fs_mgr/fs_mgr_overlayfs.cpp

/*
 * Copyright (C) 2018 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.
 */

#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <linux/fs.h>
#include <selinux/selinux.h>
#include <stdio.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/statvfs.h>
#include <sys/types.h>
#include <sys/vfs.h>
#include <unistd.h>

#include <algorithm>
#include <map>
#include <memory>
#include <string>
#include <vector>

#include <android-base/file.h>
#include <android-base/macros.h>
#include <android-base/properties.h>
#include <android-base/strings.h>
#include <android-base/unique_fd.h>
#include <ext4_utils/ext4_utils.h>
#include <fs_mgr_dm_linear.h>
#include <fs_mgr_overlayfs.h>
#include <fstab/fstab.h>
#include <libdm/dm.h>
#include <liblp/builder.h>
#include <liblp/liblp.h>

#include "fs_mgr_priv.h"

using namespace std::literals;
using namespace android::dm;
using namespace android::fs_mgr;

#if ALLOW_ADBD_DISABLE_VERITY == 0  // If we are a user build, provide stubs

bool fs_mgr_overlayfs_mount_all(const fstab*) {
    return false;
}

std::vector<std::string> fs_mgr_overlayfs_required_devices(const fstab*) {
    return {};
}

bool fs_mgr_overlayfs_setup(const char*, const char*, bool* change) {
    if (change) *change = false;
    return false;
}

bool fs_mgr_overlayfs_teardown(const char*, bool* change) {
    if (change) *change = false;
    return false;
}

#else  // ALLOW_ADBD_DISABLE_VERITY == 0

namespace {

// list of acceptable overlayfs backing storage
const auto kScratchMountPoint = "/mnt/scratch"s;
const auto kCacheMountPoint = "/cache"s;
const std::vector<const std::string> kOverlayMountPoints = {kScratchMountPoint, kCacheMountPoint};

// Return true if everything is mounted, but before adb is started.  Right
// after 'trigger load_persist_props_action' is done.
bool fs_mgr_boot_completed() {
    return android::base::GetBoolProperty("ro.persistent_properties.ready", false);
}

bool fs_mgr_is_dir(const std::string& path) {
    struct stat st;
    return !stat(path.c_str(), &st) && S_ISDIR(st.st_mode);
}

// Similar test as overlayfs workdir= validation in the kernel for read-write
// validation, except we use fs_mgr_work.  Covers space and storage issues.
bool fs_mgr_dir_is_writable(const std::string& path) {
    auto test_directory = path + "/fs_mgr_work";
    rmdir(test_directory.c_str());
    auto ret = !mkdir(test_directory.c_str(), 0700);
    return ret | !rmdir(test_directory.c_str());
}

std::string fs_mgr_get_context(const std::string& mount_point) {
    char* ctx = nullptr;
    auto len = getfilecon(mount_point.c_str(), &ctx);
    if ((len > 0) && ctx) {
        std::string context(ctx, len);
        free(ctx);
        return context;
    }
    return "";
}

// At less than 1% free space return value of false,
// means we will try to wrap with overlayfs.
bool fs_mgr_filesystem_has_space(const char* mount_point) {
    // If we have access issues to find out space remaining, return true
    // to prevent us trying to override with overlayfs.
    struct statvfs vst;
    if (statvfs(mount_point, &vst)) return true;

    static constexpr int kPercentThreshold = 1;  // 1%

    return (vst.f_bfree >= (vst.f_blocks * kPercentThreshold / 100));
}

bool fs_mgr_overlayfs_enabled(const struct fstab_rec* fsrec) {
    // readonly filesystem, can not be mount -o remount,rw
    // if squashfs or if free space is (near) zero making such a remount
    // virtually useless, or if there are shared blocks that prevent remount,rw
    return ("squashfs"s == fsrec->fs_type) ||
           fs_mgr_has_shared_blocks(fsrec->mount_point, fsrec->blk_device) ||
           !fs_mgr_filesystem_has_space(fsrec->mount_point);
}

