path: root/src/mongo/util/procparser.cpp

/**
 *    Copyright (C) 2018-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the Server Side Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */


#include "mongo/platform/basic.h"

#include "mongo/util/procparser.h"

#include <algorithm>
#include <array>
#include <boost/algorithm/string/finder.hpp>
#include <boost/algorithm/string/split.hpp>
#include <boost/filesystem.hpp>
#include <fcntl.h>
#include <string>
#include <sys/stat.h>
#include <sys/types.h>
#include <type_traits>
#include <unistd.h>

#include "mongo/base/parse_number.h"
#include "mongo/base/status.h"
#include "mongo/base/status_with.h"
#include "mongo/base/string_data.h"
#include "mongo/bson/bsonobjbuilder.h"
#include "mongo/logv2/log.h"
#include "mongo/util/pcre.h"
#include "mongo/util/scopeguard.h"
#include "mongo/util/str.h"
#include "mongo/util/text.h"

#define MONGO_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kFTDC

namespace mongo {

namespace {

/**
 * Get USER_HZ for the machine. See time(7) for an explanation.
 */
int64_t getTicksPerSecond() {
    int64_t ret = sysconf(_SC_CLK_TCK);
    return ret;
}

/**
 * Convert USER_HZ to milliseconds.
 */
double convertTicksToMilliSeconds(const int64_t ticks, const int64_t ticksPerSecond) {
    return static_cast<double>(ticks) / (static_cast<double>(ticksPerSecond) / 1000.0);
}

const size_t kFileBufferSize = 16384;
const size_t kFileReadRetryCount = 5;

constexpr auto kSysBlockDeviceDirectoryName = "device";

/**
 * Read a file from disk as a string with a null-terminating byte using the POSIX file api.
 *
 * This function is designed to get all the data it needs from small /proc files in a single read.
 * The /proc/stat and /proc/diskstats files can vary in size, but 16kb will cover most cases.
 *
 * Finally, we return errors instead of throwing to ensure that FTDC can return partial information
 * on failure instead of no information. Some container filesystems may overlay /proc so we may not
 * be reading directly from the kernel.
 */
StatusWith<std::string> readFileAsString(StringData filename) {
    int fd = open(filename.toString().c_str(), 0);
    if (fd == -1) {
        auto ec = lastSystemError();
        return Status(ErrorCodes::FileOpenFailed,
                      str::stream() << "Failed to open file " << filename
                                    << " with error: " << errorMessage(ec));
    }
    ScopeGuard scopedGuard([fd] { close(fd); });

    BufBuilder builder(kFileBufferSize);
    std::array<char, kFileBufferSize> buf;

    ssize_t size_read = 0;

    // Read until the end as needed
    do {

        // Retry if interrupted
        size_t retry = 0;

        do {
            size_read = read(fd, buf.data(), kFileBufferSize);

            if (size_read == -1) {
                auto ec = lastPosixError();

                // Retry if we hit EAGAIN or EINTR a few times before giving up
                if (retry < kFileReadRetryCount &&
                    (ec == posixError(EAGAIN) || ec == posixError(EINTR))) {
                    ++retry;
                    continue;
                }

                return Status(ErrorCodes::FileStreamFailed,
                              str::stream() << "Failed to read file " << filename
                                            << " with error: " << errorMessage(ec));
            }

            break;
        } while (true);

        if (size_read != 0) {
            builder.appendBuf(buf.data(), size_read);
        }
    } while (size_read != 0);

    // Null terminate the buffer since we are about to convert it to a string
    builder.appendChar(0);

    return std::string(builder.buf(), builder.len());
}


const char* const kAdditionCpuFields[] = {"user_ms",
                                          "nice_ms",
                                          "system_ms",
                                          "idle_ms",
                                          "iowait_ms",
                                          "irq_ms",
                                          "softirq_ms",
                                          "steal_ms",
                                          "guest_ms",
                                          "guest_nice_ms"};
const size_t kAdditionCpuFieldCount = std::extent<decltype(kAdditionCpuFields)>::value;

const char* const kDiskFields[] = {
    "reads",
    "reads_merged",
    "read_sectors",
    "read_time_ms",
    "writes",
    "writes_merged",
    "write_sectors",
    "write_time_ms",
    "io_in_progress",
    "io_time_ms",
    "io_queued_ms",
};

const size_t kDiskFieldCount = std::extent<decltype(kDiskFields)>::value;

