Repository: bitcoin/bitcoin
File: src/util/fs_helpers.cpp (C++)

Code before:
// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-present The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include <util/fs_helpers.h>

#include <bitcoin-build-config.h> // IWYU pragma: keep

#include <logging.h>
#include <sync.h>
#include <util/fs.h>
#include <util/syserror.h>

#include <cerrno>
#include <fstream>
#include <map>
#include <memory>
#include <optional>
#include <string>
#include <system_error>
#include <utility>

#ifndef WIN32
#include <fcntl.h>
#include <sys/resource.h>
#include <unistd.h>
#else
#include <io.h>
#include <shlobj.h>
#endif // WIN32

/** Mutex to protect dir_locks. */
static GlobalMutex cs_dir_locks;
/** A map that contains all the currently held directory locks. After
 * successful locking, these will be held here until the global destructor
 * cleans them up and thus automatically unlocks them, or ReleaseDirectoryLocks
 * is called.
 */
static std::map<std::string, std::unique_ptr<fsbridge::FileLock>> dir_locks GUARDED_BY(cs_dir_locks);
namespace util {
LockResult LockDirectory(const fs::path& directory, const fs::path& lockfile_name, bool probe_only)
{
    LOCK(cs_dir_locks);
    fs::path pathLockFile = directory / lockfile_name;

    // If a lock for this directory already exists in the map, don't try to re-lock it
    if (dir_locks.count(fs::PathToString(pathLockFile))) {
        return LockResult::Success;
    }

    // Create empty lock file if it doesn't exist.
    if (auto created{fsbridge::fopen(pathLockFile, "a")}) {
        std::fclose(created);
    } else {
        return LockResult::ErrorWrite;
    }
    auto lock = std::make_unique<fsbridge::FileLock>(pathLockFile);
    if (!lock->TryLock()) {
        LogError("Error while attempting to lock directory %s: %s\n", fs::PathToString(directory), lock->GetReason());
        return LockResult::ErrorLock;
    }
    if (!probe_only) {
        // Lock successful and we're not just probing, put it into the map
        dir_locks.emplace(fs::PathToString(pathLockFile), std::move(lock));
    }
    return LockResult::Success;
}
} // namespace util
void UnlockDirectory(const fs::path& directory, const fs::path& lockfile_name)
{
    LOCK(cs_dir_locks);
    dir_locks.erase(fs::PathToString(directory / lockfile_name));
}

void ReleaseDirectoryLocks()
{
    LOCK(cs_dir_locks);
    dir_locks.clear();
}

bool CheckDiskSpace(const fs::path& dir, uint64_t additional_bytes)
{
    constexpr uint64_t min_disk_space = 52428800; // 50 MiB

    uint64_t free_bytes_available = fs::space(dir).available;
    return free_bytes_available >= min_disk_space + additional_bytes;
}

std::streampos GetFileSize(const char* path, std::streamsize max)
{
    std::ifstream file{path, std::ios::binary};
    file.ignore(max);
    return file.gcount();
}

bool FileCommit(FILE* file)
{
    if (fflush(file) != 0) { // harmless if redundantly called
        LogPrintf("fflush failed: %s\n", SysErrorString(errno));
        return false;
    }
#ifdef WIN32
    HANDLE hFile = (HANDLE)_get_osfhandle(_fileno(file));
    if (FlushFileBuffers(hFile) == 0) {
        LogPrintf("FlushFileBuffers failed: %s\n", Win32ErrorString(GetLastError()));
        return false;
    }
#elif defined(__APPLE__) && defined(F_FULLFSYNC)
    if (fcntl(fileno(file), F_FULLFSYNC, 0) == -1) { // Manpage says "value other than -1" is returned on success
        LogPrintf("fcntl F_FULLFSYNC failed: %s\n", SysErrorString(errno));
        return false;
    }
#elif HAVE_FDATASYNC
    if (fdatasync(fileno(file)) != 0 && errno != EINVAL) { // Ignore EINVAL for filesystems that don't support sync
        LogPrintf("fdatasync failed: %s\n", SysErrorString(errno));
        return false;
    }
#else
    if (fsync(fileno(file)) != 0 && errno != EINVAL) {
        LogPrintf("fsync failed: %s\n", SysErrorString(errno));
        return false;
    }
#endif
    return true;
}

