diff --git a/cmds/idmap2/libidmap2/ResourceMapping.cpp b/cmds/idmap2/libidmap2/ResourceMapping.cpp
index bb31c11..b2300ce 100644
--- a/cmds/idmap2/libidmap2/ResourceMapping.cpp
+++ b/cmds/idmap2/libidmap2/ResourceMapping.cpp
@@ -89,7 +89,7 @@
     // If the overlay supplies a target overlayable name, the resource must belong to the
     // overlayable defined with the specified name to be overlaid.
     return Error(R"(<overlay> android:targetName "%s" does not match overlayable name "%s")",
-                 overlay_info.target_name.c_str(), (*overlayable_info)->name.c_str());
+                 overlay_info.target_name.c_str(), (*overlayable_info)->name.data());
   }
 
   // Enforce policy restrictions if the resource is declared as overlayable.
diff --git a/libs/androidfw/ApkAssets.cpp b/libs/androidfw/ApkAssets.cpp
old mode 100755
new mode 100644
index c0fa63a..15aaae2
--- a/libs/androidfw/ApkAssets.cpp
+++ b/libs/androidfw/ApkAssets.cpp
@@ -18,6 +18,7 @@
 
 #include "android-base/errors.h"
 #include "android-base/logging.h"
+#include "android-base/utf8.h"
 
 namespace android {
 
@@ -84,7 +85,7 @@
   }
 
   std::string overlay_path(loaded_idmap->OverlayApkPath());
-  auto fd = unique_fd(::open(overlay_path.c_str(), O_RDONLY|O_CLOEXEC));
+  auto fd = unique_fd(base::utf8::open(overlay_path.c_str(), O_RDONLY | O_CLOEXEC));
   std::unique_ptr<AssetsProvider> overlay_assets;
   if (IsFabricatedOverlay(fd)) {
     // Fabricated overlays do not contain resource definitions. All of the overlay resource values
@@ -92,7 +93,7 @@
     overlay_assets = EmptyAssetsProvider::Create(std::move(overlay_path));
   } else {
     // The overlay should be an APK.
-    overlay_assets = ZipAssetsProvider::Create(std::move(fd), std::move(overlay_path), flags);
+    overlay_assets = ZipAssetsProvider::Create(std::move(overlay_path), flags, std::move(fd));
   }
   if (overlay_assets == nullptr) {
     return {};
diff --git a/libs/androidfw/AssetManager2.cpp b/libs/androidfw/AssetManager2.cpp
index c3d153d..cc7e871 100644
--- a/libs/androidfw/AssetManager2.cpp
+++ b/libs/androidfw/AssetManager2.cpp
@@ -374,7 +374,7 @@
         const std::string name = ToFormattedResourceString(*res_name);
         output.append(base::StringPrintf(
             "resource='%s' overlayable='%s' actor='%s' policy='0x%08x'\n",
-            name.c_str(), info->name.c_str(), info->actor.c_str(), info->policy_flags));
+            name.c_str(), info->name.data(), info->actor.data(), info->policy_flags));
       }
     }
   }
@@ -1356,21 +1356,22 @@
 
 void AssetManager2::RebuildFilterList() {
   for (PackageGroup& group : package_groups_) {
-    for (ConfiguredPackage& impl : group.packages_) {
-      impl.filtered_configs_.clear();
-
+    for (ConfiguredPackage& package : group.packages_) {
+      package.filtered_configs_.forEachItem([](auto, auto& fcg) { fcg.type_entries.clear(); });
       // Create the filters here.
-      impl.loaded_package_->ForEachTypeSpec([&](const TypeSpec& type_spec, uint8_t type_id) {
+      package.loaded_package_->ForEachTypeSpec([&](const TypeSpec& type_spec, uint8_t type_id) {
         FilteredConfigGroup* group = nullptr;
         for (const auto& type_entry : type_spec.type_entries) {
           if (type_entry.config.match(configuration_)) {
             if (!group) {
-              group = &impl.filtered_configs_.editItemAt(type_id - 1);
+              group = &package.filtered_configs_.editItemAt(type_id - 1);
             }
             group->type_entries.push_back(&type_entry);
           }
         }
       });
+      package.filtered_configs_.trimBuckets(
+          [](const auto& fcg) { return fcg.type_entries.empty(); });
     }
   }
 }
@@ -1411,30 +1412,34 @@
 std::unique_ptr<Theme> AssetManager2::NewTheme() {
   constexpr size_t kInitialReserveSize = 32;
   auto theme = std::unique_ptr<Theme>(new Theme(this));
+  theme->keys_.reserve(kInitialReserveSize);
   theme->entries_.reserve(kInitialReserveSize);
   return theme;
 }
 
