diff --git a/fs_mgr/fs_mgr.cpp b/fs_mgr/fs_mgr.cpp
index 38472de..d6fd513 100644
--- a/fs_mgr/fs_mgr.cpp
+++ b/fs_mgr/fs_mgr.cpp
@@ -976,6 +976,19 @@
     }
 }
 
+static void set_type_property(int status) {
+    switch (status) {
+        case FS_MGR_MNTALL_DEV_MIGHT_BE_ENCRYPTED:
+            SetProperty("ro.crypto.type", "block");
+            break;
+        case FS_MGR_MNTALL_DEV_FILE_ENCRYPTED:
+        case FS_MGR_MNTALL_DEV_IS_METADATA_ENCRYPTED:
+        case FS_MGR_MNTALL_DEV_NEEDS_METADATA_ENCRYPTION:
+            SetProperty("ro.crypto.type", "file");
+            break;
+    }
+}
+
 static bool call_vdc(const std::vector<std::string>& args, int* ret) {
     std::vector<char const*> argv;
     argv.emplace_back("/system/bin/vdc");
@@ -1366,6 +1379,7 @@
                 avb_handle = AvbHandle::Open();
                 if (!avb_handle) {
                     LERROR << "Failed to open AvbHandle";
+                    set_type_property(encryptable);
                     return FS_MGR_MNTALL_FAIL;
                 }
             }
@@ -1422,6 +1436,7 @@
                                    attempted_entry.mount_point},
                                   nullptr)) {
                         LERROR << "Encryption failed";
+                        set_type_property(encryptable);
                         return FS_MGR_MNTALL_FAIL;
                     }
                 }
@@ -1519,6 +1534,8 @@
         }
     }
 
+    set_type_property(encryptable);
+
 #if ALLOW_ADBD_DISABLE_VERITY == 1  // "userdebug" build
     fs_mgr_overlayfs_mount_all(fstab);
 #endif
diff --git a/fs_mgr/libsnapshot/Android.bp b/fs_mgr/libsnapshot/Android.bp
index eaef180..f8e4b7a 100644
--- a/fs_mgr/libsnapshot/Android.bp
+++ b/fs_mgr/libsnapshot/Android.bp
@@ -122,6 +122,39 @@
     ],
 }
 
