, false)) {
+    LOG(WARNING) << "unexpected root device " << dev_path;
+    return "";
+  }
+  // Get the device name, e.g. "sda" from "/dev/sda".
+  dev_name = dev_path.substr(dev_prefix.length());
+  return "/sys/class/block/" + dev_name + "/stat";
+}
 
 int main(int argc, char** argv) {
   google::ParseCommandLineFlags(&argc, &argv, true);
   MetricsLibrary metrics_lib;
   metrics_lib.Init();
   MetricsDaemon daemon;
-  daemon.Init(false, &metrics_lib, kMetricsMainDiskStatsPath);
+  daemon.Init(false, &metrics_lib, MetricsMainDiskStatsPath());
   daemon.Run(FLAGS_daemon);
 }