+void AssetManager2::ForEachPackage(base::function_ref<bool(const std::string&, uint8_t)> func,
+                                   package_property_t excluded_property_flags) const {
+  for (const PackageGroup& package_group : package_groups_) {
+    const auto loaded_package = package_group.packages_.front().loaded_package_;
+    if ((loaded_package->GetPropertyFlags() & excluded_property_flags) == 0U
+        && !func(loaded_package->GetPackageName(),
+                 package_group.dynamic_ref_table->mAssignedPackageId)) {
+      return;
+    }
+  }
+}
+
 Theme::Theme(AssetManager2* asset_manager) : asset_manager_(asset_manager) {
 }
 
 Theme::~Theme() = default;
 
 struct Theme::Entry {
-  uint32_t attr_res_id;
   ApkAssetsCookie cookie;
   uint32_t type_spec_flags;
   Res_value value;
 };
 
-namespace {
-struct ThemeEntryKeyComparer {
-  bool operator() (const Theme::Entry& entry, uint32_t attr_res_id) const noexcept {
-    return entry.attr_res_id < attr_res_id;
-  }
-};
-} // namespace
-
 base::expected<std::monostate, NullOrIOError> Theme::ApplyStyle(uint32_t resid, bool force) {
   ATRACE_NAME("Theme::ApplyStyle");
 
@@ -1463,18 +1468,20 @@
       continue;
     }
 
-    auto entry_it = std::lower_bound(entries_.begin(), entries_.end(), attr_res_id,
-                                     ThemeEntryKeyComparer{});
-    if (entry_it != entries_.end() && entry_it->attr_res_id == attr_res_id) {
+    const auto key_it = std::lower_bound(keys_.begin(), keys_.end(), attr_res_id);
+    const auto entry_it = entries_.begin() + (key_it - keys_.begin());
+    if (key_it != keys_.end() && *key_it == attr_res_id) {
       if (is_undefined) {
         // DATA_NULL_UNDEFINED clears the value of the attribute in the theme only when `force` is
-        /// true.
+        // true.
+        keys_.erase(key_it);
         entries_.erase(entry_it);
       } else if (force) {
-        *entry_it = Entry{attr_res_id, it->cookie, (*bag)->type_spec_flags, it->value};
+        *entry_it = Entry{it->cookie, (*bag)->type_spec_flags, it->value};
       }
     } else {
-      entries_.insert(entry_it, Entry{attr_res_id, it->cookie, (*bag)->type_spec_flags, it->value});
+      keys_.insert(key_it, attr_res_id);
+      entries_.insert(entry_it, Entry{it->cookie, (*bag)->type_spec_flags, it->value});
     }
   }
   return {};
@@ -1485,6 +1492,7 @@
   ATRACE_NAME("Theme::Rebase");
   // Reset the entries without changing the vector capacity to prevent reallocations during
   // ApplyStyle.
+  keys_.clear();
   entries_.clear();
   asset_manager_ = am;
   for (size_t i = 0; i < style_count; i++) {
@@ -1493,16 +1501,14 @@
 }
 
 std::optional<AssetManager2::SelectedValue> Theme::GetAttribute(uint32_t resid) const {
-
   constexpr const uint32_t kMaxIterations = 20;
   uint32_t type_spec_flags = 0u;
   for (uint32_t i = 0; i <= kMaxIterations; i++) {
-    auto entry_it = std::lower_bound(entries_.begin(), entries_.end(), resid,
-                                     ThemeEntryKeyComparer{});
-    if (entry_it == entries_.end() || entry_it->attr_res_id != resid) {
+    const auto key_it = std::lower_bound(keys_.begin(), keys_.end(), resid);
+    if (key_it == keys_.end() || *key_it != resid) {
       return std::nullopt;
     }
-
+    const auto entry_it = entries_.begin() + (key_it - keys_.begin());
     type_spec_flags |= entry_it->type_spec_flags;
     if (entry_it->value.dataType == Res_value::TYPE_ATTRIBUTE) {
       resid = entry_it->value.data;
@@ -1536,6 +1542,7 @@
 }
 
 void Theme::Clear() {
+  keys_.clear();
   entries_.clear();
 }
 
@@ -1547,11 +1554,12 @@
   type_spec_flags_ = source.type_spec_flags_;
 