+cc_defaults {
+    name: "libsnapshot_cow_defaults",
+    defaults: [
+        "fs_mgr_defaults",
+    ],
+    cflags: [
+        "-D_FILE_OFFSET_BITS=64",
+        "-Wall",
+        "-Werror",
+    ],
+    export_include_dirs: ["include"],
+    srcs: [
+        "cow_reader.cpp",
+        "cow_writer.cpp",
+    ],
+}
+
+cc_library_static {
+    name: "libsnapshot_cow",
+    defaults: [
+        "libsnapshot_cow_defaults",
+    ],
+    host_supported: true,
+    shared_libs: [
+        "libbase",
+        "libcrypto",
+        "liblog",
+    ],
+    static_libs: [
+        "libz",
+    ],
+}
+
 cc_library_static {
     name: "libsnapshot_test_helpers",
     defaults: ["libsnapshot_defaults"],
@@ -343,3 +376,30 @@
     static_executable: true,
     system_shared_libs: [],
 }
+
+cc_test {
+    name: "cow_api_test",
+    defaults: [
+        "fs_mgr_defaults",
+    ],
+    srcs: [
+        "cow_api_test.cpp",
+    ],
+    cflags: [
+        "-Wall",
+        "-Werror",
+    ],
+    shared_libs: [
+        "libbase",
+        "libcrypto",
+        "liblog",
+        "libz",
+    ],
+    static_libs: [
+        "libgtest",
+        "libsnapshot_cow",
+    ],
+    test_min_api_level: 30,
+    auto_gen_config: true,
+    require_root: false,
+}
diff --git a/fs_mgr/libsnapshot/cow_api_test.cpp b/fs_mgr/libsnapshot/cow_api_test.cpp
new file mode 100644
index 0000000..3b3fc47
--- /dev/null
+++ b/fs_mgr/libsnapshot/cow_api_test.cpp
@@ -0,0 +1,244 @@
+// 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 <iostream>
+#include <memory>
+#include <string_view>
+
+#include <android-base/file.h>
+#include <gtest/gtest.h>
+#include <libsnapshot/cow_reader.h>
+#include <libsnapshot/cow_writer.h>
+
+namespace android {
+namespace snapshot {
+
+class CowTest : public ::testing::Test {
+  protected:
+    void SetUp() override {
+        cow_ = std::make_unique<TemporaryFile>();
+        ASSERT_GE(cow_->fd, 0) << strerror(errno);
+    }
+
+    void TearDown() override { cow_ = nullptr; }
+
+    std::unique_ptr<TemporaryFile> cow_;
+};
+
+// Sink that always appends to the end of a string.
+class StringSink : public IByteSink {
+  public:
+    void* GetBuffer(size_t requested, size_t* actual) override {
+        size_t old_size = stream_.size();
+        stream_.resize(old_size + requested, '\0');
+        *actual = requested;
+        return stream_.data() + old_size;
+    }
+    bool ReturnData(void*, size_t) override { return true; }
+    void Reset() { stream_.clear(); }
+
+    std::string& stream() { return stream_; }
+
+  private:
+    std::string stream_;
+};
+
+TEST_F(CowTest, ReadWrite) {
+    CowOptions options;
+    CowWriter writer(options);
+
+    ASSERT_TRUE(writer.Initialize(cow_->fd));
+
+    std::string data = "This is some data, believe it";
+    data.resize(options.block_size, '\0');
+
+    ASSERT_TRUE(writer.AddCopy(10, 20));
+    ASSERT_TRUE(writer.AddRawBlocks(50, data.data(), data.size()));
+    ASSERT_TRUE(writer.AddZeroBlocks(51, 2));
+    ASSERT_TRUE(writer.Finalize());
+
+    ASSERT_EQ(lseek(cow_->fd, 0, SEEK_SET), 0);
+
+    CowReader reader;
+    CowHeader header;
+    ASSERT_TRUE(reader.Parse(cow_->fd));
+    ASSERT_TRUE(reader.GetHeader(&header));
+    ASSERT_EQ(header.magic, kCowMagicNumber);
+    ASSERT_EQ(header.major_version, kCowVersionMajor);
+    ASSERT_EQ(header.minor_version, kCowVersionMinor);
+    ASSERT_EQ(header.block_size, options.block_size);
+    ASSERT_EQ(header.num_ops, 4);
+
+    auto iter = reader.GetOpIter();
+    ASSERT_NE(iter, nullptr);
+    ASSERT_FALSE(iter->Done());
+    auto op = &iter->Get();
+
+    ASSERT_EQ(op->type, kCowCopyOp);
+    ASSERT_EQ(op->compression, kCowCompressNone);
+    ASSERT_EQ(op->data_length, 0);
+    ASSERT_EQ(op->new_block, 10);
+    ASSERT_EQ(op->source, 20);
+
+    StringSink sink;
+
+    iter->Next();
+    ASSERT_FALSE(iter->Done());
+    op = &iter->Get();
+
+    ASSERT_EQ(op->type, kCowReplaceOp);
+    ASSERT_EQ(op->compression, kCowCompressNone);
+    ASSERT_EQ(op->data_length, 4096);
+    ASSERT_EQ(op->new_block, 50);
+    ASSERT_EQ(op->source, 104);
+    ASSERT_TRUE(reader.ReadData(*op, &sink));
+    ASSERT_EQ(sink.stream(), data);
+
+    iter->Next();
+    ASSERT_FALSE(iter->Done());
+    op = &iter->Get();
+
+    // Note: the zero operation gets split into two blocks.
+    ASSERT_EQ(op->type, kCowZeroOp);
+    ASSERT_EQ(op->compression, kCowCompressNone);
+    ASSERT_EQ(op->data_length, 0);
+    ASSERT_EQ(op->new_block, 51);
+    ASSERT_EQ(op->source, 0);
+
+    iter->Next();
+    ASSERT_FALSE(iter->Done());
+    op = &iter->Get();
+
+    ASSERT_EQ(op->type, kCowZeroOp);
+    ASSERT_EQ(op->compression, kCowCompressNone);
+    ASSERT_EQ(op->data_length, 0);
+    ASSERT_EQ(op->new_block, 52);
+    ASSERT_EQ(op->source, 0);
+
+    iter->Next();
+    ASSERT_TRUE(iter->Done());
+}
+
+TEST_F(CowTest, CompressGz) {
+    CowOptions options;
+    options.compression = "gz";
+    CowWriter writer(options);
+
+    ASSERT_TRUE(writer.Initialize(cow_->fd));
+
+    std::string data = "This is some data, believe it";
+    data.resize(options.block_size, '\0');
+
+    ASSERT_TRUE(writer.AddRawBlocks(50, data.data(), data.size()));
+    ASSERT_TRUE(writer.Finalize());
+
+    ASSERT_EQ(lseek(cow_->fd, 0, SEEK_SET), 0);
+
+    CowReader reader;
+    ASSERT_TRUE(reader.Parse(cow_->fd));
+
+    auto iter = reader.GetOpIter();
+    ASSERT_NE(iter, nullptr);
+    ASSERT_FALSE(iter->Done());
+    auto op = &iter->Get();
+
+    StringSink sink;
+
+    ASSERT_EQ(op->type, kCowReplaceOp);
+    ASSERT_EQ(op->compression, kCowCompressGz);
+    ASSERT_EQ(op->data_length, 56);  // compressed!
+    ASSERT_EQ(op->new_block, 50);
+    ASSERT_EQ(op->source, 104);
+    ASSERT_TRUE(reader.ReadData(*op, &sink));
+    ASSERT_EQ(sink.stream(), data);
+
+    iter->Next();
+    ASSERT_TRUE(iter->Done());
+}
+
+TEST_F(CowTest, CompressTwoBlocks) {
+    CowOptions options;
+    options.compression = "gz";
+    CowWriter writer(options);
+
+    ASSERT_TRUE(writer.Initialize(cow_->fd));
+
+    std::string data = "This is some data, believe it";
+    data.resize(options.block_size * 2, '\0');
+
+    ASSERT_TRUE(writer.AddRawBlocks(50, data.data(), data.size()));
+    ASSERT_TRUE(writer.Finalize());
+
+    ASSERT_EQ(lseek(cow_->fd, 0, SEEK_SET), 0);
+
+    CowReader reader;
+    ASSERT_TRUE(reader.Parse(cow_->fd));
+
+    auto iter = reader.GetOpIter();
+    ASSERT_NE(iter, nullptr);
+    ASSERT_FALSE(iter->Done());
+    iter->Next();
+    ASSERT_FALSE(iter->Done());
+
+    StringSink sink;
+
+    auto op = &iter->Get();
+    ASSERT_EQ(op->type, kCowReplaceOp);
+    ASSERT_EQ(op->compression, kCowCompressGz);
+    ASSERT_EQ(op->new_block, 51);
+    ASSERT_TRUE(reader.ReadData(*op, &sink));
+}
+
+// Only return 1-byte buffers, to stress test the partial read logic in
+// CowReader.
+class HorribleStringSink : public StringSink {
+  public:
+    void* GetBuffer(size_t, size_t* actual) override { return StringSink::GetBuffer(1, actual); }
+};
+
+TEST_F(CowTest, HorribleSink) {
+    CowOptions options;
+    options.compression = "gz";
+    CowWriter writer(options);
+
+    ASSERT_TRUE(writer.Initialize(cow_->fd));
+
+    std::string data = "This is some data, believe it";
+    data.resize(options.block_size, '\0');
+
+    ASSERT_TRUE(writer.AddRawBlocks(50, data.data(), data.size()));
+    ASSERT_TRUE(writer.Finalize());
+
+    ASSERT_EQ(lseek(cow_->fd, 0, SEEK_SET), 0);
+
+    CowReader reader;
+    ASSERT_TRUE(reader.Parse(cow_->fd));
+
+    auto iter = reader.GetOpIter();
+    ASSERT_NE(iter, nullptr);
+    ASSERT_FALSE(iter->Done());
+
+    HorribleStringSink sink;
+    auto op = &iter->Get();
+    ASSERT_TRUE(reader.ReadData(*op, &sink));
+    ASSERT_EQ(sink.stream(), data);
+}
+
+}  // namespace snapshot
+}  // namespace android
+
+int main(int argc, char** argv) {
+    ::testing::InitGoogleTest(&argc, argv);
+    return RUN_ALL_TESTS();
+}
diff --git a/fs_mgr/libsnapshot/cow_reader.cpp b/fs_mgr/libsnapshot/cow_reader.cpp
new file mode 100644
index 0000000..86565c4
--- /dev/null
+++ b/fs_mgr/libsnapshot/cow_reader.cpp
@@ -0,0 +1,264 @@
+//
+// Copyright (C) 2020 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 <sys/types.h>
+#include <unistd.h>
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+#include <libsnapshot/cow_reader.h>
+#include <openssl/sha.h>
+#include <zlib.h>
+
+namespace android {
+namespace snapshot {
+
+CowReader::CowReader() : fd_(-1), header_(), fd_size_(0) {}
+
+static void SHA256(const void* data, size_t length, uint8_t out[32]) {
+    SHA256_CTX c;
+    SHA256_Init(&c);
+    SHA256_Update(&c, data, length);
+    SHA256_Final(out, &c);
+}
+
+bool CowReader::Parse(android::base::unique_fd&& fd) {
+    owned_fd_ = std::move(fd);
+    return Parse(android::base::borrowed_fd{owned_fd_});
+}
+
+bool CowReader::Parse(android::base::borrowed_fd fd) {
+    fd_ = fd;
+
+    auto pos = lseek(fd_.get(), 0, SEEK_END);
+    if (pos < 0) {
+        PLOG(ERROR) << "lseek end failed";
+        return false;
+    }
+    fd_size_ = pos;
+
+    if (lseek(fd_.get(), 0, SEEK_SET) < 0) {
+        PLOG(ERROR) << "lseek header failed";
+        return false;
+    }
+    if (!android::base::ReadFully(fd_, &header_, sizeof(header_))) {
+        PLOG(ERROR) << "read header failed";
+        return false;
+    }
+
+    // Validity check the ops range.
+    if (header_.ops_offset >= fd_size_) {
+        LOG(ERROR) << "ops offset " << header_.ops_offset << " larger than fd size " << fd_size_;
+        return false;
+    }
+    if (fd_size_ - header_.ops_offset < header_.ops_size) {
+        LOG(ERROR) << "ops size " << header_.ops_size << " is too large";
+        return false;
+    }
+
+    uint8_t header_csum[32];
+    {
+        CowHeader tmp = header_;
+        memset(&tmp.header_checksum, 0, sizeof(tmp.header_checksum));
+        SHA256(&tmp, sizeof(tmp), header_csum);
+    }
+    if (memcmp(header_csum, header_.header_checksum, sizeof(header_csum)) != 0) {
+        LOG(ERROR) << "header checksum is invalid";
+        return false;
+    }
+    return true;
+}
+
+bool CowReader::GetHeader(CowHeader* header) {
+    *header = header_;
+    return true;
+}
+
+class CowOpIter final : public ICowOpIter {
+  public:
+    CowOpIter(std::unique_ptr<uint8_t[]>&& ops, size_t len);
+
+    bool Done() override;
+    const CowOperation& Get() override;
+    void Next() override;
+
+  private:
+    bool HasNext();
+
+    std::unique_ptr<uint8_t[]> ops_;
+    const uint8_t* pos_;
+    const uint8_t* end_;
+    bool done_;
+};
+
+CowOpIter::CowOpIter(std::unique_ptr<uint8_t[]>&& ops, size_t len)
+    : ops_(std::move(ops)), pos_(ops_.get()), end_(pos_ + len), done_(!HasNext()) {}
+
+bool CowOpIter::Done() {
+    return done_;
+}
+
+bool CowOpIter::HasNext() {
+    return pos_ < end_ && size_t(end_ - pos_) >= sizeof(CowOperation);
+}
+
+void CowOpIter::Next() {
+    CHECK(!Done());