}  // namespace

namespace procparser {
// Here is an example of the type of string it supports.
// Note: intr output has been trimmed
//
// The cpu field maps up to 10 individual fields depending on the kernel version. For other views,
// this code assumes there is only a single value.
//
// For more information, see:
// Documentation/filesystems/proc.txt in the Linux kernel
// proc(5) man page
//
// > cat /proc/stat
// cpu  41801 9179 32206 831134223 34279 0 947 0 0 0
// cpu0 2977 450 2475 69253074 1959 0 116 0 0 0
// cpu1 6213 4261 9400 69177349 845 0 539 0 0 0
// cpu2 1949 831 3699 69261035 645 0 0 0 0 0
// cpu3 2222 644 3283 69264801 783 0 0 0 0 0
// cpu4 16576 607 4757 69232589 8195 0 291 0 0 0
// cpu5 3742 391 4571 69257332 2322 0 0 0 0 0
// cpu6 2173 376 743 69284308 400 0 0 0 0 0
// cpu7 1232 375 704 69285753 218 0 0 0 0 0
// cpu8 960 127 576 69262851 18107 0 0 0 0 0
// cpu9 1755 227 744 69283938 362 0 0 0 0 0
// cpu10 1380 641 678 69285193 219 0 0 0 0 0
// cpu11 618 244 572 69285995 218 0 0 0 0 0
// intr 54084718 135 2 ....
// ctxt 190305514
// btime 1463584038
// processes 47438
// procs_running 1
// procs_blocked 0
// softirq 102690251 8 26697410 115481 23345078 816026 0 2296 26068778 0 25645174
//
Status parseProcStat(const std::vector<StringData>& keys,
                     StringData data,
                     int64_t ticksPerSecond,
                     BSONObjBuilder* builder) {
    bool foundKeys = false;

    using string_split_iterator = boost::split_iterator<StringData::const_iterator>;

    // Split the file by lines.
    // token_compress_on means the iterator skips over consecutive '\n'. This should not be a
    // problem in normal /proc/stat output.
    for (string_split_iterator lineIt = string_split_iterator(
             data.begin(),
             data.end(),
             boost::token_finder([](char c) { return c == '\n'; }, boost::token_compress_on));
         lineIt != string_split_iterator();
         ++lineIt) {

        StringData line((*lineIt).begin(), (*lineIt).end());

        // Split the line by spaces since that is the only delimiter for stat files.
        // token_compress_on means the iterator skips over consecutive ' '. This is needed for the
        // first line which is "cpu  <number>".
        string_split_iterator partIt = string_split_iterator(
            line.begin(),
            line.end(),
            boost::token_finder([](char c) { return c == ' '; }, boost::token_compress_on));

        // Skip processing this line if we do not have a key.
        if (partIt == string_split_iterator()) {
            continue;
        }

        StringData key((*partIt).begin(), (*partIt).end());

        ++partIt;

        // Skip processing this line if we only have a key, and no number.
        if (partIt == string_split_iterator()) {
            continue;
        }

        // Check if the key is in the list. /proc/stat will have extra keys, and
        // may not have the keys we want.
        if (keys.empty() || std::find(keys.begin(), keys.end(), key) != keys.end()) {

            foundKeys = true;

            if (key == "cpu") {
                // Cpu is 10 fields, we need to chew through all of them.
                // Some kernels we support lack the last field or two: guest and/or guest_nice.
                for (size_t index = 0;
                     partIt != string_split_iterator() && index < kAdditionCpuFieldCount;
                     ++partIt, ++index) {

                    StringData stringValue((*partIt).begin(), (*partIt).end() - (*partIt).begin());

                    uint64_t value;

                    if (!NumberParser{}(stringValue, &value).isOK()) {
                        value = 0;
                    }

                    builder->appendNumber(kAdditionCpuFields[index],
                                          convertTicksToMilliSeconds(value, ticksPerSecond));
                }
            } else {
                StringData stringValue((*partIt).begin(), (*partIt).end() - (*partIt).begin());

                uint64_t value;

                if (!NumberParser{}(stringValue, &value).isOK()) {
                    value = 0;
                }

                builder->appendNumber(key, static_cast<long long>(value));
            }
        }
    }

    return foundKeys ? Status::OK()
                     : Status(ErrorCodes::NoSuchKey, "Failed to find any keys in stat string");
}