const auto kUpperName = "upper"s;
const auto kWorkName = "work"s;
const auto kOverlayTopDir = "/overlay"s;

std::string fs_mgr_get_overlayfs_candidate(const std::string& mount_point) {
    if (!fs_mgr_is_dir(mount_point)) return "";
    const auto base = android::base::Basename(mount_point) + "/";
    for (const auto& overlay_mount_point : kOverlayMountPoints) {
        auto dir = overlay_mount_point + kOverlayTopDir + "/" + base;
        auto upper = dir + kUpperName;
        if (!fs_mgr_is_dir(upper)) continue;
        auto work = dir + kWorkName;
        if (!fs_mgr_is_dir(work)) continue;
        if (!fs_mgr_dir_is_writable(work)) continue;
        return dir;
    }
    return "";
}

const auto kLowerdirOption = "lowerdir="s;
const auto kUpperdirOption = "upperdir="s;

// default options for mount_point, returns empty string for none available.
std::string fs_mgr_get_overlayfs_options(const std::string& mount_point) {
    auto candidate = fs_mgr_get_overlayfs_candidate(mount_point);
    if (candidate.empty()) return "";

    return "override_creds=off,"s + kLowerdirOption + mount_point + "," + kUpperdirOption +
           candidate + kUpperName + ",workdir=" + candidate + kWorkName;
}

const char* fs_mgr_mount_point(const char* mount_point) {
    if (!mount_point) return mount_point;
    if ("/"s != mount_point) return mount_point;
    return "/system";
}

bool fs_mgr_access(const std::string& path) {
    auto save_errno = errno;
    auto ret = access(path.c_str(), F_OK) == 0;
    errno = save_errno;
    return ret;
}

bool fs_mgr_rw_access(const std::string& path) {
    if (path.empty()) return false;
    auto save_errno = errno;
    auto ret = access(path.c_str(), R_OK | W_OK) == 0;
    errno = save_errno;
    return ret;
}

// return true if system supports overlayfs
bool fs_mgr_wants_overlayfs() {
    // Properties will return empty on init first_stage_mount, so speculative
    // determination, empty (unset) _or_ "1" is true which differs from the
    // official ro.debuggable policy.  ALLOW_ADBD_DISABLE_VERITY == 0 should
    // protect us from false in any case, so this is insurance.
    auto debuggable = android::base::GetProperty("ro.debuggable", "1");
    if (debuggable != "1") return false;

    // Overlayfs available in the kernel, and patched for override_creds?
    return fs_mgr_access("/sys/module/overlay/parameters/override_creds");
}

bool fs_mgr_overlayfs_already_mounted(const std::string& mount_point, bool overlay_only = true) {
    std::unique_ptr<fstab, decltype(&fs_mgr_free_fstab)> fstab(fs_mgr_read_fstab("/proc/mounts"),
                                                               fs_mgr_free_fstab);
    if (!fstab) return false;
    const auto lowerdir = kLowerdirOption + mount_point;
    for (auto i = 0; i < fstab->num_entries; ++i) {
        const auto fsrec = &fstab->recs[i];
        const auto fs_type = fsrec->fs_type;
        if (!fs_type) continue;
        if (overlay_only && ("overlay"s != fs_type) && ("overlayfs"s != fs_type)) continue;
        auto fsrec_mount_point = fsrec->mount_point;
        if (!fsrec_mount_point) continue;
        if (mount_point != fsrec_mount_point) continue;
        if (!overlay_only) return true;
        const auto fs_options = fsrec->fs_options;
        if (!fs_options) continue;
        const auto options = android::base::Split(fs_options, ",");
        for (const auto& opt : options) {
            if (opt == lowerdir) {
                return true;
            }
        }
    }
    return false;
}

std::vector<std::string> fs_mgr_overlayfs_verity_enabled_list() {
    std::vector<std::string> ret;
    fs_mgr_update_verity_state([&ret](fstab_rec*, const char* mount_point, int, int) {
        ret.emplace_back(mount_point);
    });
    return ret;
}

bool fs_mgr_wants_overlayfs(const fstab_rec* fsrec) {
    if (!fsrec) return false;

    auto fsrec_mount_point = fsrec->mount_point;
    if (!fsrec_mount_point || !fsrec_mount_point[0]) return false;
    if (!fsrec->blk_device) return false;

    if (!fsrec->fs_type) return false;

