libsnapshot: Add vts_userspace_snapshot_test

Toggle virtual_ab.userspace.snapshots.enabled to test
both:

1: vts_libsnapshot_test - testing kernel dm-snapshot
2: vts_userspace_snapshot_test - testing user-space snapshot

Bug: 193863443
Test: vts_userspace_snapshot_test
Signed-off-by: Akilesh Kailash <akailash@google.com>
Change-Id: I873e7476d71feb9a2e12054e968443bd22ee817c
diff --git a/fs_mgr/libsnapshot/Android.bp b/fs_mgr/libsnapshot/Android.bp
index 5ab2ce2..6b0293a 100644
--- a/fs_mgr/libsnapshot/Android.bp
+++ b/fs_mgr/libsnapshot/Android.bp
@@ -258,11 +258,62 @@
     require_root: true,
 }
 
+cc_defaults {
+    name: "userspace_snapshot_test_defaults",
+    defaults: ["libsnapshot_defaults"],
+    srcs: [
+        "partition_cow_creator_test.cpp",
+        "snapshot_metadata_updater_test.cpp",
+        "snapshot_reader_test.cpp",
+        "userspace_snapshot_test.cpp",
+        "snapshot_writer_test.cpp",
+    ],
+    shared_libs: [
+        "libbinder",
+        "libcrypto",
+        "libhidlbase",
+        "libprotobuf-cpp-lite",
+        "libutils",
+        "libz",
+    ],
+    static_libs: [
+        "android.hardware.boot@1.0",
+        "android.hardware.boot@1.1",
+        "libbrotli",
+        "libc++fs",
+        "libfs_mgr_binder",
+        "libgsi",
+        "libgmock",
+        "liblp",
+        "libsnapshot",
+        "libsnapshot_cow",
+        "libsnapshot_test_helpers",
+        "libsparse",
+    ],
+    header_libs: [
+        "libstorage_literals_headers",
+    ],
+    test_suites: [
+        "vts",
+        "device-tests"
+    ],
+    test_options: {
+        min_shipping_api_level: 29,
+    },
+    auto_gen_config: true,
+    require_root: true,
+}
+
 cc_test {
     name: "vts_libsnapshot_test",
     defaults: ["libsnapshot_test_defaults"],
 }
 
+cc_test {
+    name: "vts_userspace_snapshot_test",
+    defaults: ["userspace_snapshot_test_defaults"],
+}
+
 cc_binary {
     name: "snapshotctl",
     srcs: [
diff --git a/fs_mgr/libsnapshot/userspace_snapshot_test.cpp b/fs_mgr/libsnapshot/userspace_snapshot_test.cpp
new file mode 100644
index 0000000..abe67f6
--- /dev/null
+++ b/fs_mgr/libsnapshot/userspace_snapshot_test.cpp
@@ -0,0 +1,2519 @@
+// 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 <libsnapshot/cow_format.h>
+#include <libsnapshot/snapshot.h>
+
+#include <fcntl.h>
+#include <signal.h>
+#include <sys/file.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#include <chrono>
+#include <deque>
+#include <future>
+#include <iostream>
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+#include <android-base/properties.h>
+#include <android-base/strings.h>
+#include <android-base/unique_fd.h>
+#include <fs_mgr/file_wait.h>
+#include <fs_mgr/roots.h>
+#include <fs_mgr_dm_linear.h>
+#include <gtest/gtest.h>
+#include <libdm/dm.h>
+#include <libfiemap/image_manager.h>
+#include <liblp/builder.h>
+#include <storage_literals/storage_literals.h>
+
+#include <android/snapshot/snapshot.pb.h>
+#include <libsnapshot/test_helpers.h>
+#include "partition_cow_creator.h"
+#include "utility.h"
+
+#include <android-base/properties.h>
+
+// Mock classes are not used. Header included to ensure mocked class definition aligns with the
+// class itself.
+#include <libsnapshot/mock_device_info.h>
+#include <libsnapshot/mock_snapshot.h>
+
+namespace android {
+namespace snapshot {
+
+using android::base::unique_fd;
+using android::dm::DeviceMapper;
+using android::dm::DmDeviceState;
+using android::dm::IDeviceMapper;
+using android::fiemap::FiemapStatus;
+using android::fiemap::IImageManager;
+using android::fs_mgr::BlockDeviceInfo;
+using android::fs_mgr::CreateLogicalPartitionParams;
+using android::fs_mgr::DestroyLogicalPartition;
+using android::fs_mgr::EnsurePathMounted;
+using android::fs_mgr::EnsurePathUnmounted;
+using android::fs_mgr::Extent;
+using android::fs_mgr::Fstab;
+using android::fs_mgr::GetPartitionGroupName;
+using android::fs_mgr::GetPartitionName;
+using android::fs_mgr::Interval;
+using android::fs_mgr::MetadataBuilder;
+using android::fs_mgr::SlotSuffixForSlotNumber;
+using chromeos_update_engine::DeltaArchiveManifest;
+using chromeos_update_engine::DynamicPartitionGroup;
+using chromeos_update_engine::PartitionUpdate;
+using namespace ::testing;
+using namespace android::storage_literals;
+using namespace std::chrono_literals;
+using namespace std::string_literals;
+
+// Global states. See test_helpers.h.
+std::unique_ptr<SnapshotManager> sm;
+TestDeviceInfo* test_device = nullptr;
+std::string fake_super;
+
+void MountMetadata();
+
+class SnapshotTest : public ::testing::Test {
+  public:
+    SnapshotTest() : dm_(DeviceMapper::Instance()) {}
+
+    // This is exposed for main.
+    void Cleanup() {
+        InitializeState();
+        CleanupTestArtifacts();
+    }
+
+  protected:
+    void SetUp() override {
+        SKIP_IF_NON_VIRTUAL_AB();
+
+        SnapshotTestPropertyFetcher::SetUp();
+        InitializeState();
+        CleanupTestArtifacts();
+        FormatFakeSuper();
+        MountMetadata();
+        ASSERT_TRUE(sm->BeginUpdate());
+    }
+
+    void TearDown() override {
+        RETURN_IF_NON_VIRTUAL_AB();
+
+        lock_ = nullptr;
+
+        CleanupTestArtifacts();
+        SnapshotTestPropertyFetcher::TearDown();
+    }
+
+    void InitializeState() {
+        ASSERT_TRUE(sm->EnsureImageManager());
+        image_manager_ = sm->image_manager();
+
+        test_device->set_slot_suffix("_a");
+
+        sm->set_use_first_stage_snapuserd(false);
+    }
+
+    void CleanupTestArtifacts() {
+        // Normally cancelling inside a merge is not allowed. Since these
+        // are tests, we don't care, destroy everything that might exist.
+        // Note we hardcode this list because of an annoying quirk: when
+        // completing a merge, the snapshot stops existing, so we can't
+        // get an accurate list to remove.
+        lock_ = nullptr;
+
+        std::vector<std::string> snapshots = {"test-snapshot", "test_partition_a",
+                                              "test_partition_b"};
+        for (const auto& snapshot : snapshots) {
+            ASSERT_TRUE(DeleteSnapshotDevice(snapshot));
+            DeleteBackingImage(image_manager_, snapshot + "-cow-img");
+
+            auto status_file = sm->GetSnapshotStatusFilePath(snapshot);
+            android::base::RemoveFileIfExists(status_file);
+        }
+
+        // Remove stale partitions in fake super.
+        std::vector<std::string> partitions = {
+                "base-device",
+                "test_partition_b",
+                "test_partition_b-base",
+                "test_partition_b-base",
+        };
+        for (const auto& partition : partitions) {
+            DeleteDevice(partition);
+        }
+
+        if (sm->GetUpdateState() != UpdateState::None) {
+            auto state_file = sm->GetStateFilePath();
+            unlink(state_file.c_str());
+        }
+    }
+
+    bool AcquireLock() {
+        lock_ = sm->LockExclusive();
+        return !!lock_;
+    }
+
+    // This is so main() can instantiate this to invoke Cleanup.
+    virtual void TestBody() override {}
+
+    void FormatFakeSuper() {
+        BlockDeviceInfo super_device("super", kSuperSize, 0, 0, 4096);
+        std::vector<BlockDeviceInfo> devices = {super_device};
+
+        auto builder = MetadataBuilder::New(devices, "super", 65536, 2);
+        ASSERT_NE(builder, nullptr);
+
+        auto metadata = builder->Export();
+        ASSERT_NE(metadata, nullptr);
+
+        TestPartitionOpener opener(fake_super);
+        ASSERT_TRUE(FlashPartitionTable(opener, fake_super, *metadata.get()));
+    }
+
+    // If |path| is non-null, the partition will be mapped after creation.
+    bool CreatePartition(const std::string& name, uint64_t size, std::string* path = nullptr,
+                         const std::optional<std::string> group = {}) {
+        TestPartitionOpener opener(fake_super);
+        auto builder = MetadataBuilder::New(opener, "super", 0);
+        if (!builder) return false;
+
+        std::string partition_group = std::string(android::fs_mgr::kDefaultGroup);
+        if (group) {
+            partition_group = *group;
+        }
+        return CreatePartition(builder.get(), name, size, path, partition_group);
+    }
+
+    bool CreatePartition(MetadataBuilder* builder, const std::string& name, uint64_t size,
+                         std::string* path, const std::string& group) {
+        auto partition = builder->AddPartition(name, group, 0);
+        if (!partition) return false;
+        if (!builder->ResizePartition(partition, size)) {
+            return false;
+        }
+
+        // Update the source slot.
+        auto metadata = builder->Export();
+        if (!metadata) return false;
+
+        TestPartitionOpener opener(fake_super);
+        if (!UpdatePartitionTable(opener, "super", *metadata.get(), 0)) {
+            return false;
+        }
+
+        if (!path) return true;
+
+        CreateLogicalPartitionParams params = {
+                .block_device = fake_super,
+                .metadata = metadata.get(),
+                .partition_name = name,
+                .force_writable = true,
+                .timeout_ms = 10s,
+        };
+        return CreateLogicalPartition(params, path);
+    }
+
+    AssertionResult MapUpdateSnapshot(const std::string& name,
+                                      std::unique_ptr<ISnapshotWriter>* writer) {
+        TestPartitionOpener opener(fake_super);
+        CreateLogicalPartitionParams params{
+                .block_device = fake_super,
+                .metadata_slot = 1,
+                .partition_name = name,
+                .timeout_ms = 10s,
+                .partition_opener = &opener,
+        };
+
+        auto old_partition = "/dev/block/mapper/" + GetOtherPartitionName(name);
+        auto result = sm->OpenSnapshotWriter(params, {old_partition});
+        if (!result) {
+            return AssertionFailure() << "Cannot open snapshot for writing: " << name;
+        }
+        if (!result->Initialize()) {
+            return AssertionFailure() << "Cannot initialize snapshot for writing: " << name;
+        }
+
+        if (writer) {
+            *writer = std::move(result);
+        }
+        return AssertionSuccess();
+    }
+
+    AssertionResult MapUpdateSnapshot(const std::string& name, std::string* path) {
+        TestPartitionOpener opener(fake_super);
+        CreateLogicalPartitionParams params{
+                .block_device = fake_super,
+                .metadata_slot = 1,
+                .partition_name = name,
+                .timeout_ms = 10s,
+                .partition_opener = &opener,
+        };
+
+        auto result = sm->MapUpdateSnapshot(params, path);
+        if (!result) {
+            return AssertionFailure() << "Cannot open snapshot for writing: " << name;
+        }
+        return AssertionSuccess();
+    }
+
+    AssertionResult DeleteSnapshotDevice(const std::string& snapshot) {
+        AssertionResult res = AssertionSuccess();
+        if (!(res = DeleteDevice(snapshot))) return res;
+        if (!sm->UnmapDmUserDevice(snapshot + "-user-cow")) {
+            return AssertionFailure() << "Cannot delete dm-user device for " << snapshot;
+        }
+        if (!(res = DeleteDevice(snapshot + "-inner"))) return res;
+        if (!(res = DeleteDevice(snapshot + "-cow"))) return res;
+        if (!image_manager_->UnmapImageIfExists(snapshot + "-cow-img")) {
+            return AssertionFailure() << "Cannot unmap image " << snapshot << "-cow-img";
+        }
+        if (!(res = DeleteDevice(snapshot + "-base"))) return res;
+        if (!(res = DeleteDevice(snapshot + "-src"))) return res;
+        return AssertionSuccess();
+    }
+
+    AssertionResult DeleteDevice(const std::string& device) {
+        if (!dm_.DeleteDeviceIfExists(device)) {
+            return AssertionFailure() << "Can't delete " << device;
+        }
+        return AssertionSuccess();
+    }
+
+    AssertionResult CreateCowImage(const std::string& name) {
+        if (!sm->CreateCowImage(lock_.get(), name)) {
+            return AssertionFailure() << "Cannot create COW image " << name;
+        }
+        std::string cow_device;
+        auto map_res = MapCowImage(name, 10s, &cow_device);
+        if (!map_res) {
+            return map_res;
+        }
+        if (!InitializeKernelCow(cow_device)) {
+            return AssertionFailure() << "Cannot zero fill " << cow_device;
+        }
+        if (!sm->UnmapCowImage(name)) {
+            return AssertionFailure() << "Cannot unmap " << name << " after zero filling it";
+        }
+        return AssertionSuccess();
+    }
+
+    AssertionResult MapCowImage(const std::string& name,
+                                const std::chrono::milliseconds& timeout_ms, std::string* path) {
+        auto cow_image_path = sm->MapCowImage(name, timeout_ms);
+        if (!cow_image_path.has_value()) {
+            return AssertionFailure() << "Cannot map cow image " << name;
+        }
+        *path = *cow_image_path;
+        return AssertionSuccess();
+    }
+
+    // Prepare A/B slot for a partition named "test_partition".