+
+    pos_ += sizeof(CowOperation);
+    if (!HasNext()) done_ = true;
+}
+
+const CowOperation& CowOpIter::Get() {
+    CHECK(!Done());
+    CHECK(HasNext());
+    return *reinterpret_cast<const CowOperation*>(pos_);
+}
+
+std::unique_ptr<ICowOpIter> CowReader::GetOpIter() {
+    if (lseek(fd_.get(), header_.ops_offset, SEEK_SET) < 0) {
+        PLOG(ERROR) << "lseek ops failed";
+        return nullptr;
+    }
+    auto ops_buffer = std::make_unique<uint8_t[]>(header_.ops_size);
+    if (!android::base::ReadFully(fd_, ops_buffer.get(), header_.ops_size)) {
+        PLOG(ERROR) << "read ops failed";
+        return nullptr;
+    }
+
+    uint8_t csum[32];
+    SHA256(ops_buffer.get(), header_.ops_size, csum);
+    if (memcmp(csum, header_.ops_checksum, sizeof(csum)) != 0) {
+        LOG(ERROR) << "ops checksum does not match";
+        return nullptr;
+    }
+
+    return std::make_unique<CowOpIter>(std::move(ops_buffer), header_.ops_size);
+}
+
+bool CowReader::GetRawBytes(uint64_t offset, void* buffer, size_t len) {
+    // Validate the offset, taking care to acknowledge possible overflow of offset+len.
+    if (offset < sizeof(header_) || offset >= header_.ops_offset || len >= fd_size_ ||
+        offset + len > header_.ops_offset) {
+        LOG(ERROR) << "invalid data offset: " << offset << ", " << len << " bytes";
+        return false;
+    }
+    if (lseek(fd_.get(), offset, SEEK_SET) < 0) {
+        PLOG(ERROR) << "lseek to read raw bytes failed";
+        return false;
+    }
+    if (!android::base::ReadFully(fd_, buffer, len)) {
+        PLOG(ERROR) << "read raw bytes failed";
+        return false;
+    }
+    return true;
+}
+
+bool CowReader::ReadData(const CowOperation& op, IByteSink* sink) {
+    uint64_t offset = op.source;
+
+    switch (op.compression) {
+        case kCowCompressNone: {
+            size_t remaining = op.data_length;
+            while (remaining) {
+                size_t amount = remaining;
+                void* buffer = sink->GetBuffer(amount, &amount);
+                if (!buffer) {
+                    LOG(ERROR) << "Could not acquire buffer from sink";
+                    return false;
+                }
+                if (!GetRawBytes(offset, buffer, amount)) {
+                    return false;
+                }
+                if (!sink->ReturnData(buffer, amount)) {
+                    LOG(ERROR) << "Could not return buffer to sink";
+                    return false;
+                }
+                remaining -= amount;
+                offset += amount;
+            }
+            return true;
+        }
+        case kCowCompressGz: {
+            auto input = std::make_unique<Bytef[]>(op.data_length);
+            if (!GetRawBytes(offset, input.get(), op.data_length)) {
+                return false;
+            }
+
+            z_stream z = {};
+            z.next_in = input.get();
+            z.avail_in = op.data_length;
+            if (int rv = inflateInit(&z); rv != Z_OK) {
+                LOG(ERROR) << "inflateInit returned error code " << rv;
+                return false;
+            }
+
+            while (z.total_out < header_.block_size) {
+                // If no more output buffer, grab a new buffer.
+                if (z.avail_out == 0) {
+                    size_t amount = header_.block_size - z.total_out;
+                    z.next_out = reinterpret_cast<Bytef*>(sink->GetBuffer(amount, &amount));
+                    if (!z.next_out) {
+                        LOG(ERROR) << "Could not acquire buffer from sink";
+                        return false;
+                    }
+                    z.avail_out = amount;
+                }
+
+                // Remember the position of the output buffer so we can call ReturnData.
+                auto buffer = z.next_out;
+                auto avail_out = z.avail_out;
+
+                // Decompress.
+                int rv = inflate(&z, Z_NO_FLUSH);
+                if (rv != Z_OK && rv != Z_STREAM_END) {
+                    LOG(ERROR) << "inflate returned error code " << rv;
+                    return false;
+                }
+
+                // Return the section of the buffer that was updated.
+                if (z.avail_out < avail_out && !sink->ReturnData(buffer, avail_out - z.avail_out)) {
+                    LOG(ERROR) << "Could not return buffer to sink";
+                    return false;
+                }
+
+                if (rv == Z_STREAM_END) {
+                    // Error if the stream has ended, but we didn't fill the entire block.
+                    if (z.total_out != header_.block_size) {
+                        LOG(ERROR) << "Reached gz stream end but did not read a full block of data";
+                        return false;
+                    }
+                    break;
+                }
+
+                CHECK(rv == Z_OK);
+
+                // Error if the stream is expecting more data, but we don't have any to read.
+                if (z.avail_in == 0) {
+                    LOG(ERROR) << "Gz stream ended prematurely";
+                    return false;
+                }
+            }
+            return true;
+        }
+        default:
+            LOG(ERROR) << "Unknown compression type: " << op.compression;
+            return false;
+    }
+}
+
+}  // namespace snapshot
+}  // namespace android
diff --git a/fs_mgr/libsnapshot/cow_writer.cpp b/fs_mgr/libsnapshot/cow_writer.cpp
new file mode 100644
index 0000000..ea8e534
--- /dev/null
+++ b/fs_mgr/libsnapshot/cow_writer.cpp
@@ -0,0 +1,230 @@
+//
+// Copyright (C) 2020 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 <sys/types.h>
+#include <unistd.h>
+
+#include <limits>
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+#include <libsnapshot/cow_writer.h>
+#include <openssl/sha.h>
+#include <zlib.h>
+
+namespace android {
+namespace snapshot {
+
+static_assert(sizeof(off_t) == sizeof(uint64_t));
+
+CowWriter::CowWriter(const CowOptions& options) : ICowWriter(options), fd_(-1) {
+    SetupHeaders();
+}
+
+void CowWriter::SetupHeaders() {
+    header_ = {};
+    header_.magic = kCowMagicNumber;
+    header_.major_version = kCowVersionMajor;
+    header_.minor_version = kCowVersionMinor;
+    header_.block_size = options_.block_size;
+}
+
+bool CowWriter::Initialize(android::base::unique_fd&& fd) {
+    owned_fd_ = std::move(fd);
+    return Initialize(android::base::borrowed_fd{owned_fd_});
+}
+
+bool CowWriter::Initialize(android::base::borrowed_fd fd) {
+    fd_ = fd;
+
+    // This limitation is tied to the data field size in CowOperation.
+    if (header_.block_size > std::numeric_limits<uint16_t>::max()) {
+        LOG(ERROR) << "Block size is too large";
+        return false;
+    }
+
+    if (lseek(fd_.get(), 0, SEEK_SET) < 0) {
+        PLOG(ERROR) << "lseek failed";
+        return false;
+    }
+
+    if (options_.compression == "gz") {
+        compression_ = kCowCompressGz;
+    } else if (!options_.compression.empty()) {
+        LOG(ERROR) << "unrecognized compression: " << options_.compression;
+        return false;
+    }
+
+    // Headers are not complete, but this ensures the file is at the right
+    // position.
+    if (!android::base::WriteFully(fd_, &header_, sizeof(header_))) {
+        PLOG(ERROR) << "write failed";
+        return false;
+    }
+    return true;
+}
+
+bool CowWriter::AddCopy(uint64_t new_block, uint64_t old_block) {
+    header_.num_ops++;
+
+    CowOperation op = {};
+    op.type = kCowCopyOp;
+    op.new_block = new_block;
+    op.source = old_block;
+    ops_ += std::basic_string<uint8_t>(reinterpret_cast<uint8_t*>(&op), sizeof(op));
+
+    return true;
+}
+
+bool CowWriter::AddRawBlocks(uint64_t new_block_start, const void* data, size_t size) {
+    if (size % header_.block_size != 0) {
+        LOG(ERROR) << "AddRawBlocks: size " << size << " is not a multiple of "
+                   << header_.block_size;
+        return false;
+    }
+
+    uint64_t pos;
+    if (!GetDataPos(&pos)) {
+        return false;
+    }
+
+    const uint8_t* iter = reinterpret_cast<const uint8_t*>(data);
+    for (size_t i = 0; i < size / header_.block_size; i++) {
+        header_.num_ops++;
+
+        CowOperation op = {};
+        op.type = kCowReplaceOp;
+        op.new_block = new_block_start + i;
+        op.source = pos;
+
+        if (compression_) {
+            auto data = Compress(iter, header_.block_size);
+            if (data.empty()) {
+                PLOG(ERROR) << "AddRawBlocks: compression failed";
+                return false;
+            }
+            if (data.size() > std::numeric_limits<uint16_t>::max()) {
+                LOG(ERROR) << "Compressed block is too large: " << data.size() << " bytes";
+                return false;
+            }
+            if (!android::base::WriteFully(fd_, data.data(), data.size())) {
+                PLOG(ERROR) << "AddRawBlocks: write failed";
+                return false;
+            }
+            op.compression = compression_;
+            op.data_length = static_cast<uint16_t>(data.size());
+            pos += data.size();
+        } else {
+            op.data_length = static_cast<uint16_t>(header_.block_size);
+            pos += header_.block_size;
+        }
+
+        ops_ += std::basic_string<uint8_t>(reinterpret_cast<uint8_t*>(&op), sizeof(op));
+        iter += header_.block_size;
+    }
+
+    if (!compression_ && !android::base::WriteFully(fd_, data, size)) {
+        PLOG(ERROR) << "AddRawBlocks: write failed";
+        return false;
+    }
+    return true;
+}
+
+bool CowWriter::AddZeroBlocks(uint64_t new_block_start, uint64_t num_blocks) {
+    for (uint64_t i = 0; i < num_blocks; i++) {
+        header_.num_ops++;
+
+        CowOperation op = {};
+        op.type = kCowZeroOp;
+        op.new_block = new_block_start + i;
+        op.source = 0;
+        ops_ += std::basic_string<uint8_t>(reinterpret_cast<uint8_t*>(&op), sizeof(op));
+    }
+    return true;
+}
+
+std::basic_string<uint8_t> CowWriter::Compress(const void* data, size_t length) {
+    switch (compression_) {
+        case kCowCompressGz: {
+            auto bound = compressBound(length);
+            auto buffer = std::make_unique<uint8_t[]>(bound);
+
+            uLongf dest_len = bound;
+            auto rv = compress2(buffer.get(), &dest_len, reinterpret_cast<const Bytef*>(data),
+                                length, Z_BEST_COMPRESSION);
+            if (rv != Z_OK) {
+                LOG(ERROR) << "compress2 returned: " << rv;
+                return {};
+            }
+            return std::basic_string<uint8_t>(buffer.get(), dest_len);
+        }
+        default:
+            LOG(ERROR) << "unhandled compression type: " << compression_;
+            break;
+    }
+    return {};
+}
+
+static void SHA256(const void* data, size_t length, uint8_t out[32]) {
+    SHA256_CTX c;
