incfs/incfs.cpp

/*
 * Copyright (C) 2019 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define LOG_TAG "incfs"

#include "incfs.h"

#include <IncrementalProperties.sysprop.h>
#include <android-base/file.h>
#include <android-base/logging.h>
#include <android-base/no_destructor.h>
#include <android-base/parsebool.h>
#include <android-base/properties.h>
#include <android-base/stringprintf.h>
#include <android-base/strings.h>
#include <android-base/unique_fd.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <libgen.h>
#include <openssl/sha.h>
#include <selinux/android.h>
#include <selinux/selinux.h>
#include <sys/inotify.h>
#include <sys/mount.h>
#include <sys/poll.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/vfs.h>
#include <sys/xattr.h>
#include <unistd.h>

#include <charconv>
#include <chrono>
#include <iterator>
#include <mutex>
#include <optional>
#include <string_view>

#include "MountRegistry.h"
#include "path.h"

using namespace std::literals;
using namespace android::incfs;
using namespace android::sysprop;
namespace ab = android::base;

namespace android::incfs {
extern const size_t kPageSize = getpagesize();
}

struct IncFsControl final {
    IncFsFd cmd;
    IncFsFd pendingReads;
    IncFsFd logs;
    IncFsFd blocksWritten;
    constexpr IncFsControl(IncFsFd cmd, IncFsFd pendingReads, IncFsFd logs, IncFsFd blocksWritten)
          : cmd(cmd), pendingReads(pendingReads), logs(logs), blocksWritten(blocksWritten) {}
};

static MountRegistry& registry() {
    static ab::NoDestructor<MountRegistry> instance{};
    return *instance;
}

static ab::unique_fd openRaw(std::string_view file) {
    auto fd = ab::unique_fd(::open(details::c_str(file), O_RDONLY | O_CLOEXEC));
    if (fd < 0) {
        return ab::unique_fd{-errno};
    }
    return fd;
}

static ab::unique_fd openAt(int fd, std::string_view name, int flags = 0) {
    auto res = ab::unique_fd(
            ::openat(fd, details::c_str(name), O_RDONLY | O_CLOEXEC | O_NOFOLLOW | flags));
    if (res < 0) {
        return ab::unique_fd{-errno};
    }
    return res;
}

static std::string indexPath(std::string_view root, IncFsFileId fileId) {
    return path::join(root, INCFS_INDEX_NAME, toString(fileId));
}

static std::string rootForCmd(int fd) {
    auto cmdFile = path::fromFd(fd);
    if (cmdFile.empty()) {
        LOG(INFO) << __func__ << "(): name empty for " << fd;
        return {};
    }
    auto res = path::dirName(cmdFile);
    if (res.empty()) {
        LOG(INFO) << __func__ << "(): dirname empty for " << cmdFile;
        return {};
    }
    if (!path::endsWith(cmdFile, INCFS_PENDING_READS_FILENAME)) {
        LOG(INFO) << __func__ << "(): invalid file name " << cmdFile;
        return {};
    }
    if (cmdFile.data() == res.data() || cmdFile.starts_with(res)) {
        cmdFile.resize(res.size());
        return cmdFile;
    }
    return std::string(res);
}

static bool isFsAvailable() {
    static const char kProcFilesystems[] = "/proc/filesystems";
    std::string filesystems;
    if (!ab::ReadFileToString(kProcFilesystems, &filesystems)) {
        return false;
    }
    const auto result = filesystems.find("\t" INCFS_NAME "\n") != std::string::npos;
    LOG(INFO) << "isFsAvailable: " << (result ? "true" : "false");
    return result;
}

static int getFirstApiLevel() {
    uint64_t api_level = android::base::GetUintProperty<uint64_t>("ro.product.first_api_level", 0);
    LOG(INFO) << "Initial API level of the device: " << api_level;
    return api_level;
}

static std::string_view incFsPropertyValue() {
    constexpr const int R_API = 30;
    static const auto kDefaultValue{getFirstApiLevel() > R_API ? "on" : ""};
    static const ab::NoDestructor<std::string> kValue{
            IncrementalProperties::enable().value_or(kDefaultValue)};
    LOG(INFO) << "ro.incremental.enable: " << *kValue;
    return *kValue;
}

static std::pair<bool, std::string_view> parseProperty(std::string_view property) {
    auto boolVal = ab::ParseBool(property);
    if (boolVal == ab::ParseBoolResult::kTrue) {
        return {isFsAvailable(), {}};
    }
    if (boolVal == ab::ParseBoolResult::kFalse) {
        return {false, {}};
    }

    // Don't load the module at once, but instead only check if it is loadable.
    static const auto kModulePrefix = "module:"sv;
    if (property.starts_with(kModulePrefix)) {
        const auto modulePath = property.substr(kModulePrefix.size());
        return {::access(details::c_str(modulePath), R_OK | X_OK), modulePath};
    }
    return {false, {}};
}

template <class Callback>
static IncFsErrorCode forEachFileIn(std::string_view dirPath, Callback cb) {
    auto dir = path::openDir(details::c_str(dirPath));
    if (!dir) {
        return -EINVAL;
    }

    int res = 0;
    while (auto entry = (errno = 0, ::readdir(dir.get()))) {
        if (entry->d_type != DT_REG) {
            continue;
        }
        ++res;
        if (!cb(entry->d_name)) {
            break;
        }
    }
    if (errno) {
        return -errno;
    }
    return res;
}

namespace {

class IncFsInit {
public:
    IncFsInit() {
        auto [featureEnabled, moduleName] = parseProperty(incFsPropertyValue());
        featureEnabled_ = featureEnabled;
        moduleName_ = moduleName;
        loaded_ = featureEnabled_ && isFsAvailable();
    }

    constexpr ~IncFsInit() = default;

    bool enabled() const { return featureEnabled_; }
    bool enabledAndReady() const {
        if (!featureEnabled_) {
            return false;
        }
        if (moduleName_.empty()) {
            return true;
        }
        if (loaded_) {
            return true;
        }
        std::call_once(loadedFlag_, [this] {
            if (isFsAvailable()) {
                // Loaded from a different process, I suppose.
                loaded_ = true;
                LOG(INFO) << "IncFS is already available, skipped loading";
                return;
            }
            const ab::unique_fd fd(TEMP_FAILURE_RETRY(
                    ::open(details::c_str(moduleName_), O_RDONLY | O_NOFOLLOW | O_CLOEXEC)));
            if (fd < 0) {
                PLOG(ERROR) << "could not open IncFs kernel module \"" << moduleName_ << '"';
                return;
            }

            const auto rc = syscall(__NR_finit_module, fd.get(), "", 0);
            if (rc < 0) {
                PLOG(ERROR) << "finit_module for IncFs \"" << moduleName_ << "\" failed";
                return;
            }
            if (!isFsAvailable()) {
                LOG(ERROR) << "loaded IncFs kernel module \"" << moduleName_
                           << "\" but incremental-fs is still not available";
            }
            loaded_ = true;
            LOG(INFO) << "successfully loaded IncFs kernel module \"" << moduleName_ << '"';
        });
        return loaded_;
    }

private:
    bool featureEnabled_;
    std::string_view moduleName_;
    mutable std::once_flag loadedFlag_;
    mutable bool loaded_;
};

} // namespace

static IncFsInit& init() {
    static IncFsInit initer;
    return initer;
}

bool IncFs_IsEnabled() {
    return init().enabled();
}

static Features readIncFsFeatures() {
    init().enabledAndReady();

    int res = Features::none | Features::mappingFilesProgressFixed;

    static const char kSysfsFeaturesDir[] = "/sys/fs/" INCFS_NAME "/features";
    const auto dir = path::openDir(kSysfsFeaturesDir);
    if (!dir) {
        PLOG(ERROR) << "IncFs_Features: failed to open features dir, assuming v1/none.";
        return Features(res);
    }

    while (auto entry = ::readdir(dir.get())) {
        if (entry->d_type != DT_REG) {
            continue;
        }
        if (entry->d_name == "corefs"sv) {
            res |= Features::core;
        } else if (entry->d_name == "v2"sv || entry->d_name == "report_uid"sv) {
            res |= Features::v2;
        }
    }