+    AssertionResult PrepareOneSnapshot(uint64_t device_size,
+                                       std::unique_ptr<ISnapshotWriter>* writer = nullptr) {
+        lock_ = nullptr;
+
+        DeltaArchiveManifest manifest;
+
+        auto dynamic_partition_metadata = manifest.mutable_dynamic_partition_metadata();
+        dynamic_partition_metadata->set_vabc_enabled(IsCompressionEnabled());
+        dynamic_partition_metadata->set_cow_version(android::snapshot::kCowVersionMajor);
+
+        auto group = dynamic_partition_metadata->add_groups();
+        group->set_name("group");
+        group->set_size(device_size * 2);
+        group->add_partition_names("test_partition");
+
+        auto pu = manifest.add_partitions();
+        pu->set_partition_name("test_partition");
+        pu->set_estimate_cow_size(device_size);
+        SetSize(pu, device_size);
+
+        auto extent = pu->add_operations()->add_dst_extents();
+        extent->set_start_block(0);
+        if (device_size) {
+            extent->set_num_blocks(device_size / manifest.block_size());
+        }
+
+        TestPartitionOpener opener(fake_super);
+        auto builder = MetadataBuilder::New(opener, "super", 0);
+        if (!builder) {
+            return AssertionFailure() << "Failed to open MetadataBuilder";
+        }
+        builder->AddGroup("group_a", 16_GiB);
+        builder->AddGroup("group_b", 16_GiB);
+        if (!CreatePartition(builder.get(), "test_partition_a", device_size, nullptr, "group_a")) {
+            return AssertionFailure() << "Failed create test_partition_a";
+        }
+
+        if (!sm->CreateUpdateSnapshots(manifest)) {
+            return AssertionFailure() << "Failed to create update snapshots";
+        }
+
+        if (writer) {
+            auto res = MapUpdateSnapshot("test_partition_b", writer);
+            if (!res) {
+                return res;
+            }
+        } else if (!IsCompressionEnabled()) {
+            std::string ignore;
+            if (!MapUpdateSnapshot("test_partition_b", &ignore)) {
+                return AssertionFailure() << "Failed to map test_partition_b";
+            }
+        }
+        if (!AcquireLock()) {
+            return AssertionFailure() << "Failed to acquire lock";
+        }
+        return AssertionSuccess();
+    }
+
+    // Simulate a reboot into the new slot.
+    AssertionResult SimulateReboot() {
+        lock_ = nullptr;
+        if (!sm->FinishedSnapshotWrites(false)) {
+            return AssertionFailure() << "Failed to finish snapshot writes";
+        }
+        if (!sm->UnmapUpdateSnapshot("test_partition_b")) {
+            return AssertionFailure() << "Failed to unmap COW for test_partition_b";
+        }
+        if (!dm_.DeleteDeviceIfExists("test_partition_b")) {
+            return AssertionFailure() << "Failed to delete test_partition_b";
+        }
+        if (!dm_.DeleteDeviceIfExists("test_partition_b-base")) {
+            return AssertionFailure() << "Failed to destroy test_partition_b-base";
+        }
+        return AssertionSuccess();
+    }
+
+    std::unique_ptr<SnapshotManager> NewManagerForFirstStageMount(
+            const std::string& slot_suffix = "_a") {
+        auto info = new TestDeviceInfo(fake_super, slot_suffix);
+        return NewManagerForFirstStageMount(info);
+    }
+
+    std::unique_ptr<SnapshotManager> NewManagerForFirstStageMount(TestDeviceInfo* info) {
+        info->set_first_stage_init(true);
+        auto init = SnapshotManager::NewForFirstStageMount(info);
+        if (!init) {
+            return nullptr;
+        }
+        init->SetUeventRegenCallback([](const std::string& device) -> bool {
+            return android::fs_mgr::WaitForFile(device, snapshot_timeout_);
+        });
+        return init;
+    }
+
+    static constexpr std::chrono::milliseconds snapshot_timeout_ = 5s;
+    DeviceMapper& dm_;
+    std::unique_ptr<SnapshotManager::LockedFile> lock_;
+    android::fiemap::IImageManager* image_manager_ = nullptr;
+    std::string fake_super_;
+};
+
+TEST_F(SnapshotTest, CreateSnapshot) {
+    ASSERT_TRUE(AcquireLock());
+
+    PartitionCowCreator cow_creator;
+    cow_creator.compression_enabled = IsCompressionEnabled();
+    if (cow_creator.compression_enabled) {
+        cow_creator.compression_algorithm = "gz";
+    } else {
+        cow_creator.compression_algorithm = "none";
+    }
+
+    static const uint64_t kDeviceSize = 1024 * 1024;
+    SnapshotStatus status;
+    status.set_name("test-snapshot");
+    status.set_device_size(kDeviceSize);
+    status.set_snapshot_size(kDeviceSize);
+    status.set_cow_file_size(kDeviceSize);
+    ASSERT_TRUE(sm->CreateSnapshot(lock_.get(), &cow_creator, &status));
+    ASSERT_TRUE(CreateCowImage("test-snapshot"));
+
+    std::vector<std::string> snapshots;
+    ASSERT_TRUE(sm->ListSnapshots(lock_.get(), &snapshots));
+    ASSERT_EQ(snapshots.size(), 1);
+    ASSERT_EQ(snapshots[0], "test-snapshot");
+
+    // Scope so delete can re-acquire the snapshot file lock.
+    {
+        SnapshotStatus status;
+        ASSERT_TRUE(sm->ReadSnapshotStatus(lock_.get(), "test-snapshot", &status));
+        ASSERT_EQ(status.state(), SnapshotState::CREATED);
+        ASSERT_EQ(status.device_size(), kDeviceSize);
+        ASSERT_EQ(status.snapshot_size(), kDeviceSize);
+        ASSERT_EQ(status.compression_enabled(), cow_creator.compression_enabled);
+        ASSERT_EQ(status.compression_algorithm(), cow_creator.compression_algorithm);
+    }
+
+    ASSERT_TRUE(sm->UnmapSnapshot(lock_.get(), "test-snapshot"));
+    ASSERT_TRUE(sm->UnmapCowImage("test-snapshot"));
+    ASSERT_TRUE(sm->DeleteSnapshot(lock_.get(), "test-snapshot"));
+}
+
+TEST_F(SnapshotTest, MapSnapshot) {
+    ASSERT_TRUE(AcquireLock());
+
+    PartitionCowCreator cow_creator;
+    cow_creator.compression_enabled = IsCompressionEnabled();
+
+    static const uint64_t kDeviceSize = 1024 * 1024;
+    SnapshotStatus status;
+    status.set_name("test-snapshot");
+    status.set_device_size(kDeviceSize);
+    status.set_snapshot_size(kDeviceSize);
+    status.set_cow_file_size(kDeviceSize);
+    ASSERT_TRUE(sm->CreateSnapshot(lock_.get(), &cow_creator, &status));
+    ASSERT_TRUE(CreateCowImage("test-snapshot"));
+
+    std::string base_device;
+    ASSERT_TRUE(CreatePartition("base-device", kDeviceSize, &base_device));
+
+    std::string cow_device;
+    ASSERT_TRUE(MapCowImage("test-snapshot", 10s, &cow_device));
+
+    std::string snap_device;
+    ASSERT_TRUE(sm->MapSnapshot(lock_.get(), "test-snapshot", base_device, cow_device, 10s,
+                                &snap_device));
+    ASSERT_TRUE(android::base::StartsWith(snap_device, "/dev/block/dm-"));
+}
+
+TEST_F(SnapshotTest, NoMergeBeforeReboot) {
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // Merge should fail, since the slot hasn't changed.
+    ASSERT_FALSE(sm->InitiateMerge());
+}
+
+TEST_F(SnapshotTest, CleanFirstStageMount) {
+    // If there's no update in progress, there should be no first-stage mount
+    // needed.
+    auto sm = NewManagerForFirstStageMount();
+    ASSERT_NE(sm, nullptr);
+    ASSERT_FALSE(sm->NeedSnapshotsInFirstStageMount());
+}
+
+TEST_F(SnapshotTest, FirstStageMountAfterRollback) {
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // We didn't change the slot, so we shouldn't need snapshots.
+    auto sm = NewManagerForFirstStageMount();
+    ASSERT_NE(sm, nullptr);
+    ASSERT_FALSE(sm->NeedSnapshotsInFirstStageMount());
+
+    auto indicator = sm->GetRollbackIndicatorPath();
+    ASSERT_EQ(access(indicator.c_str(), R_OK), 0);
+}
+
+TEST_F(SnapshotTest, Merge) {
+    ASSERT_TRUE(AcquireLock());
+
+    static const uint64_t kDeviceSize = 1024 * 1024;
+
+    std::unique_ptr<ISnapshotWriter> writer;
+    ASSERT_TRUE(PrepareOneSnapshot(kDeviceSize, &writer));
+
+    // Release the lock.
+    lock_ = nullptr;
+
+    std::string test_string = "This is a test string.";
+    test_string.resize(writer->options().block_size);
+    ASSERT_TRUE(writer->AddRawBlocks(0, test_string.data(), test_string.size()));
+    ASSERT_TRUE(writer->Finalize());
+    writer = nullptr;
+
+    // Done updating.
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    ASSERT_TRUE(sm->UnmapUpdateSnapshot("test_partition_b"));
+
+    test_device->set_slot_suffix("_b");
+    ASSERT_TRUE(sm->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+    ASSERT_TRUE(sm->InitiateMerge());
+
+    // The device should have been switched to a snapshot-merge target.
+    DeviceMapper::TargetInfo target;
+    ASSERT_TRUE(sm->IsSnapshotDevice("test_partition_b", &target));
+    ASSERT_EQ(DeviceMapper::GetTargetType(target.spec), "user");
+
+    // We should not be able to cancel an update now.
+    ASSERT_FALSE(sm->CancelUpdate());
+
+    ASSERT_EQ(sm->ProcessUpdateState(), UpdateState::MergeCompleted);
+    ASSERT_EQ(sm->GetUpdateState(), UpdateState::None);
+
+    // The device should no longer be a snapshot or snapshot-merge.
+    ASSERT_FALSE(sm->IsSnapshotDevice("test_partition_b"));
+
+    // Test that we can read back the string we wrote to the snapshot. Note
+    // that the base device is gone now. |snap_device| contains the correct
+    // partition.
+    unique_fd fd(open("/dev/block/mapper/test_partition_b", O_RDONLY | O_CLOEXEC));
+    ASSERT_GE(fd, 0);
+
+    std::string buffer(test_string.size(), '\0');
+    ASSERT_TRUE(android::base::ReadFully(fd, buffer.data(), buffer.size()));
+    ASSERT_EQ(test_string, buffer);
+}
+
+TEST_F(SnapshotTest, FirstStageMountAndMerge) {
+    ASSERT_TRUE(AcquireLock());
+
+    static const uint64_t kDeviceSize = 1024 * 1024;
+    ASSERT_TRUE(PrepareOneSnapshot(kDeviceSize));
+    ASSERT_TRUE(SimulateReboot());
+
+    auto init = NewManagerForFirstStageMount("_b");
+    ASSERT_NE(init, nullptr);
+    ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    ASSERT_TRUE(AcquireLock());
+
+    // Validate that we have a snapshot device.