Status parseProcStatFile(StringData filename,
                         const std::vector<StringData>& keys,
                         BSONObjBuilder* builder) {
    auto swString = readFileAsString(filename);
    if (!swString.isOK()) {
        return swString.getStatus();
    }

    return parseProcStat(keys, swString.getValue(), getTicksPerSecond(), builder);
}

// Here is an example of the type of string it supports:
// Note: output has been trimmed
//
// For more information, see:
// Documentation/filesystems/proc.txt in the Linux kernel
// proc(5) man page
//
// > cat /proc/meminfo
// MemTotal:       12294392 kB
// MemFree:         3652612 kB
// MemAvailable:   11831704 kB
// Buffers:          568536 kB
// Cached:          6421520 kB
// SwapCached:            0 kB
// HugePages_Total:       0
//
// Note: HugePages_* do not end in kB, it is not a typo
//
Status parseProcMemInfo(const std::vector<StringData>& keys,
                        StringData data,
                        BSONObjBuilder* builder) {
    bool foundKeys = false;

    using string_split_iterator = boost::split_iterator<StringData::const_iterator>;

    // Split the file by lines.
    // token_compress_on means the iterator skips over consecutive '\n'. This should not be a
    // problem in normal /proc/memInfo output.
    for (string_split_iterator lineIt = string_split_iterator(
             data.begin(),
             data.end(),
             boost::token_finder([](char c) { return c == '\n'; }, boost::token_compress_on));
         lineIt != string_split_iterator();
         ++lineIt) {

        StringData line((*lineIt).begin(), (*lineIt).end());

        // Split the line by spaces and colons since these are the delimiters for meminfo files.
        // token_compress_on means the iterator skips over consecutive ' '. This is needed for
        // every line.
        string_split_iterator partIt =
            string_split_iterator(line.begin(),
                                  line.end(),
                                  boost::token_finder([](char c) { return c == ' ' || c == ':'; },
                                                      boost::token_compress_on));

        // Skip processing this line if we do not have a key.
        if (partIt == string_split_iterator()) {
            continue;
        }

        StringData key((*partIt).begin(), (*partIt).end());

        ++partIt;

        // Skip processing this line if we only have a key, and no number.
        if (partIt == string_split_iterator()) {
            continue;
        }

        // Check if the key is in the list. /proc/meminfo will have extra keys, and may not have the
        // keys we want.
        if (keys.empty() || std::find(keys.begin(), keys.end(), key) != keys.end()) {
            foundKeys = true;

            StringData stringValue((*partIt).begin(), (*partIt).end());

            uint64_t value;

            if (!NumberParser{}(stringValue, &value).isOK()) {
                value = 0;
            }

            // Check if the line ends in "kB"
            ++partIt;

            // If there is one last token, check if it is actually "kB"
            if (partIt != string_split_iterator()) {
                StringData kb_token((*partIt).begin(), (*partIt).end());
                auto keyWithSuffix = key.toString();

                if (kb_token == "kB") {
                    keyWithSuffix.append("_kb");
                }

                builder->appendNumber(keyWithSuffix, static_cast<long long>(value));
            } else {

                builder->appendNumber(key, static_cast<long long>(value));
            }
        }
    }

    return foundKeys ? Status::OK()
                     : Status(ErrorCodes::NoSuchKey, "Failed to find any keys in meminfo string");
}