    LOG(INFO) << "IncFs_Features: " << ((res & Features::v2) ? "v2" : "v1");

    return Features(res);
}

IncFsFeatures IncFs_Features() {
    static const auto features = IncFsFeatures(readIncFsFeatures());
    return features;
}

bool isIncFsFdImpl(int fd) {
    struct statfs fs = {};
    if (::fstatfs(fd, &fs) != 0) {
        PLOG(WARNING) << __func__ << "(): could not fstatfs fd " << fd;
        return false;
    }

    return fs.f_type == (decltype(fs.f_type))INCFS_MAGIC_NUMBER;
}

bool isIncFsPathImpl(const char* path) {
    struct statfs fs = {};
    if (::statfs(path, &fs) != 0) {
        PLOG(WARNING) << __func__ << "(): could not statfs " << path;
        return false;
    }

    return fs.f_type == (decltype(fs.f_type))INCFS_MAGIC_NUMBER;
}

static int isDir(const char* path) {
    struct stat st;
    if (::stat(path, &st) != 0) {
        return -errno;
    }
    if (!S_ISDIR(st.st_mode)) {
        return -ENOTDIR;
    }
    return 0;
}

static bool isAbsolute(const char* path) {
    return path && path[0] == '/';
}

static int isValidMountTarget(const char* path) {
    if (!isAbsolute(path)) {
        return -EINVAL;
    }
    if (isIncFsPath(path)) {
        LOG(ERROR) << "[incfs] mounting over existing incfs mount is not allowed";
        return -EINVAL;
    }
    if (const auto err = isDir(path); err != 0) {
        return err;
    }
    if (const auto err = path::isEmptyDir(path); err != 0) {
        return err;
    }
    return 0;
}

static int rmDirContent(int dirFd) {
    auto dir = path::openDir(dirFd);
    if (!dir) {
        return -errno;
    }
    while (auto entry = ::readdir(dir.get())) {
        if (entry->d_name == "."sv || entry->d_name == ".."sv) {
            continue;
        }
        if (entry->d_type == DT_DIR) {
            auto fd = openAt(dirFd, entry->d_name, O_DIRECTORY);
            if (!fd.ok()) {
                return -errno;
            }
            if (const auto err = rmDirContent(fd.get())) {
                return err;
            }
            if (::unlinkat(fd.get(), entry->d_name, AT_REMOVEDIR)) {
                return -errno;
            }
        } else {
            auto fd = openAt(dirFd, entry->d_name);
            if (!fd.ok()) {
                return -errno;
            }
            if (::unlinkat(fd.get(), entry->d_name, 0)) {
                return -errno;
            }
        }
    }
    return 0;
}

static int rmDirContent(const char* path) {
    auto fd = openAt(-1, path, O_DIRECTORY);
    if (!fd.ok()) {
        return -errno;
    }
    return rmDirContent(fd.get());
}

static std::string makeMountOptionsString(IncFsMountOptions options) {
    auto opts = ab::StringPrintf("read_timeout_ms=%u,readahead=0,rlog_pages=%u,rlog_wakeup_cnt=1,",
                                 unsigned(options.defaultReadTimeoutMs),
                                 unsigned(options.readLogBufferPages < 0
                                                  ? INCFS_DEFAULT_PAGE_READ_BUFFER_PAGES
                                                  : options.readLogBufferPages));
    if (features() & Features::v2) {
        ab::StringAppendF(&opts, "report_uid,");
        if (options.sysfsName && *options.sysfsName) {
            ab::StringAppendF(&opts, "sysfs_name=%s,", options.sysfsName);
        }
    }
    return opts;
}

static IncFsControl* makeControl(int fd) {
    auto cmd = openAt(fd, INCFS_PENDING_READS_FILENAME);
    if (!cmd.ok()) {
        return nullptr;
    }
    ab::unique_fd pendingReads(fcntl(cmd.get(), F_DUPFD_CLOEXEC, cmd.get()));
    if (!pendingReads.ok()) {
        return nullptr;
    }
    auto logs = openAt(fd, INCFS_LOG_FILENAME);
    if (!logs.ok()) {
        return nullptr;
    }
    ab::unique_fd blocksWritten;
    if (features() & Features::v2) {
        blocksWritten = openAt(fd, INCFS_BLOCKS_WRITTEN_FILENAME);
        if (!blocksWritten.ok()) {
            return nullptr;
        }
    }
    auto control =
            IncFs_CreateControl(cmd.get(), pendingReads.get(), logs.get(), blocksWritten.get());
    if (control) {
        (void)cmd.release();
        (void)pendingReads.release();
        (void)logs.release();
        (void)blocksWritten.release();
    } else {
        errno = ENOMEM;
    }
    return control;
}

static std::string makeCommandPath(std::string_view root, std::string_view item) {
    auto [itemRoot, subpath] = registry().rootAndSubpathFor(item);
    if (itemRoot != root) {
        return {};
    }
    // TODO: add "/.cmd/" if we decide to use a separate control tree.
    return path::join(itemRoot, subpath);
}

static void toString(IncFsFileId id, char* out) {
    // Make sure this function matches the one in the kernel (e.g. same case for a-f digits).
    static constexpr char kHexChar[] = "0123456789abcdef";

    for (auto item = std::begin(id.data); item != std::end(id.data); ++item, out += 2) {
        out[0] = kHexChar[(*item & 0xf0) >> 4];
        out[1] = kHexChar[(*item & 0x0f)];
    }
}

static std::string toStringImpl(IncFsFileId id) {
    std::string res(kIncFsFileIdStringLength, '\0');
    toString(id, res.data());
    return res;
}

static IncFsFileId toFileIdImpl(std::string_view str) {
    if (str.size() != kIncFsFileIdStringLength) {
        return kIncFsInvalidFileId;
    }

    IncFsFileId res;
    auto out = (char*)&res;
    for (auto it = str.begin(); it != str.end(); it += 2, ++out) {
        static const auto fromChar = [](char src) -> int {
            if (src >= '0' && src <= '9') {
                return src - '0';
            }
            if (src >= 'a' && src <= 'f') {
                return src - 'a' + 10;
            }
            return -1;
        };

        const int c[2] = {fromChar(it[0]), fromChar(it[1])};
        if (c[0] == -1 || c[1] == -1) {
            errno = EINVAL;
            return kIncFsInvalidFileId;
        }
        *out = (c[0] << 4) | c[1];
    }
    return res;
}

int IncFs_FileIdToString(IncFsFileId id, char* out) {
    if (!out) {
        return -EINVAL;
    }
    toString(id, out);
    return 0;
}

IncFsFileId IncFs_FileIdFromString(const char* in) {
    return toFileIdImpl({in, kIncFsFileIdStringLength});
}

IncFsFileId IncFs_FileIdFromMetadata(IncFsSpan metadata) {
    IncFsFileId id = {};
    if (size_t(metadata.size) <= sizeof(id)) {
        memcpy(&id, metadata.data, metadata.size);
    } else {
        uint8_t buffer[SHA_DIGEST_LENGTH];
        static_assert(sizeof(buffer) >= sizeof(id));

        SHA_CTX ctx;
        SHA1_Init(&ctx);
        SHA1_Update(&ctx, metadata.data, metadata.size);
        SHA1_Final(buffer, &ctx);
        memcpy(&id, buffer, sizeof(id));
    }
    return id;
}

static bool restoreconControlFiles(std::string_view targetDir) {
    static constexpr auto restorecon = [](const char* name) {
        if (const auto err = selinux_android_restorecon(name, SELINUX_ANDROID_RESTORECON_FORCE);
            err != 0) {
            errno = -err;
            PLOG(ERROR) << "[incfs] Failed to restorecon: " << name;
            return false;
        }
        return true;
    };
    if (!restorecon(path::join(targetDir, INCFS_PENDING_READS_FILENAME).c_str())) {
        return false;
    }
    if (!restorecon(path::join(targetDir, INCFS_LOG_FILENAME).c_str())) {
        return false;
    }
    if ((features() & Features::v2) &&
        !restorecon(path::join(targetDir, INCFS_BLOCKS_WRITTEN_FILENAME).c_str())) {
        return false;
    }
    return true;
}

IncFsControl* IncFs_Mount(const char* backingPath, const char* targetDir,
                          IncFsMountOptions options) {
    if (!init().enabledAndReady()) {
        LOG(WARNING) << "[incfs] Feature is not enabled";
        errno = ENOTSUP;
        return nullptr;
    }

    if (auto err = isValidMountTarget(targetDir); err != 0) {
        errno = -err;
        return nullptr;
    }
    if (!isAbsolute(backingPath)) {
        errno = EINVAL;
        return nullptr;
    }

    if (options.flags & createOnly) {
        if (const auto err = path::isEmptyDir(backingPath); err != 0) {
            errno = -err;
            return nullptr;
        }
    } else if (options.flags & android::incfs::truncate) {
        if (const auto err = rmDirContent(backingPath); err != 0) {
            errno = -err;
            return nullptr;
        }
    }

    const auto opts = makeMountOptionsString(options);
    if (::mount(backingPath, targetDir, INCFS_NAME, MS_NOSUID | MS_NODEV | MS_NOATIME,
                opts.c_str())) {
        PLOG(ERROR) << "[incfs] Failed to mount IncFS filesystem: " << targetDir;
        return nullptr;
    }

    // in case when the path is given in a form of a /proc/.../fd/ link, we need to update
    // it here: old fd refers to the original empty directory, not to the mount
    std::string updatedTargetDir;
    if (path::dirName(targetDir) == path::procfsFdDir) {
        updatedTargetDir = path::readlink(targetDir);
    } else {
        updatedTargetDir = targetDir;
    }

    auto rootFd = ab::unique_fd(::open(updatedTargetDir.c_str(), O_PATH | O_CLOEXEC | O_DIRECTORY));
    if (updatedTargetDir != targetDir) {
        // ensure that the new directory is still the same after reopening
        if (path::fromFd(rootFd) != updatedTargetDir) {
            errno = EINVAL;
            return nullptr;
        }
    }

    if (!restoreconControlFiles(path::procfsForFd(rootFd))) {
        (void)IncFs_Unmount(targetDir);
        return nullptr;
    }

    auto control = makeControl(rootFd);
    if (control == nullptr) {
        (void)IncFs_Unmount(targetDir);
        return nullptr;
    }
    return control;
}