+    SnapshotStatus status;
+    ASSERT_TRUE(init->ReadSnapshotStatus(lock_.get(), "test_partition_b", &status));
+    ASSERT_EQ(status.state(), SnapshotState::CREATED);
+    if (IsCompressionEnabled()) {
+        ASSERT_EQ(status.compression_algorithm(), "gz");
+    } else {
+        ASSERT_EQ(status.compression_algorithm(), "none");
+    }
+
+    DeviceMapper::TargetInfo target;
+    ASSERT_TRUE(init->IsSnapshotDevice("test_partition_b", &target));
+    ASSERT_EQ(DeviceMapper::GetTargetType(target.spec), "user");
+}
+
+TEST_F(SnapshotTest, FlashSuperDuringUpdate) {
+    ASSERT_TRUE(AcquireLock());
+
+    static const uint64_t kDeviceSize = 1024 * 1024;
+    ASSERT_TRUE(PrepareOneSnapshot(kDeviceSize));
+    ASSERT_TRUE(SimulateReboot());
+
+    // Reflash the super partition.
+    FormatFakeSuper();
+    ASSERT_TRUE(CreatePartition("test_partition_b", kDeviceSize));
+
+    auto init = NewManagerForFirstStageMount("_b");
+    ASSERT_NE(init, nullptr);
+    ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    ASSERT_TRUE(AcquireLock());
+
+    SnapshotStatus status;
+    ASSERT_TRUE(init->ReadSnapshotStatus(lock_.get(), "test_partition_b", &status));
+
+    // We should not get a snapshot device now.
+    DeviceMapper::TargetInfo target;
+    ASSERT_FALSE(init->IsSnapshotDevice("test_partition_b", &target));
+
+    // We should see a cancelled update as well.
+    lock_ = nullptr;
+    ASSERT_EQ(sm->ProcessUpdateState(), UpdateState::Cancelled);
+}
+
+TEST_F(SnapshotTest, FlashSuperDuringMerge) {
+    ASSERT_TRUE(AcquireLock());
+
+    static const uint64_t kDeviceSize = 1024 * 1024;
+    ASSERT_TRUE(PrepareOneSnapshot(kDeviceSize));
+    ASSERT_TRUE(SimulateReboot());
+
+    auto init = NewManagerForFirstStageMount("_b");
+    ASSERT_NE(init, nullptr);
+    ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+    ASSERT_TRUE(init->InitiateMerge());
+
+    // Now, reflash super. Note that we haven't called ProcessUpdateState, so the
+    // status is still Merging.
+    ASSERT_TRUE(DeleteSnapshotDevice("test_partition_b"));
+    ASSERT_TRUE(init->image_manager()->UnmapImageIfExists("test_partition_b-cow-img"));
+    FormatFakeSuper();
+    ASSERT_TRUE(CreatePartition("test_partition_b", kDeviceSize));
+    ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    // Because the status is Merging, we must call ProcessUpdateState, which should
+    // detect a cancelled update.
+    ASSERT_EQ(init->ProcessUpdateState(), UpdateState::Cancelled);
+    ASSERT_EQ(init->GetUpdateState(), UpdateState::None);
+}
+
+TEST_F(SnapshotTest, UpdateBootControlHal) {
+    ASSERT_TRUE(AcquireLock());
+
+    ASSERT_TRUE(sm->WriteUpdateState(lock_.get(), UpdateState::None));
+    ASSERT_EQ(test_device->merge_status(), MergeStatus::NONE);
+
+    ASSERT_TRUE(sm->WriteUpdateState(lock_.get(), UpdateState::Initiated));
+    ASSERT_EQ(test_device->merge_status(), MergeStatus::NONE);
+
+    ASSERT_TRUE(sm->WriteUpdateState(lock_.get(), UpdateState::Unverified));
+    ASSERT_EQ(test_device->merge_status(), MergeStatus::SNAPSHOTTED);
+
+    ASSERT_TRUE(sm->WriteUpdateState(lock_.get(), UpdateState::Merging));
+    ASSERT_EQ(test_device->merge_status(), MergeStatus::MERGING);
+
+    ASSERT_TRUE(sm->WriteUpdateState(lock_.get(), UpdateState::MergeNeedsReboot));
+    ASSERT_EQ(test_device->merge_status(), MergeStatus::NONE);
+
+    ASSERT_TRUE(sm->WriteUpdateState(lock_.get(), UpdateState::MergeCompleted));
+    ASSERT_EQ(test_device->merge_status(), MergeStatus::NONE);
+
+    ASSERT_TRUE(sm->WriteUpdateState(lock_.get(), UpdateState::MergeFailed));
+    ASSERT_EQ(test_device->merge_status(), MergeStatus::MERGING);
+}
+
+TEST_F(SnapshotTest, MergeFailureCode) {
+    ASSERT_TRUE(AcquireLock());
+
+    ASSERT_TRUE(sm->WriteUpdateState(lock_.get(), UpdateState::MergeFailed,
+                                     MergeFailureCode::ListSnapshots));
+    ASSERT_EQ(test_device->merge_status(), MergeStatus::MERGING);
+
+    SnapshotUpdateStatus status = sm->ReadSnapshotUpdateStatus(lock_.get());
+    ASSERT_EQ(status.state(), UpdateState::MergeFailed);
+    ASSERT_EQ(status.merge_failure_code(), MergeFailureCode::ListSnapshots);
+}
+
+enum class Request { UNKNOWN, LOCK_SHARED, LOCK_EXCLUSIVE, UNLOCK, EXIT };
+std::ostream& operator<<(std::ostream& os, Request request) {
+    switch (request) {
+        case Request::LOCK_SHARED:
+            return os << "Shared";
+        case Request::LOCK_EXCLUSIVE:
+            return os << "Exclusive";
+        case Request::UNLOCK:
+            return os << "Unlock";
+        case Request::EXIT:
+            return os << "Exit";
+        case Request::UNKNOWN:
+            [[fallthrough]];
+        default:
+            return os << "Unknown";
+    }
+}
+
+class LockTestConsumer {
+  public:
+    AssertionResult MakeRequest(Request new_request) {
+        {
+            std::unique_lock<std::mutex> ulock(mutex_);
+            requests_.push_back(new_request);
+        }
+        cv_.notify_all();
+        return AssertionSuccess() << "Request " << new_request << " successful";
+    }
+
+    template <typename R, typename P>
+    AssertionResult WaitFulfill(std::chrono::duration<R, P> timeout) {
+        std::unique_lock<std::mutex> ulock(mutex_);
+        if (cv_.wait_for(ulock, timeout, [this] { return requests_.empty(); })) {
+            return AssertionSuccess() << "All requests_ fulfilled.";
+        }
+        return AssertionFailure() << "Timeout waiting for fulfilling " << requests_.size()
+                                  << " request(s), first one is "
+                                  << (requests_.empty() ? Request::UNKNOWN : requests_.front());
+    }
+
+    void StartHandleRequestsInBackground() {
+        future_ = std::async(std::launch::async, &LockTestConsumer::HandleRequests, this);
+    }
+
+  private:
+    void HandleRequests() {
+        static constexpr auto consumer_timeout = 3s;
+
+        auto next_request = Request::UNKNOWN;
+        do {
+            // Peek next request.
+            {
+                std::unique_lock<std::mutex> ulock(mutex_);
+                if (cv_.wait_for(ulock, consumer_timeout, [this] { return !requests_.empty(); })) {
+                    next_request = requests_.front();
+                } else {
+                    next_request = Request::EXIT;
+                }
+            }
+
+            // Handle next request.
+            switch (next_request) {
+                case Request::LOCK_SHARED: {
+                    lock_ = sm->LockShared();
+                } break;
+                case Request::LOCK_EXCLUSIVE: {
+                    lock_ = sm->LockExclusive();
+                } break;
+                case Request::EXIT:
+                    [[fallthrough]];
+                case Request::UNLOCK: {
+                    lock_.reset();
+                } break;
+                case Request::UNKNOWN:
+                    [[fallthrough]];
+                default:
+                    break;
+            }
+
+            // Pop next request. This thread is the only thread that
+            // pops from the front of the requests_ deque.
+            {
+                std::unique_lock<std::mutex> ulock(mutex_);
+                if (next_request == Request::EXIT) {
+                    requests_.clear();
+                } else {
+                    requests_.pop_front();
+                }
+            }
+            cv_.notify_all();
+        } while (next_request != Request::EXIT);
+    }
+
+    std::mutex mutex_;
+    std::condition_variable cv_;
+    std::deque<Request> requests_;
+    std::unique_ptr<SnapshotManager::LockedFile> lock_;
+    std::future<void> future_;
+};
+
+class LockTest : public ::testing::Test {
+  public:
+    void SetUp() {
+        SKIP_IF_NON_VIRTUAL_AB();
+        first_consumer.StartHandleRequestsInBackground();
+        second_consumer.StartHandleRequestsInBackground();
+    }
+
+    void TearDown() {
+        RETURN_IF_NON_VIRTUAL_AB();
+        EXPECT_TRUE(first_consumer.MakeRequest(Request::EXIT));
+        EXPECT_TRUE(second_consumer.MakeRequest(Request::EXIT));
+    }
+
+    static constexpr auto request_timeout = 500ms;
+    LockTestConsumer first_consumer;
+    LockTestConsumer second_consumer;
+};
+
+TEST_F(LockTest, SharedShared) {
+    ASSERT_TRUE(first_consumer.MakeRequest(Request::LOCK_SHARED));
+    ASSERT_TRUE(first_consumer.WaitFulfill(request_timeout));
+    ASSERT_TRUE(second_consumer.MakeRequest(Request::LOCK_SHARED));
+    ASSERT_TRUE(second_consumer.WaitFulfill(request_timeout));
+}
+
+using LockTestParam = std::pair<Request, Request>;
+class LockTestP : public LockTest, public ::testing::WithParamInterface<LockTestParam> {};
+TEST_P(LockTestP, Test) {
+    ASSERT_TRUE(first_consumer.MakeRequest(GetParam().first));
+    ASSERT_TRUE(first_consumer.WaitFulfill(request_timeout));
+    ASSERT_TRUE(second_consumer.MakeRequest(GetParam().second));
+    ASSERT_FALSE(second_consumer.WaitFulfill(request_timeout))
+            << "Should not be able to " << GetParam().second << " while separate thread "
+            << GetParam().first;
+    ASSERT_TRUE(first_consumer.MakeRequest(Request::UNLOCK));
+    ASSERT_TRUE(second_consumer.WaitFulfill(request_timeout))
+            << "Should be able to hold lock that is released by separate thread";
+}
+INSTANTIATE_TEST_SUITE_P(
+        LockTest, LockTestP,
+        testing::Values(LockTestParam{Request::LOCK_EXCLUSIVE, Request::LOCK_EXCLUSIVE},
+                        LockTestParam{Request::LOCK_EXCLUSIVE, Request::LOCK_SHARED},
+                        LockTestParam{Request::LOCK_SHARED, Request::LOCK_EXCLUSIVE}),
+        [](const testing::TestParamInfo<LockTestP::ParamType>& info) {
+            std::stringstream ss;
+            ss << info.param.first << info.param.second;
+            return ss.str();
+        });
+
+class SnapshotUpdateTest : public SnapshotTest {
+  public:
+    void SetUp() override {
+        SKIP_IF_NON_VIRTUAL_AB();
+
+        SnapshotTest::SetUp();
+        Cleanup();
+
+        // Cleanup() changes slot suffix, so initialize it again.
+        test_device->set_slot_suffix("_a");
+
+        opener_ = std::make_unique<TestPartitionOpener>(fake_super);
+
+        auto dynamic_partition_metadata = manifest_.mutable_dynamic_partition_metadata();
+        dynamic_partition_metadata->set_vabc_enabled(IsCompressionEnabled());
+        dynamic_partition_metadata->set_cow_version(android::snapshot::kCowVersionMajor);
+
+        // Create a fake update package metadata.
+        // Not using full name "system", "vendor", "product" because these names collide with the
+        // mapped partitions on the running device.
+        // Each test modifies manifest_ slightly to indicate changes to the partition layout.