+    SHA256_Init(&c);
+    SHA256_Update(&c, data, length);
+    SHA256_Final(out, &c);
+}
+
+bool CowWriter::Finalize() {
+    auto offs = lseek(fd_.get(), 0, SEEK_CUR);
+    if (offs < 0) {
+        PLOG(ERROR) << "lseek failed";
+        return false;
+    }
+    header_.ops_offset = offs;
+    header_.ops_size = ops_.size();
+
+    SHA256(ops_.data(), ops_.size(), header_.ops_checksum);
+    SHA256(&header_, sizeof(header_), header_.header_checksum);
+
+    if (lseek(fd_.get(), 0, SEEK_SET) < 0) {
+        PLOG(ERROR) << "lseek start failed";
+        return false;
+    }
+    if (!android::base::WriteFully(fd_, &header_, sizeof(header_))) {
+        PLOG(ERROR) << "write header failed";
+        return false;
+    }
+    if (lseek(fd_.get(), header_.ops_offset, SEEK_SET) < 0) {
+        PLOG(ERROR) << "lseek ops failed";
+        return false;
+    }
+    if (!android::base::WriteFully(fd_, ops_.data(), ops_.size())) {
+        PLOG(ERROR) << "write ops failed";
+        return false;
+    }
+    return true;
+}
+
+bool CowWriter::GetDataPos(uint64_t* pos) {
+    off_t offs = lseek(fd_.get(), 0, SEEK_CUR);
+    if (offs < 0) {
+        PLOG(ERROR) << "lseek failed";
+        return false;
+    }
+    *pos = offs;
+    return true;
+}
+
+}  // namespace snapshot
+}  // namespace android
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/cow_format.h b/fs_mgr/libsnapshot/include/libsnapshot/cow_format.h
new file mode 100644
index 0000000..6d500e7
--- /dev/null
+++ b/fs_mgr/libsnapshot/include/libsnapshot/cow_format.h
@@ -0,0 +1,103 @@
+// Copyright (C) 2019 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#include <stdint.h>
+
+namespace android {
+namespace snapshot {
+
+static constexpr uint64_t kCowMagicNumber = 0x436f77634f572121ULL;
+static constexpr uint32_t kCowVersionMajor = 1;
+static constexpr uint32_t kCowVersionMinor = 0;
+
+// This header appears as the first sequence of bytes in the COW. All fields
+// in the layout are little-endian encoded. The on-disk layout is:
+//
+//      +-----------------------+
+//      |     Header (fixed)    |
+//      +-----------------------+
+//      |  Raw Data (variable)  |
+//      +-----------------------+
+//      | Operations (variable) |
+//      +-----------------------+
+//
+// The "raw data" occurs immediately after the header, and the operation
+// sequence occurs after the raw data. This ordering is intentional. While
+// streaming an OTA, we can immediately write compressed data, but store the
+// metadata in memory. At the end, we can simply append the metadata and flush
+// the file. There is no need to create separate files to store the metadata
+// and block data.
+struct CowHeader {
+    uint64_t magic;
+    uint16_t major_version;
+    uint16_t minor_version;
+
+    // Offset to the location of the operation sequence, and size of the
+    // operation sequence buffer. |ops_offset| is also the end of the
+    // raw data region.
+    uint64_t ops_offset;
+    uint64_t ops_size;
+    uint64_t num_ops;
+
+    // The size of block operations, in bytes.
+    uint32_t block_size;
+
+    // SHA256 checksums of this header, with this field set to 0.
+    uint8_t header_checksum[32];
+
+    // SHA256 of the operation sequence.
+    uint8_t ops_checksum[32];
+} __attribute__((packed));
+
+// Cow operations are currently fixed-size entries, but this may change if
+// needed.
+struct CowOperation {
+    // The operation code (see the constants and structures below).
+    uint8_t type;
+
+    // If this operation reads from the data section of the COW, this contains
+    // the compression type of that data (see constants below).
+    uint8_t compression;
+
+    // If this operation reads from the data section of the COW, this contains
+    // the length.
+    uint16_t data_length;
+
+    // The block of data in the new image that this operation modifies.
+    uint64_t new_block;
+
+    // The value of |source| depends on the operation code.
+    //
+    // For copy operations, this is a block location in the source image.
+    //
+    // For replace operations, this is a byte offset within the COW's data
+    // section (eg, not landing within the header or metadata). It is an
+    // absolute position within the image.
+    //
+    // For zero operations (replace with all zeroes), this is unused and must
+    // be zero.
+    uint64_t source;
+} __attribute__((packed));
+
+static constexpr uint8_t kCowCopyOp = 1;
+static constexpr uint8_t kCowReplaceOp = 2;
+static constexpr uint8_t kCowZeroOp = 3;
+
+static constexpr uint8_t kCowCompressNone = 0;
+static constexpr uint8_t kCowCompressGz = 1;
+
+}  // namespace snapshot
+}  // namespace android
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/cow_reader.h b/fs_mgr/libsnapshot/include/libsnapshot/cow_reader.h
new file mode 100644
index 0000000..a3b1291
--- /dev/null
+++ b/fs_mgr/libsnapshot/include/libsnapshot/cow_reader.h
@@ -0,0 +1,107 @@
+// Copyright (C) 2019 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#include <stdint.h>
+
+#include <functional>
+#include <memory>
+
+#include <android-base/unique_fd.h>
+#include <libsnapshot/cow_format.h>
+
+namespace android {
+namespace snapshot {
+
+class ICowOpIter;
+
+// A ByteSink object handles requests for a buffer of a specific size. It
+// always owns the underlying buffer. It's designed to minimize potential
+// copying as we parse or decompress the COW.
+class IByteSink {
+  public:
+    virtual ~IByteSink() {}
+
+    // Called when the reader has data. The size of the request is given. The
+    // sink must return a valid pointer (or null on failure), and return the
+    // maximum number of bytes that can be written to the returned buffer.
+    //
+    // The returned buffer is owned by IByteSink, but must remain valid until
+    // the ready operation has completed (or the entire buffer has been
+    // covered by calls to ReturnData).
+    //
+    // After calling GetBuffer(), all previous buffers returned are no longer
+    // valid.
+    virtual void* GetBuffer(size_t requested, size_t* actual) = 0;
+
+    // Called when a section returned by |GetBuffer| has been filled with data.
+    virtual bool ReturnData(void* buffer, size_t length) = 0;
+};
+
+// Interface for reading from a snapuserd COW.
+class ICowReader {
+  public:
+    virtual ~ICowReader() {}
+
+    // Return the file header.
+    virtual bool GetHeader(CowHeader* header) = 0;
+
+    // Return an iterator for retrieving CowOperation entries.
+    virtual std::unique_ptr<ICowOpIter> GetOpIter() = 0;
+
+    // Get raw bytes from the data section.
+    virtual bool GetRawBytes(uint64_t offset, void* buffer, size_t len) = 0;
+
+    // Get decoded bytes from the data section, handling any decompression.
+    // All retrieved data is passed to the sink.
+    virtual bool ReadData(const CowOperation& op, IByteSink* sink) = 0;
+};
+
+// Iterate over a sequence of COW operations.
+class ICowOpIter {
+  public:
+    virtual ~ICowOpIter() {}
+
+    // True if there are more items to read, false otherwise.
+    virtual bool Done() = 0;
+
+    // Read the current operation.
+    virtual const CowOperation& Get() = 0;
+
+    // Advance to the next item.
+    virtual void Next() = 0;
+};
+
+class CowReader : public ICowReader {
+  public:
+    CowReader();
+
+    bool Parse(android::base::unique_fd&& fd);
+    bool Parse(android::base::borrowed_fd fd);
+
+    bool GetHeader(CowHeader* header) override;
+    std::unique_ptr<ICowOpIter> GetOpIter() override;
+    bool GetRawBytes(uint64_t offset, void* buffer, size_t len) override;
+    bool ReadData(const CowOperation& op, IByteSink* sink) override;
+
+  private:
+    android::base::unique_fd owned_fd_;
+    android::base::borrowed_fd fd_;
+    CowHeader header_;
+    uint64_t fd_size_;
+};
+
+}  // namespace snapshot
+}  // namespace android
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h b/fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h
new file mode 100644
index 0000000..5a2cbd6
--- /dev/null
+++ b/fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h
@@ -0,0 +1,86 @@
+// Copyright (C) 2019 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#include <stdint.h>
+
+#include <string>
+
+#include <android-base/unique_fd.h>
+#include <libsnapshot/cow_format.h>
+
+namespace android {
+namespace snapshot {
+
+struct CowOptions {
+    uint32_t block_size = 4096;
+    std::string compression;
+};
+
+// Interface for writing to a snapuserd COW. All operations are ordered; merges
+// will occur in the sequence they were added to the COW.
+class ICowWriter {
+  public:
+    explicit ICowWriter(const CowOptions& options) : options_(options) {}
+
+    virtual ~ICowWriter() {}
+
+    // Encode an operation that copies the contents of |old_block| to the
+    // location of |new_block|.
+    virtual bool AddCopy(uint64_t new_block, uint64_t old_block) = 0;
+
+    // Encode a sequence of raw blocks. |size| must be a multiple of the block size.
+    virtual bool AddRawBlocks(uint64_t new_block_start, const void* data, size_t size) = 0;
+
+    // Encode a sequence of zeroed blocks. |size| must be a multiple of the block size.
+    virtual bool AddZeroBlocks(uint64_t new_block_start, uint64_t num_blocks) = 0;
+
+  protected:
+    CowOptions options_;
+};
+
+class CowWriter : public ICowWriter {
+  public:
+    explicit CowWriter(const CowOptions& options);
+
+    // Set up the writer.
+    bool Initialize(android::base::unique_fd&& fd);
+    bool Initialize(android::base::borrowed_fd fd);
+
+    bool AddCopy(uint64_t new_block, uint64_t old_block) override;
+    bool AddRawBlocks(uint64_t new_block_start, const void* data, size_t size) override;
+    bool AddZeroBlocks(uint64_t new_block_start, uint64_t num_blocks) override;
+
+    // Finalize all COW operations and flush pending writes.
+    bool Finalize();
+
+  private:
+    void SetupHeaders();
+    bool GetDataPos(uint64_t* pos);
+    std::basic_string<uint8_t> Compress(const void* data, size_t length);
+
+  private:
+    android::base::unique_fd owned_fd_;
+    android::base::borrowed_fd fd_;
+    CowHeader header_;
+    int compression_ = 0;
+
+    // :TODO: this is not efficient, but stringstream ubsan aborts because some
+    // bytes overflow a signed char.
+    std::basic_string<uint8_t> ops_;
+};
+
+}  // namespace snapshot
+}  // namespace android
diff --git a/init/Android.mk b/init/Android.mk
index 2fbbf4a..da94daf 100644
--- a/init/Android.mk
+++ b/init/Android.mk
@@ -119,13 +119,6 @@
 # First stage init is weird: it may start without stdout/stderr, and no /proc.
 LOCAL_NOSANITIZE := hwaddress
 include $(BUILD_EXECUTABLE)
-
-# LOCAL_FORCE_STATIC_EXECUTABLE targets are skipped and not defined for ASAN builds
-init_vendor_deps :=
-ifneq (true,$(my_skip_this_target))
-  init_vendor_deps += init_first_stage
-endif # my_skip_this_target is true
-
 endif
 