IncFsControl* IncFs_Open(const char* dir) {
    auto root = registry().rootFor(dir);
    if (root.empty()) {
        errno = EINVAL;
        return nullptr;
    }
    auto rootFd = ab::unique_fd(::open(details::c_str(root), O_PATH | O_CLOEXEC | O_DIRECTORY));
    return makeControl(rootFd);
}

IncFsFd IncFs_GetControlFd(const IncFsControl* control, IncFsFdType type) {
    if (!control) {
        return -EINVAL;
    }
    switch (type) {
        case CMD:
            return control->cmd;
        case PENDING_READS:
            return control->pendingReads;
        case LOGS:
            return control->logs;
        case BLOCKS_WRITTEN:
            return control->blocksWritten;
        default:
            return -EINVAL;
    }
}

IncFsSize IncFs_ReleaseControlFds(IncFsControl* control, IncFsFd out[], IncFsSize outSize) {
    if (!control || !out) {
        return -EINVAL;
    }
    if (outSize < IncFsFdType::FDS_COUNT) {
        return -ERANGE;
    }
    out[CMD] = std::exchange(control->cmd, -1);
    out[PENDING_READS] = std::exchange(control->pendingReads, -1);
    out[LOGS] = std::exchange(control->logs, -1);
    out[BLOCKS_WRITTEN] = std::exchange(control->blocksWritten, -1);
    return IncFsFdType::FDS_COUNT;
}

IncFsControl* IncFs_CreateControl(IncFsFd cmd, IncFsFd pendingReads, IncFsFd logs,
                                  IncFsFd blocksWritten) {
    return new IncFsControl(cmd, pendingReads, logs, blocksWritten);
}

void IncFs_DeleteControl(IncFsControl* control) {
    if (control) {
        if (control->cmd >= 0) {
            close(control->cmd);
        }
        if (control->pendingReads >= 0) {
            close(control->pendingReads);
        }
        if (control->logs >= 0) {
            close(control->logs);
        }
        if (control->blocksWritten >= 0) {
            close(control->blocksWritten);
        }
        delete control;
    }
}

IncFsErrorCode IncFs_SetOptions(const IncFsControl* control, IncFsMountOptions options) {
    if (!control) {
        return -EINVAL;
    }
    auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        return -EINVAL;
    }
    auto opts = makeMountOptionsString(options);
    if (::mount(nullptr, root.c_str(), nullptr, MS_REMOUNT | MS_NOSUID | MS_NODEV | MS_NOATIME,
                opts.c_str()) != 0) {
        const auto error = errno;
        PLOG(ERROR) << "[incfs] Failed to remount IncFS filesystem: " << root;
        return -error;
    }
    return 0;
}

IncFsErrorCode IncFs_Root(const IncFsControl* control, char buffer[], size_t* bufferSize) {
    if (!control) {
        return -EINVAL;
    }
    std::string result = rootForCmd(control->cmd);
    if (*bufferSize <= result.size()) {
        *bufferSize = result.size() + 1;
        return -EOVERFLOW;
    }
    result.copy(buffer, result.size());
    buffer[result.size()] = '\0';
    *bufferSize = result.size();
    return 0;
}

template <class T>
std::optional<T> read(IncFsSpan& data) {
    if (data.size < (int32_t)sizeof(T)) {
        return {};
    }
    T res;
    memcpy(&res, data.data, sizeof(res));
    data.data += sizeof(res);
    data.size -= sizeof(res);
    return res;
}

static IncFsErrorCode validateSignatureFormat(IncFsSpan signature) {
    if (signature.data == nullptr && signature.size == 0) {
        return 0; // it's fine to have unverified files too
    }
    if ((signature.data == nullptr) != (signature.size == 0)) {
        return -EINVAL;
    }

    // These structs are here purely for checking the minimum size. Maybe will use them for
    // parsing later.
    struct __attribute__((packed)) Hashing {
        int32_t size;
        int32_t algorithm;
        int8_t log2_blocksize;
        int32_t salt_size;
        int32_t raw_root_hash_size;
    };
    struct __attribute__((packed)) Signing {
        int32_t size;
        int32_t apk_digest_size;
        int32_t certificate_size;
        int32_t addl_data_size;
        int32_t public_key_size;
        int32_t algorithm;
        int32_t signature_size;
    };
    struct __attribute__((packed)) MinSignature {
        int32_t version;
        Hashing hashing_info;
        Signing signing_info;
    };

    if (signature.size < (int32_t)sizeof(MinSignature)) {
        return -ERANGE;
    }
    if (signature.size > INCFS_MAX_SIGNATURE_SIZE) {
        return -ERANGE;
    }

    auto version = read<int32_t>(signature);
    if (version.value_or(-1) != INCFS_SIGNATURE_VERSION) {
        return -EINVAL;
    }
    auto hashSize = read<int32_t>(signature);
    if (!hashSize || signature.size < *hashSize) {
        return -EINVAL;
    }
    auto hashAlgo = read<int32_t>(signature);
    if (hashAlgo.value_or(-1) != INCFS_HASH_TREE_SHA256) {
        return -EINVAL;
    }
    auto logBlockSize = read<int8_t>(signature);
    if (logBlockSize.value_or(-1) != 12 /* 2^12 == 4096 */) {
        return -EINVAL;
    }
    auto saltSize = read<int32_t>(signature);
    if (saltSize.value_or(-1) != 0) {
        return -EINVAL;
    }
    auto rootHashSize = read<int32_t>(signature);
    if (rootHashSize.value_or(-1) != INCFS_MAX_HASH_SIZE) {
        return -EINVAL;
    }
    if (signature.size < *rootHashSize) {
        return -EINVAL;
    }
    signature.data += *rootHashSize;
    signature.size -= *rootHashSize;
    auto signingSize = read<int32_t>(signature);
    // everything remaining has to be in the signing info
    if (signingSize.value_or(-1) != signature.size) {
        return -EINVAL;
    }

    // TODO: validate the signature part too.
    return 0;
}

IncFsErrorCode IncFs_MakeFile(const IncFsControl* control, const char* path, int32_t mode,
                              IncFsFileId id, IncFsNewFileParams params) {
    if (!control) {
        return -EINVAL;
    }

    auto [root, subpath] = registry().rootAndSubpathFor(path);
    if (root.empty()) {
        PLOG(WARNING) << "[incfs] makeFile failed for path " << path << ", root is empty.";
        return -EINVAL;
    }
    if (params.size < 0) {
        LOG(WARNING) << "[incfs] makeFile failed for path " << path
                     << ", size is invalid: " << params.size;
        return -ERANGE;
    }

    const auto [subdir, name] = path::splitDirBase(subpath);
    incfs_new_file_args args = {
            .size = (uint64_t)params.size,
            .mode = (uint16_t)mode,
            .directory_path = (uint64_t)subdir.data(),
            .file_name = (uint64_t)name.data(),
            .file_attr = (uint64_t)params.metadata.data,
            .file_attr_len = (uint32_t)params.metadata.size,
    };
    static_assert(sizeof(args.file_id.bytes) == sizeof(id.data));
    memcpy(args.file_id.bytes, id.data, sizeof(args.file_id.bytes));

    if (auto err = validateSignatureFormat(params.signature)) {
        return err;
    }
    args.signature_info = (uint64_t)(uintptr_t)params.signature.data;
    args.signature_size = (uint64_t)params.signature.size;

    if (::ioctl(control->cmd, INCFS_IOC_CREATE_FILE, &args)) {
        PLOG(WARNING) << "[incfs] makeFile failed for " << root << " / " << subdir << " / " << name
                      << " of " << params.size << " bytes";
        return -errno;
    }
    if (::chmod(path::join(root, subdir, name).c_str(), mode)) {
        PLOG(WARNING) << "[incfs] couldn't change file mode to 0" << std::oct << mode;
    }

    return 0;
}

IncFsErrorCode IncFs_MakeMappedFile(const IncFsControl* control, const char* path, int32_t mode,
                                    IncFsNewMappedFileParams params) {
    if (!control) {
        return -EINVAL;
    }

    auto [root, subpath] = registry().rootAndSubpathFor(path);
    if (root.empty()) {
        PLOG(WARNING) << "[incfs] makeMappedFile failed for path " << path << ", root is empty.";
        return -EINVAL;
    }
    if (params.size < 0) {
        LOG(WARNING) << "[incfs] makeMappedFile failed for path " << path
                     << ", size is invalid: " << params.size;
        return -ERANGE;
    }