+        group_ = dynamic_partition_metadata->add_groups();
+        group_->set_name("group");
+        group_->set_size(kGroupSize);
+        group_->add_partition_names("sys");
+        group_->add_partition_names("vnd");
+        group_->add_partition_names("prd");
+        sys_ = manifest_.add_partitions();
+        sys_->set_partition_name("sys");
+        sys_->set_estimate_cow_size(2_MiB);
+        SetSize(sys_, 3_MiB);
+        vnd_ = manifest_.add_partitions();
+        vnd_->set_partition_name("vnd");
+        vnd_->set_estimate_cow_size(2_MiB);
+        SetSize(vnd_, 3_MiB);
+        prd_ = manifest_.add_partitions();
+        prd_->set_partition_name("prd");
+        prd_->set_estimate_cow_size(2_MiB);
+        SetSize(prd_, 3_MiB);
+
+        // Initialize source partition metadata using |manifest_|.
+        src_ = MetadataBuilder::New(*opener_, "super", 0);
+        ASSERT_NE(src_, nullptr);
+        ASSERT_TRUE(FillFakeMetadata(src_.get(), manifest_, "_a"));
+        // Add sys_b which is like system_other.
+        ASSERT_TRUE(src_->AddGroup("group_b", kGroupSize));
+        auto partition = src_->AddPartition("sys_b", "group_b", 0);
+        ASSERT_NE(nullptr, partition);
+        ASSERT_TRUE(src_->ResizePartition(partition, 1_MiB));
+        auto metadata = src_->Export();
+        ASSERT_NE(nullptr, metadata);
+        ASSERT_TRUE(UpdatePartitionTable(*opener_, "super", *metadata.get(), 0));
+
+        // Map source partitions. Additionally, map sys_b to simulate system_other after flashing.
+        std::string path;
+        for (const auto& name : {"sys_a", "vnd_a", "prd_a", "sys_b"}) {
+            ASSERT_TRUE(CreateLogicalPartition(
+                    CreateLogicalPartitionParams{
+                            .block_device = fake_super,
+                            .metadata_slot = 0,
+                            .partition_name = name,
+                            .timeout_ms = 1s,
+                            .partition_opener = opener_.get(),
+                    },
+                    &path));
+            ASSERT_TRUE(WriteRandomData(path));
+            auto hash = GetHash(path);
+            ASSERT_TRUE(hash.has_value());
+            hashes_[name] = *hash;
+        }
+
+        // OTA client blindly unmaps all partitions that are possibly mapped.
+        for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+            ASSERT_TRUE(sm->UnmapUpdateSnapshot(name));
+        }
+    }
+    void TearDown() override {
+        RETURN_IF_NON_VIRTUAL_AB();
+
+        Cleanup();
+        SnapshotTest::TearDown();
+    }
+    void Cleanup() {
+        if (!image_manager_) {
+            InitializeState();
+        }
+        MountMetadata();
+        for (const auto& suffix : {"_a", "_b"}) {
+            test_device->set_slot_suffix(suffix);
+
+            // Cheat our way out of merge failed states.
+            if (sm->ProcessUpdateState() == UpdateState::MergeFailed) {
+                ASSERT_TRUE(AcquireLock());
+                ASSERT_TRUE(sm->WriteUpdateState(lock_.get(), UpdateState::None));
+                lock_ = {};
+            }
+
+            EXPECT_TRUE(sm->CancelUpdate()) << suffix;
+        }
+        EXPECT_TRUE(UnmapAll());
+    }
+
+    AssertionResult IsPartitionUnchanged(const std::string& name) {
+        std::string path;
+        if (!dm_.GetDmDevicePathByName(name, &path)) {
+            return AssertionFailure() << "Path of " << name << " cannot be determined";
+        }
+        auto hash = GetHash(path);
+        if (!hash.has_value()) {
+            return AssertionFailure() << "Cannot read partition " << name << ": " << path;
+        }
+        auto it = hashes_.find(name);
+        if (it == hashes_.end()) {
+            return AssertionFailure() << "No existing hash for " << name << ". Bad test code?";
+        }
+        if (it->second != *hash) {
+            return AssertionFailure() << "Content of " << name << " has changed";
+        }
+        return AssertionSuccess();
+    }
+
+    std::optional<uint64_t> GetSnapshotSize(const std::string& name) {
+        if (!AcquireLock()) {
+            return std::nullopt;
+        }
+        auto local_lock = std::move(lock_);
+
+        SnapshotStatus status;
+        if (!sm->ReadSnapshotStatus(local_lock.get(), name, &status)) {
+            return std::nullopt;
+        }
+        return status.snapshot_size();
+    }
+
+    AssertionResult UnmapAll() {
+        for (const auto& name : {"sys", "vnd", "prd", "dlkm"}) {
+            if (!dm_.DeleteDeviceIfExists(name + "_a"s)) {
+                return AssertionFailure() << "Cannot unmap " << name << "_a";
+            }
+            if (!DeleteSnapshotDevice(name + "_b"s)) {
+                return AssertionFailure() << "Cannot delete snapshot " << name << "_b";
+            }
+        }
+        return AssertionSuccess();
+    }
+
+    AssertionResult MapOneUpdateSnapshot(const std::string& name) {
+        if (IsCompressionEnabled()) {
+            std::unique_ptr<ISnapshotWriter> writer;
+            return MapUpdateSnapshot(name, &writer);
+        } else {
+            std::string path;
+            return MapUpdateSnapshot(name, &path);
+        }
+    }
+
+    AssertionResult WriteSnapshotAndHash(const std::string& name) {
+        if (IsCompressionEnabled()) {
+            std::unique_ptr<ISnapshotWriter> writer;
+            auto res = MapUpdateSnapshot(name, &writer);
+            if (!res) {
+                return res;
+            }
+            if (!WriteRandomData(writer.get(), &hashes_[name])) {
+                return AssertionFailure() << "Unable to write random data to snapshot " << name;
+            }
+            if (!writer->Finalize()) {
+                return AssertionFailure() << "Unable to finalize COW for " << name;
+            }
+        } else {
+            std::string path;
+            auto res = MapUpdateSnapshot(name, &path);
+            if (!res) {
+                return res;
+            }
+            if (!WriteRandomData(path, std::nullopt, &hashes_[name])) {
+                return AssertionFailure() << "Unable to write random data to snapshot " << name;
+            }
+        }
+
+        // Make sure updates to one device are seen by all devices.
+        sync();
+
+        return AssertionSuccess() << "Written random data to snapshot " << name
+                                  << ", hash: " << hashes_[name];
+    }
+
+    // Generate a snapshot that moves all the upper blocks down to the start.
+    // It doesn't really matter the order, we just want copies that reference
+    // blocks that won't exist if the partition shrinks.
+    AssertionResult ShiftAllSnapshotBlocks(const std::string& name, uint64_t old_size) {
+        std::unique_ptr<ISnapshotWriter> writer;
+        if (auto res = MapUpdateSnapshot(name, &writer); !res) {
+            return res;
+        }
+        if (!writer->options().max_blocks || !*writer->options().max_blocks) {
+            return AssertionFailure() << "No max blocks set for " << name << " writer";
+        }
+
+        uint64_t src_block = (old_size / writer->options().block_size) - 1;
+        uint64_t dst_block = 0;
+        uint64_t max_blocks = *writer->options().max_blocks;
+        while (dst_block < max_blocks && dst_block < src_block) {
+            if (!writer->AddCopy(dst_block, src_block)) {
+                return AssertionFailure() << "Unable to add copy for " << name << " for blocks "
+                                          << src_block << ", " << dst_block;
+            }
+            dst_block++;
+            src_block--;
+        }
+        if (!writer->Finalize()) {
+            return AssertionFailure() << "Unable to finalize writer for " << name;
+        }
+
+        auto hash = HashSnapshot(writer.get());
+        if (hash.empty()) {
+            return AssertionFailure() << "Unable to hash snapshot writer for " << name;
+        }
+        hashes_[name] = hash;
+
+        return AssertionSuccess();
+    }
+
+    AssertionResult MapUpdateSnapshots(const std::vector<std::string>& names = {"sys_b", "vnd_b",
+                                                                                "prd_b"}) {
+        for (const auto& name : names) {
+            auto res = MapOneUpdateSnapshot(name);
+            if (!res) {
+                return res;
+            }
+        }
+        return AssertionSuccess();
+    }
+
+    // Create fake install operations to grow the COW device size.
+    void AddOperation(PartitionUpdate* partition_update, uint64_t size_bytes = 0) {
+        auto e = partition_update->add_operations()->add_dst_extents();
+        e->set_start_block(0);
+        if (size_bytes == 0) {
+            size_bytes = GetSize(partition_update);
+        }
+        e->set_num_blocks(size_bytes / manifest_.block_size());
+    }
+
+    void AddOperationForPartitions(std::vector<PartitionUpdate*> partitions = {}) {
+        if (partitions.empty()) {
+            partitions = {sys_, vnd_, prd_};
+        }
+        for (auto* partition : partitions) {
+            AddOperation(partition);
+        }
+    }
+
+    std::unique_ptr<TestPartitionOpener> opener_;
+    DeltaArchiveManifest manifest_;
+    std::unique_ptr<MetadataBuilder> src_;
+    std::map<std::string, std::string> hashes_;
+
+    PartitionUpdate* sys_ = nullptr;
+    PartitionUpdate* vnd_ = nullptr;
+    PartitionUpdate* prd_ = nullptr;
+    DynamicPartitionGroup* group_ = nullptr;
+};
+
+// Test full update flow executed by update_engine. Some partitions uses super empty space,
+// some uses images, and some uses both.
+// Also test UnmapUpdateSnapshot unmaps everything.
+// Also test first stage mount and merge after this.
+TEST_F(SnapshotUpdateTest, FullUpdateFlow) {
+    // Grow all partitions. Set |prd| large enough that |sys| and |vnd|'s COWs
+    // fit in super, but not |prd|.
+    constexpr uint64_t partition_size = 3788_KiB;
+    SetSize(sys_, partition_size);
+    SetSize(vnd_, partition_size);
+    SetSize(prd_, 18_MiB);
+
+    // Make sure |prd| does not fit in super at all. On VABC, this means we
+    // fake an extra large COW for |vnd| to fill up super.
+    vnd_->set_estimate_cow_size(30_MiB);
+    prd_->set_estimate_cow_size(30_MiB);
+
+    AddOperationForPartitions();
+
+    // Execute the update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+
+    // Test that partitions prioritize using space in super.
+    auto tgt = MetadataBuilder::New(*opener_, "super", 1);
+    ASSERT_NE(tgt, nullptr);
+    ASSERT_NE(nullptr, tgt->FindPartition("sys_b-cow"));
+    ASSERT_NE(nullptr, tgt->FindPartition("vnd_b-cow"));
+    ASSERT_EQ(nullptr, tgt->FindPartition("prd_b-cow"));
+
+    // Write some data to target partitions.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(WriteSnapshotAndHash(name));
+    }
+
+    // Assert that source partitions aren't affected.
+    for (const auto& name : {"sys_a", "vnd_a", "prd_a"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name));
+    }
+
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    // After reboot, init does first stage mount.
+    auto init = NewManagerForFirstStageMount("_b");
+    ASSERT_NE(init, nullptr);
+    ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    auto indicator = sm->GetRollbackIndicatorPath();
+    ASSERT_NE(access(indicator.c_str(), R_OK), 0);
+
+    // Check that the target partitions have the same content.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name));
+    }
+
+    // Initiate the merge and wait for it to be completed.
+    ASSERT_TRUE(init->InitiateMerge());
+    ASSERT_EQ(init->IsSnapuserdRequired(), IsCompressionEnabled());
+    {
+        // We should have started in SECOND_PHASE since nothing shrinks.
+        ASSERT_TRUE(AcquireLock());
+        auto local_lock = std::move(lock_);
+        auto status = init->ReadSnapshotUpdateStatus(local_lock.get());
+        ASSERT_EQ(status.merge_phase(), MergePhase::SECOND_PHASE);
+    }
+    ASSERT_EQ(UpdateState::MergeCompleted, init->ProcessUpdateState());
+
+    // Make sure the second phase ran and deleted snapshots.
+    {
+        ASSERT_TRUE(AcquireLock());
+        auto local_lock = std::move(lock_);
+        std::vector<std::string> snapshots;
+        ASSERT_TRUE(init->ListSnapshots(local_lock.get(), &snapshots));
+        ASSERT_TRUE(snapshots.empty());
+    }
+
+    // Check that the target partitions have the same content after the merge.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name))
+                << "Content of " << name << " changes after the merge";
+    }
+}
+
+TEST_F(SnapshotUpdateTest, DuplicateOps) {
+    if (!IsCompressionEnabled()) {
+        GTEST_SKIP() << "Compression-only test";
+    }
+
+    // Execute the update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+
+    // Write some data to target partitions.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(WriteSnapshotAndHash(name));
+    }
+
+    std::vector<PartitionUpdate*> partitions = {sys_, vnd_, prd_};
+    for (auto* partition : partitions) {
+        AddOperation(partition);
+
+        std::unique_ptr<ISnapshotWriter> writer;
+        auto res = MapUpdateSnapshot(partition->partition_name() + "_b", &writer);
+        ASSERT_TRUE(res);
+        ASSERT_TRUE(writer->AddZeroBlocks(0, 1));
+        ASSERT_TRUE(writer->AddZeroBlocks(0, 1));
+        ASSERT_TRUE(writer->Finalize());
+    }
+
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    // After reboot, init does first stage mount.