   if (asset_manager_ == source.asset_manager_) {
+    keys_ = source.keys_;
     entries_ = source.entries_;
   } else {
-    std::map<ApkAssetsCookie, ApkAssetsCookie> src_to_dest_asset_cookies;
-    typedef std::map<int, int> SourceToDestinationRuntimePackageMap;
-    std::map<ApkAssetsCookie, SourceToDestinationRuntimePackageMap> src_asset_cookie_id_map;
+    std::unordered_map<ApkAssetsCookie, ApkAssetsCookie> src_to_dest_asset_cookies;
+    using SourceToDestinationRuntimePackageMap = std::unordered_map<int, int>;
+    std::unordered_map<ApkAssetsCookie, SourceToDestinationRuntimePackageMap> src_asset_cookie_id_map;
 
     // Determine which ApkAssets are loaded in both theme AssetManagers.
     const auto src_assets = source.asset_manager_->GetApkAssets();
@@ -1579,15 +1587,17 @@
         }
 
         src_to_dest_asset_cookies.insert(std::make_pair(i, j));
-        src_asset_cookie_id_map.insert(std::make_pair(i, package_map));
+        src_asset_cookie_id_map.insert(std::make_pair(i, std::move(package_map)));
         break;
       }
     }
 
     // Reset the data in the destination theme.
+    keys_.clear();
     entries_.clear();
 
-    for (const auto& entry : source.entries_) {
+    for (size_t i = 0, size = source.entries_.size(); i != size; ++i) {
+      const auto& entry = source.entries_[i];
       bool is_reference = (entry.value.dataType == Res_value::TYPE_ATTRIBUTE
                            || entry.value.dataType == Res_value::TYPE_REFERENCE
                            || entry.value.dataType == Res_value::TYPE_DYNAMIC_ATTRIBUTE
@@ -1627,13 +1637,15 @@
         }
       }
 
+      const auto source_res_id = source.keys_[i];
+
       // The package id of the attribute needs to be rewritten to the package id of the
       // attribute in the destination.
-      int attribute_dest_package_id = get_package_id(entry.attr_res_id);
+      int attribute_dest_package_id = get_package_id(source_res_id);
       if (attribute_dest_package_id != 0x01) {
         // Find the cookie of the attribute resource id in the source AssetManager
         base::expected<FindEntryResult, NullOrIOError> attribute_entry_result =
-            source.asset_manager_->FindEntry(entry.attr_res_id, 0 /* density_override */ ,
+            source.asset_manager_->FindEntry(source_res_id, 0 /* density_override */ ,
                                              true /* stop_at_first_match */,
                                              true /* ignore_configuration */);
         if (UNLIKELY(IsIOError(attribute_entry_result))) {
@@ -1657,16 +1669,15 @@
         attribute_dest_package_id = attribute_dest_package->second;
       }
 
-      auto dest_attr_id = make_resid(attribute_dest_package_id, get_type_id(entry.attr_res_id),
-                                     get_entry_id(entry.attr_res_id));
-      Theme::Entry new_entry{dest_attr_id, data_dest_cookie, entry.type_spec_flags,
-                                            Res_value{.dataType = entry.value.dataType,
-                                                      .data = attribute_data}};
-
+      auto dest_attr_id = make_resid(attribute_dest_package_id, get_type_id(source_res_id),
+                                     get_entry_id(source_res_id));
+      const auto key_it = std::lower_bound(keys_.begin(), keys_.end(), dest_attr_id);
+      const auto entry_it = entries_.begin() + (key_it - keys_.begin());
       // Since the entries were cleared, the attribute resource id has yet been mapped to any value.
-      auto entry_it = std::lower_bound(entries_.begin(), entries_.end(), dest_attr_id,
-                                       ThemeEntryKeyComparer{});
-      entries_.insert(entry_it, new_entry);
+      keys_.insert(key_it, dest_attr_id);
+      entries_.insert(entry_it, Entry{data_dest_cookie, entry.type_spec_flags,
+                                      Res_value{.dataType = entry.value.dataType,
+                                                .data = attribute_data}});
     }
   }
   return {};
@@ -1674,9 +1685,11 @@
 