    const auto [subdir, name] = path::splitDirBase(subpath);
    incfs_create_mapped_file_args args = {
            .size = (uint64_t)params.size,
            .mode = (uint16_t)mode,
            .directory_path = (uint64_t)subdir.data(),
            .file_name = (uint64_t)name.data(),
            .source_offset = (uint64_t)params.sourceOffset,
    };
    static_assert(sizeof(args.source_file_id.bytes) == sizeof(params.sourceId.data));
    memcpy(args.source_file_id.bytes, params.sourceId.data, sizeof(args.source_file_id.bytes));

    if (::ioctl(control->cmd, INCFS_IOC_CREATE_MAPPED_FILE, &args)) {
        PLOG(WARNING) << "[incfs] makeMappedFile failed for " << root << " / " << subdir << " / "
                      << name << " of " << params.size << " bytes starting at "
                      << params.sourceOffset;
        return -errno;
    }
    if (::chmod(path::join(root, subpath).c_str(), mode)) {
        PLOG(WARNING) << "[incfs] makeMappedFile error: couldn't change file mode to 0" << std::oct
                      << mode;
    }

    return 0;
}

static IncFsErrorCode makeDir(const char* commandPath, int32_t mode, bool allowExisting) {
    if (!::mkdir(commandPath, mode)) {
        if (::chmod(commandPath, mode)) {
            PLOG(WARNING) << "[incfs] couldn't change directory mode to 0" << std::oct << mode;
        }
        return 0;
    }
    // don't touch the existing dir's mode - mkdir(1) works that way.
    return (allowExisting && errno == EEXIST) ? 0 : -errno;
}

static IncFsErrorCode makeDirs(std::string_view commandPath, std::string_view path,
                               std::string_view root, int32_t mode) {
    auto commandCPath = details::c_str(commandPath);
    const auto mkdirRes = makeDir(commandCPath, mode, true);
    if (!mkdirRes) {
        return 0;
    }
    if (mkdirRes != -ENOENT) {
        LOG(ERROR) << __func__ << "(): mkdir failed for " << path << " - " << mkdirRes;
        return mkdirRes;
    }

    const auto parent = path::dirName(commandPath);
    if (!path::startsWith(parent, root)) {
        // went too far, already out of the root mount
        return -EINVAL;
    }

    if (auto parentMkdirRes = makeDirs(parent, path::dirName(path), root, mode)) {
        return parentMkdirRes;
    }
    return makeDir(commandCPath, mode, true);
}

IncFsErrorCode IncFs_MakeDir(const IncFsControl* control, const char* path, int32_t mode) {
    if (!control) {
        return -EINVAL;
    }
    const auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        LOG(ERROR) << __func__ << "(): root is empty for " << path;
        return -EINVAL;
    }
    auto commandPath = makeCommandPath(root, path);
    if (commandPath.empty()) {
        LOG(ERROR) << __func__ << "(): commandPath is empty for " << path;
        return -EINVAL;
    }
    if (auto res = makeDir(commandPath.c_str(), mode, false)) {
        LOG(ERROR) << __func__ << "(): mkdir failed for " << commandPath << " - " << res;
        return res;
    }
    return 0;
}

IncFsErrorCode IncFs_MakeDirs(const IncFsControl* control, const char* path, int32_t mode) {
    if (!control) {
        return -EINVAL;
    }
    const auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        LOG(ERROR) << __func__ << "(): root is empty for " << path;
        return -EINVAL;
    }
    auto commandPath = makeCommandPath(root, path);
    if (commandPath.empty()) {
        LOG(ERROR) << __func__ << "(): commandPath is empty for " << path;
        return -EINVAL;
    }
    return makeDirs(commandPath, path, root, mode);
}

static IncFsErrorCode getMetadata(const char* path, char buffer[], size_t* bufferSize) {
    const auto res = ::getxattr(path, kMetadataAttrName, buffer, *bufferSize);
    if (res < 0) {
        if (errno == ERANGE) {
            auto neededSize = ::getxattr(path, kMetadataAttrName, buffer, 0);
            if (neededSize >= 0) {
                *bufferSize = neededSize;
                return 0;
            }
        }
        return -errno;
    }
    *bufferSize = res;
    return 0;
}

IncFsErrorCode IncFs_GetMetadataById(const IncFsControl* control, IncFsFileId fileId, char buffer[],
                                     size_t* bufferSize) {
    if (!control) {
        return -EINVAL;
    }

    const auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        return -EINVAL;
    }
    auto name = indexPath(root, fileId);
    return getMetadata(details::c_str(name), buffer, bufferSize);
}

IncFsErrorCode IncFs_GetMetadataByPath(const IncFsControl* control, const char* path, char buffer[],
                                       size_t* bufferSize) {
    if (!control) {
        return -EINVAL;
    }
    const auto pathRoot = registry().rootFor(path);
    const auto root = rootForCmd(control->cmd);
    if (root.empty() || root != pathRoot) {
        return -EINVAL;
    }

    return getMetadata(path, buffer, bufferSize);
}

template <class GetterFunc, class Param>
static IncFsFileId getId(GetterFunc getter, Param param) {
    char buffer[kIncFsFileIdStringLength];
    const auto res = getter(param, kIdAttrName, buffer, sizeof(buffer));
    if (res != sizeof(buffer)) {
        return kIncFsInvalidFileId;
    }
    return toFileIdImpl({buffer, std::size(buffer)});
}

IncFsFileId IncFs_GetId(const IncFsControl* control, const char* path) {
    if (!control) {
        return kIncFsInvalidFileId;
    }
    const auto pathRoot = registry().rootFor(path);
    const auto root = rootForCmd(control->cmd);
    if (root.empty() || root != pathRoot) {
        errno = EINVAL;
        return kIncFsInvalidFileId;
    }
    return getId(::getxattr, path);
}

static IncFsErrorCode getSignature(int fd, char buffer[], size_t* bufferSize) {
    incfs_get_file_sig_args args = {
            .file_signature = (uint64_t)buffer,
            .file_signature_buf_size = (uint32_t)*bufferSize,
    };

    auto res = ::ioctl(fd, INCFS_IOC_READ_FILE_SIGNATURE, &args);
    if (res < 0) {
        if (errno == E2BIG) {
            *bufferSize = INCFS_MAX_SIGNATURE_SIZE;
        }
        return -errno;
    }
    *bufferSize = args.file_signature_len_out;
    return 0;
}

IncFsErrorCode IncFs_GetSignatureById(const IncFsControl* control, IncFsFileId fileId,
                                      char buffer[], size_t* bufferSize) {
    if (!control) {
        return -EINVAL;
    }

    const auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        return -EINVAL;
    }
    auto file = indexPath(root, fileId);
    auto fd = openRaw(file);
    if (fd < 0) {
        return fd.get();
    }
    return getSignature(fd, buffer, bufferSize);
}

IncFsErrorCode IncFs_GetSignatureByPath(const IncFsControl* control, const char* path,
                                        char buffer[], size_t* bufferSize) {
    if (!control) {
        return -EINVAL;
    }

    const auto pathRoot = registry().rootFor(path);
    const auto root = rootForCmd(control->cmd);
    if (root.empty() || root != pathRoot) {
        return -EINVAL;
    }
    return IncFs_UnsafeGetSignatureByPath(path, buffer, bufferSize);
}

IncFsErrorCode IncFs_UnsafeGetSignatureByPath(const char* path, char buffer[], size_t* bufferSize) {
    if (!isIncFsPath(path)) {
        return -EINVAL;
    }
    auto fd = openRaw(path);
    if (fd < 0) {
        return fd.get();
    }
    return getSignature(fd, buffer, bufferSize);
}

IncFsErrorCode IncFs_Link(const IncFsControl* control, const char* fromPath,
                          const char* wherePath) {
    if (!control) {
        return -EINVAL;
    }

    auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        return -EINVAL;
    }
    auto cmdFrom = makeCommandPath(root, fromPath);
    if (cmdFrom.empty()) {
        return -EINVAL;
    }
    auto cmdWhere = makeCommandPath(root, wherePath);
    if (cmdWhere.empty()) {
        return -EINVAL;
    }
    if (::link(cmdFrom.c_str(), cmdWhere.c_str())) {
        return -errno;
    }
    return 0;
}