Status parseProcMemInfoFile(StringData filename,
                            const std::vector<StringData>& keys,
                            BSONObjBuilder* builder) {
    auto swString = readFileAsString(filename);
    if (!swString.isOK()) {
        return swString.getStatus();
    }

    return parseProcMemInfo(keys, swString.getValue(), builder);
}

//
// Here is an example of the type of string it supports (long lines elided for clarity).
// > cat /proc/net/netstat
// TcpExt: SyncookiesSent SyncookiesRecv SyncookiesFailed ...
// TcpExt: 3437 5938 13368 ...
// IpExt: InNoRoutes InTruncatedPkts InMcastPkts ...
// IpExt: 999 1 4819969 ...
//
// Parser assumes file consists of alternating lines of keys and values
// key and value lines consist of space-separated tokens
// first token is a key prefix that is prepended in the output to each key
// all prefixed keys and corresponding values are copied to output as-is
//

Status parseProcNetstat(const std::vector<StringData>& keys,
                        StringData data,
                        BSONObjBuilder* builder) {

    using string_split_iterator = boost::split_iterator<StringData::const_iterator>;

    string_split_iterator keysIt;
    bool foundKeys = false;

    // Split the file by lines.
    uint32_t lineNum = 0;
    for (string_split_iterator lineIt = string_split_iterator(
             data.begin(),
             data.end(),
             boost::token_finder([](char c) { return c == '\n'; }, boost::token_compress_on));
         lineIt != string_split_iterator();
         ++lineIt, ++lineNum) {

        if (lineNum % 2 == 0) {

            // even numbered lines are keys
            keysIt = string_split_iterator(
                (*lineIt).begin(),
                (*lineIt).end(),
                boost::token_finder([](char c) { return c == ' '; }, boost::token_compress_on));

        } else {

            // odd numbered lines are values
            string_split_iterator valuesIt = string_split_iterator(
                (*lineIt).begin(),
                (*lineIt).end(),
                boost::token_finder([](char c) { return c == ' '; }, boost::token_compress_on));

            StringData prefix;

            // iterate over the keys and values in parallel
            for (uint32_t keyNum = 0;
                 keysIt != string_split_iterator() && valuesIt != string_split_iterator();
                 ++keysIt, ++valuesIt, ++keyNum) {

                if (keyNum == 0) {

                    // first token is a prefix to be applied to remaining keys
                    prefix = StringData((*keysIt).begin(), (*keysIt).end());

                    // ignore line if prefix isn't in requested list
                    if (!keys.empty() && std::find(keys.begin(), keys.end(), prefix) == keys.end())
                        break;

                } else {

                    // remaining tokens are key/value pairs
                    StringData key((*keysIt).begin(), (*keysIt).end());
                    StringData stringValue((*valuesIt).begin(), (*valuesIt).end());
                    uint64_t value;
                    if (NumberParser{}(stringValue, &value).isOK()) {
                        builder->appendNumber(prefix.toString() + key.toString(),
                                              static_cast<long long>(value));
                        foundKeys = true;
                    }
                }
            }
        }
    }

    return foundKeys ? Status::OK()
                     : Status(ErrorCodes::NoSuchKey, "Failed to find any keys in netstats string");
}

Status parseProcNetstatFile(const std::vector<StringData>& keys,
                            StringData filename,
                            BSONObjBuilder* builder) {
    auto swString = readFileAsString(filename);
    if (!swString.isOK()) {
        return swString.getStatus();
    }
    return parseProcNetstat(keys, swString.getValue(), builder);
}


// Here is an example of the type of string it supports:
//
// For more information, see:
// Documentation/iostats.txt in the Linux kernel
// proc(5) man page
//
// > cat /proc/diskstats
//   8       0 sda 120611 33630 6297628 96550 349797 167398 11311562 2453603 0 117514 2554160
//   8       1 sda1 138 37 8642 315 3 0 18 14 0 292 329
//   8       2 sda2 120409 33593 6285754 96158 329029 167398 11311544 2450573 0 115611 2550739
//   8      16 sdb 12707 3876 1525418 57507 997 3561 297576 97976 0 37870 155619
//   8      17 sdb1 12601 3876 1521090 57424 992 3561 297576 97912 0 37738 155468
//  11       0 sr0 0 0 0 0 0 0 0 0 0 0 0
// 253       0 dm-0 154910 0 6279522 177681 506513 0 11311544 5674418 0 117752 5852275
// 253       1 dm-1 109 0 4584 226 0 0 0 0 0 172 226
//
Status parseProcDiskStats(const std::vector<StringData>& disks,
                          StringData data,
                          BSONObjBuilder* builder) {
    bool foundKeys = false;
    std::vector<uint64_t> stats;
    stats.reserve(kDiskFieldCount);

    using string_split_iterator = boost::split_iterator<StringData::const_iterator>;