+    auto init = NewManagerForFirstStageMount("_b");
+    ASSERT_NE(init, nullptr);
+    ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    // Initiate the merge and wait for it to be completed.
+    ASSERT_TRUE(init->InitiateMerge());
+    ASSERT_EQ(UpdateState::MergeCompleted, init->ProcessUpdateState());
+}
+
+// Test that shrinking and growing partitions at the same time is handled
+// correctly in VABC.
+TEST_F(SnapshotUpdateTest, SpaceSwapUpdate) {
+    if (!IsCompressionEnabled()) {
+        // b/179111359
+        GTEST_SKIP() << "Skipping Virtual A/B Compression test";
+    }
+
+    auto old_sys_size = GetSize(sys_);
+    auto old_prd_size = GetSize(prd_);
+
+    // Grow |sys| but shrink |prd|.
+    SetSize(sys_, old_sys_size * 2);
+    sys_->set_estimate_cow_size(8_MiB);
+    SetSize(prd_, old_prd_size / 2);
+    prd_->set_estimate_cow_size(1_MiB);
+
+    AddOperationForPartitions();
+
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+
+    // Check that the old partition sizes were saved correctly.
+    {
+        ASSERT_TRUE(AcquireLock());
+        auto local_lock = std::move(lock_);
+
+        SnapshotStatus status;
+        ASSERT_TRUE(sm->ReadSnapshotStatus(local_lock.get(), "prd_b", &status));
+        ASSERT_EQ(status.old_partition_size(), 3145728);
+        ASSERT_TRUE(sm->ReadSnapshotStatus(local_lock.get(), "sys_b", &status));
+        ASSERT_EQ(status.old_partition_size(), 3145728);
+    }
+
+    ASSERT_TRUE(WriteSnapshotAndHash("sys_b"));
+    ASSERT_TRUE(WriteSnapshotAndHash("vnd_b"));
+    ASSERT_TRUE(ShiftAllSnapshotBlocks("prd_b", old_prd_size));
+
+    sync();
+
+    // Assert that source partitions aren't affected.
+    for (const auto& name : {"sys_a", "vnd_a", "prd_a"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name));
+    }
+
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    // After reboot, init does first stage mount.
+    auto init = NewManagerForFirstStageMount("_b");
+    ASSERT_NE(init, nullptr);
+    ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    auto indicator = sm->GetRollbackIndicatorPath();
+    ASSERT_NE(access(indicator.c_str(), R_OK), 0);
+
+    // Check that the target partitions have the same content.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name));
+    }
+
+    // Initiate the merge and wait for it to be completed.
+    ASSERT_TRUE(init->InitiateMerge());
+    ASSERT_EQ(init->IsSnapuserdRequired(), IsCompressionEnabled());
+    {
+        // Check that the merge phase is FIRST_PHASE until at least one call
+        // to ProcessUpdateState() occurs.
+        ASSERT_TRUE(AcquireLock());
+        auto local_lock = std::move(lock_);
+        auto status = init->ReadSnapshotUpdateStatus(local_lock.get());
+        ASSERT_EQ(status.merge_phase(), MergePhase::FIRST_PHASE);
+    }
+
+    // Simulate shutting down the device and creating partitions again.
+    ASSERT_TRUE(UnmapAll());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    // Check that we used the correct types after rebooting mid-merge.
+    DeviceMapper::TargetInfo target;
+    ASSERT_TRUE(init->IsSnapshotDevice("prd_b", &target));
+    ASSERT_EQ(DeviceMapper::GetTargetType(target.spec), "user");
+    ASSERT_TRUE(init->IsSnapshotDevice("sys_b", &target));
+    ASSERT_EQ(DeviceMapper::GetTargetType(target.spec), "user");
+    ASSERT_TRUE(init->IsSnapshotDevice("vnd_b", &target));
+    ASSERT_EQ(DeviceMapper::GetTargetType(target.spec), "user");
+
+    // Complete the merge.
+    ASSERT_EQ(UpdateState::MergeCompleted, init->ProcessUpdateState());
+
+    // Make sure the second phase ran and deleted snapshots.
+    {
+        ASSERT_TRUE(AcquireLock());
+        auto local_lock = std::move(lock_);
+        std::vector<std::string> snapshots;
+        ASSERT_TRUE(init->ListSnapshots(local_lock.get(), &snapshots));
+        ASSERT_TRUE(snapshots.empty());
+    }
+
+    // Check that the target partitions have the same content after the merge.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name))
+                << "Content of " << name << " changes after the merge";
+    }
+}
+
+// Test that if new system partitions uses empty space in super, that region is not snapshotted.
+TEST_F(SnapshotUpdateTest, DirectWriteEmptySpace) {
+    GTEST_SKIP() << "b/141889746";
+    SetSize(sys_, 4_MiB);
+    // vnd_b and prd_b are unchanged.
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+    ASSERT_EQ(3_MiB, GetSnapshotSize("sys_b").value_or(0));
+}
+
+// Test that if new system partitions uses space of old vendor partition, that region is
+// snapshotted.
+TEST_F(SnapshotUpdateTest, SnapshotOldPartitions) {
+    SetSize(sys_, 4_MiB);  // grows
+    SetSize(vnd_, 2_MiB);  // shrinks
+    // prd_b is unchanged
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+    ASSERT_EQ(4_MiB, GetSnapshotSize("sys_b").value_or(0));
+}
+
+// Test that even if there seem to be empty space in target metadata, COW partition won't take
+// it because they are used by old partitions.
+TEST_F(SnapshotUpdateTest, CowPartitionDoNotTakeOldPartitions) {
+    SetSize(sys_, 2_MiB);  // shrinks
+    // vnd_b and prd_b are unchanged.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+
+    auto tgt = MetadataBuilder::New(*opener_, "super", 1);
+    ASSERT_NE(nullptr, tgt);
+    auto metadata = tgt->Export();
+    ASSERT_NE(nullptr, metadata);
+    std::vector<std::string> written;
+    // Write random data to all COW partitions in super
+    for (auto p : metadata->partitions) {
+        if (GetPartitionGroupName(metadata->groups[p.group_index]) != kCowGroupName) {
+            continue;
+        }
+        std::string path;
+        ASSERT_TRUE(CreateLogicalPartition(
+                CreateLogicalPartitionParams{
+                        .block_device = fake_super,
+                        .metadata = metadata.get(),
+                        .partition = &p,
+                        .timeout_ms = 1s,
+                        .partition_opener = opener_.get(),
+                },
+                &path));
+        ASSERT_TRUE(WriteRandomData(path));
+        written.push_back(GetPartitionName(p));
+    }
+    ASSERT_FALSE(written.empty())
+            << "No COW partitions are created even if there are empty space in super partition";
+
+    // Make sure source partitions aren't affected.
+    for (const auto& name : {"sys_a", "vnd_a", "prd_a"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name));
+    }
+}
+
+// Test that it crashes after creating snapshot status file but before creating COW image, then
+// calling CreateUpdateSnapshots again works.
+TEST_F(SnapshotUpdateTest, SnapshotStatusFileWithoutCow) {
+    // Write some trash snapshot files to simulate leftovers from previous runs.
+    {
+        ASSERT_TRUE(AcquireLock());
+        auto local_lock = std::move(lock_);
+        SnapshotStatus status;
+        status.set_name("sys_b");
+        ASSERT_TRUE(sm->WriteSnapshotStatus(local_lock.get(), status));
+        ASSERT_TRUE(image_manager_->CreateBackingImage("sys_b-cow-img", 1_MiB,
+                                                       IImageManager::CREATE_IMAGE_DEFAULT));
+    }
+
+    // Redo the update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->UnmapUpdateSnapshot("sys_b"));
+
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+
+    // Check that target partitions can be mapped.
+    EXPECT_TRUE(MapUpdateSnapshots());
+}
+
+// Test that the old partitions are not modified.
+TEST_F(SnapshotUpdateTest, TestRollback) {
+    // Execute the update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->UnmapUpdateSnapshot("sys_b"));
+
+    AddOperationForPartitions();
+
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+
+    // Write some data to target partitions.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(WriteSnapshotAndHash(name));
+    }
+
+    // Assert that source partitions aren't affected.
+    for (const auto& name : {"sys_a", "vnd_a", "prd_a"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name));
+    }
+
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    // After reboot, init does first stage mount.
+    auto init = NewManagerForFirstStageMount("_b");
+    ASSERT_NE(init, nullptr);
+    ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    // Check that the target partitions have the same content.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name));
+    }
+
+    // Simulate shutting down the device again.
+    ASSERT_TRUE(UnmapAll());
+    init = NewManagerForFirstStageMount("_a");
+    ASSERT_NE(init, nullptr);
+    ASSERT_FALSE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    // Assert that the source partitions aren't affected.
+    for (const auto& name : {"sys_a", "vnd_a", "prd_a"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name));
+    }
+}
+
+// Test that if an update is applied but not booted into, it can be canceled.
+TEST_F(SnapshotUpdateTest, CancelAfterApply) {
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+    ASSERT_TRUE(sm->CancelUpdate());
+}
+
+static std::vector<Interval> ToIntervals(const std::vector<std::unique_ptr<Extent>>& extents) {
+    std::vector<Interval> ret;
+    std::transform(extents.begin(), extents.end(), std::back_inserter(ret),
+                   [](const auto& extent) { return extent->AsLinearExtent()->AsInterval(); });
+    return ret;
+}
+
+// Test that at the second update, old COW partition spaces are reclaimed.
+TEST_F(SnapshotUpdateTest, ReclaimCow) {
+    // Make sure VABC cows are small enough that they fit in fake_super.
+    sys_->set_estimate_cow_size(64_KiB);
+    vnd_->set_estimate_cow_size(64_KiB);
+    prd_->set_estimate_cow_size(64_KiB);
+
+    // Execute the first update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+    ASSERT_TRUE(MapUpdateSnapshots());
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    // After reboot, init does first stage mount.
+    auto init = NewManagerForFirstStageMount("_b");
+    ASSERT_NE(init, nullptr);
+    ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+    init = nullptr;
+
+    // Initiate the merge and wait for it to be completed.
+    auto new_sm = SnapshotManager::New(new TestDeviceInfo(fake_super, "_b"));
+    ASSERT_TRUE(new_sm->InitiateMerge());
+    ASSERT_EQ(UpdateState::MergeCompleted, new_sm->ProcessUpdateState());
+
+    // Execute the second update.
+    ASSERT_TRUE(new_sm->BeginUpdate());
+    ASSERT_TRUE(new_sm->CreateUpdateSnapshots(manifest_));
+
+    // Check that the old COW space is reclaimed and does not occupy space of mapped partitions.
+    auto src = MetadataBuilder::New(*opener_, "super", 1);
+    ASSERT_NE(src, nullptr);
+    auto tgt = MetadataBuilder::New(*opener_, "super", 0);
+    ASSERT_NE(tgt, nullptr);
+    for (const auto& cow_part_name : {"sys_a-cow", "vnd_a-cow", "prd_a-cow"}) {
+        auto* cow_part = tgt->FindPartition(cow_part_name);
+        ASSERT_NE(nullptr, cow_part) << cow_part_name << " does not exist in target metadata";
+        auto cow_intervals = ToIntervals(cow_part->extents());
+        for (const auto& old_part_name : {"sys_b", "vnd_b", "prd_b"}) {
+            auto* old_part = src->FindPartition(old_part_name);
+            ASSERT_NE(nullptr, old_part) << old_part_name << " does not exist in source metadata";
+            auto old_intervals = ToIntervals(old_part->extents());
+
+            auto intersect = Interval::Intersect(cow_intervals, old_intervals);
+            ASSERT_TRUE(intersect.empty()) << "COW uses space of source partitions";
+        }
+    }
+}
+
+TEST_F(SnapshotUpdateTest, RetrofitAfterRegularAb) {
+    constexpr auto kRetrofitGroupSize = kGroupSize / 2;
+
+    // Initialize device-mapper / disk
+    ASSERT_TRUE(UnmapAll());
+    FormatFakeSuper();
+
+    // Setup source partition metadata to have both _a and _b partitions.
