cashew: add local byte counters

src/procfs_byte_counter.cc

+// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/procfs_byte_counter.h"
+
+#include <stdio.h>
+
+#include <glog/logging.h>
+
+namespace cashew {
+
+static const char *kProcNetDevPath = "/proc/net/dev";
+static const int kLineBufferSize = 256;
+
+// /proc/net/dev output format
+// must remain consistent with kernel (see net/core/dev.c)
+static const char *kProcNetDevExpectedLine1 =
+    "Inter-|   Receive                            "
+    "                    |  Transmit\n";
+static const char *kProcNetDevExpectedLine2 =
+    " face |bytes    packets errs drop fifo frame "
+    "compressed multicast|bytes    packets errs "
+    "drop fifo colls carrier compressed\n";
+static const char *kProcNetDevLineFormat =
+    "%s %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu\n";
+static const int kProcNetDevLineFormatNumElements = 17;
+
+// ReadStats timer interval
+// TODO(vlaviano): can reduce this once we implement a smarter ShouldEmitSignal
+// policy than 'return true'
+static const guint kReadStatsIntervalSeconds = 60;
+
+ProcfsByteCounter::ProcfsByteCounter(const std::string& interface)
+    : interface_(interface), proc_net_dev_fp_(NULL), read_stats_source_id_(0),
+      counter_rx_bytes_(0), counter_tx_bytes_(0), baseline_stats_(),
+      baseline_initialized_(false), delegate_(NULL) {
+  DCHECK(!interface_.empty());
+  // initialize our counter state
+  if (!ReadStats()) {
+    LOG(WARNING) << interface_ << ": ctor: ReadStats failed";
+    // fall through so that we'll try again later
+  }
+  // schedule periodic ReadStats() calls to update counter state in the future
+  read_stats_source_id_ = g_timeout_add_seconds(kReadStatsIntervalSeconds,
+                                                StaticReadStatsCallback, this);
+  if (read_stats_source_id_ == 0) {
+    LOG(ERROR) << interface_ << ": ctor: g_idle_add failed";
+    return;
+  }
+}
+
+ProcfsByteCounter::~ProcfsByteCounter() {
+  DCHECK(proc_net_dev_fp_ == NULL);
+  if (read_stats_source_id_ != 0 && !g_source_remove(read_stats_source_id_)) {
+    DLOG(WARNING) << interface_ << ": dtor: g_source_remove_failed";
+  }
+}
+
+const std::string& ProcfsByteCounter::GetInterface() const {
+  return interface_;
+}
+
+uint64 ProcfsByteCounter::GetRxBytes() const {
+  return counter_rx_bytes_;
+}
+
+uint64 ProcfsByteCounter::GetTxBytes() const {
+  return counter_tx_bytes_;
+}
+
+void ProcfsByteCounter::SetDelegate(ByteCounterDelegate *delegate) {
+  DLOG(INFO) << interface_ << ": SetDelegate";
+  delegate_ = delegate;
+}
+
+// private methods
+
+bool ProcfsByteCounter::OpenProcNetDev() {
+  DCHECK(proc_net_dev_fp_ == NULL);
+  if ((proc_net_dev_fp_ = fopen(kProcNetDevPath, "r")) == NULL) {
+    PLOG(ERROR) << interface_ << ": OpenProcNetDev: couldn't open "
+        << kProcNetDevPath;
+    return false;
+  }
+  return true;
+}
+
+void ProcfsByteCounter::CloseProcNetDev() {
+  if (proc_net_dev_fp_ != NULL) {
+    if (fclose(proc_net_dev_fp_)) {
+      PLOG(WARNING) << interface_ << ": CloseProcNetDev: fclose failed";
+    }
+    proc_net_dev_fp_ = NULL;
+  }
+  DCHECK(proc_net_dev_fp_ == NULL);
+}
+
+// static
+gboolean ProcfsByteCounter::StaticReadStatsCallback(gpointer data) {
+  ProcfsByteCounter *counter = reinterpret_cast<ProcfsByteCounter*>(data);
+  CHECK_NOTNULL(counter);
+  if (!counter->ReadStats()) {
+    DLOG(WARNING) << counter->GetInterface() << ": StaticReadStatsCallback: "
+        << "ReadStats failed";
+  }
+  return TRUE;  // we want to be called again later
+}
+
+bool ProcfsByteCounter::ReadStats() {
+  // we open and close the virtual file each time through, because we get stale
+  // data if we keep the file open and rewind/read repeatedly
+  if (!OpenProcNetDev()) {
+    LOG(ERROR) << interface_ << ": ReadStats: OpenProcDevNet failed";
+    return false;
+  }
+  char line_buffer[kLineBufferSize];
+  for (int line_number = 1;  // use 1-based counting to make log msgs sensible
+       fgets(line_buffer, sizeof(line_buffer), proc_net_dev_fp_) != NULL;
+       ++line_number) {
+    // the first two lines contain human-friendly column headers
+    // skip them, while ensuring that they are as we expect
+    // this provides some confidence that the format hasn't changed on us
+    if (line_number == 1 || line_number == 2) {
+      if (strncmp(line_buffer, (line_number == 1) ? kProcNetDevExpectedLine1 :
+                  kProcNetDevExpectedLine2, sizeof(line_buffer))) {
+        LOG(ERROR) << interface_ << ": ReadStats: line " << line_number
+            << " is not as we expect";
+        CloseProcNetDev();
+        return false;
+      }
+      continue;
+    }
+    // each subsequent line contains the name and stats for a network interface
+    // parse it, reading stats, and see if the name matches |interface_|
+    //
+    // replace first colon in string (immediately after device name) with a
+    // space so that sscanf greedy string parsing doesn't cause the colon and
+    // possibly the rx byte count following it to all be consumed as part of the
+    // device name.