IncFsErrorCode IncFs_Unlink(const IncFsControl* control, const char* path) {
    if (!control) {
        return -EINVAL;
    }

    auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        return -EINVAL;
    }
    auto cmdPath = makeCommandPath(root, path);
    if (cmdPath.empty()) {
        return -EINVAL;
    }
    if (::unlink(cmdPath.c_str())) {
        if (errno == EISDIR) {
            if (!::rmdir(cmdPath.c_str())) {
                return 0;
            }
        }
        return -errno;
    }
    return 0;
}

template <class RawPendingRead>
static int waitForReadsImpl(int fd, int32_t timeoutMs, RawPendingRead pendingReadsBuffer[],
                            size_t* pendingReadsBufferSize) {
    using namespace std::chrono;
    auto hrTimeout = steady_clock::duration(milliseconds(timeoutMs));

    while (hrTimeout > hrTimeout.zero() || (!pendingReadsBuffer && hrTimeout == hrTimeout.zero())) {
        const auto startTs = steady_clock::now();

        pollfd pfd = {fd, POLLIN, 0};
        const auto res = ::poll(&pfd, 1, duration_cast<milliseconds>(hrTimeout).count());
        if (res > 0) {
            break;
        }
        if (res == 0) {
            if (pendingReadsBufferSize) {
                *pendingReadsBufferSize = 0;
            }
            return -ETIMEDOUT;
        }
        const auto error = errno;
        if (error != EINTR) {
            PLOG(ERROR) << "poll() failed";
            return -error;
        }
        hrTimeout -= steady_clock::now() - startTs;
    }
    if (!pendingReadsBuffer) {
        return hrTimeout < hrTimeout.zero() ? -ETIMEDOUT : 0;
    }

    auto res =
            ::read(fd, pendingReadsBuffer, *pendingReadsBufferSize * sizeof(*pendingReadsBuffer));
    if (res < 0) {
        const auto error = errno;
        PLOG(ERROR) << "read() failed";
        return -error;
    }
    if (res == 0) {
        *pendingReadsBufferSize = 0;
        return -ETIMEDOUT;
    }
    if ((res % sizeof(*pendingReadsBuffer)) != 0) {
        PLOG(ERROR) << "read() returned half of a struct??";
        return -EFAULT;
    }
    *pendingReadsBufferSize = res / sizeof(*pendingReadsBuffer);
    return 0;
}

template <class PublicPendingRead, class RawPendingRead>
PublicPendingRead convertRead(RawPendingRead rawRead) {
    PublicPendingRead res = {
            .bootClockTsUs = rawRead.timestamp_us,
            .block = (IncFsBlockIndex)rawRead.block_index,
            .serialNo = rawRead.serial_number,
    };
    memcpy(&res.id.data, rawRead.file_id.bytes, sizeof(res.id.data));

    if constexpr (std::is_same_v<PublicPendingRead, IncFsReadInfoWithUid>) {
        if constexpr (std::is_same_v<RawPendingRead, incfs_pending_read_info2>) {
            res.uid = rawRead.uid;
        } else {
            res.uid = kIncFsNoUid;
        }
    }
    return res;
}

template <class RawPendingRead, class PublicPendingRead>
static int waitForReads(IncFsFd readFd, int32_t timeoutMs, PublicPendingRead buffer[],
                        size_t* bufferSize) {
    std::vector<RawPendingRead> pendingReads(*bufferSize);
    if (const auto res = waitForReadsImpl(readFd, timeoutMs, pendingReads.data(), bufferSize)) {
        return res;
    }
    for (size_t i = 0; i != *bufferSize; ++i) {
        buffer[i] = convertRead<PublicPendingRead>(pendingReads[i]);
    }
    return 0;
}

template <class PublicPendingRead>
static int waitForReads(IncFsFd readFd, int32_t timeoutMs, PublicPendingRead buffer[],
                        size_t* bufferSize) {
    if (features() & Features::v2) {
        return waitForReads<incfs_pending_read_info2>(readFd, timeoutMs, buffer, bufferSize);
    }
    return waitForReads<incfs_pending_read_info>(readFd, timeoutMs, buffer, bufferSize);
}

IncFsErrorCode IncFs_WaitForPendingReads(const IncFsControl* control, int32_t timeoutMs,
                                         IncFsReadInfo buffer[], size_t* bufferSize) {
    if (!control || control->pendingReads < 0) {
        return -EINVAL;
    }

    return waitForReads(control->pendingReads, timeoutMs, buffer, bufferSize);
}

IncFsErrorCode IncFs_WaitForPendingReadsWithUid(const IncFsControl* control, int32_t timeoutMs,
                                                IncFsReadInfoWithUid buffer[], size_t* bufferSize) {
    if (!control || control->pendingReads < 0) {
        return -EINVAL;
    }

    return waitForReads(control->pendingReads, timeoutMs, buffer, bufferSize);
}

IncFsErrorCode IncFs_WaitForPageReads(const IncFsControl* control, int32_t timeoutMs,
                                      IncFsReadInfo buffer[], size_t* bufferSize) {
    if (!control || control->logs < 0) {
        return -EINVAL;
    }

    return waitForReads(control->logs, timeoutMs, buffer, bufferSize);
}

IncFsErrorCode IncFs_WaitForPageReadsWithUid(const IncFsControl* control, int32_t timeoutMs,
                                             IncFsReadInfoWithUid buffer[], size_t* bufferSize) {
    if (!control || control->logs < 0) {
        return -EINVAL;
    }

    return waitForReads(control->logs, timeoutMs, buffer, bufferSize);
}

static IncFsFd openForSpecialOps(int cmd, const char* path) {
    ab::unique_fd fd(::open(path, O_RDONLY | O_CLOEXEC));
    if (fd < 0) {
        return -errno;
    }
    struct incfs_permit_fill args = {.file_descriptor = (uint32_t)fd.get()};
    auto err = ::ioctl(cmd, INCFS_IOC_PERMIT_FILL, &args);
    if (err < 0) {
        return -errno;
    }
    return fd.release();
}

IncFsFd IncFs_OpenForSpecialOpsByPath(const IncFsControl* control, const char* path) {
    if (!control) {
        return -EINVAL;
    }

    const auto pathRoot = registry().rootFor(path);
    const auto cmd = control->cmd;
    const auto root = rootForCmd(cmd);
    if (root.empty() || root != pathRoot) {
        return -EINVAL;
    }
    return openForSpecialOps(cmd, makeCommandPath(root, path).c_str());
}

IncFsFd IncFs_OpenForSpecialOpsById(const IncFsControl* control, IncFsFileId id) {
    if (!control) {
        return -EINVAL;
    }

    const auto cmd = control->cmd;
    const auto root = rootForCmd(cmd);
    if (root.empty()) {
        return -EINVAL;
    }
    auto name = indexPath(root, id);
    return openForSpecialOps(cmd, makeCommandPath(root, name).c_str());
}

static int writeBlocks(int fd, const incfs_fill_block blocks[], int blocksCount) {
    if (fd < 0 || blocksCount == 0) {
        return 0;
    }
    if (blocksCount < 0) {
        return -EINVAL;
    }

    auto ptr = blocks;
    const auto end = blocks + blocksCount;
    do {
        struct incfs_fill_blocks args = {.count = uint64_t(end - ptr),
                                         .fill_blocks = (uint64_t)(uintptr_t)ptr};
        const auto written = ::ioctl(fd, INCFS_IOC_FILL_BLOCKS, &args);
        if (written < 0) {
            if (errno == EINTR) {
                continue;
            }
            const auto error = errno;
            PLOG(WARNING) << "writing IncFS blocks failed";
            if (ptr == blocks) {
                return -error;
            }
            // something has been written, return a success here and let the
            // next call handle the error.
            break;
        }
        ptr += written;
    } while (ptr < end);
    return ptr - blocks;
}

IncFsErrorCode IncFs_WriteBlocks(const IncFsDataBlock blocks[], size_t blocksCount) {
    incfs_fill_block incfsBlocks[128];
    int writtenCount = 0;
    int incfsBlocksUsed = 0;
    int lastBlockFd = -1;
    for (size_t i = 0; i < blocksCount; ++i) {
        if (lastBlockFd != blocks[i].fileFd || incfsBlocksUsed == std::size(incfsBlocks)) {
            auto count = writeBlocks(lastBlockFd, incfsBlocks, incfsBlocksUsed);
            if (count > 0) {
                writtenCount += count;
            }
            if (count != incfsBlocksUsed) {
                return writtenCount ? writtenCount : count;
            }
            lastBlockFd = blocks[i].fileFd;
            incfsBlocksUsed = 0;
        }
        incfsBlocks[incfsBlocksUsed] = incfs_fill_block{
                .block_index = (uint32_t)blocks[i].pageIndex,
                .data_len = blocks[i].dataSize,
                .data = (uint64_t)blocks[i].data,
                .compression = (uint8_t)blocks[i].compression,
                .flags = uint8_t(blocks[i].kind == INCFS_BLOCK_KIND_HASH ? INCFS_BLOCK_FLAGS_HASH
                                                                         : 0),
        };
        ++incfsBlocksUsed;
    }
    auto count = writeBlocks(lastBlockFd, incfsBlocks, incfsBlocksUsed);
    if (count > 0) {
        writtenCount += count;
    }
    return writtenCount ? writtenCount : count;
}

IncFsErrorCode IncFs_BindMount(const char* sourceDir, const char* targetDir) {
    if (!enabled()) {
        return -ENOTSUP;
    }

    if (path::dirName(sourceDir) == path::procfsFdDir) {
        // can't find such path in the mount registry, but still can verify the filesystem
        // via the stat() call
        if (!isIncFsPathImpl(sourceDir)) {
            return -EINVAL;
        }
    } else {
        auto [sourceRoot, subpath] = registry().rootAndSubpathFor(sourceDir);
        if (sourceRoot.empty()) {
            return -EINVAL;
        }
        if (subpath.empty()) {
            LOG(WARNING) << "[incfs] Binding the root mount '" << sourceRoot << "' is not allowed";
            return -EINVAL;
        }
    }

    if (auto err = isValidMountTarget(targetDir); err != 0) {
        return err;
    }

    if (::mount(sourceDir, targetDir, nullptr, MS_BIND, nullptr)) {
        PLOG(ERROR) << "[incfs] Failed to bind mount '" << sourceDir << "' to '" << targetDir
                    << '\'';
        return -errno;
    }
    return 0;
}