 void Theme::Dump() const {
   LOG(INFO) << base::StringPrintf("Theme(this=%p, AssetManager2=%p)", this, asset_manager_);
-  for (auto& entry : entries_) {
+  for (size_t i = 0, size = keys_.size(); i != size; ++i) {
+    auto res_id = keys_[i];
+    const auto& entry = entries_[i];
     LOG(INFO) << base::StringPrintf("  entry(0x%08x)=(0x%08x) type=(0x%02x), cookie(%d)",
-                                    entry.attr_res_id, entry.value.data, entry.value.dataType,
+                                    res_id, entry.value.data, entry.value.dataType,
                                     entry.cookie);
   }
 }
diff --git a/libs/androidfw/AssetsProvider.cpp b/libs/androidfw/AssetsProvider.cpp
index 80e5607..b9264c5 100644
--- a/libs/androidfw/AssetsProvider.cpp
+++ b/libs/androidfw/AssetsProvider.cpp
@@ -92,21 +92,27 @@
       last_mod_time_(last_mod_time) {}
 
 std::unique_ptr<ZipAssetsProvider> ZipAssetsProvider::Create(std::string path,
-                                                             package_property_t flags) {
+                                                             package_property_t flags,
+                                                             base::unique_fd fd) {
+  const auto released_fd = fd.ok() ? fd.release() : -1;
   ZipArchiveHandle handle;
-  if (int32_t result = OpenArchive(path.c_str(), &handle); result != 0) {
+  if (int32_t result = released_fd < 0 ? OpenArchive(path.c_str(), &handle)
+                                       : OpenArchiveFd(released_fd, path.c_str(), &handle)) {
     LOG(ERROR) << "Failed to open APK '" << path << "': " << ::ErrorCodeString(result);
     CloseArchive(handle);
     return {};
   }
 
   struct stat sb{.st_mtime = -1};
-  if (stat(path.c_str(), &sb) < 0) {
-    // Stat requires execute permissions on all directories path to the file. If the process does
-    // not have execute permissions on this file, allow the zip to be opened but IsUpToDate() will
-    // always have to return true.
-    LOG(WARNING) << "Failed to stat file '" << path << "': "
-                 << base::SystemErrorCodeToString(errno);
+  // Skip all up-to-date checks if the file won't ever change.
+  if (!isReadonlyFilesystem(path.c_str())) {
+    if ((released_fd < 0 ? stat(path.c_str(), &sb) : fstat(released_fd, &sb)) < 0) {
+      // Stat requires execute permissions on all directories path to the file. If the process does
+      // not have execute permissions on this file, allow the zip to be opened but IsUpToDate() will
+      // always have to return true.
+      LOG(WARNING) << "Failed to stat file '" << path << "': "
+                   << base::SystemErrorCodeToString(errno);
+    }
   }
 
   return std::unique_ptr<ZipAssetsProvider>(
@@ -133,12 +139,15 @@
   }
 
   struct stat sb{.st_mtime = -1};
-  if (fstat(released_fd, &sb) < 0) {
-    // Stat requires execute permissions on all directories path to the file. If the process does
-    // not have execute permissions on this file, allow the zip to be opened but IsUpToDate() will
-    // always have to return true.
-    LOG(WARNING) << "Failed to fstat file '" << friendly_name << "': "
-                 << base::SystemErrorCodeToString(errno);
+  // Skip all up-to-date checks if the file won't ever change.
+  if (!isReadonlyFilesystem(released_fd)) {
+    if (fstat(released_fd, &sb) < 0) {
+      // Stat requires execute permissions on all directories path to the file. If the process does
+      // not have execute permissions on this file, allow the zip to be opened but IsUpToDate() will
+      // always have to return true.
+      LOG(WARNING) << "Failed to fstat file '" << friendly_name
+                   << "': " << base::SystemErrorCodeToString(errno);
+    }
   }
 
   return std::unique_ptr<ZipAssetsProvider>(
@@ -275,6 +284,9 @@
 }
 
 bool ZipAssetsProvider::IsUpToDate() const {
+  if (last_mod_time_ == -1) {
+    return true;
+  }
   struct stat sb{};
   if (fstat(GetFileDescriptor(zip_handle_.get()), &sb) < 0) {
     // If fstat fails on the zip archive, return true so the zip archive the resource system does
@@ -288,7 +300,7 @@
     : dir_(std::forward<std::string>(path)), last_mod_time_(last_mod_time) {}
 
 std::unique_ptr<DirectoryAssetsProvider> DirectoryAssetsProvider::Create(std::string path) {
-  struct stat sb{};
+  struct stat sb;
   const int result = stat(path.c_str(), &sb);
   if (result == -1) {
     LOG(ERROR) << "Failed to find directory '" << path << "'.";
@@ -304,8 +316,9 @@
     path += OS_PATH_SEPARATOR;
   }
 