    // Split the file by lines.
    // token_compress_on means the iterator skips over consecutive '\n'. This should not be a
    // problem in normal /proc/diskstats output.
    for (string_split_iterator lineIt = string_split_iterator(
             data.begin(),
             data.end(),
             boost::token_finder([](char c) { return c == '\n'; }, boost::token_compress_on));
         lineIt != string_split_iterator();
         ++lineIt) {

        StringData line((*lineIt).begin(), (*lineIt).end());

        // Skip leading whitespace so that the split_iterator starts on non-whitespace otherwise we
        // get an empty first token. Device major numbers (the first number on each line) are right
        // aligned to 4 spaces and start from
        // single digits.
        auto beginNonWhitespace =
            std::find_if_not(line.begin(), line.end(), [](char c) { return c == ' '; });

        // Split the line by spaces since that is the only delimiter for diskstats files.
        // token_compress_on means the iterator skips over consecutive ' '.
        string_split_iterator partIt = string_split_iterator(
            beginNonWhitespace,
            line.end(),
            boost::token_finder([](char c) { return c == ' '; }, boost::token_compress_on));

        // Skip processing this line if the line is blank
        if (partIt == string_split_iterator()) {
            continue;
        }

        ++partIt;

        // Skip processing this line if we only have a device major number.
        if (partIt == string_split_iterator()) {
            continue;
        }

        ++partIt;

        // Skip processing this line if we only have a device major minor.
        if (partIt == string_split_iterator()) {
            continue;
        }

        StringData disk((*partIt).begin(), (*partIt).end());

        // Skip processing this line if we only have a block device name.
        if (partIt == string_split_iterator()) {
            continue;
        }

        ++partIt;

        // Check if the disk is in the list. /proc/diskstats will have extra disks, and may not have
        // the disk we want.
        if (disks.empty() || std::find(disks.begin(), disks.end(), disk) != disks.end()) {
            foundKeys = true;

            stats.clear();

            // Only generate a disk document if the disk has some activity. For instance, there
            // could be a CD-ROM drive that is not used.
            bool hasSomeNonZeroStats = false;

            for (size_t index = 0; partIt != string_split_iterator() && index < kDiskFieldCount;
                 ++partIt, ++index) {

                StringData stringValue((*partIt).begin(), (*partIt).end());

                uint64_t value;

                if (!NumberParser{}(stringValue, &value).isOK()) {
                    value = 0;
                }

                if (value != 0) {
                    hasSomeNonZeroStats = true;
                }

                stats.push_back(value);
            }

            if (hasSomeNonZeroStats) {
                // Start a new document with disk as the name.
                BSONObjBuilder sub(builder->subobjStart(disk));

                for (size_t index = 0; index < stats.size() && index < kDiskFieldCount; ++index) {
                    sub.appendNumber(kDiskFields[index], static_cast<long long>(stats[index]));
                }

                sub.doneFast();
            }
        }
    }

    return foundKeys ? Status::OK()
                     : Status(ErrorCodes::NoSuchKey, "Failed to find any keys in diskstats string");
}

Status parseProcDiskStatsFile(StringData filename,
                              const std::vector<StringData>& disks,
                              BSONObjBuilder* builder) {
    auto swString = readFileAsString(filename);
    if (!swString.isOK()) {
        return swString.getStatus();
    }