    // Don't check entries that are managed by vold.
    if (fsrec->fs_mgr_flags & (MF_VOLDMANAGED | MF_RECOVERYONLY)) return false;

    // Only concerned with readonly partitions.
    if (!(fsrec->flags & MS_RDONLY)) return false;

    // If unbindable, do not allow overlayfs as this could expose us to
    // security issues.  On Android, this could also be used to turn off
    // the ability to overlay an otherwise acceptable filesystem since
    // /system and /vendor are never bound(sic) to.
    if (fsrec->flags & MS_UNBINDABLE) return false;

    if (!fs_mgr_overlayfs_enabled(fsrec)) return false;

    return true;
}

bool fs_mgr_rm_all(const std::string& path, bool* change = nullptr) {
    auto save_errno = errno;
    std::unique_ptr<DIR, decltype(&closedir)> dir(opendir(path.c_str()), closedir);
    if (!dir) {
        if (errno == ENOENT) {
            errno = save_errno;
            return true;
        }
        PERROR << "opendir " << path;
        return false;
    }
    dirent* entry;
    auto ret = true;
    while ((entry = readdir(dir.get()))) {
        if (("."s == entry->d_name) || (".."s == entry->d_name)) continue;
        auto file = path + "/" + entry->d_name;
        if (entry->d_type == DT_UNKNOWN) {
            struct stat st;
            if (!lstat(file.c_str(), &st) && (st.st_mode & S_IFDIR)) entry->d_type = DT_DIR;
        }
        if (entry->d_type == DT_DIR) {
            ret &= fs_mgr_rm_all(file, change);
            if (!rmdir(file.c_str())) {
                if (change) *change = true;
            } else {
                ret = false;
                PERROR << "rmdir " << file;
            }
            continue;
        }
        if (!unlink(file.c_str())) {
            if (change) *change = true;
        } else {
            ret = false;
            PERROR << "rm " << file;
        }
    }
    return ret;
}

constexpr char kOverlayfsFileContext[] = "u:object_r:overlayfs_file:s0";

bool fs_mgr_overlayfs_setup_dir(const std::string& dir, std::string* overlay, bool* change) {
    auto ret = true;
    auto top = dir + kOverlayTopDir;
    if (setfscreatecon(kOverlayfsFileContext)) {
        ret = false;
        PERROR << "setfscreatecon " << kOverlayfsFileContext;
    }
    auto save_errno = errno;
    if (!mkdir(top.c_str(), 0755)) {
        if (change) *change = true;
    } else if (errno != EEXIST) {
        ret = false;
        PERROR << "mkdir " << top;
    } else {
        errno = save_errno;
    }
    setfscreatecon(nullptr);

    if (overlay) *overlay = std::move(top);
    return ret;
}

bool fs_mgr_overlayfs_setup_one(const std::string& overlay, const std::string& mount_point,
                                bool* change) {
    auto ret = true;
    auto fsrec_mount_point = overlay + "/" + android::base::Basename(mount_point) + "/";

    if (setfscreatecon(kOverlayfsFileContext)) {
        ret = false;
        PERROR << "setfscreatecon " << kOverlayfsFileContext;
    }
    auto save_errno = errno;
    if (!mkdir(fsrec_mount_point.c_str(), 0755)) {
        if (change) *change = true;
    } else if (errno != EEXIST) {
        ret = false;
        PERROR << "mkdir " << fsrec_mount_point;
    } else {
        errno = save_errno;
    }