-  return std::unique_ptr<DirectoryAssetsProvider>(new DirectoryAssetsProvider(std::move(path),
-                                                                              sb.st_mtime));
+  const bool isReadonly = isReadonlyFilesystem(path.c_str());
+  return std::unique_ptr<DirectoryAssetsProvider>(
+      new DirectoryAssetsProvider(std::move(path), isReadonly ? -1 : sb.st_mtime));
 }
 
 std::unique_ptr<Asset> DirectoryAssetsProvider::OpenInternal(const std::string& path,
@@ -335,7 +348,10 @@
 }
 
 bool DirectoryAssetsProvider::IsUpToDate() const {
-  struct stat sb{};
+  if (last_mod_time_ == -1) {
+    return true;
+  }
+  struct stat sb;
   if (stat(dir_.c_str(), &sb) < 0) {
     // If stat fails on the zip archive, return true so the zip archive the resource system does
     // attempt to refresh the ApkAsset.
@@ -431,4 +447,4 @@
   return true;
 }
 
-} // namespace android
\ No newline at end of file
+} // namespace android
diff --git a/libs/androidfw/LoadedArsc.cpp b/libs/androidfw/LoadedArsc.cpp
index 386f718..c0fdfe2 100644
--- a/libs/androidfw/LoadedArsc.cpp
+++ b/libs/androidfw/LoadedArsc.cpp
@@ -645,16 +645,16 @@
         }
 
         std::string name;
-        util::ReadUtf16StringFromDevice(overlayable->name, arraysize(overlayable->name), &name);
+        util::ReadUtf16StringFromDevice(overlayable->name, std::size(overlayable->name), &name);
         std::string actor;
-        util::ReadUtf16StringFromDevice(overlayable->actor, arraysize(overlayable->actor), &actor);
-
-        if (loaded_package->overlayable_map_.find(name) !=
-            loaded_package->overlayable_map_.end()) {
-          LOG(ERROR) << "Multiple <overlayable> blocks with the same name '" << name << "'.";
+        util::ReadUtf16StringFromDevice(overlayable->actor, std::size(overlayable->actor), &actor);
+        auto [name_to_actor_it, inserted] =
+            loaded_package->overlayable_map_.emplace(std::move(name), std::move(actor));
+        if (!inserted) {
+          LOG(ERROR) << "Multiple <overlayable> blocks with the same name '"
+                     << name_to_actor_it->first << "'.";
           return {};
         }
-        loaded_package->overlayable_map_.emplace(name, actor);
 
         // Iterate over the overlayable policy chunks contained within the overlayable chunk data
         ChunkIterator overlayable_iter(child_chunk.data_ptr(), child_chunk.data_size());
@@ -669,7 +669,6 @@
                 LOG(ERROR) << "RES_TABLE_OVERLAYABLE_POLICY_TYPE too small.";
                 return {};
               }
-
               if ((overlayable_child_chunk.data_size() / sizeof(ResTable_ref))
                   < dtohl(policy_header->entry_count)) {
                 LOG(ERROR) <<  "RES_TABLE_OVERLAYABLE_POLICY_TYPE too small to hold entries.";
@@ -691,8 +690,8 @@
 
               // Add the pairing of overlayable properties and resource ids to the package
               OverlayableInfo overlayable_info {
-                .name = name,
-                .actor = actor,
+                .name = name_to_actor_it->first,
+                .actor = name_to_actor_it->second,
                 .policy_flags = policy_header->policy_flags
               };
               loaded_package->overlayable_infos_.emplace_back(std::move(overlayable_info), std::move(ids));
@@ -736,6 +735,7 @@
         const auto entry_end = entry_begin + dtohl(lib_alias->count);
         std::unordered_set<uint32_t> finalized_ids;
         finalized_ids.reserve(entry_end - entry_begin);
+        loaded_package->alias_id_map_.reserve(entry_end - entry_begin);
         for (auto entry_iter = entry_begin; entry_iter != entry_end; ++entry_iter) {
           if (!entry_iter) {
             LOG(ERROR) << "NULL ResTable_staged_alias_entry record??";
@@ -749,13 +749,20 @@
           }
 
