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* Copyright (C) 2008 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include "sysdeps.h"
#include <errno.h>
#include <fcntl.h>
#include <mntent.h>
#include <spawn.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/statvfs.h>
#include <sys/vfs.h>
#include <unistd.h>
#include <memory>
#include <set>
#include <string>
#include <vector>
#include <android-base/file.h>
#include <android-base/properties.h>
#include <bootloader_message/bootloader_message.h>
#include <cutils/android_reboot.h>
#include <fs_mgr.h>
#include <fs_mgr_overlayfs.h>
#include "adb.h"
#include "adb_io.h"
#include "adb_unique_fd.h"
#include "adb_utils.h"
#include "set_verity_enable_state_service.h"
using android::base::Realpath;
// Returns the last device used to mount a directory in /proc/mounts.
// This will find overlayfs entry where upperdir=lowerdir, to make sure
// remount is associated with the correct directory.
static std::string find_proc_mount(const char* dir) {
std::unique_ptr<FILE, int(*)(FILE*)> fp(setmntent("/proc/mounts", "r"), endmntent);
std::string mnt_fsname;
if (!fp) return mnt_fsname;
// dir might be a symlink, e.g., /product -> /system/product in GSI.
std::string canonical_path;
if (!Realpath(dir, &canonical_path)) {
PLOG(ERROR) << "Realpath failed: " << dir;
mntent* e;
while ((e = getmntent(fp.get())) != nullptr) {
if (canonical_path == e->mnt_dir) {
mnt_fsname = e->mnt_fsname;
return mnt_fsname;
// Returns the device used to mount a directory in the fstab.
static std::string find_fstab_mount(const char* dir) {
std::unique_ptr<fstab, decltype(&fs_mgr_free_fstab)> fstab(fs_mgr_read_fstab_default(),
struct fstab_rec* rec = fs_mgr_get_entry_for_mount_point(fstab.get(), dir);
return rec ? rec->blk_device : "";
// The proc entry for / is full of lies, so check fstab instead.
// /proc/mounts lists rootfs and /dev/root, neither of which is what we want.
static std::string find_mount(const char* dir, bool is_root) {
if (is_root) {
return find_fstab_mount(dir);
} else {
return find_proc_mount(dir);
bool make_block_device_writable(const std::string& dev) {
if ((dev == "overlay") || (dev == "overlayfs")) return true;
int fd = unix_open(dev.c_str(), O_RDONLY | O_CLOEXEC);
if (fd == -1) {
return false;
int OFF = 0;
bool result = (ioctl(fd, BLKROSET, &OFF) != -1);
return result;
static bool can_unshare_blocks(int fd, const char* dev) {
const char* E2FSCK_BIN = "/system/bin/e2fsck";
if (access(E2FSCK_BIN, X_OK)) {
WriteFdFmt(fd, "e2fsck is not available, cannot undo deduplication on %s\n", dev);
return false;
pid_t child;
char* env[] = {nullptr};
const char* argv[] = {E2FSCK_BIN, "-n", "-E", "unshare_blocks", dev, nullptr};
if (posix_spawn(&child, E2FSCK_BIN, nullptr, nullptr, const_cast<char**>(argv), env)) {
WriteFdFmt(fd, "failed to e2fsck to check deduplication: %s\n", strerror(errno));
return false;
int status = 0;
int ret = TEMP_FAILURE_RETRY(waitpid(child, &status, 0));
if (ret < 0) {
WriteFdFmt(fd, "failed to get e2fsck status: %s\n", strerror(errno));
return false;
if (!WIFEXITED(status)) {
WriteFdFmt(fd, "e2fsck exited abnormally with status %d\n", status);
return false;
int rc = WEXITSTATUS(status);
if (rc != 0) {
"%s is deduplicated, and an e2fsck check failed. It might not "
"have enough free-space to be remounted as writable.\n",
return false;
return true;
static unsigned long get_mount_flags(int fd, const char* dir) {
struct statvfs st_vfs;
if (statvfs(dir, &st_vfs) == -1) {
// Even though we could not get the original mount flags, assume that
// the mount was originally read-only.
WriteFdFmt(fd, "statvfs of the %s mount failed: %s.\n", dir, strerror(errno));
return MS_RDONLY;
return st_vfs.f_flag;
static bool remount_partition(int fd, const char* dir) {
if (!directory_exists(dir)) {
return true;
bool is_root = strcmp(dir, "/") == 0;
if (is_root && !find_mount("/system", false).empty()) {
dir = "/system";
is_root = false;
std::string dev = find_mount(dir, is_root);
// Even if the device for the root is not found, we still try to remount it
// as rw. This typically only happens when running Android in a container:
// the root will almost always be in a loop device, which is dynamic, so
// it's not convenient to put in the fstab.
if (dev.empty() && !is_root) {
return true;
if (!dev.empty() && !make_block_device_writable(dev)) {
WriteFdFmt(fd, "remount of %s failed; couldn't make block device %s writable: %s\n",
dir, dev.c_str(), strerror(errno));
return false;
unsigned long remount_flags = get_mount_flags(fd, dir);
remount_flags &= ~MS_RDONLY;
remount_flags |= MS_REMOUNT;
if (mount(dev.c_str(), dir, "none", remount_flags | MS_BIND, nullptr) == -1) {
// This is useful for cases where the superblock is already marked as
// read-write, but the mount itself is read-only, such as containers
// where the remount with just MS_REMOUNT is forbidden by the kernel.
