qtbase/src/corelib/io/qstorageinfo_linux.cpp

// Copyright (C) 2021 The Qt Company Ltd.
// Copyright (C) 2014 Ivan Komissarov <ABBAPOH@gmail.com>
// Copyright (C) 2016 Intel Corporation.
// Copyright (C) 2023 Ahmad Samir <a.samirh78@gmail.com>
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only

#include "qstorageinfo_linux_p.h"

#include "qdiriterator.h"
#include <private/qcore_unix_p.h>
#include <private/qtools_p.h>

#include <q20memory.h>

#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/statfs.h>

// so we don't have to #include <linux/fs.h>, which is known to cause conflicts
#ifndef FSLABEL_MAX
#  define FSLABEL_MAX           256
#endif
#ifndef FS_IOC_GETFSLABEL
#  define FS_IOC_GETFSLABEL     _IOR(0x94, 49, char[FSLABEL_MAX])
#endif

// or <linux/statfs.h>
#ifndef ST_RDONLY
#  define ST_RDONLY             0x0001  /* mount read-only */
#endif

#if defined(Q_OS_ANDROID)
// statx() is disabled on Android because quite a few systems
// come with sandboxes that kill applications that make system calls outside a
// whitelist and several Android vendors can't be bothered to update the list.
#  undef STATX_BASIC_STATS
#endif

QT_BEGIN_NAMESPACE

using namespace Qt::StringLiterals;

namespace {
struct AutoFileDescriptor
{
    int fd = -1;
    AutoFileDescriptor(const QString &path, int mode = QT_OPEN_RDONLY)
        : fd(qt_safe_open(QFile::encodeName(path), mode))
    {}
    ~AutoFileDescriptor() { if (fd >= 0) qt_safe_close(fd); }
    operator int() const noexcept { return fd; }
};
}

// udev encodes the labels with ID_LABEL_FS_ENC which is done with
// blkid_encode_string(). Within this function some 1-byte utf-8
// characters not considered safe (e.g. '\' or ' ') are encoded as hex
static QString decodeFsEncString(QString &&str)
{
    using namespace QtMiscUtils;
    qsizetype start = str.indexOf(u'\\');
    if (start < 0)
        return std::move(str);

    // decode in-place
    QString decoded = std::move(str);
    auto ptr = reinterpret_cast<char16_t *>(decoded.begin());
    qsizetype in = start;
    qsizetype out = start;
    qsizetype size = decoded.size();

    while (in < size) {
        Q_ASSERT(ptr[in] == u'\\');
        if (size - in >= 4 && ptr[in + 1] == u'x') {    // we need four characters: \xAB
            int c = fromHex(ptr[in + 2]) << 4;
            c |= fromHex(ptr[in + 3]);
            if (Q_UNLIKELY(c < 0))
                c = QChar::ReplacementCharacter;        // bad hex sequence
            ptr[out++] = c;
            in += 4;
        }

        for ( ; in < size; ++in) {
            char16_t c = ptr[in];
            if (c == u'\\')
                break;
            ptr[out++] = c;
        }
    }
    decoded.resize(out);
    return decoded;
}

static inline dev_t deviceIdForPath(const QString &device)
{
    QT_STATBUF st;
    if (QT_STAT(QFile::encodeName(device), &st) < 0)
        return 0;
    return st.st_dev;
}

static inline quint64 mountIdForPath(int fd)
{
    if (fd < 0)
        return 0;
#if defined(STATX_BASIC_STATS) && defined(STATX_MNT_ID)
    // STATX_MNT_ID was added in kernel v5.8
    struct statx st;
    int r = statx(fd, "", AT_EMPTY_PATH | AT_NO_AUTOMOUNT, STATX_MNT_ID, &st);
    if (r == 0 && (st.stx_mask & STATX_MNT_ID))
        return st.stx_mnt_id;
#endif
    return 0;
}

static inline quint64 retrieveDeviceId(const QByteArray &device, quint64 deviceId = 0)
{
    // major = 0 implies an anonymous block device, so we need to stat() the
    // actual device to get its dev_t. This is required for btrfs (and possibly
    // others), which always uses them for all the subvolumes (including the
    // root):
    // https://codebrowser.dev/linux/linux/fs/btrfs/disk-io.c.html#btrfs_init_fs_root
    // https://codebrowser.dev/linux/linux/fs/super.c.html#get_anon_bdev
    // For everything else, we trust the parameter.
    if (major(deviceId) != 0)
        return deviceId;