IncFsErrorCode IncFs_Unmount(const char* dir) {
    if (!enabled()) {
        return -ENOTSUP;
    }
    if (!isIncFsPathImpl(dir)) {
        LOG(WARNING) << __func__ << ": umount() called on non-incfs directory '" << dir << '\'';
        return -EINVAL;
    }

    errno = 0;
    if (::umount2(dir, MNT_FORCE) == 0 || errno == EINVAL || errno == ENOENT) {
        // EINVAL - not a mount point, ENOENT - doesn't exist at all
        if (errno == 0) {
            LOG(INFO) << __func__ << ": succeeded on the first try for '" << dir << '\'';
        }
        return -errno;
    }
    errno = 0;
    if (!::umount2(dir, MNT_DETACH)) {
        return 0;
    }
    PLOG(WARNING) << __func__ << ": umount(detach) returned non-zero for '" << dir << '\'';
    return 0;
}

bool IncFs_IsIncFsFd(int fd) {
    return isIncFsFdImpl(fd);
}

bool IncFs_IsIncFsPath(const char* path) {
    return isIncFsPathImpl(path);
}

IncFsErrorCode IncFs_GetFilledRanges(int fd, IncFsSpan outBuffer, IncFsFilledRanges* filledRanges) {
    return IncFs_GetFilledRangesStartingFrom(fd, 0, outBuffer, filledRanges);
}

IncFsErrorCode IncFs_GetFilledRangesStartingFrom(int fd, int startBlockIndex, IncFsSpan outBuffer,
                                                 IncFsFilledRanges* filledRanges) {
    if (fd < 0) {
        return -EBADF;
    }
    if (startBlockIndex < 0) {
        return -EINVAL;
    }
    if (!outBuffer.data && outBuffer.size > 0) {
        return -EINVAL;
    }
    if (!filledRanges) {
        return -EINVAL;
    }
    // Use this to optimize the incfs call and have the same buffer for both the incfs and the
    // public structs.
    static_assert(sizeof(IncFsBlockRange) == sizeof(incfs_filled_range));

    *filledRanges = {};

    auto outStart = (IncFsBlockRange*)outBuffer.data;
    auto outEnd = outStart + outBuffer.size / sizeof(*outStart);

    auto outPtr = outStart;
    int error = 0;
    int dataBlocks;
    incfs_get_filled_blocks_args args = {};
    for (;;) {
        auto start = args.index_out ? args.index_out : startBlockIndex;
        args = incfs_get_filled_blocks_args{
                .range_buffer = (uint64_t)(uintptr_t)outPtr,
                .range_buffer_size = uint32_t((outEnd - outPtr) * sizeof(*outPtr)),
                .start_index = start,
        };
        errno = 0;
        auto res = ::ioctl(fd, INCFS_IOC_GET_FILLED_BLOCKS, &args);
        error = errno;
        if (res && error != EINTR && error != ERANGE) {
            return -error;
        }

        dataBlocks = args.data_blocks_out;
        outPtr += args.range_buffer_size_out / sizeof(incfs_filled_range);
        if (!res || error == ERANGE) {
            break;
        }
        // in case of EINTR we want to continue calling the function
    }

    if (outPtr > outEnd) {
        outPtr = outEnd;
        error = ERANGE;
    }

    filledRanges->endIndex = args.index_out;
    auto hashStartPtr = outPtr;
    if (outPtr != outStart) {
        // figure out the ranges for data block and hash blocks in the output
        for (; hashStartPtr != outStart; --hashStartPtr) {
            if ((hashStartPtr - 1)->begin < dataBlocks) {
                break;
            }
        }
        auto lastDataPtr = hashStartPtr - 1;
        // here we go, this is the first block that's before or at the hashes
        if (lastDataPtr->end <= dataBlocks) {
            ; // we're good, the boundary is between the ranges - |hashStartPtr| is correct
        } else {
            // the hard part: split the |lastDataPtr| range into the data and the hash pieces
            if (outPtr == outEnd) {
                // the buffer turned out to be too small, even though it actually wasn't
                error = ERANGE;
                if (hashStartPtr == outEnd) {
                    // this is even worse: there's no room to put even a single hash block into.
                    filledRanges->endIndex = lastDataPtr->end = dataBlocks;
                } else {
                    std::copy_backward(lastDataPtr, outPtr - 1, outPtr);
                    lastDataPtr->end = hashStartPtr->begin = dataBlocks;
                    filledRanges->endIndex = (outPtr - 1)->end;
                }
            } else {
                std::copy_backward(lastDataPtr, outPtr, outPtr + 1);
                lastDataPtr->end = hashStartPtr->begin = dataBlocks;
                ++outPtr;
            }
        }
        // now fix the indices of all hash blocks - no one should know they're simply past the
        // regular data blocks in the file!
        for (auto ptr = hashStartPtr; ptr != outPtr; ++ptr) {
            ptr->begin -= dataBlocks;
            ptr->end -= dataBlocks;
        }
    }

    filledRanges->dataRanges = outStart;
    filledRanges->dataRangesCount = hashStartPtr - outStart;
    filledRanges->hashRanges = hashStartPtr;
    filledRanges->hashRangesCount = outPtr - hashStartPtr;

    return -error;
}

static IncFsErrorCode isFullyLoadedV2(std::string_view root, IncFsFileId id) {
    if (::access(path::join(root, INCFS_INCOMPLETE_NAME, toStringImpl(id)).c_str(), F_OK)) {
        if (errno == ENOENT) {
            return 0; // no such incomplete file -> it's fully loaded.
        }
        return -errno;
    }
    return -ENODATA;
}

static IncFsErrorCode isFullyLoadedSlow(int fd) {
    char buffer[2 * sizeof(IncFsBlockRange)];
    IncFsFilledRanges ranges;
    auto res = IncFs_GetFilledRanges(fd, IncFsSpan{.data = buffer, .size = std::size(buffer)},
                                     &ranges);
    if (res == -ERANGE) {
        // need room for more than two ranges - definitely not fully loaded
        return -ENODATA;
    }
    if (res != 0) {
        return res;
    }
    // empty file
    if (ranges.endIndex == 0) {
        return 0;
    }
    // file with no hash tree
    if (ranges.dataRangesCount == 1 && ranges.hashRangesCount == 0) {
        return (ranges.dataRanges[0].begin == 0 && ranges.dataRanges[0].end == ranges.endIndex)
                ? 0
                : -ENODATA;
    }
    // file with a hash tree
    if (ranges.dataRangesCount == 1 && ranges.hashRangesCount == 1) {
        // calculate the expected data size from the size of the hash range and |endIndex|, which is
        // the total number of blocks in the file, both data and hash blocks together.
        if (ranges.hashRanges[0].begin != 0) {
            return -ENODATA;
        }
        const auto expectedDataBlocks =
                ranges.endIndex - (ranges.hashRanges[0].end - ranges.hashRanges[0].begin);
        return (ranges.dataRanges[0].begin == 0 && ranges.dataRanges[0].end == expectedDataBlocks)
                ? 0
                : -ENODATA;
    }
    return -ENODATA;
}

IncFsErrorCode IncFs_IsFullyLoaded(int fd) {
    if (features() & Features::v2) {
        const auto fdPath = path::fromFd(fd);
        if (fdPath.empty()) {
            return errno ? -errno : -EINVAL;
        }
        const auto id = getId(::fgetxattr, fd);
        if (id == kIncFsInvalidFileId) {
            return -errno;
        }
        return isFullyLoadedV2(registry().rootFor(fdPath), id);
    }
    return isFullyLoadedSlow(fd);
}
IncFsErrorCode IncFs_IsFullyLoadedByPath(const IncFsControl* control, const char* path) {
    if (!control || !path) {
        return -EINVAL;
    }
    const auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        return -EINVAL;
    }
    const auto pathRoot = registry().rootFor(path);
    if (pathRoot != root) {
        return -EINVAL;
    }
    if (features() & Features::v2) {
        const auto id = getId(::getxattr, path);
        if (id == kIncFsInvalidFileId) {
            return -ENOTSUP;
        }
        return isFullyLoadedV2(root, id);
    }
    auto fd = ab::unique_fd(openForSpecialOps(control->cmd, makeCommandPath(root, path).c_str()));
    return isFullyLoadedSlow(fd.get());
}
IncFsErrorCode IncFs_IsFullyLoadedById(const IncFsControl* control, IncFsFileId fileId) {
    if (!control) {
        return -EINVAL;
    }
    const auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        return -EINVAL;
    }
    if (features() & Features::v2) {
        return isFullyLoadedV2(root, fileId);
    }
    auto fd = ab::unique_fd(
            openForSpecialOps(control->cmd,
                              makeCommandPath(root, indexPath(root, fileId)).c_str()));
    return isFullyLoadedSlow(fd.get());
}