    return parseProcDiskStats(disks, swString.getValue(), builder);
}

Status parseProcSelfMountStatsImpl(
    StringData data,
    BSONObjBuilder* builder,
    boost::filesystem::space_info (*getSpace)(const boost::filesystem::path&,
                                              boost::system::error_code&)) {
    invariant(getSpace);
    std::istringstream iss(data.toString());
    for (std::string line; std::getline(iss, line);) {
        // As described in the /proc/[pid]/mountinfo section of `man 5 proc`:
        //
        // 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
        // |  |  |    |     |     |          |          |      |     |
        // (1)(2)(3:4)(5)   (6)   (7)        (8)        (9)   (10)   (11)
        static const pcre::Regex kRe(R"re(\d+ \d+ \d+:\d+ \S+ (\S+))re");
        if (auto m = kRe.matchView(line)) {
            std::string mountPoint{m[1]};
            boost::filesystem::path p(mountPoint);
            boost::system::error_code ec;
            boost::filesystem::space_info spaceInfo = getSpace(p, ec);
            if (!ec.failed() && spaceInfo.capacity) {
                BSONObjBuilder bob(builder->subobjStart(mountPoint));
                bob.appendNumber("capacity", static_cast<long long>(spaceInfo.capacity));
                bob.appendNumber("available", static_cast<long long>(spaceInfo.available));
                bob.appendNumber("free", static_cast<long long>(spaceInfo.free));
                bob.doneFast();
            }
        }
    }

    return Status::OK();
}

Status parseProcSelfMountStats(StringData data, BSONObjBuilder* builder) {
    return parseProcSelfMountStatsImpl(data, builder, &boost::filesystem::space);
}

Status parseProcSelfMountStatsFile(StringData filename, BSONObjBuilder* builder) {
    auto swString = readFileAsString(filename);
    if (!swString.isOK()) {
        return swString.getStatus();
    }

    return parseProcSelfMountStats(swString.getValue(), builder);
}

namespace {

/**
 * Is this a disk that is interesting to us? We only want physical disks, not multiple disk devices,
 * LVM2 devices, partitions, or RAM disks.
 *
 * A physical disk has a symlink to a directory at /sys/block/<device name>/device.
 *
 * Note: returns false upon any errors such as access denied.
 */
bool isInterestingDisk(const boost::filesystem::path& path) {
    boost::filesystem::path blockDevicePath(path);
    blockDevicePath /= kSysBlockDeviceDirectoryName;

    boost::system::error_code ec;
    auto statusSysBlock = boost::filesystem::status(blockDevicePath, ec);
    if (!boost::filesystem::exists(statusSysBlock)) {
        return false;
    }

    if (ec) {
        LOGV2_WARNING(23912,
                      "Error checking directory '{blockDevicePath_generic_string}': {ec_message}",
                      "blockDevicePath_generic_string"_attr = blockDevicePath.generic_string(),
                      "ec_message"_attr = ec.message());
        return false;
    }

    if (!boost::filesystem::is_directory(statusSysBlock)) {
        return false;
    }

    return true;
}

}  // namespace

std::vector<std::string> findPhysicalDisks(StringData sysBlockPath) {
    boost::system::error_code ec;
    auto sysBlockPathStr = sysBlockPath.toString();

    auto statusSysBlock = boost::filesystem::status(sysBlockPathStr, ec);
    if (ec) {
        LOGV2_WARNING(23913,
                      "Error checking directory '{sysBlockPathStr}': {ec_message}",
                      "sysBlockPathStr"_attr = sysBlockPathStr,
                      "ec_message"_attr = ec.message());
        return {};
    }

    if (!(boost::filesystem::exists(statusSysBlock) &&
          boost::filesystem::is_directory(statusSysBlock))) {
        LOGV2_WARNING(23914,
                      "Could not find directory '{sysBlockPathStr}': {ec_message}",
                      "sysBlockPathStr"_attr = sysBlockPathStr,
                      "ec_message"_attr = ec.message());
        return {};
    }

    std::vector<std::string> files;

    // Iterate through directories in /sys/block. The directories in this directory can be physical
    // block devices (like SSD or HDD) or virtual devices like the LVM2 device mapper or a multiple
    // disk device. It does not contain disk partitions.
    boost::filesystem::directory_iterator di(sysBlockPathStr, ec);
    if (ec) {
        LOGV2_WARNING(23915,
                      "Error getting directory iterator '{sysBlockPathStr}': {ec_message}",
                      "sysBlockPathStr"_attr = sysBlockPathStr,
                      "ec_message"_attr = ec.message());
        return {};
    }

    for (; di != boost::filesystem::directory_iterator(); di++) {
        auto path = (*di).path();

        if (isInterestingDisk(path)) {
            files.push_back(path.filename().generic_string());
        }
    }