+    src_ = MetadataBuilder::New(*opener_, "super", 0);
+    ASSERT_NE(nullptr, src_);
+    for (const auto& suffix : {"_a"s, "_b"s}) {
+        ASSERT_TRUE(src_->AddGroup(group_->name() + suffix, kRetrofitGroupSize));
+        for (const auto& name : {"sys"s, "vnd"s, "prd"s}) {
+            auto partition = src_->AddPartition(name + suffix, group_->name() + suffix, 0);
+            ASSERT_NE(nullptr, partition);
+            ASSERT_TRUE(src_->ResizePartition(partition, 2_MiB));
+        }
+    }
+    auto metadata = src_->Export();
+    ASSERT_NE(nullptr, metadata);
+    ASSERT_TRUE(UpdatePartitionTable(*opener_, "super", *metadata.get(), 0));
+
+    // Flash source partitions
+    std::string path;
+    for (const auto& name : {"sys_a", "vnd_a", "prd_a"}) {
+        ASSERT_TRUE(CreateLogicalPartition(
+                CreateLogicalPartitionParams{
+                        .block_device = fake_super,
+                        .metadata_slot = 0,
+                        .partition_name = name,
+                        .timeout_ms = 1s,
+                        .partition_opener = opener_.get(),
+                },
+                &path));
+        ASSERT_TRUE(WriteRandomData(path));
+        auto hash = GetHash(path);
+        ASSERT_TRUE(hash.has_value());
+        hashes_[name] = *hash;
+    }
+
+    // Setup manifest.
+    group_->set_size(kRetrofitGroupSize);
+    for (auto* partition : {sys_, vnd_, prd_}) {
+        SetSize(partition, 2_MiB);
+    }
+    AddOperationForPartitions();
+
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+
+    // Test that COW image should not be created for retrofit devices; super
+    // should be big enough.
+    ASSERT_FALSE(image_manager_->BackingImageExists("sys_b-cow-img"));
+    ASSERT_FALSE(image_manager_->BackingImageExists("vnd_b-cow-img"));
+    ASSERT_FALSE(image_manager_->BackingImageExists("prd_b-cow-img"));
+
+    // Write some data to target partitions.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(WriteSnapshotAndHash(name));
+    }
+
+    // Assert that source partitions aren't affected.
+    for (const auto& name : {"sys_a", "vnd_a", "prd_a"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name));
+    }
+
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+}
+
+TEST_F(SnapshotUpdateTest, MergeCannotRemoveCow) {
+    // Make source partitions as big as possible to force COW image to be created.
+    SetSize(sys_, 10_MiB);
+    SetSize(vnd_, 10_MiB);
+    SetSize(prd_, 10_MiB);
+    sys_->set_estimate_cow_size(12_MiB);
+    vnd_->set_estimate_cow_size(12_MiB);
+    prd_->set_estimate_cow_size(12_MiB);
+
+    src_ = MetadataBuilder::New(*opener_, "super", 0);
+    ASSERT_NE(src_, nullptr);
+    src_->RemoveGroupAndPartitions(group_->name() + "_a");
+    src_->RemoveGroupAndPartitions(group_->name() + "_b");
+    ASSERT_TRUE(FillFakeMetadata(src_.get(), manifest_, "_a"));
+    auto metadata = src_->Export();
+    ASSERT_NE(nullptr, metadata);
+    ASSERT_TRUE(UpdatePartitionTable(*opener_, "super", *metadata.get(), 0));
+
+    // Add operations for sys. The whole device is written.
+    AddOperation(sys_);
+
+    // Execute the update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+    ASSERT_TRUE(MapUpdateSnapshots());
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    // After reboot, init does first stage mount.
+    // Normally we should use NewManagerForFirstStageMount, but if so,
+    // "gsid.mapped_image.sys_b-cow-img" won't be set.
+    auto init = SnapshotManager::New(new TestDeviceInfo(fake_super, "_b"));
+    ASSERT_NE(init, nullptr);
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    // Keep an open handle to the cow device. This should cause the merge to
+    // be incomplete.
+    auto cow_path = android::base::GetProperty("gsid.mapped_image.sys_b-cow-img", "");
+    unique_fd fd(open(cow_path.c_str(), O_RDONLY | O_CLOEXEC));
+    ASSERT_GE(fd, 0);
+
+    // COW cannot be removed due to open fd, so expect a soft failure.
+    ASSERT_TRUE(init->InitiateMerge());
+    ASSERT_EQ(UpdateState::MergeNeedsReboot, init->ProcessUpdateState());
+
+    // Simulate shutting down the device.
+    fd.reset();
+    ASSERT_TRUE(UnmapAll());
+
+    // init does first stage mount again.
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    // sys_b should be mapped as a dm-linear device directly.
+    ASSERT_FALSE(sm->IsSnapshotDevice("sys_b", nullptr));
+
+    // Merge should be able to complete now.
+    ASSERT_EQ(UpdateState::MergeCompleted, init->ProcessUpdateState());
+}
+
+class MetadataMountedTest : public ::testing::Test {
+  public:
+    // This is so main() can instantiate this to invoke Cleanup.
+    virtual void TestBody() override {}
+    void SetUp() override {
+        SKIP_IF_NON_VIRTUAL_AB();
+        metadata_dir_ = test_device->GetMetadataDir();
+        ASSERT_TRUE(ReadDefaultFstab(&fstab_));
+    }
+    void TearDown() override {
+        RETURN_IF_NON_VIRTUAL_AB();
+        SetUp();
+        // Remount /metadata
+        test_device->set_recovery(false);
+        EXPECT_TRUE(android::fs_mgr::EnsurePathMounted(&fstab_, metadata_dir_));
+    }
+    AssertionResult IsMetadataMounted() {
+        Fstab mounted_fstab;
+        if (!ReadFstabFromFile("/proc/mounts", &mounted_fstab)) {
+            ADD_FAILURE() << "Failed to scan mounted volumes";
+            return AssertionFailure() << "Failed to scan mounted volumes";
+        }
+
+        auto entry = GetEntryForPath(&fstab_, metadata_dir_);
+        if (entry == nullptr) {
+            return AssertionFailure() << "No mount point found in fstab for path " << metadata_dir_;
+        }
+
+        auto mv = GetEntryForMountPoint(&mounted_fstab, entry->mount_point);
+        if (mv == nullptr) {
+            return AssertionFailure() << metadata_dir_ << " is not mounted";
+        }
+        return AssertionSuccess() << metadata_dir_ << " is mounted";
+    }
+    std::string metadata_dir_;
+    Fstab fstab_;
+};
+
+void MountMetadata() {
+    MetadataMountedTest().TearDown();
+}
+
+TEST_F(MetadataMountedTest, Android) {
+    auto device = sm->EnsureMetadataMounted();
+    EXPECT_NE(nullptr, device);
+    device.reset();
+
+    EXPECT_TRUE(IsMetadataMounted());
+    EXPECT_TRUE(sm->CancelUpdate()) << "Metadata dir should never be unmounted in Android mode";
+}
+
+TEST_F(MetadataMountedTest, Recovery) {
+    test_device->set_recovery(true);
+    metadata_dir_ = test_device->GetMetadataDir();
+
+    EXPECT_TRUE(android::fs_mgr::EnsurePathUnmounted(&fstab_, metadata_dir_));
+    EXPECT_FALSE(IsMetadataMounted());
+
+    auto device = sm->EnsureMetadataMounted();
+    EXPECT_NE(nullptr, device);
+    EXPECT_TRUE(IsMetadataMounted());
+
+    device.reset();
+    EXPECT_FALSE(IsMetadataMounted());
+}
+
+// Test that during a merge, we can wipe data in recovery.
+TEST_F(SnapshotUpdateTest, MergeInRecovery) {
+    // Execute the first update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+    ASSERT_TRUE(MapUpdateSnapshots());
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    // After reboot, init does first stage mount.
+    auto init = NewManagerForFirstStageMount("_b");
+    ASSERT_NE(init, nullptr);
+    ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+    init = nullptr;
+
+    // Initiate the merge and then immediately stop it to simulate a reboot.
+    auto new_sm = SnapshotManager::New(new TestDeviceInfo(fake_super, "_b"));
+    ASSERT_TRUE(new_sm->InitiateMerge());
+    ASSERT_TRUE(UnmapAll());
+
+    // Simulate a reboot into recovery.
+    auto test_device = std::make_unique<TestDeviceInfo>(fake_super, "_b");
+    test_device->set_recovery(true);
+    new_sm = NewManagerForFirstStageMount(test_device.release());
+
+    ASSERT_TRUE(new_sm->HandleImminentDataWipe());
+    ASSERT_EQ(new_sm->GetUpdateState(), UpdateState::None);
+}
+
+// Test that a merge does not clear the snapshot state in fastboot.
+TEST_F(SnapshotUpdateTest, MergeInFastboot) {
+    // Execute the first update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+    ASSERT_TRUE(MapUpdateSnapshots());
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    // After reboot, init does first stage mount.
+    auto init = NewManagerForFirstStageMount("_b");
+    ASSERT_NE(init, nullptr);
+    ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+    init = nullptr;
+
+    // Initiate the merge and then immediately stop it to simulate a reboot.
+    auto new_sm = SnapshotManager::New(new TestDeviceInfo(fake_super, "_b"));
+    ASSERT_TRUE(new_sm->InitiateMerge());
+    ASSERT_TRUE(UnmapAll());
+
+    // Simulate a reboot into recovery.
+    auto test_device = std::make_unique<TestDeviceInfo>(fake_super, "_b");
+    test_device->set_recovery(true);
+    new_sm = NewManagerForFirstStageMount(test_device.release());
+
+    ASSERT_TRUE(new_sm->FinishMergeInRecovery());
+
+    ASSERT_TRUE(UnmapAll());
+
+    auto mount = new_sm->EnsureMetadataMounted();
+    ASSERT_TRUE(mount && mount->HasDevice());
+    ASSERT_EQ(new_sm->ProcessUpdateState(), UpdateState::MergeCompleted);
+
+    // Finish the merge in a normal boot.
+    test_device = std::make_unique<TestDeviceInfo>(fake_super, "_b");
+    init = NewManagerForFirstStageMount(test_device.release());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+    init = nullptr;
+
+    test_device = std::make_unique<TestDeviceInfo>(fake_super, "_b");
+    new_sm = NewManagerForFirstStageMount(test_device.release());
+    ASSERT_EQ(new_sm->ProcessUpdateState(), UpdateState::MergeCompleted);
+    ASSERT_EQ(new_sm->ProcessUpdateState(), UpdateState::None);
+}
+
+// Test that after an OTA, before a merge, we can wipe data in recovery.
+TEST_F(SnapshotUpdateTest, DataWipeRollbackInRecovery) {
+    // Execute the first update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+    ASSERT_TRUE(MapUpdateSnapshots());
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    // Simulate a reboot into recovery.
+    auto test_device = new TestDeviceInfo(fake_super, "_b");
+    test_device->set_recovery(true);
+    auto new_sm = NewManagerForFirstStageMount(test_device);
+
+    ASSERT_TRUE(new_sm->HandleImminentDataWipe());
+    // Manually mount metadata so that we can call GetUpdateState() below.
+    MountMetadata();
+    EXPECT_EQ(new_sm->GetUpdateState(), UpdateState::None);
+    EXPECT_TRUE(test_device->IsSlotUnbootable(1));
+    EXPECT_FALSE(test_device->IsSlotUnbootable(0));
+}
+
+// Test that after an OTA and a bootloader rollback with no merge, we can wipe
+// data in recovery.
+TEST_F(SnapshotUpdateTest, DataWipeAfterRollback) {
+    // Execute the first update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+    ASSERT_TRUE(MapUpdateSnapshots());
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    // Simulate a rollback, with reboot into recovery.
+    auto test_device = new TestDeviceInfo(fake_super, "_a");
+    test_device->set_recovery(true);
+    auto new_sm = NewManagerForFirstStageMount(test_device);
+
+    ASSERT_TRUE(new_sm->HandleImminentDataWipe());
+    EXPECT_EQ(new_sm->GetUpdateState(), UpdateState::None);
+    EXPECT_FALSE(test_device->IsSlotUnbootable(0));
+    EXPECT_FALSE(test_device->IsSlotUnbootable(1));
+}
+
+// Test update package that requests data wipe.
+TEST_F(SnapshotUpdateTest, DataWipeRequiredInPackage) {
+    AddOperationForPartitions();
+    // Execute the update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+
+    // Write some data to target partitions.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(WriteSnapshotAndHash(name)) << name;
+    }
+
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(true /* wipe */));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    // Simulate a reboot into recovery.