 include $(CLEAR_VARS)
@@ -140,7 +133,8 @@
 
 LOCAL_MODULE := init_vendor
 ifneq ($(BOARD_BUILD_SYSTEM_ROOT_IMAGE),true)
-LOCAL_REQUIRED_MODULES := $(init_vendor_deps)
+LOCAL_REQUIRED_MODULES := \
+   init_first_stage \
+
 endif
 include $(BUILD_PHONY_PACKAGE)
-init_vendor_deps :=
diff --git a/init/builtins.cpp b/init/builtins.cpp
index 0b456e7..f5de1ad 100644
--- a/init/builtins.cpp
+++ b/init/builtins.cpp
@@ -570,7 +570,6 @@
             trigger_shutdown("reboot,requested-userdata-remount-on-fde-device");
         }
         SetProperty("ro.crypto.state", "encrypted");
-        SetProperty("ro.crypto.type", "block");
         ActionManager::GetInstance().QueueEventTrigger("defaultcrypto");
         return {};
     } else if (code == FS_MGR_MNTALL_DEV_NOT_ENCRYPTED) {
@@ -595,7 +594,6 @@
             return Error() << "FscryptInstallKeyring() failed";
         }
         SetProperty("ro.crypto.state", "encrypted");
-        SetProperty("ro.crypto.type", "file");
 
         // Although encrypted, we have device key, so we do not need to
         // do anything different from the nonencrypted case.
@@ -606,7 +604,6 @@
             return Error() << "FscryptInstallKeyring() failed";
         }
         SetProperty("ro.crypto.state", "encrypted");
-        SetProperty("ro.crypto.type", "file");
 