    return files;
}

// Here is an example of the type of string it supports:
// Note: output has been trimmed
//
// For more information, see:
// proc(5) man page
//
// > cat /proc/vmstat
// nr_free_pages 2732282
// nr_zone_inactive_anon 686253
// nr_zone_active_anon 4975441
// nr_zone_inactive_file 2332485
// nr_zone_active_file 4791149
// nr_zone_unevictable 0
// nr_zone_write_pending 0
// nr_mlock 0
//
Status parseProcVMStat(const std::vector<StringData>& keys,
                       StringData data,
                       BSONObjBuilder* builder) {
    bool foundKeys = false;

    using string_split_iterator = boost::split_iterator<StringData::const_iterator>;

    // Split the file by lines.
    // token_compress_on means the iterator skips over consecutive '\n'. This should not be a
    // problem in normal /proc/vmstat output.
    for (string_split_iterator lineIt = string_split_iterator(
             data.begin(),
             data.end(),
             boost::token_finder([](char c) { return c == '\n'; }, boost::token_compress_on));
         lineIt != string_split_iterator();
         ++lineIt) {

        StringData line(lineIt->begin(), lineIt->end());

        // Split the line by spaces since this the delimiters for vmstat files.
        // token_compress_on means the iterator skips over consecutive ' '. This is needed for
        // every line.
        string_split_iterator partIt = string_split_iterator(
            line.begin(),
            line.end(),
            boost::token_finder([](char c) { return c == ' '; }, boost::token_compress_on));

        // Skip processing this line if we do not have a key.
        if (partIt == string_split_iterator()) {
            continue;
        }

        StringData key(partIt->begin(), partIt->end());

        ++partIt;

        // Skip processing this line if we only have a key, and no number.
        if (partIt == string_split_iterator()) {
            continue;
        }

        // Check if the key is in the list. /proc/vmstat will have extra keys, and may not have the
        // keys we want.
        if (keys.empty() || std::find(keys.begin(), keys.end(), key) != keys.end()) {
            foundKeys = true;

            StringData stringValue(partIt->begin(), partIt->end());

            uint64_t value;

            if (!NumberParser{}(stringValue, &value).isOK()) {
                value = 0;
            }

            builder->appendNumber(key, static_cast<long long>(value));
        }
    }

    return foundKeys ? Status::OK()
                     : Status(ErrorCodes::NoSuchKey, "Failed to find any keys in vmstat string");
}

Status parseProcVMStatFile(StringData filename,
                           const std::vector<StringData>& keys,
                           BSONObjBuilder* builder) {
    auto swString = readFileAsString(filename);
    if (!swString.isOK()) {
        return swString.getStatus();
    }

    return parseProcVMStat(keys, swString.getValue(), builder);
}

Status parseProcSysFsFileNr(FileNrKey key, StringData data, BSONObjBuilder* builder) {
    // Format: HANDLES_IN_USE<whitespace>UNUSED_HANDLES<whitespace>MAX_HANDLES<return>
    using string_split_iterator = boost::split_iterator<StringData::const_iterator>;
    string_split_iterator partIt = string_split_iterator(
        data.begin(),
        data.end(),
        boost::token_finder([](char c) { return c == ' ' || c == '\t' || c == '\n'; },
                            boost::token_compress_on));

    if (partIt == string_split_iterator()) {
        return Status(ErrorCodes::FailedToParse, "Couldn't find first token");
    }

    if (key == FileNrKey::kFileHandlesInUse) {
        StringData stringValue(partIt->begin(), partIt->end());
        uint64_t value;
        if (!NumberParser{}(stringValue, &value).isOK()) {
            return Status(ErrorCodes::FailedToParse, "Couldn't parse first token to number");
        }

        builder->appendNumber(kFileHandlesInUseKey, static_cast<long long>(value));
        return Status::OK();
    }
    ++partIt;

    if (partIt == string_split_iterator()) {
        return Status(ErrorCodes::FailedToParse, "Couldn't find second token");
    }
    // The second value is the number of allocated but unused file handles, which should always be
    // 0; we ignore this.
    ++partIt;

    if (partIt == string_split_iterator()) {
        return Status(ErrorCodes::FailedToParse, "Couldn't find third token");
    }