static IncFsErrorCode isEverythingLoadedV2(const IncFsControl* control) {
    const auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        return -EINVAL;
    }
    auto res = forEachFileIn(path::join(root, INCFS_INCOMPLETE_NAME), [](auto) { return false; });
    return res < 0 ? res : res > 0 ? -ENODATA : 0;
}

static IncFsErrorCode isEverythingLoadedSlow(const IncFsControl* control) {
    const auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        return -EINVAL;
    }
    // No special API for this version of the driver, need to recurse and check each file
    // separately. Can at least speed it up by iterating over the .index/ dir and not dealing with
    // the directory tree.
    const auto indexPath = path::join(root, INCFS_INDEX_NAME);
    const auto dir = path::openDir(indexPath.c_str());
    if (!dir) {
        return -EINVAL;
    }
    while (const auto entry = ::readdir(dir.get())) {
        if (entry->d_type != DT_REG) {
            continue;
        }
        const auto name = path::join(indexPath, entry->d_name);
        auto fd =
                ab::unique_fd(openForSpecialOps(control->cmd, makeCommandPath(root, name).c_str()));
        if (fd.get() < 0) {
            PLOG(WARNING) << __func__ << "(): can't open " << entry->d_name << " for special ops";
            return fd.release();
        }
        const auto checkFullyLoaded = IncFs_IsFullyLoaded(fd.get());
        if (checkFullyLoaded == 0 || checkFullyLoaded == -EOPNOTSUPP ||
            checkFullyLoaded == -ENOTSUP || checkFullyLoaded == -ENOENT) {
            // special kinds of files may return an error here, but it still means
            // _this_ file is OK - you simply need to check the rest. E.g. can't query
            // a mapped file, instead need to check its parent.
            continue;
        }
        return checkFullyLoaded;
    }
    return 0;
}

IncFsErrorCode IncFs_IsEverythingFullyLoaded(const IncFsControl* control) {
    if (!control) {
        return -EINVAL;
    }
    if (features() & Features::v2) {
        return isEverythingLoadedV2(control);
    }
    return isEverythingLoadedSlow(control);
}

IncFsErrorCode IncFs_SetUidReadTimeouts(const IncFsControl* control,
                                        const IncFsUidReadTimeouts timeouts[], size_t count) {
    if (!control) {
        return -EINVAL;
    }
    if (!(features() & Features::v2)) {
        return -ENOTSUP;
    }

    std::vector<incfs_per_uid_read_timeouts> argTimeouts(count);
    for (size_t i = 0; i != count; ++i) {
        argTimeouts[i] = incfs_per_uid_read_timeouts{
                .uid = (uint32_t)timeouts[i].uid,
                .min_time_us = timeouts[i].minTimeUs,
                .min_pending_time_us = timeouts[i].minPendingTimeUs,
                .max_pending_time_us = timeouts[i].maxPendingTimeUs,
        };
    }
    incfs_set_read_timeouts_args args = {.timeouts_array = (uint64_t)(uintptr_t)argTimeouts.data(),
                                         .timeouts_array_size = uint32_t(
                                                 argTimeouts.size() * sizeof(*argTimeouts.data()))};
    if (::ioctl(control->cmd, INCFS_IOC_SET_READ_TIMEOUTS, &args)) {
        PLOG(WARNING) << "[incfs] setUidReadTimeouts failed";
        return -errno;
    }
    return 0;
}

IncFsErrorCode IncFs_GetUidReadTimeouts(const IncFsControl* control,
                                        IncFsUidReadTimeouts timeouts[], size_t* bufferSize) {
    if (!control || !bufferSize) {
        return -EINVAL;
    }
    if (!(features() & Features::v2)) {
        return -ENOTSUP;
    }

    std::vector<incfs_per_uid_read_timeouts> argTimeouts(*bufferSize);
    incfs_get_read_timeouts_args args = {.timeouts_array = (uint64_t)(uintptr_t)argTimeouts.data(),
                                         .timeouts_array_size = uint32_t(
                                                 argTimeouts.size() * sizeof(*argTimeouts.data())),
                                         .timeouts_array_size_out = args.timeouts_array_size};
    if (::ioctl(control->cmd, INCFS_IOC_GET_READ_TIMEOUTS, &args)) {
        if (errno == E2BIG) {
            *bufferSize = args.timeouts_array_size_out / sizeof(*argTimeouts.data());
        }
        return -errno;
    }

    *bufferSize = args.timeouts_array_size_out / sizeof(*argTimeouts.data());
    for (size_t i = 0; i != *bufferSize; ++i) {
        timeouts[i].uid = argTimeouts[i].uid;
        timeouts[i].minTimeUs = argTimeouts[i].min_time_us;
        timeouts[i].minPendingTimeUs = argTimeouts[i].min_pending_time_us;
        timeouts[i].maxPendingTimeUs = argTimeouts[i].max_pending_time_us;
    }
    return 0;
}

// Trying to detect if this is a mapped file.
// Not the best way as it might return true for other system files.
// TODO: remove after IncFS returns ENOTSUP for such files.
static bool isMapped(int fd) {
    char buffer[kIncFsFileIdStringLength];
    const auto res = ::fgetxattr(fd, kIdAttrName, buffer, sizeof(buffer));
    return res != sizeof(buffer);
}

static IncFsErrorCode getFileBlockCount(int fd, IncFsBlockCounts* blockCount) {
    if (isMapped(fd)) {
        return -ENOTSUP;
    }

    incfs_get_block_count_args args = {};
    auto res = ::ioctl(fd, INCFS_IOC_GET_BLOCK_COUNT, &args);
    if (res < 0) {
        return -errno;
    }
    *blockCount = IncFsBlockCounts{
            .totalDataBlocks = args.total_data_blocks_out,
            .filledDataBlocks = args.filled_data_blocks_out,
            .totalHashBlocks = args.total_hash_blocks_out,
            .filledHashBlocks = args.filled_hash_blocks_out,
    };
    return 0;
}

IncFsErrorCode IncFs_GetFileBlockCountById(const IncFsControl* control, IncFsFileId id,
                                           IncFsBlockCounts* blockCount) {
    if (!control) {
        return -EINVAL;
    }
    if (!(features() & Features::v2)) {
        return -ENOTSUP;
    }
    const auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        return -EINVAL;
    }
    auto name = indexPath(root, id);
    auto fd = openRaw(name);
    if (fd < 0) {
        return fd.get();
    }
    return getFileBlockCount(fd, blockCount);
}

IncFsErrorCode IncFs_GetFileBlockCountByPath(const IncFsControl* control, const char* path,
                                             IncFsBlockCounts* blockCount) {
    if (!control) {
        return -EINVAL;
    }
    if (!(features() & Features::v2)) {
        return -ENOTSUP;
    }
    const auto pathRoot = registry().rootFor(path);
    const auto root = rootForCmd(control->cmd);
    if (root.empty() || root != pathRoot) {
        return -EINVAL;
    }
    auto fd = openRaw(path);
    if (fd < 0) {
        return fd.get();
    }
    return getFileBlockCount(fd, blockCount);
}

IncFsErrorCode IncFs_ListIncompleteFiles(const IncFsControl* control, IncFsFileId ids[],
                                         size_t* bufferSize) {
    if (!control || !bufferSize) {
        return -EINVAL;
    }
    if (!(features() & Features::v2)) {
        return -ENOTSUP;
    }
    const auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        return -EINVAL;
    }
    size_t index = 0;
    int error = 0;
    const auto res = forEachFileIn(path::join(root, INCFS_INCOMPLETE_NAME), [&](const char* name) {
        if (index >= *bufferSize) {
            error = -E2BIG;
        } else {
            ids[index] = IncFs_FileIdFromString(name);
        }
        ++index;
        return true;
    });
    if (res < 0) {
        return res;
    }
    *bufferSize = index;
    return error ? error : 0;
}

IncFsErrorCode IncFs_ForEachFile(const IncFsControl* control, void* context, FileCallback cb) {
    if (!control || !cb) {
        return -EINVAL;
    }
    const auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        return -EINVAL;
    }
    return forEachFileIn(path::join(root, INCFS_INDEX_NAME), [&](const char* name) {
        return cb(context, control, IncFs_FileIdFromString(name));
    });
}

IncFsErrorCode IncFs_ForEachIncompleteFile(const IncFsControl* control, void* context,
                                           FileCallback cb) {
    if (!control || !cb) {
        return -EINVAL;
    }
    if (!(features() & Features::v2)) {
        return -ENOTSUP;
    }
    const auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        return -EINVAL;
    }
    return forEachFileIn(path::join(root, INCFS_INCOMPLETE_NAME), [&](const char* name) {
        return cb(context, control, IncFs_FileIdFromString(name));
    });
}