           auto staged_id = dtohl(entry_iter->stagedResId);
-          auto [_, success] = loaded_package->alias_id_map_.emplace(staged_id, finalized_id);
-          if (!success) {
+          loaded_package->alias_id_map_.emplace_back(staged_id, finalized_id);
+        }
+
+        std::sort(loaded_package->alias_id_map_.begin(), loaded_package->alias_id_map_.end(),
+            [](auto&& l, auto&& r) { return l.first < r.first; });
+        const auto duplicate_it =
+            std::adjacent_find(loaded_package->alias_id_map_.begin(),
+                               loaded_package->alias_id_map_.end(),
+                               [](auto&& l, auto&& r) { return l.first == r.first; });
+          if (duplicate_it != loaded_package->alias_id_map_.end()) {
             LOG(ERROR) << StringPrintf("Repeated staged resource id '%08x' in staged aliases.",
-                                       staged_id);
+                                       duplicate_it->first);
             return {};
           }
-        }
       } break;
 
       default:
diff --git a/libs/androidfw/include/androidfw/AssetManager2.h b/libs/androidfw/include/androidfw/AssetManager2.h
index e9aaedc..e4d1218 100644
--- a/libs/androidfw/include/androidfw/AssetManager2.h
+++ b/libs/androidfw/include/androidfw/AssetManager2.h
@@ -17,6 +17,7 @@
 #ifndef ANDROIDFW_ASSETMANAGER2_H_
 #define ANDROIDFW_ASSETMANAGER2_H_
 
+#include "android-base/function_ref.h"
 #include "android-base/macros.h"
 
 #include <array>
@@ -320,17 +321,8 @@
   // Creates a new Theme from this AssetManager.
   std::unique_ptr<Theme> NewTheme();
 
-  void ForEachPackage(const std::function<bool(const std::string&, uint8_t)> func,
-                      package_property_t excluded_property_flags = 0U) const {
-    for (const PackageGroup& package_group : package_groups_) {
-      const auto loaded_package = package_group.packages_.front().loaded_package_;
-      if ((loaded_package->GetPropertyFlags() & excluded_property_flags) == 0U
-          && !func(loaded_package->GetPackageName(),
-                   package_group.dynamic_ref_table->mAssignedPackageId)) {
-        return;
-      }
-    }
-  }
+  void ForEachPackage(base::function_ref<bool(const std::string&, uint8_t)> func,
+                      package_property_t excluded_property_flags = 0U) const;
 
   void DumpToLog() const;
 
@@ -571,6 +563,7 @@
   AssetManager2* asset_manager_ = nullptr;
   uint32_t type_spec_flags_ = 0u;
 
+  std::vector<uint32_t> keys_;
   std::vector<Entry> entries_;
 };
 
diff --git a/libs/androidfw/include/androidfw/AssetsProvider.h b/libs/androidfw/include/androidfw/AssetsProvider.h
index af6e7f4..7891194 100644
--- a/libs/androidfw/include/androidfw/AssetsProvider.h
+++ b/libs/androidfw/include/androidfw/AssetsProvider.h
@@ -80,8 +80,8 @@
 
 // Supplies assets from a zip archive.
 struct ZipAssetsProvider : public AssetsProvider {
-  static std::unique_ptr<ZipAssetsProvider> Create(std::string path,
-                                                   package_property_t flags);
+  static std::unique_ptr<ZipAssetsProvider> Create(std::string path, package_property_t flags,
+                                                   base::unique_fd fd = {});
 
   static std::unique_ptr<ZipAssetsProvider> Create(base::unique_fd fd,
                                                    std::string friendly_name,
diff --git a/libs/androidfw/include/androidfw/ByteBucketArray.h b/libs/androidfw/include/androidfw/ByteBucketArray.h
index 05a2c4d..ca0a9ed 100644
--- a/libs/androidfw/include/androidfw/ByteBucketArray.h
+++ b/libs/androidfw/include/androidfw/ByteBucketArray.h
@@ -17,6 +17,7 @@
 #ifndef __BYTE_BUCKET_ARRAY_H
 #define __BYTE_BUCKET_ARRAY_H
 
+#include <algorithm>
 #include <cstdint>
 #include <cstring>
 
@@ -36,15 +37,11 @@
   }
 
   ~ByteBucketArray() {
-    clear();
+    deleteBuckets();
   }
 
   void clear() {
-    for (size_t i = 0; i < kNumBuckets; i++) {
-      if (buckets_[i] != NULL) {
-        delete[] buckets_[i];
-      }
-    }
+    deleteBuckets();
     memset(buckets_, 0, sizeof(buckets_));
   }
 