    save_errno = errno;
    if (!mkdir((fsrec_mount_point + kWorkName).c_str(), 0755)) {
        if (change) *change = true;
    } else if (errno != EEXIST) {
        ret = false;
        PERROR << "mkdir " << fsrec_mount_point << kWorkName;
    } else {
        errno = save_errno;
    }
    setfscreatecon(nullptr);

    auto new_context = fs_mgr_get_context(mount_point);
    if (!new_context.empty() && setfscreatecon(new_context.c_str())) {
        ret = false;
        PERROR << "setfscreatecon " << new_context;
    }
    auto upper = fsrec_mount_point + kUpperName;
    save_errno = errno;
    if (!mkdir(upper.c_str(), 0755)) {
        if (change) *change = true;
    } else if (errno != EEXIST) {
        ret = false;
        PERROR << "mkdir " << upper;
    } else {
        errno = save_errno;
    }
    if (!new_context.empty()) setfscreatecon(nullptr);

    return ret;
}

uint32_t fs_mgr_overlayfs_slot_number() {
    return SlotNumberForSlotSuffix(fs_mgr_get_slot_suffix());
}

std::string fs_mgr_overlayfs_super_device(uint32_t slot_number) {
    return "/dev/block/by-name/" + fs_mgr_get_super_partition_name(slot_number);
}

bool fs_mgr_overlayfs_has_logical(const fstab* fstab) {
    if (!fstab) return false;
    for (auto i = 0; i < fstab->num_entries; i++) {
        const auto fsrec = &fstab->recs[i];
        if (fs_mgr_is_logical(fsrec)) return true;
    }
    return false;
}

// reduce 'DM_DEV_STATUS failed for scratch: No such device or address' noise
std::string scratch_device_cache;

bool fs_mgr_overlayfs_teardown_scratch(const std::string& overlay, bool* change) {
    // umount and delete kScratchMountPoint storage if we have logical partitions
    if (overlay != kScratchMountPoint) return true;
    scratch_device_cache.erase();
    auto slot_number = fs_mgr_overlayfs_slot_number();
    auto super_device = fs_mgr_overlayfs_super_device(slot_number);
    if (!fs_mgr_rw_access(super_device)) return true;

    auto save_errno = errno;
    if (fs_mgr_overlayfs_already_mounted(kScratchMountPoint, false)) {
        // Lazy umount will allow us to move on and possibly later
        // establish a new fresh mount without requiring a reboot should
        // the developer wish to restart.  Old references should melt
        // away or have no data.  Main goal is to shut the door on the
        // current overrides with an expectation of a subsequent reboot,
        // thus any errors here are ignored.
        umount2(kScratchMountPoint.c_str(), MNT_DETACH);
    }
    auto builder = MetadataBuilder::New(super_device, slot_number);
    if (!builder) {
        errno = save_errno;
        return true;
    }
    const auto partition_name = android::base::Basename(kScratchMountPoint);
    if (builder->FindPartition(partition_name) == nullptr) {
        errno = save_errno;
        return true;
    }
    builder->RemovePartition(partition_name);
    auto metadata = builder->Export();
    if (metadata && UpdatePartitionTable(super_device, *metadata.get(), slot_number)) {
        if (change) *change = true;
        if (!DestroyLogicalPartition(partition_name, 0s)) return false;
    } else {
        PERROR << "delete partition " << overlay;
        return false;
    }
    errno = save_errno;
    return true;
}

bool fs_mgr_overlayfs_teardown_one(const std::string& overlay, const std::string& mount_point,
                                   bool* change) {
    const auto top = overlay + kOverlayTopDir;

    if (!fs_mgr_access(top)) return false;