void DirectoryCommit(const fs::path& dirname)
{
#ifndef WIN32
    FILE* file = fsbridge::fopen(dirname, "r");
    if (file) {
        fsync(fileno(file));
        fclose(file);
    }
#endif
}

bool TruncateFile(FILE* file, unsigned int length)
{
#if defined(WIN32)
    return _chsize(_fileno(file), length) == 0;
#else
    return ftruncate(fileno(file), length) == 0;
#endif
}

/**
 * this function tries to raise the file descriptor limit to the requested number.
 * It returns the actual file descriptor limit (which may be more or less than nMinFD)
 */
int RaiseFileDescriptorLimit(int nMinFD)
{
#if defined(WIN32)
    return 2048;
#else
    struct rlimit limitFD;
    if (getrlimit(RLIMIT_NOFILE, &limitFD) != -1) {
        if (limitFD.rlim_cur < (rlim_t)nMinFD) {
            limitFD.rlim_cur = nMinFD;
            if (limitFD.rlim_cur > limitFD.rlim_max)
                limitFD.rlim_cur = limitFD.rlim_max;
            setrlimit(RLIMIT_NOFILE, &limitFD);
            getrlimit(RLIMIT_NOFILE, &limitFD);
        }
        return limitFD.rlim_cur;
    }
    return nMinFD; // getrlimit failed, assume it's fine
#endif
}

/**
 * this function tries to make a particular range of a file allocated (corresponding to disk space)
 * it is advisory, and the range specified in the arguments will never contain live data
 */
void AllocateFileRange(FILE* file, unsigned int offset, unsigned int length)
{
#if defined(WIN32)
    // Windows-specific version
    HANDLE hFile = (HANDLE)_get_osfhandle(_fileno(file));
    LARGE_INTEGER nFileSize;
    int64_t nEndPos = (int64_t)offset + length;
    nFileSize.u.LowPart = nEndPos & 0xFFFFFFFF;
    nFileSize.u.HighPart = nEndPos >> 32;
    SetFilePointerEx(hFile, nFileSize, 0, FILE_BEGIN);
    SetEndOfFile(hFile);
#elif defined(__APPLE__)
    // OSX specific version
    // NOTE: Contrary to other OS versions, the OSX version assumes that
    // NOTE: offset is the size of the file.
    fstore_t fst;
    fst.fst_flags = F_ALLOCATECONTIG;
    fst.fst_posmode = F_PEOFPOSMODE;
    fst.fst_offset = 0;
    fst.fst_length = length; // mac os fst_length takes the # of free bytes to allocate, not desired file size
    fst.fst_bytesalloc = 0;
    if (fcntl(fileno(file), F_PREALLOCATE, &fst) == -1) {
        fst.fst_flags = F_ALLOCATEALL;
        fcntl(fileno(file), F_PREALLOCATE, &fst);
    }
    ftruncate(fileno(file), static_cast<off_t>(offset) + length);
#else
#if defined(HAVE_POSIX_FALLOCATE)
    // Version using posix_fallocate
    off_t nEndPos = (off_t)offset + length;
    if (0 == posix_fallocate(fileno(file), 0, nEndPos)) return;
#endif
    // Fallback version
    // TODO: just write one byte per block
    static const char buf[65536] = {};
    if (fseek(file, offset, SEEK_SET)) {
        return;
    }
    while (length > 0) {
        unsigned int now = 65536;
        if (length < now)
            now = length;
        fwrite(buf, 1, now, file); // allowed to fail; this function is advisory anyway
        length -= now;
    }
#endif
}