         // Although encrypted, vold has already set the device up, so we do not need to
         // do anything different from the nonencrypted case.
@@ -617,7 +614,6 @@
             return Error() << "FscryptInstallKeyring() failed";
         }
         SetProperty("ro.crypto.state", "encrypted");
-        SetProperty("ro.crypto.type", "file");
 
         // Although encrypted, vold has already set the device up, so we do not need to
         // do anything different from the nonencrypted case.
diff --git a/liblog/event_tag_map.cpp b/liblog/event_tag_map.cpp
index 2c0156e..85556e8 100644
--- a/liblog/event_tag_map.cpp
+++ b/liblog/event_tag_map.cpp
@@ -31,84 +31,13 @@
 #include <unordered_map>
 
 #include <log/event_tag_map.h>
-#include <log/log_properties.h>
 #include <private/android_logger.h>
 #include <utils/FastStrcmp.h>
 #include <utils/RWLock.h>
 
-#include "logd_reader.h"
-
 #define OUT_TAG "EventTagMap"
 
-class MapString {
- private:
-  const std::string* alloc;                  // HAS-AN
-  const std::string_view str;                // HAS-A
-
- public:
-  operator const std::string_view() const {
-    return str;
-  }
-
-  const char* data() const {
-    return str.data();
-  }
-  size_t length() const {
-    return str.length();
-  }
-
-  bool operator==(const MapString& rval) const {
-    if (length() != rval.length()) return false;
-    if (length() == 0) return true;
-    return fastcmp<strncmp>(data(), rval.data(), length()) == 0;
-  }
-  bool operator!=(const MapString& rval) const {
-    return !(*this == rval);
-  }
-
-  MapString(const char* str, size_t len) : alloc(NULL), str(str, len) {
-  }
-  explicit MapString(const std::string& str)
-      : alloc(new std::string(str)), str(alloc->data(), alloc->length()) {
-  }
-  MapString(MapString&& rval) noexcept
-      : alloc(rval.alloc), str(rval.data(), rval.length()) {
-    rval.alloc = NULL;
-  }
-  explicit MapString(const MapString& rval)
-      : alloc(rval.alloc ? new std::string(*rval.alloc) : NULL),
-        str(alloc ? alloc->data() : rval.data(), rval.length()) {
-  }
-
-  ~MapString() {
-    if (alloc) delete alloc;
-  }
-};
-
-// Hash for MapString
-template <>
-struct std::hash<MapString>
-    : public std::unary_function<const MapString&, size_t> {
-  size_t operator()(const MapString& __t) const noexcept {
-    if (!__t.length()) return 0;
-    return std::hash<std::string_view>()(std::string_view(__t));
-  }
-};
-
-typedef std::pair<MapString, MapString> TagFmt;
-
-template <>
-struct std::hash<TagFmt> : public std::unary_function<const TagFmt&, size_t> {
-  size_t operator()(const TagFmt& __t) const noexcept {
-    // Tag is typically unique.  Will cost us an extra 100ns for the
-    // unordered_map lookup if we instead did a hash that combined
-    // both of tag and fmt members, e.g.:
-    //
-    // return std::hash<MapString>()(__t.first) ^
-    //        std::hash<MapString>()(__t.second);
-    return std::hash<MapString>()(__t.first);
-  }
-};
+typedef std::pair<std::string_view, std::string_view> TagFmt;
 
 // Map
 struct EventTagMap {
@@ -119,8 +48,7 @@
 
  private:
   std::unordered_map<uint32_t, TagFmt> Idx2TagFmt;
-  std::unordered_map<TagFmt, uint32_t> TagFmt2Idx;
-  std::unordered_map<MapString, uint32_t> Tag2Idx;
+  std::unordered_map<std::string_view, uint32_t> Tag2Idx;
   // protect unordered sets
   android::RWLock rwlock;
 
@@ -132,7 +60,6 @@
 
   ~EventTagMap() {
     Idx2TagFmt.clear();
-    TagFmt2Idx.clear();
     Tag2Idx.clear();
     for (size_t which = 0; which < NUM_MAPS; ++which) {
       if (mapAddr[which]) {
@@ -144,8 +71,7 @@
 
   bool emplaceUnique(uint32_t tag, const TagFmt& tagfmt, bool verbose = false);
   const TagFmt* find(uint32_t tag) const;
-  int find(TagFmt&& tagfmt) const;
-  int find(MapString&& tag) const;
+  int find(std::string_view tag) const;
 };
 
 bool EventTagMap::emplaceUnique(uint32_t tag, const TagFmt& tagfmt,
@@ -156,8 +82,7 @@
               ":%.*s:%.*s)\n";
   android::RWLock::AutoWLock writeLock(rwlock);
   {
-    std::unordered_map<uint32_t, TagFmt>::const_iterator it;
-    it = Idx2TagFmt.find(tag);
+    auto it = Idx2TagFmt.find(tag);
     if (it != Idx2TagFmt.end()) {
       if (verbose) {
         fprintf(stderr, errorFormat, it->first, (int)it->second.first.length(),
@@ -173,25 +98,7 @@
   }
 
   {
-    std::unordered_map<TagFmt, uint32_t>::const_iterator it;
-    it = TagFmt2Idx.find(tagfmt);
-    if (it != TagFmt2Idx.end()) {
-      if (verbose) {
-        fprintf(stderr, errorFormat, it->second, (int)it->first.first.length(),
-                it->first.first.data(), (int)it->first.second.length(),
-                it->first.second.data(), tag, (int)tagfmt.first.length(),
-                tagfmt.first.data(), (int)tagfmt.second.length(),
-                tagfmt.second.data());
-      }
-      ret = false;
-    } else {
-      TagFmt2Idx.emplace(std::make_pair(tagfmt, tag));
-    }
-  }
-
-  {
-    std::unordered_map<MapString, uint32_t>::const_iterator it;
-    it = Tag2Idx.find(tagfmt.first);
+    auto it = Tag2Idx.find(tagfmt.first);
     if (!tagfmt.second.length() && (it != Tag2Idx.end())) {
       Tag2Idx.erase(it);
       it = Tag2Idx.end();
@@ -205,25 +112,15 @@
 }
 
 const TagFmt* EventTagMap::find(uint32_t tag) const {
-  std::unordered_map<uint32_t, TagFmt>::const_iterator it;
   android::RWLock::AutoRLock readLock(const_cast<android::RWLock&>(rwlock));
-  it = Idx2TagFmt.find(tag);
+  auto it = Idx2TagFmt.find(tag);
   if (it == Idx2TagFmt.end()) return NULL;
   return &(it->second);
 }
 
-int EventTagMap::find(TagFmt&& tagfmt) const {
-  std::unordered_map<TagFmt, uint32_t>::const_iterator it;
+int EventTagMap::find(std::string_view tag) const {
   android::RWLock::AutoRLock readLock(const_cast<android::RWLock&>(rwlock));
-  it = TagFmt2Idx.find(std::move(tagfmt));
-  if (it == TagFmt2Idx.end()) return -1;
-  return it->second;
-}
-
-int EventTagMap::find(MapString&& tag) const {
-  std::unordered_map<MapString, uint32_t>::const_iterator it;
-  android::RWLock::AutoRLock readLock(const_cast<android::RWLock&>(rwlock));
-  it = Tag2Idx.find(std::move(tag));
+  auto it = Tag2Idx.find(std::move(tag));
   if (it == Tag2Idx.end()) return -1;
   return it->second;
 }
@@ -241,29 +138,20 @@
 // successful return, it will be pointing to the last character in the
 // tag line (i.e. the character before the start of the next line).
 //
-// lineNum = 0 removes verbose comments and requires us to cache the
-// content rather than make direct raw references since the content
-// will disappear after the call. A non-zero lineNum means we own the
-// data and it will outlive the call.
-//
 // Returns 0 on success, nonzero on failure.
-static int scanTagLine(EventTagMap* map, const char*& pData, int lineNum) {
+static int scanTagLine(EventTagMap* map, const char*& pData, int line_num) {
   char* ep;
   unsigned long val = strtoul(pData, &ep, 10);
   const char* cp = ep;
   if (cp == pData) {
-    if (lineNum) {
-      fprintf(stderr, OUT_TAG ": malformed tag number on line %d\n", lineNum);
-    }
+    fprintf(stderr, OUT_TAG ": malformed tag number on line %d\n", line_num);
     errno = EINVAL;
     return -1;
   }
 