    // don't even try to stat() a relative path or "/"
    if (device.size() < 2 || !device.startsWith('/'))
        return 0;

    QT_STATBUF st;
    if (QT_STAT(device, &st) < 0)
        return 0;
    if (!S_ISBLK(st.st_mode))
        return 0;
    return st.st_rdev;
}

static QDirIterator devicesByLabel()
{
    static const char pathDiskByLabel[] = "/dev/disk/by-label";
    static constexpr auto LabelFileFilter =
            QDir::AllEntries | QDir::System | QDir::Hidden | QDir::NoDotAndDotDot;

    return QDirIterator(QLatin1StringView(pathDiskByLabel), LabelFileFilter);
}

static inline auto retrieveLabels()
{
    struct Entry {
        QString label;
        quint64 deviceId;
    };
    QList<Entry> result;

    QDirIterator it = devicesByLabel();
    while (it.hasNext()) {
        QFileInfo fileInfo = it.nextFileInfo();
        quint64 deviceId = retrieveDeviceId(QFile::encodeName(fileInfo.filePath()));
        if (!deviceId)
            continue;
        result.emplaceBack(Entry{ decodeFsEncString(fileInfo.fileName()), deviceId });
    }
    return result;
}

static std::optional<QString> retrieveLabelViaIoctl(int fd)
{
    // FS_IOC_GETFSLABEL was introduced in v4.18; previously it was btrfs-specific.
    if (fd < 0)
        return std::nullopt;

    // Note: it doesn't append the null terminator (despite what the man page
    // says) and the return code on success (0) does not indicate the length.
    char label[FSLABEL_MAX] = {};
    int r = ioctl(fd, FS_IOC_GETFSLABEL, &label);
    if (r < 0)
        return std::nullopt;
    return QString::fromUtf8(label);
}

static inline QString retrieveLabel(const QStorageInfoPrivate &d, int fd, quint64 deviceId)
{
    if (auto label = retrieveLabelViaIoctl(fd))
        return *label;

    deviceId = retrieveDeviceId(d.device, deviceId);
    if (!deviceId)
        return QString();

    QDirIterator it = devicesByLabel();
    while (it.hasNext()) {
        QFileInfo fileInfo = it.nextFileInfo();
        QString name = fileInfo.fileName();
        if (retrieveDeviceId(QFile::encodeName(fileInfo.filePath())) == deviceId)
            return decodeFsEncString(std::move(name));
    }
    return QString();
}

void QStorageInfoPrivate::retrieveVolumeInfo()
{
    struct statfs64 statfs_buf;
    int result;
    QT_EINTR_LOOP(result, statfs64(QFile::encodeName(rootPath).constData(), &statfs_buf));
    if (result == 0) {
        valid = true;
        ready = true;

        bytesTotal = statfs_buf.f_blocks * statfs_buf.f_frsize;
        bytesFree = statfs_buf.f_bfree * statfs_buf.f_frsize;
        bytesAvailable = statfs_buf.f_bavail * statfs_buf.f_frsize;
        blockSize = int(statfs_buf.f_bsize);
        readOnly = (statfs_buf.f_flags & ST_RDONLY) != 0;
    }
}

static std::vector<MountInfo> parseMountInfo(FilterMountInfo filter = FilterMountInfo::All)
{
    QFile file(u"/proc/self/mountinfo"_s);
    if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
        return {};

    QByteArray mountinfo = file.readAll();
    file.close();

    return doParseMountInfo(mountinfo, filter);
}

void QStorageInfoPrivate::doStat()
{
    retrieveVolumeInfo();
    if (!ready)
        return;

    rootPath = QFileInfo(rootPath).canonicalFilePath();
    if (rootPath.isEmpty())
        return;

    std::vector<MountInfo> infos = parseMountInfo();
    if (infos.empty()) {
        rootPath = u'/';
        return;
    }