    auto cleanup_all = mount_point.empty();
    const auto oldpath = top + (cleanup_all ? "" : ("/"s + mount_point));
    const auto newpath = oldpath + ".teardown";
    auto ret = fs_mgr_rm_all(newpath);
    auto save_errno = errno;
    if (!rename(oldpath.c_str(), newpath.c_str())) {
        if (change) *change = true;
    } else if (errno != ENOENT) {
        ret = false;
        PERROR << "mv " << oldpath << " " << newpath;
    } else {
        errno = save_errno;
    }
    ret &= fs_mgr_rm_all(newpath, change);
    save_errno = errno;
    if (!rmdir(newpath.c_str())) {
        if (change) *change = true;
    } else if (errno != ENOENT) {
        ret = false;
        PERROR << "rmdir " << newpath;
    } else {
        errno = save_errno;
    }
    if (!cleanup_all) {
        save_errno = errno;
        if (!rmdir(top.c_str())) {
            if (change) *change = true;
            cleanup_all = true;
        } else if ((errno != ENOENT) && (errno != ENOTEMPTY)) {
            ret = false;
            PERROR << "rmdir " << top;
        } else {
            errno = save_errno;
            cleanup_all = true;
        }
    }
    if (cleanup_all) ret &= fs_mgr_overlayfs_teardown_scratch(overlay, change);
    return ret;
}

bool fs_mgr_overlayfs_mount(const std::string& mount_point) {
    auto options = fs_mgr_get_overlayfs_options(mount_point);
    if (options.empty()) return false;

    // hijack __mount() report format to help triage
    auto report = "__mount(source=overlay,target="s + mount_point + ",type=overlay";
    const auto opt_list = android::base::Split(options, ",");
    for (const auto opt : opt_list) {
        if (android::base::StartsWith(opt, kUpperdirOption)) {
            report = report + "," + opt;
            break;
        }
    }
    report = report + ")=";

    auto ret = mount("overlay", mount_point.c_str(), "overlay", MS_RDONLY | MS_RELATIME,
                     options.c_str());
    if (ret) {
        PERROR << report << ret;
        return false;
    } else {
        LINFO << report << ret;
        return true;
    }
}

std::vector<std::string> fs_mgr_candidate_list(const fstab* fstab,
                                               const char* mount_point = nullptr) {
    std::vector<std::string> mounts;
    if (!fstab) return mounts;

    auto verity = fs_mgr_overlayfs_verity_enabled_list();
    for (auto i = 0; i < fstab->num_entries; i++) {
        const auto fsrec = &fstab->recs[i];
        if (!fs_mgr_wants_overlayfs(fsrec)) continue;
        std::string new_mount_point(fs_mgr_mount_point(fsrec->mount_point));
        if (mount_point && (new_mount_point != mount_point)) continue;
        if (std::find(verity.begin(), verity.end(), android::base::Basename(new_mount_point)) !=
            verity.end()) {
            continue;
        }
        auto duplicate_or_more_specific = false;
        for (auto it = mounts.begin(); it != mounts.end();) {
            if ((*it == new_mount_point) ||
                (android::base::StartsWith(new_mount_point, *it + "/"))) {
                duplicate_or_more_specific = true;
                break;
            }
            if (android::base::StartsWith(*it, new_mount_point + "/")) {
                it = mounts.erase(it);
            } else {
                ++it;
            }
        }
        if (!duplicate_or_more_specific) mounts.emplace_back(new_mount_point);
    }

    // if not itemized /system or /, system as root, fake one up?

    // do we want or need to?
    if (mount_point && ("/system"s != mount_point)) return mounts;
    if (std::find(mounts.begin(), mounts.end(), "/system") != mounts.end()) return mounts;

    // fs_mgr_overlayfs_verity_enabled_list says not to?
    if (std::find(verity.begin(), verity.end(), "system") != verity.end()) return mounts;

    // confirm that fstab is missing system
    if (fs_mgr_get_entry_for_mount_point(const_cast<struct fstab*>(fstab), "/")) {
        return mounts;
    }
    if (fs_mgr_get_entry_for_mount_point(const_cast<struct fstab*>(fstab), "/system")) {
        return mounts;
    }