+    auto test_device = new TestDeviceInfo(fake_super, "_b");
+    test_device->set_recovery(true);
+    auto new_sm = NewManagerForFirstStageMount(test_device);
+
+    ASSERT_TRUE(new_sm->HandleImminentDataWipe());
+    // Manually mount metadata so that we can call GetUpdateState() below.
+    MountMetadata();
+    EXPECT_EQ(new_sm->GetUpdateState(), UpdateState::None);
+    ASSERT_FALSE(test_device->IsSlotUnbootable(1));
+    ASSERT_FALSE(test_device->IsSlotUnbootable(0));
+
+    ASSERT_TRUE(UnmapAll());
+
+    // Now reboot into new slot.
+    test_device = new TestDeviceInfo(fake_super, "_b");
+    auto init = NewManagerForFirstStageMount(test_device);
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+    // Verify that we are on the downgraded build.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name)) << name;
+    }
+}
+
+// Test update package that requests data wipe.
+TEST_F(SnapshotUpdateTest, DataWipeWithStaleSnapshots) {
+    AddOperationForPartitions();
+
+    // Execute the update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+
+    // Write some data to target partitions.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(WriteSnapshotAndHash(name)) << name;
+    }
+
+    // Create a stale snapshot that should not exist.
+    {
+        ASSERT_TRUE(AcquireLock());
+
+        PartitionCowCreator cow_creator = {
+                .compression_enabled = IsCompressionEnabled(),
+                .compression_algorithm = IsCompressionEnabled() ? "gz" : "none",
+        };
+        SnapshotStatus status;
+        status.set_name("sys_a");
+        status.set_device_size(1_MiB);
+        status.set_snapshot_size(2_MiB);
+        status.set_cow_partition_size(2_MiB);
+
+        ASSERT_TRUE(sm->CreateSnapshot(lock_.get(), &cow_creator, &status));
+        lock_ = nullptr;
+
+        ASSERT_TRUE(sm->EnsureImageManager());
+        ASSERT_TRUE(sm->image_manager()->CreateBackingImage("sys_a", 1_MiB, 0));
+    }
+
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(true /* wipe */));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    // Simulate a reboot into recovery.
+    auto test_device = new TestDeviceInfo(fake_super, "_b");
+    test_device->set_recovery(true);
+    auto new_sm = NewManagerForFirstStageMount(test_device);
+
+    ASSERT_TRUE(new_sm->HandleImminentDataWipe());
+    // Manually mount metadata so that we can call GetUpdateState() below.
+    MountMetadata();
+    EXPECT_EQ(new_sm->GetUpdateState(), UpdateState::None);
+    ASSERT_FALSE(test_device->IsSlotUnbootable(1));
+    ASSERT_FALSE(test_device->IsSlotUnbootable(0));
+
+    ASSERT_TRUE(UnmapAll());
+
+    // Now reboot into new slot.
+    test_device = new TestDeviceInfo(fake_super, "_b");
+    auto init = NewManagerForFirstStageMount(test_device);
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+    // Verify that we are on the downgraded build.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name)) << name;
+    }
+}
+
+TEST_F(SnapshotUpdateTest, Hashtree) {
+    constexpr auto partition_size = 4_MiB;
+    constexpr auto data_size = 3_MiB;
+    constexpr auto hashtree_size = 512_KiB;
+    constexpr auto fec_size = partition_size - data_size - hashtree_size;
+
+    const auto block_size = manifest_.block_size();
+    SetSize(sys_, partition_size);
+    AddOperation(sys_, data_size);
+
+    sys_->set_estimate_cow_size(partition_size + data_size);
+
+    // Set hastree extents.
+    sys_->mutable_hash_tree_data_extent()->set_start_block(0);
+    sys_->mutable_hash_tree_data_extent()->set_num_blocks(data_size / block_size);
+
+    sys_->mutable_hash_tree_extent()->set_start_block(data_size / block_size);
+    sys_->mutable_hash_tree_extent()->set_num_blocks(hashtree_size / block_size);
+
+    // Set FEC extents.
+    sys_->mutable_fec_data_extent()->set_start_block(0);
+    sys_->mutable_fec_data_extent()->set_num_blocks((data_size + hashtree_size) / block_size);
+
+    sys_->mutable_fec_extent()->set_start_block((data_size + hashtree_size) / block_size);
+    sys_->mutable_fec_extent()->set_num_blocks(fec_size / block_size);
+
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+
+    // Map and write some data to target partition.
+    ASSERT_TRUE(MapUpdateSnapshots({"vnd_b", "prd_b"}));
+    ASSERT_TRUE(WriteSnapshotAndHash("sys_b"));
+
+    // Finish update.
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    // After reboot, init does first stage mount.
+    auto init = NewManagerForFirstStageMount("_b");
+    ASSERT_NE(init, nullptr);
+    ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    // Check that the target partition have the same content. Hashtree and FEC extents
+    // should be accounted for.
+    ASSERT_TRUE(IsPartitionUnchanged("sys_b"));
+}
+
+// Test for overflow bit after update
+TEST_F(SnapshotUpdateTest, Overflow) {
+    if (IsCompressionEnabled()) {
+        GTEST_SKIP() << "No overflow bit set for userspace COWs";
+    }
+
+    const auto actual_write_size = GetSize(sys_);
+    const auto declared_write_size = actual_write_size - 1_MiB;
+
+    AddOperation(sys_, declared_write_size);
+
+    // Execute the update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+
+    // Map and write some data to target partitions.
+    ASSERT_TRUE(MapUpdateSnapshots({"vnd_b", "prd_b"}));
+    ASSERT_TRUE(WriteSnapshotAndHash("sys_b"));
+
+    std::vector<android::dm::DeviceMapper::TargetInfo> table;
+    ASSERT_TRUE(DeviceMapper::Instance().GetTableStatus("sys_b", &table));
+    ASSERT_EQ(1u, table.size());
+    EXPECT_TRUE(table[0].IsOverflowSnapshot());
+
+    ASSERT_FALSE(sm->FinishedSnapshotWrites(false))
+            << "FinishedSnapshotWrites should detect overflow of CoW device.";
+}
+
+TEST_F(SnapshotUpdateTest, LowSpace) {
+    static constexpr auto kMaxFree = 10_MiB;
+    auto userdata = std::make_unique<LowSpaceUserdata>();
+    ASSERT_TRUE(userdata->Init(kMaxFree));
+
+    // Grow all partitions to 10_MiB, total 30_MiB. This requires 30 MiB of CoW space. After
+    // using the empty space in super (< 1 MiB), it uses 30 MiB of /userdata space.
+    constexpr uint64_t partition_size = 10_MiB;
+    SetSize(sys_, partition_size);
+    SetSize(vnd_, partition_size);
+    SetSize(prd_, partition_size);
+    sys_->set_estimate_cow_size(partition_size);
+    vnd_->set_estimate_cow_size(partition_size);
+    prd_->set_estimate_cow_size(partition_size);
+
+    AddOperationForPartitions();
+
+    // Execute the update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    auto res = sm->CreateUpdateSnapshots(manifest_);
+    ASSERT_FALSE(res);
+    ASSERT_EQ(Return::ErrorCode::NO_SPACE, res.error_code());
+    ASSERT_GE(res.required_size(), 14_MiB);
+    ASSERT_LT(res.required_size(), 40_MiB);
+}
+
+TEST_F(SnapshotUpdateTest, AddPartition) {
+    group_->add_partition_names("dlkm");
+
+    auto dlkm = manifest_.add_partitions();
+    dlkm->set_partition_name("dlkm");
+    dlkm->set_estimate_cow_size(2_MiB);
+    SetSize(dlkm, 3_MiB);
+
+    // Grow all partitions. Set |prd| large enough that |sys| and |vnd|'s COWs
+    // fit in super, but not |prd|.
+    constexpr uint64_t partition_size = 3788_KiB;
+    SetSize(sys_, partition_size);
+    SetSize(vnd_, partition_size);
+    SetSize(prd_, partition_size);
+    SetSize(dlkm, partition_size);
+
+    AddOperationForPartitions({sys_, vnd_, prd_, dlkm});
+
+    // Execute the update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+
+    // Write some data to target partitions.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b", "dlkm_b"}) {
+        ASSERT_TRUE(WriteSnapshotAndHash(name));
+    }
+
+    // Assert that source partitions aren't affected.
+    for (const auto& name : {"sys_a", "vnd_a", "prd_a"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name));
+    }
+
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    // After reboot, init does first stage mount.
+    auto init = NewManagerForFirstStageMount("_b");
+    ASSERT_NE(init, nullptr);
+
+    ASSERT_TRUE(init->EnsureSnapuserdConnected());
+    init->set_use_first_stage_snapuserd(true);
+
+    ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    // Check that the target partitions have the same content.
+    std::vector<std::string> partitions = {"sys_b", "vnd_b", "prd_b", "dlkm_b"};
+    for (const auto& name : partitions) {
+        ASSERT_TRUE(IsPartitionUnchanged(name));
+    }
+
+    ASSERT_TRUE(init->PerformInitTransition(SnapshotManager::InitTransition::SECOND_STAGE));
+    for (const auto& name : partitions) {
+        ASSERT_TRUE(init->snapuserd_client()->WaitForDeviceDelete(name + "-user-cow-init"));
+    }
+
+    // Initiate the merge and wait for it to be completed.
+    ASSERT_TRUE(init->InitiateMerge());
+    ASSERT_EQ(UpdateState::MergeCompleted, init->ProcessUpdateState());
+
+    // Check that the target partitions have the same content after the merge.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b", "dlkm_b"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name))
+                << "Content of " << name << " changes after the merge";
+    }
+}
+
+class AutoKill final {
+  public:
+    explicit AutoKill(pid_t pid) : pid_(pid) {}
+    ~AutoKill() {
+        if (pid_ > 0) kill(pid_, SIGKILL);
+    }
+
+    bool valid() const { return pid_ > 0; }
+
+  private:
+    pid_t pid_;
+};
+
+TEST_F(SnapshotUpdateTest, DaemonTransition) {
+    if (!IsCompressionEnabled()) {
+        GTEST_SKIP() << "Skipping Virtual A/B Compression test";
+    }
+
+    // Ensure a connection to the second-stage daemon, but use the first-stage
+    // code paths thereafter.
+    ASSERT_TRUE(sm->EnsureSnapuserdConnected());
+    sm->set_use_first_stage_snapuserd(true);
+
+    AddOperationForPartitions();
+    // Execute the update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+    ASSERT_TRUE(MapUpdateSnapshots());
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+    ASSERT_TRUE(UnmapAll());
+
+    auto init = NewManagerForFirstStageMount("_b");
+    ASSERT_NE(init, nullptr);
+
+    ASSERT_TRUE(init->EnsureSnapuserdConnected());
+    init->set_use_first_stage_snapuserd(true);
+
+    ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    ASSERT_EQ(access("/dev/dm-user/sys_b-init", F_OK), 0);
+    ASSERT_EQ(access("/dev/dm-user/sys_b", F_OK), -1);
+
+    ASSERT_TRUE(init->PerformInitTransition(SnapshotManager::InitTransition::SECOND_STAGE));
+
+    // :TODO: this is a workaround to ensure the handler list stays empty. We
+    // should make this test more like actual init, and spawn two copies of
+    // snapuserd, given how many other tests we now have for normal snapuserd.
+    ASSERT_TRUE(init->snapuserd_client()->WaitForDeviceDelete("sys_b-init"));
+    ASSERT_TRUE(init->snapuserd_client()->WaitForDeviceDelete("vnd_b-init"));
+    ASSERT_TRUE(init->snapuserd_client()->WaitForDeviceDelete("prd_b-init"));
+
+    // The control device should have been renamed.
+    ASSERT_TRUE(android::fs_mgr::WaitForFileDeleted("/dev/dm-user/sys_b-init", 10s));
+    ASSERT_EQ(access("/dev/dm-user/sys_b", F_OK), 0);
+}
+
+TEST_F(SnapshotUpdateTest, MapAllSnapshots) {
+    AddOperationForPartitions();
+    // Execute the update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(WriteSnapshotAndHash(name));
+    }
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+    ASSERT_TRUE(sm->MapAllSnapshots(10s));
+
+    // Read bytes back and verify they match the cache.
+    ASSERT_TRUE(IsPartitionUnchanged("sys_b"));
+
+    ASSERT_TRUE(sm->UnmapAllSnapshots());
+}
+
+TEST_F(SnapshotUpdateTest, CancelOnTargetSlot) {
+    AddOperationForPartitions();
+
+    // Execute the update from B->A.