    MountInfo *best = nullptr;
    AutoFileDescriptor fd(rootPath);
    if (quint64 mntid = mountIdForPath(fd)) {
        // We have the mount ID for this path, so find the matching line.
        auto it = std::find_if(infos.begin(), infos.end(),
                               [mntid](const MountInfo &info) { return info.mntid == mntid; });
        if (it != infos.end())
            best = q20::to_address(it);
    } else {
        // We have failed to get the mount ID for this path, usually because
        // the path cannot be open()ed by this user (e.g., /root), so we fall
        // back to a string search.
        // We iterate over the /proc/self/mountinfo list backwards because then any
        // matching isParentOf must be the actual mount point because it's the most
        // recent mount on that path. Linux does allow mounting over non-empty
        // directories, such as in:
        //   # mount | tail -2
        //   tmpfs on /tmp/foo/bar type tmpfs (rw,relatime,inode64)
        //   tmpfs on /tmp/foo type tmpfs (rw,relatime,inode64)
        //
        // We try to match the device ID in case there's a mount --move.
        // We can't *rely* on it because some filesystems like btrfs will assign
        // device IDs to subvolumes that aren't listed in /proc/self/mountinfo.

        const QString oldRootPath = std::exchange(rootPath, QString());
        const dev_t rootPathDevId = deviceIdForPath(oldRootPath);
        for (auto it = infos.rbegin(); it != infos.rend(); ++it) {
            if (!isParentOf(it->mountPoint, oldRootPath))
                continue;
            if (rootPathDevId == it->stDev) {
                // device ID matches; this is definitely the best option
                best = q20::to_address(it);
                break;
            }
            if (!best) {
                // if we can't find a device ID match, this parent path is probably
                // the correct one
                best = q20::to_address(it);
            }
        }
    }
    if (best) {
        auto stDev = best->stDev;
        setFromMountInfo(std::move(*best));
        name = retrieveLabel(*this, fd, stDev);
    }
}

QList<QStorageInfo> QStorageInfoPrivate::mountedVolumes()
{
    std::vector<MountInfo> infos = parseMountInfo(FilterMountInfo::Filtered);
    if (infos.empty())
        return QList{root()};

    std::optional<decltype(retrieveLabels())> labelMap;
    auto labelForDevice = [&labelMap](const QStorageInfoPrivate &d, int fd, quint64 devid) {
        if (d.fileSystemType == "tmpfs")
            return QString();

        if (auto label = retrieveLabelViaIoctl(fd))
            return *label;

        devid = retrieveDeviceId(d.device, devid);
        if (!devid)
            return QString();

        if (!labelMap)
            labelMap = retrieveLabels();
        for (auto &[deviceLabel, deviceId] : std::as_const(*labelMap)) {
            if (devid == deviceId)
                return deviceLabel;
        }
        return QString();
    };

    QList<QStorageInfo> volumes;
    volumes.reserve(infos.size());
    for (auto it = infos.begin(); it != infos.end(); ++it) {
        MountInfo &info = *it;
        AutoFileDescriptor fd(info.mountPoint);

        // find out if the path as we see it matches this line from mountinfo
        quint64 mntid = mountIdForPath(fd);
        if (mntid == 0) {
            // statx failed, so scan the later lines to see if any is a parent
            // to this
            auto isParent = [&info](const MountInfo &maybeParent) {
                return isParentOf(maybeParent.mountPoint, info.mountPoint);
            };
            if (std::find_if(it + 1, infos.end(), isParent) != infos.end())
                continue;
        } else if (mntid != info.mntid) {
            continue;
        }

        const auto infoStDev = info.stDev;
        QStorageInfoPrivate d(std::move(info));
        d.retrieveVolumeInfo();
        if (d.bytesTotal <= 0 && d.rootPath != u'/')
            continue;
        d.name = labelForDevice(d, fd, infoStDev);
        volumes.emplace_back(QStorageInfo(*new QStorageInfoPrivate(std::move(d))));
    }
    return volumes;
}

QT_END_NAMESPACE