    invariant(key == FileNrKey::kMaxFileHandles);
    StringData stringValue(partIt->begin(), partIt->end());
    uint64_t value;
    if (!NumberParser{}(stringValue, &value).isOK()) {
        return Status(ErrorCodes::FailedToParse, "Couldn't parse third token to number");
    }

    builder->appendNumber(kMaxFileHandlesKey, static_cast<long long>(value));

    return Status::OK();
}

Status parseProcSysFsFileNrFile(StringData filename, FileNrKey key, BSONObjBuilder* builder) {
    auto swString = readFileAsString(filename);
    if (!swString.isOK()) {
        return swString.getStatus();
    }

    return parseProcSysFsFileNr(key, swString.getValue(), builder);
}

// Here is an example of the type of string it supports:
//
// > cat /proc/pressure/<cpu|io|memory>
// some avg10=0.00 avg60=0.00 avg300=0.14 total=1434509127
// full avg10=0.00 avg60=0.00 avg300=0.14 total=1035574668
//
// Note: /proc/pressure/cpu only has 'some' entry
//
Status parseProcPressure(StringData data, BSONObjBuilder* builder) {
    using string_split_iterator = boost::split_iterator<StringData::const_iterator>;

    // Split the file by lines.
    // token_compress_on means the iterator skips over consecutive '\n'.
    for (string_split_iterator lineIt = string_split_iterator(
             data.begin(),
             data.end(),
             boost::token_finder([](char c) { return c == '\n'; }, boost::token_compress_on));
         lineIt != string_split_iterator();
         ++lineIt) {

        StringData line((*lineIt).begin(), (*lineIt).end());

        // Split the line by spaces and equal signs since these are the delimiters for pressure
        // files. token_compress_on means the iterator skips over consecutive ' '. This is needed
        // for every line.
        string_split_iterator partIt =
            string_split_iterator(line.begin(),
                                  line.end(),
                                  boost::token_finder([](char c) { return c == ' ' || c == '='; },
                                                      boost::token_compress_on));

        // Skip processing this line if we do not have a key.
        if (partIt == string_split_iterator()) {
            continue;
        }

        StringData time((*partIt).begin(), (*partIt).end());

        ++partIt;

        // Skip processing this line if we only have a key, and no arguments.
        if (partIt == string_split_iterator()) {
            continue;
        }

        // Share of time is either 'some' or 'full'.
        if (time != kPressureSomeTime && time != kPressureFullTime) {
            return Status(ErrorCodes::FailedToParse, "Couldn't find the share of time");
        }

        // Lookup for 'total' token in the parts.
        auto totalIt = std::find_if(partIt, string_split_iterator(), [](const auto& vec) {
            return StringData(vec.begin(), vec.end()) == "total"_sd;
        });

        // If 'total' token is not found on the row return an error.
        if (totalIt == string_split_iterator()) {
            return Status(ErrorCodes::NoSuchKey, "Failed to find 'total' token");
        }

        StringData totalToken((*totalIt).begin(), (*totalIt).end());

        ++totalIt;

        if (totalIt == string_split_iterator()) {
            return Status(ErrorCodes::FailedToParse, "No value found for 'total' token");
        }

        StringData stringValue((*totalIt).begin(), (*totalIt).end());

        double value;

        if (!NumberParser{}(stringValue, &value).isOK()) {
            return Status(ErrorCodes::FailedToParse,
                          str::stream() << "Couldn't parse '" << stringValue << "' to number");
        }

        *builder << time << BSON("totalMicros" << value);
    }

    return Status::OK();
}

// Example of BSONObjBuilder created:
//  cpu : {
//    some : {
//       totalMicros : ...
//    },
//    fulll: {
//       totalMicros : ...
//     }
//  }
Status parseProcPressureFile(StringData key, StringData filename, BSONObjBuilder* builder) {
    auto swString = readFileAsString(filename);
    if (!swString.isOK()) {
        return swString.getStatus();
    }

    BSONObjBuilder sub(builder->subobjStart(key));
    Status status = parseProcPressure(swString.getValue(), &sub);
    sub.doneFast();

    return status;
}

}  // namespace procparser
}  // namespace mongo