text: // Copyright (c) 2012 The Chromium 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 "base/process/internal_linux.h"
  
  #include <limits.h>
  #include <unistd.h>
  
  #include <map>
  #include <string>
  #include <vector>
  
  #include "base/files/file_util.h"
  #include "base/logging.h"
  #include "base/strings/string_number_conversions.h"
  #include "base/strings/string_split.h"
  #include "base/strings/string_util.h"
  #include "base/threading/thread_restrictions.h"
  #include "base/time/time.h"
  
  namespace base {
  namespace internal {
  
  const char kProcDir[] = "/proc";
  
  const char kStatFile[] = "stat";
  
  FilePath GetProcPidDir(pid_t pid) {
    return FilePath(kProcDir).Append(IntToString(pid));
  }
  
  pid_t ProcDirSlotToPid(const char* d_name) {
    int i;
    for (i = 0; i < NAME_MAX && d_name[i]; ++i) {
      if (!IsAsciiDigit(d_name[i])) {
        return 0;
      }
    }
    if (i == NAME_MAX)
      return 0;
  
    // Read the process's command line.
    pid_t pid;
    std::string pid_string(d_name);
    if (!StringToInt(pid_string, &pid)) {
      NOTREACHED();
      return 0;
    }
    return pid;
  }
  
  bool ReadProcFile(const FilePath& file, std::string* buffer) {
    buffer->clear();
    // Synchronously reading files in /proc is safe.
    ThreadRestrictions::ScopedAllowIO allow_io;
  
    if (!ReadFileToString(file, buffer)) {
      DLOG(WARNING) << "Failed to read " << file.MaybeAsASCII();
      return false;
    }
    return !buffer->empty();
  }
  
  bool ReadProcStats(pid_t pid, std::string* buffer) {
    FilePath stat_file = internal::GetProcPidDir(pid).Append(kStatFile);
    return ReadProcFile(stat_file, buffer);
  }
  
  bool ParseProcStats(const std::string& stats_data,
                      std::vector<std::string>* proc_stats) {
    // |stats_data| may be empty if the process disappeared somehow.
    // e.g. http://crbug.com/145811
    if (stats_data.empty())
      return false;
  
    // The stat file is formatted as:
    // pid (process name) data1 data2 .... dataN
    // Look for the closing paren by scanning backwards, to avoid being fooled by
    // processes with ')' in the name.
    size_t open_parens_idx = stats_data.find(" (");
    size_t close_parens_idx = stats_data.rfind(") ");
    if (open_parens_idx == std::string::npos ||
        close_parens_idx == std::string::npos ||
        open_parens_idx > close_parens_idx) {
      DLOG(WARNING) << "Failed to find matched parens in '" << stats_data << "'";
      NOTREACHED();
      return false;
    }
    open_parens_idx++;
  
    proc_stats->clear();
    // PID.
    proc_stats->push_back(stats_data.substr(0, open_parens_idx));
    // Process name without parentheses.
    proc_stats->push_back(
        stats_data.substr(open_parens_idx + 1,
                          close_parens_idx - (open_parens_idx + 1)));
  
    // Split the rest.
    std::vector<std::string> other_stats = SplitString(
        stats_data.substr(close_parens_idx + 2), " ",
        base::TRIM_WHITESPACE, base::SPLIT_WANT_ALL);
    for (size_t i = 0; i < other_stats.size(); ++i)
      proc_stats->push_back(other_stats[i]);
    return true;
  }
  
  typedef std::map<std::string, std::string> ProcStatMap;
  void ParseProcStat(const std::string& contents, ProcStatMap* output) {
    StringPairs key_value_pairs;
    SplitStringIntoKeyValuePairs(contents, ' ', '\n', &key_value_pairs);
    for (size_t i = 0; i < key_value_pairs.size(); ++i) {
      output->insert(key_value_pairs[i]);
    }
  }
  
  int64_t GetProcStatsFieldAsInt64(const std::vector<std::string>& proc_stats,
                                   ProcStatsFields field_num) {
    DCHECK_GE(field_num, VM_PPID);
    CHECK_LT(static_cast<size_t>(field_num), proc_stats.size());
  
    int64_t value;
    return StringToInt64(proc_stats[field_num], &value) ? value : 0;
  }
  
  size_t GetProcStatsFieldAsSizeT(const std::vector<std::string>& proc_stats,
                                  ProcStatsFields field_num) {
    DCHECK_GE(field_num, VM_PPID);
    CHECK_LT(static_cast<size_t>(field_num), proc_stats.size());
  
    size_t value;
    return StringToSizeT(proc_stats[field_num], &value) ? value : 0;
  }
  
  int64_t ReadProcStatsAndGetFieldAsInt64(pid_t pid, ProcStatsFields field_num) {
    std::string stats_data;
    if (!ReadProcStats(pid, &stats_data))
      return 0;
    std::vector<std::string> proc_stats;
    if (!ParseProcStats(stats_data, &proc_stats))
      return 0;
    return GetProcStatsFieldAsInt64(proc_stats, field_num);
  }
  
  size_t ReadProcStatsAndGetFieldAsSizeT(pid_t pid,
                                         ProcStatsFields field_num) {
    std::string stats_data;
    if (!ReadProcStats(pid, &stats_data))
      return 0;
    std::vector<std::string> proc_stats;
    if (!ParseProcStats(stats_data, &proc_stats))
      return 0;
    return GetProcStatsFieldAsSizeT(proc_stats, field_num);
  }
  
  Time GetBootTime() {
    FilePath path("/proc/stat");
    std::string contents;
    if (!ReadProcFile(path, &contents))
      return Time();
    ProcStatMap proc_stat;
    ParseProcStat(contents, &proc_stat);
    ProcStatMap::const_iterator btime_it = proc_stat.find("btime");
    if (btime_it == proc_stat.end())
      return Time();
    int btime;
    if (!StringToInt(btime_it->second, &btime))
      return Time();
    return Time::FromTimeT(btime);
  }
  
  TimeDelta ClockTicksToTimeDelta(int clock_ticks) {
    // This queries the /proc-specific scaling factor which is
    // conceptually the system hertz.  To dump this value on another
    // system, try
    //   od -t dL /proc/self/auxv
    // and look for the number after 17 in the output; mine is
    //   0000040          17         100           3   134512692
    // which means the answer is 100.
    // It may be the case that this value is always 100.
    static const int kHertz = sysconf(_SC_CLK_TCK);
  
    return TimeDelta::FromMicroseconds(
        Time::kMicrosecondsPerSecond * clock_ticks / kHertz);
  }
  
  }  // namespace internal
  }  // namespace base
  