#ifdef WIN32
fs::path GetSpecialFolderPath(int nFolder, bool fCreate)
{
    WCHAR pszPath[MAX_PATH] = L"";

    if (SHGetSpecialFolderPathW(nullptr, pszPath, nFolder, fCreate)) {
        return fs::path(pszPath);
    }

    LogPrintf("SHGetSpecialFolderPathW() failed, could not obtain requested path.\n");
    return fs::path("");
}
#endif

bool RenameOver(fs::path src, fs::path dest)
{
    std::error_code error;
    fs::rename(src, dest, error);
    return !error;
}

/**
 * Ignores exceptions thrown by create_directories if the requested directory exists.
 * Specifically handles case where path p exists, but it wasn't possible for the user to
 * write to the parent directory.
 */
bool TryCreateDirectories(const fs::path& p)
{
    try {
        return fs::create_directories(p);
    } catch (const fs::filesystem_error&) {
        if (!fs::exists(p) || !fs::is_directory(p))
            throw;
    }

    // create_directories didn't create the directory, it had to have existed already
    return false;
}

std::string PermsToSymbolicString(fs::perms p)
{
    std::string perm_str(9, '-');

    auto set_perm = [&](size_t pos, fs::perms required_perm, char letter) {
        if ((p & required_perm) != fs::perms::none) {
            perm_str[pos] = letter;
        }
    };

    set_perm(0, fs::perms::owner_read,   'r');
    set_perm(1, fs::perms::owner_write,  'w');
    set_perm(2, fs::perms::owner_exec,   'x');
    set_perm(3, fs::perms::group_read,   'r');
    set_perm(4, fs::perms::group_write,  'w');
    set_perm(5, fs::perms::group_exec,   'x');
    set_perm(6, fs::perms::others_read,  'r');
    set_perm(7, fs::perms::others_write, 'w');
    set_perm(8, fs::perms::others_exec,  'x');

    return perm_str;
}

std::optional<fs::perms> InterpretPermString(const std::string& s)
{
    if (s == "owner") {
        return fs::perms::owner_read | fs::perms::owner_write;
    } else if (s == "group") {
        return fs::perms::owner_read | fs::perms::owner_write |
               fs::perms::group_read;
    } else if (s == "all") {
        return fs::perms::owner_read | fs::perms::owner_write |
               fs::perms::group_read |
               fs::perms::others_read;
    } else {
        return std::nullopt;
    }
}


Review comment (refactor):
First, while I believe this to be correct, could you provide a documentation that shows the possible values? I'm wondering if it's always written like this or if it's sometimes exFAT (like you refer to it) or [ExFAT](https://support.apple.com/guide/disk-utility/file-system-formats-dsku19ed921c/mac) (like the apple doc does sometimes) - or even if it would/should work with something like https://github.com/relan/exfat (found this accidentally, ignore if not important)

Second: nit, we don't have to keep this C-style comparison, we can also compare `string_views`, something like:
```C++
FSType GetFilesystemType(const fs::path& path)
{
    if (struct statfs fs_info; statfs(path.c_str(), &fs_info)) {
        return FSType::ERROR;
    } else if (std::string_view{fs_info.f_fstypename} == "exfat") {
        return FSType::EXFAT;
    }
    return FSType::OTHER;
}
```

Code after:
}

std::optional<fs::perms> InterpretPermString(const std::string& s)
{
    if (s == "owner") {
        return fs::perms::owner_read | fs::perms::owner_write;
    } else if (s == "group") {
        return fs::perms::owner_read | fs::perms::owner_write |
               fs::perms::group_read;
    } else if (s == "all") {
        return fs::perms::owner_read | fs::perms::owner_write |
               fs::perms::group_read |
               fs::perms::others_read;
    } else {
        return std::nullopt;
    }
}

#ifdef __APPLE__
FSType GetFilesystemType(const fs::path& path)
{
    if (struct statfs fs_info; statfs(path.c_str(), &fs_info)) {
        return FSType::ERROR;
    } else if (std::string_view{fs_info.f_fstypename} == "exfat") {
        return FSType::EXFAT;
    }
    return FSType::OTHER;
}
#endif