IncFsErrorCode IncFs_WaitForLoadingComplete(const IncFsControl* control, int32_t timeoutMs) {
    if (!control) {
        return -EINVAL;
    }
    if (!(features() & Features::v2)) {
        return -ENOTSUP;
    }

    using namespace std::chrono;
    auto hrTimeout = steady_clock::duration(milliseconds(timeoutMs));

    const auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        return -EINVAL;
    }

    ab::unique_fd fd(inotify_init1(IN_NONBLOCK | IN_CLOEXEC));
    if (!fd.ok()) {
        return -EFAULT;
    }

    // first create all the watches, and only then list existing files to prevent races
    auto dirPath = path::join(root, INCFS_INCOMPLETE_NAME);
    int watchFd = inotify_add_watch(fd.get(), dirPath.c_str(), IN_DELETE);
    if (watchFd < 0) {
        return -errno;
    }

    size_t count = 0;
    auto res = IncFs_ListIncompleteFiles(control, nullptr, &count);
    if (!res) {
        return 0;
    }
    if (res != -E2BIG) {
        return res;
    }

    while (hrTimeout > hrTimeout.zero()) {
        const auto startTs = steady_clock::now();

        pollfd pfd = {fd.get(), POLLIN, 0};
        const auto res = ::poll(&pfd, 1, duration_cast<milliseconds>(hrTimeout).count());
        if (res == 0) {
            return -ETIMEDOUT;
        }
        if (res < 0) {
            const auto error = errno;
            if (error != EINTR) {
                PLOG(ERROR) << "poll() failed";
                return -error;
            }
        } else {
            // empty the inotify fd first to not miss any new deletions,
            // then check if the directory is empty.
            char buffer[sizeof(inotify_event) + NAME_MAX + 1];
            for (;;) {
                auto err = TEMP_FAILURE_RETRY(::read(fd.get(), buffer, sizeof(buffer)));
                if (err < 0) {
                    if (errno == EAGAIN) { // no new events
                        break;
                    }
                    return -errno;
                }
            }

            size_t count = 0;
            auto res = IncFs_ListIncompleteFiles(control, nullptr, &count);
            if (!res) {
                return 0;
            }
            if (res != -E2BIG) {
                return res;
            }
        }
        hrTimeout -= steady_clock::now() - startTs;
    }

    return -ETIMEDOUT;
}

IncFsErrorCode IncFs_WaitForFsWrittenBlocksChange(const IncFsControl* control, int32_t timeoutMs,
                                                  IncFsSize* count) {
    if (!control || !count) {
        return -EINVAL;
    }
    if (!(features() & Features::v2)) {
        return -ENOTSUP;
    }

    using namespace std::chrono;
    auto hrTimeout = steady_clock::duration(milliseconds(timeoutMs));

    while (hrTimeout > hrTimeout.zero()) {
        const auto startTs = steady_clock::now();

        pollfd pfd = {control->blocksWritten, POLLIN, 0};
        const auto res = ::poll(&pfd, 1, duration_cast<milliseconds>(hrTimeout).count());
        if (res > 0) {
            break;
        }
        if (res == 0) {
            return -ETIMEDOUT;
        }
        const auto error = errno;
        if (error != EINTR) {
            PLOG(ERROR) << "poll() failed";
            return -error;
        }
        hrTimeout -= steady_clock::now() - startTs;
    }

    char str[32];
    auto size = ::read(control->blocksWritten, str, sizeof(str));
    if (size < 0) {
        const auto error = errno;
        PLOG(ERROR) << "read() failed";
        return -error;
    }
    const auto res = std::from_chars(str, str + size, *count);
    if (res.ec != std::errc{}) {
        return res.ec == std::errc::invalid_argument ? -EINVAL : -ERANGE;
    }

    return 0;
}

static IncFsErrorCode reserveSpace(const char* backingPath, IncFsSize size) {
    auto fd = ab::unique_fd(::open(backingPath, O_WRONLY | O_CLOEXEC));
    if (fd < 0) {
        return -errno;
    }
    struct stat st = {};
    if (::fstat(fd.get(), &st)) {
        return -errno;
    }
    if (size == kIncFsTrimReservedSpace) {
        if (::ftruncate(fd.get(), st.st_size)) {
            return -errno;
        }
    } else {
        // Add 1.5% of the size for the hash tree and the blockmap, and some more blocks
        // for fixed overhead.
        // hash tree is ~33 bytes / page, and blockmap is 10 bytes / page
        // no need to round to a page size as filesystems already do that.
        const auto backingSize = IncFsSize(size * 1.015) + INCFS_DATA_FILE_BLOCK_SIZE * 4;
        if (backingSize < st.st_size) {
            return -EPERM;
        }
        if (::fallocate(fd.get(), FALLOC_FL_KEEP_SIZE, 0, backingSize)) {
            return -errno;
        }
    }
    return 0;
}

IncFsErrorCode IncFs_ReserveSpaceByPath(const IncFsControl* control, const char* path,
                                        IncFsSize size) {
    if (!control || (size != kIncFsTrimReservedSpace && size < 0)) {
        return -EINVAL;
    }
    const auto [pathRoot, backingRoot, subpath] = registry().detailsFor(path);
    const auto root = rootForCmd(control->cmd);
    if (root.empty() || root != pathRoot) {
        return -EINVAL;
    }
    return reserveSpace(path::join(backingRoot, subpath).c_str(), size);
}

IncFsErrorCode IncFs_ReserveSpaceById(const IncFsControl* control, IncFsFileId id, IncFsSize size) {
    if (!control || (size != kIncFsTrimReservedSpace && size < 0)) {
        return -EINVAL;
    }
    const auto root = rootForCmd(control->cmd);
    if (root.empty()) {
        return -EINVAL;
    }
    auto path = indexPath(root, id);
    const auto [pathRoot, backingRoot, subpath] = registry().detailsFor(path);
    if (root != pathRoot) {
        return -EINVAL;
    }
    return reserveSpace(path::join(backingRoot, subpath).c_str(), size);
}

template <class IntType>
static int readIntFromFile(std::string_view rootDir, std::string_view subPath, IntType& result) {
    std::string content;
    if (!ab::ReadFileToString(path::join(rootDir, subPath), &content)) {
        PLOG(ERROR) << "IncFs_GetMetrics: failed to read file: " << rootDir << "/" << subPath;
        return -errno;
    }
    const auto res = std::from_chars(content.data(), content.data() + content.size(), result);
    if (res.ec != std::errc()) {
        return -static_cast<int>(res.ec);
    }
    return 0;
}

IncFsErrorCode IncFs_GetMetrics(const char* sysfsName, IncFsMetrics* metrics) {
    if (!sysfsName || !*sysfsName) {
        return -EINVAL;
    }

    const auto kSysfsMetricsDir =
            ab::StringPrintf("/sys/fs/%s/instances/%s", INCFS_NAME, sysfsName);

    int err;
    if (err = readIntFromFile(kSysfsMetricsDir, "reads_delayed_min", metrics->readsDelayedMin);
        err != 0) {
        return err;
    }
    if (err = readIntFromFile(kSysfsMetricsDir, "reads_delayed_min_us", metrics->readsDelayedMinUs);
        err != 0) {
        return err;
    }
    if (err = readIntFromFile(kSysfsMetricsDir, "reads_delayed_pending",
                              metrics->readsDelayedPending);
        err != 0) {
        return err;
    }
    if (err = readIntFromFile(kSysfsMetricsDir, "reads_delayed_pending_us",
                              metrics->readsDelayedPendingUs);
        err != 0) {
        return err;
    }
    if (err = readIntFromFile(kSysfsMetricsDir, "reads_failed_hash_verification",
                              metrics->readsFailedHashVerification);
        err != 0) {
        return err;
    }
    if (err = readIntFromFile(kSysfsMetricsDir, "reads_failed_other", metrics->readsFailedOther);
        err != 0) {
        return err;
    }
    if (err = readIntFromFile(kSysfsMetricsDir, "reads_failed_timed_out",
                              metrics->readsFailedTimedOut);
        err != 0) {
        return err;
    }
    return 0;
}

IncFsErrorCode IncFs_GetLastReadError(const IncFsControl* control,
                                      IncFsLastReadError* lastReadError) {
    if (!control) {
        return -EINVAL;
    }
    if (!(features() & Features::v2)) {
        return -ENOTSUP;
    }
    incfs_get_last_read_error_args args = {};
    auto res = ::ioctl(control->cmd, INCFS_IOC_GET_LAST_READ_ERROR, &args);
    if (res < 0) {
        PLOG(ERROR) << "[incfs] IncFs_GetLastReadError failed.";
        return -errno;
    }
    *lastReadError = IncFsLastReadError{
            .timestampUs = args.time_us_out,
            .block = static_cast<IncFsBlockIndex>(args.page_out),
            .errorNo = args.errno_out,
            .uid = static_cast<IncFsUid>(args.uid_out),
    };
    static_assert(sizeof(args.file_id_out.bytes) == sizeof(lastReadError->id.data));
    memcpy(lastReadError->id.data, args.file_id_out.bytes, sizeof(args.file_id_out.bytes));
    return 0;
}

MountRegistry& android::incfs::defaultMountRegistry() {
    return registry();
}