    // Manually check dm state because stunted fstab (w/o system as root) borken
    auto& dm = DeviceMapper::Instance();
    auto found = false;
    for (auto& system : {"system", "vroot"}) {
        if (dm.GetState(system) == DmDeviceState::INVALID) continue;
        std::vector<DeviceMapper::TargetInfo> table;
        found = !dm.GetTableStatus(system, &table) || table.empty() || table[0].data.empty() ||
                (table[0].data[0] == 'C') || (table[0].data[0] == 'V');
        if (found) break;
    }
    if (!found) mounts.emplace_back("/system");
    return mounts;
}

// Mount kScratchMountPoint
bool fs_mgr_overlayfs_mount_scratch(const std::string& device_path, const std::string mnt_type) {
    if (setfscreatecon(kOverlayfsFileContext)) {
        PERROR << "setfscreatecon " << kOverlayfsFileContext;
    }
    if (mkdir(kScratchMountPoint.c_str(), 0755) && (errno != EEXIST)) {
        PERROR << "create " << kScratchMountPoint;
    }

    std::unique_ptr<fstab, decltype(&fs_mgr_free_fstab)> local_fstab(
            static_cast<fstab*>(calloc(1, sizeof(fstab))), fs_mgr_free_fstab);
    auto fsrec = static_cast<fstab_rec*>(calloc(1, sizeof(fstab_rec)));
    local_fstab->num_entries = 1;
    local_fstab->recs = fsrec;
    fsrec->blk_device = strdup(device_path.c_str());
    fsrec->mount_point = strdup(kScratchMountPoint.c_str());
    fsrec->fs_type = strdup(mnt_type.c_str());
    fsrec->flags = MS_RELATIME;
    fsrec->fs_options = strdup("");
    auto mounted = fs_mgr_do_mount_one(fsrec) == 0;
    auto save_errno = errno;
    setfscreatecon(nullptr);
    if (!mounted) rmdir(kScratchMountPoint.c_str());
    errno = save_errno;
    return mounted;
}

const std::string kMkF2fs("/system/bin/make_f2fs");
const std::string kMkExt4("/system/bin/mke2fs");

std::string fs_mgr_overlayfs_scratch_mount_type() {
    if (!access(kMkF2fs.c_str(), X_OK)) return "f2fs";
    if (!access(kMkExt4.c_str(), X_OK)) return "ext4";
    return "auto";
}

std::string fs_mgr_overlayfs_scratch_device() {
    if (!scratch_device_cache.empty()) return scratch_device_cache;

    auto& dm = DeviceMapper::Instance();
    const auto partition_name = android::base::Basename(kScratchMountPoint);
    std::string path;
    if (!dm.GetDmDevicePathByName(partition_name, &path)) return "";
    return scratch_device_cache = path;
}

// Create and mount kScratchMountPoint storage if we have logical partitions
bool fs_mgr_overlayfs_setup_scratch(const fstab* fstab, bool* change) {
    if (fs_mgr_overlayfs_already_mounted(kScratchMountPoint, false)) return true;
    auto mnt_type = fs_mgr_overlayfs_scratch_mount_type();
    auto scratch_device = fs_mgr_overlayfs_scratch_device();
    auto partition_exists = fs_mgr_rw_access(scratch_device);
    if (!partition_exists) {
        auto slot_number = fs_mgr_overlayfs_slot_number();
        auto super_device = fs_mgr_overlayfs_super_device(slot_number);
        if (!fs_mgr_rw_access(super_device)) return false;
        if (!fs_mgr_overlayfs_has_logical(fstab)) return false;
        auto builder = MetadataBuilder::New(super_device, slot_number);
        if (!builder) {
            PERROR << "open " << super_device << " metadata";
            return false;
        }
        const auto partition_name = android::base::Basename(kScratchMountPoint);
        partition_exists = builder->FindPartition(partition_name) != nullptr;
        if (!partition_exists) {
            auto partition = builder->AddPartition(partition_name, LP_PARTITION_ATTR_NONE);
            if (!partition) {
                PERROR << "create " << partition_name;
                return false;
            }
            auto partition_size = builder->AllocatableSpace() - builder->UsedSpace();
            // 512MB or half the remaining available space, whichever is greater.
            partition_size = std::max(uint64_t(512 * 1024 * 1024), partition_size / 2);
            if (!builder->ResizePartition(partition, partition_size)) {
                PERROR << "resize " << partition_name;
                return false;
            }