+    test_device->set_slot_suffix("_b");
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+
+    ASSERT_TRUE(UnmapAll());
+    std::string path;
+    ASSERT_TRUE(CreateLogicalPartition(
+            CreateLogicalPartitionParams{
+                    .block_device = fake_super,
+                    .metadata_slot = 0,
+                    .partition_name = "sys_a",
+                    .timeout_ms = 1s,
+                    .partition_opener = opener_.get(),
+            },
+            &path));
+
+    // Switch back to "A", make sure we can cancel. Instead of unmapping sys_a
+    // we should simply delete the old snapshots.
+    test_device->set_slot_suffix("_a");
+    ASSERT_TRUE(sm->BeginUpdate());
+}
+
+class FlashAfterUpdateTest : public SnapshotUpdateTest,
+                             public WithParamInterface<std::tuple<uint32_t, bool>> {
+  public:
+    AssertionResult InitiateMerge(const std::string& slot_suffix) {
+        auto sm = SnapshotManager::New(new TestDeviceInfo(fake_super, slot_suffix));
+        if (!sm->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_)) {
+            return AssertionFailure() << "Cannot CreateLogicalAndSnapshotPartitions";
+        }
+        if (!sm->InitiateMerge()) {
+            return AssertionFailure() << "Cannot initiate merge";
+        }
+        return AssertionSuccess();
+    }
+};
+
+TEST_P(FlashAfterUpdateTest, FlashSlotAfterUpdate) {
+    // Execute the update.
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+    ASSERT_TRUE(MapUpdateSnapshots());
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    bool after_merge = std::get<1>(GetParam());
+    if (after_merge) {
+        ASSERT_TRUE(InitiateMerge("_b"));
+        // Simulate shutting down the device after merge has initiated.
+        ASSERT_TRUE(UnmapAll());
+    }
+
+    auto flashed_slot = std::get<0>(GetParam());
+    auto flashed_slot_suffix = SlotSuffixForSlotNumber(flashed_slot);
+
+    // Simulate flashing |flashed_slot|. This clears the UPDATED flag.
+    auto flashed_builder = MetadataBuilder::New(*opener_, "super", flashed_slot);
+    ASSERT_NE(flashed_builder, nullptr);
+    flashed_builder->RemoveGroupAndPartitions(group_->name() + flashed_slot_suffix);
+    flashed_builder->RemoveGroupAndPartitions(kCowGroupName);
+    ASSERT_TRUE(FillFakeMetadata(flashed_builder.get(), manifest_, flashed_slot_suffix));
+
+    // Deliberately remove a partition from this build so that
+    // InitiateMerge do not switch state to "merging". This is possible in
+    // practice because the list of dynamic partitions may change.
+    ASSERT_NE(nullptr, flashed_builder->FindPartition("prd" + flashed_slot_suffix));
+    flashed_builder->RemovePartition("prd" + flashed_slot_suffix);
+
+    // Note that fastbootd always updates the partition table of both slots.
+    auto flashed_metadata = flashed_builder->Export();
+    ASSERT_NE(nullptr, flashed_metadata);
+    ASSERT_TRUE(UpdatePartitionTable(*opener_, "super", *flashed_metadata, 0));
+    ASSERT_TRUE(UpdatePartitionTable(*opener_, "super", *flashed_metadata, 1));
+
+    std::string path;
+    for (const auto& name : {"sys", "vnd"}) {
+        ASSERT_TRUE(CreateLogicalPartition(
+                CreateLogicalPartitionParams{
+                        .block_device = fake_super,
+                        .metadata_slot = flashed_slot,
+                        .partition_name = name + flashed_slot_suffix,
+                        .timeout_ms = 1s,
+                        .partition_opener = opener_.get(),
+                },
+                &path));
+        ASSERT_TRUE(WriteRandomData(path));
+        auto hash = GetHash(path);
+        ASSERT_TRUE(hash.has_value());
+        hashes_[name + flashed_slot_suffix] = *hash;
+    }
+
+    // Simulate shutting down the device after flash.
+    ASSERT_TRUE(UnmapAll());
+
+    // Simulate reboot. After reboot, init does first stage mount.
+    auto init = NewManagerForFirstStageMount(flashed_slot_suffix);
+    ASSERT_NE(init, nullptr);
+
+    if (flashed_slot && after_merge) {
+        ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    }
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    // Check that the target partitions have the same content.
+    for (const auto& name : {"sys", "vnd"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name + flashed_slot_suffix));
+    }
+
+    // There should be no snapshot to merge.
+    auto new_sm = SnapshotManager::New(new TestDeviceInfo(fake_super, flashed_slot_suffix));
+    if (flashed_slot == 0 && after_merge) {
+        ASSERT_EQ(UpdateState::MergeCompleted, new_sm->ProcessUpdateState());
+    } else {
+        // update_engine calls ProcessUpdateState first -- should see Cancelled.
+        ASSERT_EQ(UpdateState::Cancelled, new_sm->ProcessUpdateState());
+    }
+
+    // Next OTA calls CancelUpdate no matter what.
+    ASSERT_TRUE(new_sm->CancelUpdate());
+}
+
+INSTANTIATE_TEST_SUITE_P(Snapshot, FlashAfterUpdateTest, Combine(Values(0, 1), Bool()),
+                         [](const TestParamInfo<FlashAfterUpdateTest::ParamType>& info) {
+                             return "Flash"s + (std::get<0>(info.param) ? "New"s : "Old"s) +
+                                    "Slot"s + (std::get<1>(info.param) ? "After"s : "Before"s) +
+                                    "Merge"s;
+                         });
+
+// Test behavior of ImageManager::Create on low space scenario. These tests assumes image manager
+// uses /data as backup device.
+class ImageManagerTest : public SnapshotTest, public WithParamInterface<uint64_t> {
+  protected:
+    void SetUp() override {
+        SKIP_IF_NON_VIRTUAL_AB();
+        SnapshotTest::SetUp();
+        userdata_ = std::make_unique<LowSpaceUserdata>();
+        ASSERT_TRUE(userdata_->Init(GetParam()));
+    }
+    void TearDown() override {
+        RETURN_IF_NON_VIRTUAL_AB();
+        return;  // BUG(149738928)
+
+        EXPECT_TRUE(!image_manager_->BackingImageExists(kImageName) ||
+                    image_manager_->DeleteBackingImage(kImageName));
+    }
+    static constexpr const char* kImageName = "my_image";
+    std::unique_ptr<LowSpaceUserdata> userdata_;
+};
+
+TEST_P(ImageManagerTest, CreateImageEnoughAvailSpace) {
+    if (userdata_->available_space() == 0) {
+        GTEST_SKIP() << "/data is full (" << userdata_->available_space()
+                     << " bytes available), skipping";
+    }
+    ASSERT_TRUE(image_manager_->CreateBackingImage(kImageName, userdata_->available_space(),
+                                                   IImageManager::CREATE_IMAGE_DEFAULT))
+            << "Should be able to create image with size = " << userdata_->available_space()
+            << " bytes";
+    ASSERT_TRUE(image_manager_->DeleteBackingImage(kImageName))
+            << "Should be able to delete created image";
+}
+
+TEST_P(ImageManagerTest, CreateImageNoSpace) {
+    uint64_t to_allocate = userdata_->free_space() + userdata_->bsize();
+    auto res = image_manager_->CreateBackingImage(kImageName, to_allocate,
+                                                  IImageManager::CREATE_IMAGE_DEFAULT);
+    ASSERT_FALSE(res) << "Should not be able to create image with size = " << to_allocate
+                      << " bytes because only " << userdata_->free_space() << " bytes are free";
+    ASSERT_EQ(FiemapStatus::ErrorCode::NO_SPACE, res.error_code()) << res.string();
+}
+
+std::vector<uint64_t> ImageManagerTestParams() {
+    std::vector<uint64_t> ret;
+    for (uint64_t size = 1_MiB; size <= 512_MiB; size *= 2) {
+        ret.push_back(size);
+    }
+    return ret;
+}
+
+INSTANTIATE_TEST_SUITE_P(ImageManagerTest, ImageManagerTest, ValuesIn(ImageManagerTestParams()));
+
+bool Mkdir(const std::string& path) {
+    if (mkdir(path.c_str(), 0700) && errno != EEXIST) {
+        std::cerr << "Could not mkdir " << path << ": " << strerror(errno) << std::endl;
+        return false;
+    }
+    return true;
+}
+
+class SnapshotTestEnvironment : public ::testing::Environment {
+  public:
+    ~SnapshotTestEnvironment() override {}
+    void SetUp() override;
+    void TearDown() override;
+
+  private:
+    bool CreateFakeSuper();
+
+    std::unique_ptr<IImageManager> super_images_;
+};
+
+bool SnapshotTestEnvironment::CreateFakeSuper() {
+    // Create and map the fake super partition.
+    static constexpr int kImageFlags =
+            IImageManager::CREATE_IMAGE_DEFAULT | IImageManager::CREATE_IMAGE_ZERO_FILL;
+    if (!super_images_->CreateBackingImage("fake-super", kSuperSize, kImageFlags)) {
+        LOG(ERROR) << "Could not create fake super partition";
+        return false;
+    }
+    if (!super_images_->MapImageDevice("fake-super", 10s, &fake_super)) {
+        LOG(ERROR) << "Could not map fake super partition";
+        return false;
+    }
+    test_device->set_fake_super(fake_super);
+    return true;
+}
+
+void SnapshotTestEnvironment::SetUp() {
+    // b/163082876: GTEST_SKIP in Environment will make atest report incorrect results. Until
+    // that is fixed, don't call GTEST_SKIP here, but instead call GTEST_SKIP in individual test
+    // suites.
+    RETURN_IF_NON_VIRTUAL_AB_MSG("Virtual A/B is not enabled, skipping global setup.\n");
+
+    std::vector<std::string> paths = {
+            // clang-format off
+            "/data/gsi/ota/test",
+            "/data/gsi/ota/test/super",
+            "/metadata/gsi/ota/test",
+            "/metadata/gsi/ota/test/super",
+            "/metadata/ota/test",
+            "/metadata/ota/test/snapshots",
+            // clang-format on
+    };
+    for (const auto& path : paths) {
+        ASSERT_TRUE(Mkdir(path));
+    }
+
+    // Create this once, otherwise, gsid will start/stop between each test.
+    test_device = new TestDeviceInfo();
+    sm = SnapshotManager::New(test_device);
+    ASSERT_NE(nullptr, sm) << "Could not create snapshot manager";
+
+    // Use a separate image manager for our fake super partition.
+    super_images_ = IImageManager::Open("ota/test/super", 10s);
+    ASSERT_NE(nullptr, super_images_) << "Could not create image manager";
+
+    // Map the old image if one exists so we can safely unmap everything that
+    // depends on it.
+    bool recreate_fake_super;
+    if (super_images_->BackingImageExists("fake-super")) {
+        if (super_images_->IsImageMapped("fake-super")) {
+            ASSERT_TRUE(super_images_->GetMappedImageDevice("fake-super", &fake_super));
+        } else {
+            ASSERT_TRUE(super_images_->MapImageDevice("fake-super", 10s, &fake_super));
+        }
+        test_device->set_fake_super(fake_super);
+        recreate_fake_super = true;
+    } else {
+        ASSERT_TRUE(CreateFakeSuper());
+        recreate_fake_super = false;
+    }
+
+    // Clean up previous run.
+    MetadataMountedTest().TearDown();
+    SnapshotUpdateTest().Cleanup();
+    SnapshotTest().Cleanup();
+
+    if (recreate_fake_super) {
+        // Clean up any old copy.
+        DeleteBackingImage(super_images_.get(), "fake-super");
+        ASSERT_TRUE(CreateFakeSuper());
+    }
+}
+
+void SnapshotTestEnvironment::TearDown() {
+    RETURN_IF_NON_VIRTUAL_AB();
+    if (super_images_ != nullptr) {
+        DeleteBackingImage(super_images_.get(), "fake-super");
+    }
+}
+
+}  // namespace snapshot
+}  // namespace android
+
+int main(int argc, char** argv) {
+    ::testing::InitGoogleTest(&argc, argv);
+    ::testing::AddGlobalTestEnvironment(new ::android::snapshot::SnapshotTestEnvironment());
+
+    android::base::SetProperty("ctl.stop", "snapuserd");
+    android::base::SetProperty("snapuserd.test.dm.snapshots", "0");
+
+    return RUN_ALL_TESTS();
+}