WriteFdFmt(fd, "remount of the %s mount failed: %s.\n", dir, strerror(errno));
return false;
if (mount(dev.c_str(), dir, "none", MS_REMOUNT, nullptr) == -1) {
WriteFdFmt(fd, "remount of the %s superblock failed: %s\n", dir, strerror(errno));
return false;
return true;
static void reboot_for_remount(int fd, bool need_fsck) {
std::string reboot_cmd = "reboot";
if (need_fsck) {
const std::vector<std::string> options = {"--fsck_unshare_blocks"};
std::string err;
if (!write_bootloader_message(options, &err)) {
WriteFdFmt(fd, "Failed to set bootloader message: %s\n", err.c_str());
"The device will now reboot to recovery and attempt "
reboot_cmd = "reboot,recovery";
android::base::SetProperty(ANDROID_RB_PROPERTY, reboot_cmd.c_str());
void remount_service(unique_fd fd, const std::string& cmd) {
bool user_requested_reboot = cmd == "-R";
if (getuid() != 0) {
WriteFdExactly(fd.get(), "Not running as root. Try \"adb root\" first.\n");
bool system_verified = !(android::base::GetProperty("partition.system.verified", "").empty());
bool vendor_verified = !(android::base::GetProperty("partition.vendor.verified", "").empty());
std::vector<std::string> partitions{"/", "/odm", "/oem", "/product_services",
"/product", "/vendor"};
bool verity_enabled = (system_verified || vendor_verified);
// If we can use overlayfs, lets get it in place first
// before we struggle with determining deduplication operations.
if (!verity_enabled && fs_mgr_overlayfs_setup()) {
std::unique_ptr<fstab, decltype(&fs_mgr_free_fstab)> fstab(fs_mgr_read_fstab_default(),
if (fs_mgr_overlayfs_mount_all(fstab.get())) {
WriteFdExactly(fd.get(), "overlayfs mounted\n");
// Find partitions that are deduplicated, and can be un-deduplicated.
std::set<std::string> dedup;
for (const auto& part : partitions) {
auto partition = part;
if ((part == "/") && !find_mount("/system", false).empty()) partition = "/system";
std::string dev = find_mount(partition.c_str(), partition == "/");
if (dev.empty() || !fs_mgr_has_shared_blocks(partition, dev)) {
if (can_unshare_blocks(fd.get(), dev.c_str())) {
// Reboot now if the user requested it (and an operation needs a reboot).
if (user_requested_reboot) {
if (!dedup.empty() || verity_enabled) {
if (verity_enabled) {
set_verity_enabled_state_service(unique_fd(dup(fd.get())), false);
reboot_for_remount(fd.get(), !dedup.empty());
WriteFdExactly(fd.get(), "No reboot needed, skipping -R.\n");
// If we need to disable-verity, but we also need to perform a recovery
// fsck for deduplicated partitions, hold off on warning about verity. We
// can handle both verity and the recovery fsck in the same reboot cycle.
if (verity_enabled && dedup.empty()) {
// Allow remount but warn of likely bad effects
bool both = system_verified && vendor_verified;
WriteFdFmt(fd.get(), "dm_verity is enabled on the %s%s%s partition%s.\n",
system_verified ? "system" : "", both ? " and " : "",
vendor_verified ? "vendor" : "", both ? "s" : "");
"Use \"adb disable-verity\" to disable verity.\n"
"If you do not, remount may succeed, however, you will still "
"not be able to write to these volumes.\n");
"Alternately, use \"adb remount -R\" to disable verity "
"and automatically reboot.\n");
bool success = true;
for (const auto& partition : partitions) {
// Don't try to remount partitions that need an fsck in recovery.
if (dedup.count(partition)) {
success &= remount_partition(fd.get(), partition.c_str());
if (!dedup.empty()) {
"The following partitions are deduplicated and cannot "
"yet be remounted:\n");
for (const std::string& name : dedup) {
WriteFdFmt(fd.get(), " %s\n", name.c_str());
"To reboot and un-deduplicate the listed partitions, "
"please retry with adb remount -R.\n");
if (system_verified || vendor_verified) {
WriteFdExactly(fd.get(), "Note: verity will be automatically disabled after reboot.\n");
if (!success) {
WriteFdExactly(fd.get(), "remount failed\n");
} else {
WriteFdExactly(fd.get(), "remount succeeded\n");