   uint32_t tagIndex = val;
   if (tagIndex != val) {
-    if (lineNum) {
-      fprintf(stderr, OUT_TAG ": tag number too large on line %d\n", lineNum);
-    }
+    fprintf(stderr, OUT_TAG ": tag number too large on line %d\n", line_num);
     errno = ERANGE;
     return -1;
   }
@@ -272,9 +160,7 @@
   }
 
   if (*cp == '\n') {
-    if (lineNum) {
-      fprintf(stderr, OUT_TAG ": missing tag string on line %d\n", lineNum);
-    }
+    fprintf(stderr, OUT_TAG ": missing tag string on line %d\n", line_num);
     errno = EINVAL;
     return -1;
   }
@@ -284,10 +170,7 @@
   size_t tagLen = cp - tag;
 
   if (!isspace(*cp)) {
-    if (lineNum) {
-      fprintf(stderr, OUT_TAG ": invalid tag char %c on line %d\n", *cp,
-              lineNum);
-    }
+    fprintf(stderr, OUT_TAG ": invalid tag char %c on line %d\n", *cp, line_num);
     errno = EINVAL;
     return -1;
   }
@@ -317,25 +200,15 @@
 
   while (*cp && (*cp != '\n')) ++cp;
 #ifdef DEBUG
-  fprintf(stderr, "%d: %p: %.*s\n", lineNum, tag, (int)(cp - pData), pData);
+  fprintf(stderr, "%d: %p: %.*s\n", line_num, tag, (int)(cp - pData), pData);
 #endif
   pData = cp;
 
-  if (lineNum) {
-    if (map->emplaceUnique(tagIndex,
-                           TagFmt(std::make_pair(MapString(tag, tagLen),
-                                                 MapString(fmt, fmtLen))),
-                           verbose)) {
-      return 0;
-    }
-  } else {
-    // cache
-    if (map->emplaceUnique(
-            tagIndex,
-            TagFmt(std::make_pair(MapString(std::string(tag, tagLen)),
-                                  MapString(std::string(fmt, fmtLen)))))) {
-      return 0;
-    }
+  if (map->emplaceUnique(
+          tagIndex,
+          TagFmt(std::make_pair(std::string_view(tag, tagLen), std::string_view(fmt, fmtLen))),
+          verbose)) {
+    return 0;
   }
   errno = EMLINK;
   return -1;
@@ -491,57 +364,10 @@
   if (map) delete map;
 }
 
-// Cache miss, go to logd to acquire a public reference.
-// Because we lack access to a SHARED PUBLIC /dev/event-log-tags file map?
-static const TagFmt* __getEventTag([[maybe_unused]] EventTagMap* map, unsigned int tag) {
-  // call event tag service to arrange for a new tag
-  char* buf = NULL;
-  // Can not use android::base::StringPrintf, asprintf + free instead.
-  static const char command_template[] = "getEventTag id=%u";
-  int ret = asprintf(&buf, command_template, tag);
-  if (ret > 0) {
-    // Add some buffer margin for an estimate of the full return content.
-    size_t size =
-        ret - strlen(command_template) +
-        strlen("65535\n4294967295\t?\t\t\t?\t# uid=32767\n\n\f?success?");
-    if (size > (size_t)ret) {
-      char* np = static_cast<char*>(realloc(buf, size));
-      if (np) {
-        buf = np;
-      } else {
-        size = ret;
-      }
-    } else {
-      size = ret;
-    }
-#ifdef __ANDROID__
-    // Ask event log tag service for an existing entry
-    if (SendLogdControlMessage(buf, size) >= 0) {
-      buf[size - 1] = '\0';
-      char* ep;
-      unsigned long val = strtoul(buf, &ep, 10);  // return size
-      const char* cp = ep;
-      if ((buf != cp) && (val > 0) && (*cp == '\n')) {  // truncation OK
-        ++cp;
-        if (!scanTagLine(map, cp, 0)) {
-          free(buf);
-          return map->find(tag);
-        }
-      }
-    }
-#endif
-    free(buf);
-  }
-  return NULL;
-}
-
 // Look up an entry in the map.
 const char* android_lookupEventTag_len(const EventTagMap* map, size_t* len, unsigned int tag) {
   if (len) *len = 0;
   const TagFmt* str = map->find(tag);
-  if (!str) {
-    str = __getEventTag(const_cast<EventTagMap*>(map), tag);
-  }
   if (!str) return NULL;
   if (len) *len = str->first.length();
   return str->first.data();
@@ -551,83 +377,8 @@
 const char* android_lookupEventFormat_len(const EventTagMap* map, size_t* len, unsigned int tag) {
   if (len) *len = 0;
   const TagFmt* str = map->find(tag);
-  if (!str) {
-    str = __getEventTag(const_cast<EventTagMap*>(map), tag);
-  }
   if (!str) return NULL;
   if (len) *len = str->second.length();
   return str->second.data();
 }
 
-// Look up tagname, generate one if necessary, and return a tag
-int android_lookupEventTagNum(EventTagMap* map, const char* tagname, const char* format, int prio) {
-  const char* ep = endOfTag(tagname);
-  size_t len = ep - tagname;
-  if (!len || *ep) {
-    errno = EINVAL;
-    return -1;
-  }
-
-  if ((prio != ANDROID_LOG_UNKNOWN) && (prio < ANDROID_LOG_SILENT) &&
-      !__android_log_is_loggable_len(prio, tagname, len,
-                                     __android_log_is_debuggable()
-                                         ? ANDROID_LOG_VERBOSE
-                                         : ANDROID_LOG_DEBUG)) {
-    errno = EPERM;
-    return -1;
-  }
-
-  if (!format) format = "";
-  ssize_t fmtLen = strlen(format);
-  int ret = map->find(TagFmt(
-      std::make_pair(MapString(tagname, len), MapString(format, fmtLen))));
-  if (ret != -1) return ret;
-
-  // call event tag service to arrange for a new tag
-  char* buf = NULL;
-  // Can not use android::base::StringPrintf, asprintf + free instead.
-  static const char command_template[] = "getEventTag name=%s format=\"%s\"";
-  ret = asprintf(&buf, command_template, tagname, format);
-  if (ret > 0) {
-    // Add some buffer margin for an estimate of the full return content.
-    char* cp;
-    size_t size =
-        ret - strlen(command_template) +
-        strlen("65535\n4294967295\t?\t\t\t?\t# uid=32767\n\n\f?success?");
-    if (size > (size_t)ret) {
-      cp = static_cast<char*>(realloc(buf, size));
-      if (cp) {
-        buf = cp;
-      } else {
-        size = ret;
-      }
-    } else {
-      size = ret;
-    }
-#ifdef __ANDROID__
-    // Ask event log tag service for an allocation
-    if (SendLogdControlMessage(buf, size) >= 0) {
-      buf[size - 1] = '\0';
-      unsigned long val = strtoul(buf, &cp, 10);        // return size
-      if ((buf != cp) && (val > 0) && (*cp == '\n')) {  // truncation OK
-        val = strtoul(cp + 1, &cp, 10);                 // allocated tag number
-        if ((val > 0) && (val < UINT32_MAX) && (*cp == '\t')) {
-          free(buf);
-          ret = val;
-          // cache
-          map->emplaceUnique(ret, TagFmt(std::make_pair(
-                                      MapString(std::string(tagname, len)),
-                                      MapString(std::string(format, fmtLen)))));
-          return ret;
-        }
-      }
-    }
-#endif
-    free(buf);
-  }
-
-  // Hail Mary
-  ret = map->find(MapString(tagname, len));
-  if (ret == -1) errno = ESRCH;
-  return ret;
-}
diff --git a/liblog/include/log/event_tag_map.h b/liblog/include/log/event_tag_map.h
index 4d0ebf9..de49fbf 100644
--- a/liblog/include/log/event_tag_map.h
+++ b/liblog/include/log/event_tag_map.h
@@ -53,12 +53,6 @@
 const char* android_lookupEventFormat_len(const EventTagMap* map, size_t* len,
                                           unsigned int tag);
 