@@ -59,7 +56,7 @@
 
     uint8_t bucket_index = static_cast<uint8_t>(index) >> 4;
     T* bucket = buckets_[bucket_index];
-    if (bucket == NULL) {
+    if (bucket == nullptr) {
       return default_;
     }
     return bucket[0x0f & static_cast<uint8_t>(index)];
@@ -70,9 +67,9 @@
                           << ") with size=" << size();
 
     uint8_t bucket_index = static_cast<uint8_t>(index) >> 4;
-    T* bucket = buckets_[bucket_index];
-    if (bucket == NULL) {
-      bucket = buckets_[bucket_index] = new T[kBucketSize]();
+    T*& bucket = buckets_[bucket_index];
+    if (bucket == nullptr) {
+      bucket = new T[kBucketSize]();
     }
     return bucket[0x0f & static_cast<uint8_t>(index)];
   }
@@ -86,9 +83,42 @@
     return true;
   }
 
+  template <class Func>
+  void forEachItem(Func f) {
+    for (size_t i = 0; i < kNumBuckets; i++) {
+      const auto bucket = buckets_[i];
+      if (bucket != nullptr) {
+        for (size_t j = 0; j < kBucketSize; j++) {
+          f((i << 4) | j, bucket[j]);
+        }
+      }
+    }
+  }
+
+  template <class Func>
+  void trimBuckets(Func isEmptyFunc) {
+    for (size_t i = 0; i < kNumBuckets; i++) {
+      const auto bucket = buckets_[i];
+      if (bucket != nullptr) {
+        if (std::all_of(bucket, bucket + kBucketSize, isEmptyFunc)) {
+          delete[] bucket;
+          buckets_[i] = nullptr;
+        }
+      }
+    }
+  }
+
  private:
   enum { kNumBuckets = 16, kBucketSize = 16 };
 
+  void deleteBuckets() {
+    for (size_t i = 0; i < kNumBuckets; i++) {
+      if (buckets_[i] != nullptr) {
+        delete[] buckets_[i];
+      }
+    }
+  }
+
   T* buckets_[kNumBuckets];
   static inline const T default_ = {};
 };
diff --git a/libs/androidfw/include/androidfw/LoadedArsc.h b/libs/androidfw/include/androidfw/LoadedArsc.h
index 79d96282..4d12885 100644
--- a/libs/androidfw/include/androidfw/LoadedArsc.h
+++ b/libs/androidfw/include/androidfw/LoadedArsc.h
@@ -99,8 +99,8 @@
 };
 
 struct OverlayableInfo {
-  std::string name;
-  std::string actor;
+  std::string_view name;
+  std::string_view actor;
   uint32_t policy_flags;
 };
 
@@ -275,7 +275,7 @@
     return overlayable_map_;
   }
 
-  const std::map<uint32_t, uint32_t>& GetAliasResourceIdMap() const {
+  const std::vector<std::pair<uint32_t, uint32_t>>& GetAliasResourceIdMap() const {
     return alias_id_map_;
   }
 
@@ -295,8 +295,8 @@
   std::unordered_map<uint8_t, TypeSpec> type_specs_;
   ByteBucketArray<uint32_t> resource_ids_;
   std::vector<DynamicPackageEntry> dynamic_package_map_;
-  std::vector<const std::pair<OverlayableInfo, std::unordered_set<uint32_t>>> overlayable_infos_;
-  std::map<uint32_t, uint32_t> alias_id_map_;
+  std::vector<std::pair<OverlayableInfo, std::unordered_set<uint32_t>>> overlayable_infos_;
+  std::vector<std::pair<uint32_t, uint32_t>> alias_id_map_;
 
   // A map of overlayable name to actor
   std::unordered_map<std::string, std::string> overlayable_map_;
diff --git a/libs/androidfw/include/androidfw/misc.h b/libs/androidfw/include/androidfw/misc.h
index 5a5a0e2..d40d24e 100644
--- a/libs/androidfw/include/androidfw/misc.h
+++ b/libs/androidfw/include/androidfw/misc.h
@@ -44,6 +44,10 @@
 /* get the file's modification date; returns -1 w/errno set on failure */
 time_t getFileModDate(const char* fileName);
 
+// Check if |path| or |fd| resides on a readonly filesystem.
+bool isReadonlyFilesystem(const char* path);
+bool isReadonlyFilesystem(int fd);
+
 }; // namespace android
 