+    char *colon_ptr = strchr(line_buffer, ':');
+    if (colon_ptr == NULL) {
+      LOG(ERROR) << interface_ << ": ReadStats: line " << line_number
+          << ": strchr failed to find colon";
+      CloseProcNetDev();
+      return false;
+    }
+    *colon_ptr = ' ';
+    char device_name[IFNAMSIZ];
+    struct net_device_stats stats;
+    memset(&stats, 0, sizeof(stats));
+    // cpplint tells us that sscanf, while not prohibited, is sketchy
+    // we'll risk it since this data is from the kernel proc fs and we provide
+    //   the format string
+    //
+    // note that some fields of net_device_stats are combined when producing the
+    //   contents of /proc/net/dev
+    // we assign these combined values to the field named in the column header
+    int result = sscanf(line_buffer, kProcNetDevLineFormat,  // NOLINT
+                        device_name, &stats.rx_bytes, &stats.rx_packets,
+                        &stats.rx_errors, &stats.rx_dropped,
+                        &stats.rx_fifo_errors, &stats.rx_frame_errors,
+                        &stats.rx_compressed, &stats.multicast, &stats.tx_bytes,
+                        &stats.tx_packets, &stats.tx_errors, &stats.tx_dropped,
+                        &stats.tx_fifo_errors, &stats.collisions,
+                        &stats.tx_carrier_errors, &stats.tx_compressed);
+    if (result == EOF && ferror(proc_net_dev_fp_)) {
+      PLOG(ERROR) << interface_ << ": ReadStats: line " << line_number
+          << ": sscanf failed";
+      CloseProcNetDev();
+      return false;
+    }
+    if (result != kProcNetDevLineFormatNumElements) {
+      LOG(ERROR) << interface_ << ": ReadStats: line " << line_number
+          << ": sscanf matched " << ((result == EOF) ? 0 : result)
+          << " elements (" << kProcNetDevLineFormatNumElements << " expected)";
+      CloseProcNetDev();
+      return false;
+    }
+    if (device_name != interface_) {
+      continue;
+    }
+    // we found a match
+    // update our counter based on new stats
+    OnStatsUpdate(stats);
+    CloseProcNetDev();
+    return true;
+  }
+  LOG(ERROR) << interface_ << ": ReadStats: no matching device";
+  CloseProcNetDev();
+  return false;
+}
+
+void ProcfsByteCounter::OnStatsUpdate(const struct net_device_stats& stats) {
+  DLOG(INFO) << interface_ << ": OnStatsUpdate: stats: rx_bytes = "
+      << stats.rx_bytes << ", tx_bytes = " << stats.tx_bytes;
+  if (baseline_initialized_) {
+    DLOG(INFO) << interface_ << ": OnStatsUpdate: baseline: rx_bytes = "
+        << baseline_stats_.rx_bytes << ", tx_bytes = "
+        << baseline_stats_.tx_bytes;
+    uint64 old_counter_rx_bytes = counter_rx_bytes_;
+    uint64 old_counter_tx_bytes = counter_tx_bytes_;
+    DLOG(INFO) << interface_ << ": OnStatsUpdate: old counter: rx_bytes = "
+        << old_counter_rx_bytes << ", tx_bytes = " << old_counter_tx_bytes;
+    // these seemingly naive computations handle wraparound due to the modular
+    // nature of unsigned subtraction
+    counter_rx_bytes_ += stats.rx_bytes - baseline_stats_.rx_bytes;
+    counter_tx_bytes_ += stats.tx_bytes - baseline_stats_.tx_bytes;
+    DLOG(INFO) << interface_ << ": OnStatsUpdate: new counter: rx_bytes = "
+        << counter_rx_bytes_ << ", tx_bytes = " << counter_tx_bytes_;
+    bool counter_changed = counter_rx_bytes_ != old_counter_rx_bytes ||
+        counter_tx_bytes_ != old_counter_tx_bytes;
+    if (delegate_ != NULL && counter_changed) {
+      delegate_->OnByteCounterUpdate(this, counter_rx_bytes_,
+                                     counter_tx_bytes_);
+    }
+  } else {
+    baseline_initialized_ = true;
+  }
+  // We update the baseline on each new sample so that we aren't confused about
+  // how many times the device counter has wrapped around since we've started.
+  // This works as long as the sample interval is short enough to prevent wrap
+  // around between consecutive samples.
+  baseline_stats_ = stats;
+}
+
+}  // namespace cashew