            auto metadata = builder->Export();
            if (!metadata) {
                LERROR << "generate new metadata " << partition_name;
                return false;
            }
            if (!UpdatePartitionTable(super_device, *metadata.get(), slot_number)) {
                LERROR << "update " << partition_name;
                return false;
            }

            if (change) *change = true;
        }

        if (!CreateLogicalPartition(super_device, slot_number, partition_name, true, 0s,
                                    &scratch_device))
            return false;
    }

    if (partition_exists) {
        if (fs_mgr_overlayfs_mount_scratch(scratch_device, mnt_type)) {
            if (change) *change = true;
            return true;
        }
        // partition existed, but was not initialized;
        errno = 0;
    }

    auto ret = system((mnt_type == "f2fs")
                              ? ((kMkF2fs + " -d1 " + scratch_device).c_str())
                              : ((kMkExt4 + " -b 4096 -t ext4 -m 0 -M "s + kScratchMountPoint +
                                  " -O has_journal " + scratch_device)
                                         .c_str()));
    if (ret) {
        LERROR << "make " << mnt_type << " filesystem on " << scratch_device << " error=" << ret;
        return false;
    }

    if (change) *change = true;

    return fs_mgr_overlayfs_mount_scratch(scratch_device, mnt_type);
}

bool fs_mgr_overlayfs_scratch_can_be_mounted(const std::string& scratch_device) {
    if (scratch_device.empty()) return false;
    if (fs_mgr_overlayfs_already_mounted(kScratchMountPoint, false)) return false;
    if (fs_mgr_rw_access(scratch_device)) return true;
    auto slot_number = fs_mgr_overlayfs_slot_number();
    auto super_device = fs_mgr_overlayfs_super_device(slot_number);
    if (!fs_mgr_rw_access(super_device)) return false;
    auto builder = MetadataBuilder::New(super_device, slot_number);
    if (!builder) return false;
    return builder->FindPartition(android::base::Basename(kScratchMountPoint)) != nullptr;
}

}  // namespace

bool fs_mgr_overlayfs_mount_all(const fstab* fstab) {
    auto ret = false;

    if (!fs_mgr_wants_overlayfs()) return ret;

    if (!fstab) return ret;

    auto scratch_can_be_mounted = true;
    for (const auto& mount_point : fs_mgr_candidate_list(fstab)) {
        if (fs_mgr_overlayfs_already_mounted(mount_point)) continue;
        if (scratch_can_be_mounted) {
            scratch_can_be_mounted = false;
            auto scratch_device = fs_mgr_overlayfs_scratch_device();
            if (fs_mgr_overlayfs_scratch_can_be_mounted(scratch_device) &&
                fs_mgr_wait_for_file(scratch_device, 10s) &&
                fs_mgr_overlayfs_mount_scratch(scratch_device,
                                               fs_mgr_overlayfs_scratch_mount_type()) &&
                !fs_mgr_access(kScratchMountPoint + kOverlayTopDir)) {
                umount2(kScratchMountPoint.c_str(), MNT_DETACH);
                rmdir(kScratchMountPoint.c_str());
            }
        }
        if (fs_mgr_overlayfs_mount(mount_point)) ret = true;
    }
    return ret;
}

std::vector<std::string> fs_mgr_overlayfs_required_devices(const fstab* fstab) {
    if (fs_mgr_get_entry_for_mount_point(const_cast<struct fstab*>(fstab), kScratchMountPoint)) {
        return {};
    }

    for (const auto& mount_point : fs_mgr_candidate_list(fstab)) {
        if (fs_mgr_overlayfs_already_mounted(mount_point)) continue;
        auto device = fs_mgr_overlayfs_scratch_device();
        if (!fs_mgr_overlayfs_scratch_can_be_mounted(device)) break;
        return {device};
    }
    return {};
}

