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

metrics_daemon_main.cc

Index: metrics_daemon_main.cc
diff --git a/metrics_daemon_main.cc b/metrics_daemon_main.cc
index 899256cffccbd6948d2699b4b12ebbfbff5951fc..1ee06117745126415ca1143cf67042c14f19967a 100644
--- a/metrics_daemon_main.cc
+++ b/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);
 }