-/*
- * Look up tagname, generate one if necessary, and return a tag
- */
-int android_lookupEventTagNum(EventTagMap* map, const char* tagname,
-                              const char* format, int prio);
-
 #ifdef __cplusplus
 }
 #endif
diff --git a/liblog/liblog.map.txt b/liblog/liblog.map.txt
index 8beb679..f8d5ef0 100644
--- a/liblog/liblog.map.txt
+++ b/liblog/liblog.map.txt
@@ -89,6 +89,5 @@
     android_log_processLogBuffer;
     android_log_read_next;
     android_log_write_list_buffer;
-    android_lookupEventTagNum;
     create_android_log_parser;
 };
diff --git a/liblog/tests/liblog_benchmark.cpp b/liblog/tests/liblog_benchmark.cpp
index 3bd5cf2..d2f12d6 100644
--- a/liblog/tests/liblog_benchmark.cpp
+++ b/liblog/tests/liblog_benchmark.cpp
@@ -879,30 +879,6 @@
 }
 BENCHMARK(BM_lookupEventFormat);
 
-/*
- *	Measure the time it takes for android_lookupEventTagNum plus above
- */
-static void BM_lookupEventTagNum(benchmark::State& state) {
-  prechargeEventMap();
-
-  std::unordered_set<uint32_t>::const_iterator it = set.begin();
-
-  while (state.KeepRunning()) {
-    size_t len;
-    const char* name = android_lookupEventTag_len(map, &len, (*it));
-    std::string Name(name, len);
-    const char* format = android_lookupEventFormat_len(map, &len, (*it));
-    std::string Format(format, len);
-    state.ResumeTiming();
-    android_lookupEventTagNum(map, Name.c_str(), Format.c_str(),
-                              ANDROID_LOG_UNKNOWN);
-    state.PauseTiming();
-    ++it;
-    if (it == set.end()) it = set.begin();
-  }
-}
-BENCHMARK(BM_lookupEventTagNum);
-
 // Must be functionally identical to liblog internal SendLogdControlMessage()
 static void send_to_control(char* buf, size_t len) {
   int sock =
diff --git a/liblog/tests/liblog_test.cpp b/liblog/tests/liblog_test.cpp
index fbc3d7a..c49d87b 100644
--- a/liblog/tests/liblog_test.cpp
+++ b/liblog/tests/liblog_test.cpp
@@ -2768,20 +2768,3 @@
 #endif
 }
 #endif  // ENABLE_FLAKY_TESTS
-
-TEST(liblog, android_lookupEventTagNum) {
-#ifdef __ANDROID__
-  EventTagMap* map = android_openEventTagMap(NULL);
-  EXPECT_TRUE(NULL != map);
-  std::string Name = android::base::StringPrintf("a%d", getpid());
-  int tag = android_lookupEventTagNum(map, Name.c_str(), "(new|1)",
-                                      ANDROID_LOG_UNKNOWN);
-  android_closeEventTagMap(map);
-  if (tag == -1) system("tail -3 /dev/event-log-tags >&2");
-  EXPECT_NE(-1, tag);
-  EXPECT_NE(0, tag);
-  EXPECT_GT(UINT32_MAX, (unsigned)tag);
-#else
-  GTEST_LOG_(INFO) << "This test does nothing.\n";
-#endif
-}
diff --git a/libutils/include/utils/Debug.h b/libutils/include/utils/Debug.h
index 96bd70e..c3b9026 100644
--- a/libutils/include/utils/Debug.h
+++ b/libutils/include/utils/Debug.h
@@ -14,27 +14,9 @@
  * limitations under the License.
  */
 
-#ifndef ANDROID_UTILS_DEBUG_H
-#define ANDROID_UTILS_DEBUG_H
+#pragma once
 
-#include <stdint.h>
-#include <sys/types.h>
+// Note: new code should use static_assert directly.
 
-namespace android {
-// ---------------------------------------------------------------------------
-
-#ifdef __cplusplus
-template<bool> struct CompileTimeAssert;
-template<> struct CompileTimeAssert<true> {};
-#define COMPILE_TIME_ASSERT(_exp) \
-    template class CompileTimeAssert< (_exp) >;
-#endif
-
-// DO NOT USE: Please use static_assert instead
-#define COMPILE_TIME_ASSERT_FUNCTION_SCOPE(_exp) \
-    CompileTimeAssert<( _exp )>();
-
-// ---------------------------------------------------------------------------
-}  // namespace android
-
-#endif // ANDROID_UTILS_DEBUG_H
+#define COMPILE_TIME_ASSERT static_assert
+#define COMPILE_TIME_ASSERT_FUNCTION_SCOPE static_assert
diff --git a/libutils/include/utils/Flattenable.h b/libutils/include/utils/Flattenable.h
index 17c5e10..8aa381a 100644
--- a/libutils/include/utils/Flattenable.h
+++ b/libutils/include/utils/Flattenable.h
@@ -14,8 +14,7 @@
  * limitations under the License.
  */
 
-#ifndef ANDROID_UTILS_FLATTENABLE_H
-#define ANDROID_UTILS_FLATTENABLE_H
+#pragma once
 
 // DO NOT USE: please use parcelable instead
 // This code is deprecated and will not be supported via AIDL code gen. For data
@@ -25,7 +24,6 @@
 #include <string.h>
 #include <sys/types.h>
 #include <utils/Errors.h>
-#include <utils/Debug.h>
 
 #include <type_traits>
 
@@ -217,5 +215,3 @@
 };
 
 }  // namespace android
-
-#endif /* ANDROID_UTILS_FLATTENABLE_H */
diff --git a/logcat/tests/logcat_test.cpp b/logcat/tests/logcat_test.cpp
index 61aa938..0860000 100644
--- a/logcat/tests/logcat_test.cpp
+++ b/logcat/tests/logcat_test.cpp
@@ -1654,48 +1654,6 @@
         EXPECT_GE(ret, 0);
         EXPECT_TRUE(End_to_End(sync.tagStr, ""));
     }
-
-    {
-        // Invent new entries because existing can not serve
-        EventTagMap* map = android_openEventTagMap(nullptr);
-        ASSERT_TRUE(nullptr != map);
-        static const char name[] = logcat_executable ".descriptive-monotonic";
-        int myTag = android_lookupEventTagNum(map, name, "(new|1|s)",
-                                              ANDROID_LOG_UNKNOWN);
-        android_closeEventTagMap(map);
-        ASSERT_NE(-1, myTag);
-
-        const struct tag sync = { (uint32_t)myTag, name };
-
-        {
-            android_log_event_list ctx(sync.tagNo);
-            ctx << (uint32_t)7;
-            for (ret = -EBUSY; ret == -EBUSY; rest()) ret = ctx.write();
-            EXPECT_GE(ret, 0);
-            EXPECT_TRUE(End_to_End(sync.tagStr, "new=7s"));
-        }
-        {
-            android_log_event_list ctx(sync.tagNo);
-            ctx << (uint32_t)62;
-            for (ret = -EBUSY; ret == -EBUSY; rest()) ret = ctx.write();
-            EXPECT_GE(ret, 0);
-            EXPECT_TRUE(End_to_End(sync.tagStr, "new=1:02"));
-        }
-        {
-            android_log_event_list ctx(sync.tagNo);
-            ctx << (uint32_t)3673;
-            for (ret = -EBUSY; ret == -EBUSY; rest()) ret = ctx.write();
-            EXPECT_GE(ret, 0);
-            EXPECT_TRUE(End_to_End(sync.tagStr, "new=1:01:13"));
-        }
-        {
-            android_log_event_list ctx(sync.tagNo);
-            ctx << (uint32_t)(86400 + 7200 + 180 + 58);
-            for (ret = -EBUSY; ret == -EBUSY; rest()) ret = ctx.write();
-            EXPECT_GE(ret, 0);
-            EXPECT_TRUE(End_to_End(sync.tagStr, "new=1d 2:03:58"));
-        }
-    }
 }
 
 static bool reportedSecurity(const char* command) {