// Returns false if setup not permitted, errno set to last error.
// If something is altered, set *change.
bool fs_mgr_overlayfs_setup(const char* backing, const char* mount_point, bool* change) {
    if (change) *change = false;
    auto ret = false;
    if (!fs_mgr_wants_overlayfs()) return ret;
    if (!fs_mgr_boot_completed()) {
        errno = EBUSY;
        PERROR << "setup";
        return ret;
    }

    std::unique_ptr<fstab, decltype(&fs_mgr_free_fstab)> fstab(fs_mgr_read_fstab_default(),
                                                               fs_mgr_free_fstab);
    if (!fstab) return ret;
    auto mounts = fs_mgr_candidate_list(fstab.get(), fs_mgr_mount_point(mount_point));
    if (mounts.empty()) return ret;

    std::string dir;
    for (const auto& overlay_mount_point : kOverlayMountPoints) {
        if (backing && backing[0] && (overlay_mount_point != backing)) continue;
        if (overlay_mount_point == kScratchMountPoint) {
            if (!fs_mgr_rw_access(fs_mgr_overlayfs_super_device(fs_mgr_overlayfs_slot_number())) ||
                !fs_mgr_overlayfs_has_logical(fstab.get())) {
                continue;
            }
            if (!fs_mgr_overlayfs_setup_scratch(fstab.get(), change)) continue;
        } else {
            if (!fs_mgr_get_entry_for_mount_point(fstab.get(), overlay_mount_point)) continue;
        }
        dir = overlay_mount_point;
        break;
    }
    if (dir.empty()) {
        errno = ESRCH;
        return ret;
    }

    std::string overlay;
    ret |= fs_mgr_overlayfs_setup_dir(dir, &overlay, change);
    for (const auto& fsrec_mount_point : mounts) {
        ret |= fs_mgr_overlayfs_setup_one(overlay, fsrec_mount_point, change);
    }
    return ret;
}

// Returns false if teardown not permitted, errno set to last error.
// If something is altered, set *change.
bool fs_mgr_overlayfs_teardown(const char* mount_point, bool* change) {
    if (change) *change = false;
    mount_point = fs_mgr_mount_point(mount_point);
    auto ret = true;
    for (const auto& overlay_mount_point : kOverlayMountPoints) {
        ret &= fs_mgr_overlayfs_teardown_one(overlay_mount_point, mount_point ?: "", change);
    }
    if (!fs_mgr_wants_overlayfs()) {
        // After obligatory teardown to make sure everything is clean, but if
        // we didn't want overlayfs in the the first place, we do not want to
        // waste time on a reboot (or reboot request message).
        if (change) *change = false;
    }
    // And now that we did what we could, lets inform
    // caller that there may still be more to do.
    if (!fs_mgr_boot_completed()) {
        errno = EBUSY;
        PERROR << "teardown";
        ret = false;
    }
    return ret;
}

#endif  // ALLOW_ADBD_DISABLE_VERITY != 0

bool fs_mgr_has_shared_blocks(const std::string& mount_point, const std::string& dev) {
    struct statfs fs;
    if ((statfs((mount_point + "/lost+found").c_str(), &fs) == -1) ||
        (fs.f_type != EXT4_SUPER_MAGIC)) {
        return false;
    }

    android::base::unique_fd fd(open(dev.c_str(), O_RDONLY | O_CLOEXEC));
    if (fd < 0) return false;

    struct ext4_super_block sb;
    if ((TEMP_FAILURE_RETRY(lseek64(fd, 1024, SEEK_SET)) < 0) ||
        (TEMP_FAILURE_RETRY(read(fd, &sb, sizeof(sb))) < 0)) {
        return false;
    }

    struct fs_info info;
    if (ext4_parse_sb(&sb, &info) < 0) return false;

    return (info.feat_ro_compat & EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS) != 0;
}