 #endif // _LIBS_ANDROID_FW_MISC_H
diff --git a/libs/androidfw/misc.cpp b/libs/androidfw/misc.cpp
index 5285420..7af5066 100644
--- a/libs/androidfw/misc.cpp
+++ b/libs/androidfw/misc.cpp
@@ -21,12 +21,17 @@
 //
 #include <androidfw/misc.h>
 
-#include <sys/stat.h>
-#include <cstring>
-#include <errno.h>
-#include <cstdio>
+#include "android-base/logging.h"
 
-using namespace android;
+#ifndef _WIN32
+#include <sys/statvfs.h>
+#include <sys/vfs.h>
+#endif  // _WIN32
+
+#include <cstring>
+#include <cstdio>
+#include <errno.h>
+#include <sys/stat.h>
 
 namespace android {
 
@@ -41,8 +46,7 @@
         if (errno == ENOENT || errno == ENOTDIR)
             return kFileTypeNonexistent;
         else {
-            fprintf(stderr, "getFileType got errno=%d on '%s'\n",
-                errno, fileName);
+            PLOG(ERROR) << "getFileType(): stat(" << fileName << ") failed";
             return kFileTypeUnknown;
         }
     } else {
@@ -82,4 +86,32 @@
     return sb.st_mtime;
 }
 
+#ifdef _WIN32
+// No need to implement these for Windows, the functions only matter on a device.
+bool isReadonlyFilesystem(const char*) {
+    return false;
+}
+bool isReadonlyFilesystem(int) {
+    return false;
+}
+#else   // _WIN32
+bool isReadonlyFilesystem(const char* path) {
+    struct statfs sfs;
+    if (::statfs(path, &sfs)) {
+        PLOG(ERROR) << "isReadonlyFilesystem(): statfs(" << path << ") failed";
+        return false;
+    }
+    return (sfs.f_flags & ST_RDONLY) != 0;
+}
+
+bool isReadonlyFilesystem(int fd) {
+    struct statfs sfs;
+    if (::fstatfs(fd, &sfs)) {
+        PLOG(ERROR) << "isReadonlyFilesystem(): fstatfs(" << fd << ") failed";
+        return false;
+    }
+    return (sfs.f_flags & ST_RDONLY) != 0;
+}
+#endif  // _WIN32
+
 }; // namespace android
diff --git a/libs/androidfw/tests/ByteBucketArray_test.cpp b/libs/androidfw/tests/ByteBucketArray_test.cpp
index 5d464c7..9c36cfb 100644
--- a/libs/androidfw/tests/ByteBucketArray_test.cpp
+++ b/libs/androidfw/tests/ByteBucketArray_test.cpp
@@ -52,4 +52,57 @@
   }
 }
 
+TEST(ByteBucketArrayTest, TestForEach) {
+  ByteBucketArray<int> bba;
+  ASSERT_TRUE(bba.set(0, 1));
+  ASSERT_TRUE(bba.set(10, 2));
+  ASSERT_TRUE(bba.set(26, 3));
+  ASSERT_TRUE(bba.set(129, 4));
+  ASSERT_TRUE(bba.set(234, 5));
+
+  int count = 0;
+  bba.forEachItem([&count](auto i, auto val) {
+    ++count;
+    switch (i) {
+      case 0:
+        EXPECT_EQ(1, val);
+        break;
+      case 10:
+        EXPECT_EQ(2, val);
+        break;
+      case 26:
+        EXPECT_EQ(3, val);
+        break;
+      case 129:
+        EXPECT_EQ(4, val);
+        break;
+      case 234:
+        EXPECT_EQ(5, val);
+        break;
+      default:
+        EXPECT_EQ(0, val);
+        break;
+    }
+  });
+  ASSERT_EQ(4 * 16, count);
+}
+
+TEST(ByteBucketArrayTest, TestTrimBuckets) {
+  ByteBucketArray<int> bba;
+  ASSERT_TRUE(bba.set(0, 1));
+  ASSERT_TRUE(bba.set(255, 2));
+  {
+    bba.trimBuckets([](auto val) { return val < 2; });
+    int count = 0;
+    bba.forEachItem([&count](auto, auto) { ++count; });
+    ASSERT_EQ(1 * 16, count);
+  }
+  {
+    bba.trimBuckets([](auto val) { return val < 3; });
+    int count = 0;
+    bba.forEachItem([&count](auto, auto) { ++count; });
+    ASSERT_EQ(0, count);
+  }
+}
+
 }  // namespace android