diff --git a/libc/system_properties/context_node.cpp b/libc/system_properties/context_node.cpp
new file mode 100644
index 0000000..440b865
--- /dev/null
+++ b/libc/system_properties/context_node.cpp
@@ -0,0 +1,105 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "context_node.h"
+
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include <async_safe/log.h>
+
+#include "system_property_globals.h"
+
+// pthread_mutex_lock() calls into system_properties in the case of contention.
+// This creates a risk of dead lock if any system_properties functions
+// use pthread locks after system_property initialization.
+//
+// For this reason, the below three functions use a bionic Lock and static
+// allocation of memory for each filename.
+
+bool ContextNode::Open(bool access_rw, bool* fsetxattr_failed) {
+  lock_.lock();
+  if (pa_) {
+    lock_.unlock();
+    return true;
+  }
+
+  char filename[PROP_FILENAME_MAX];
+  int len =
+      async_safe_format_buffer(filename, sizeof(filename), "%s/%s", property_filename, context_);
+  if (len < 0 || len > PROP_FILENAME_MAX) {
+    lock_.unlock();
+    return false;
+  }
+
+  if (access_rw) {
+    pa_ = prop_area::map_prop_area_rw(filename, context_, fsetxattr_failed);
+  } else {
+    pa_ = prop_area::map_prop_area(filename);
+  }
+  lock_.unlock();
+  return pa_;
+}
+
+bool ContextNode::CheckAccessAndOpen() {
+  if (!pa_ && !no_access_) {
+    if (!CheckAccess() || !Open(false, nullptr)) {
+      no_access_ = true;
+    }
+  }
+  return pa_;
+}
+
+void ContextNode::ResetAccess() {
+  if (!CheckAccess()) {
+    Unmap();
+    no_access_ = true;
+  } else {
+    no_access_ = false;
+  }
+}
+
+bool ContextNode::CheckAccess() {
+  char filename[PROP_FILENAME_MAX];
+  int len =
+      async_safe_format_buffer(filename, sizeof(filename), "%s/%s", property_filename, context_);
+  if (len < 0 || len > PROP_FILENAME_MAX) {
+    return false;
+  }
+
+  return access(filename, R_OK) == 0;
+}
+
+void ContextNode::Unmap() {
+  if (!pa_) {
+    return;
+  }
+
+  munmap(pa_, pa_size);
+  pa_ = nullptr;
+}
diff --git a/libc/system_properties/context_node.h b/libc/system_properties/context_node.h
new file mode 100644
index 0000000..1c6cbbb
--- /dev/null
+++ b/libc/system_properties/context_node.h
@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef SYSTEM_PROPERTIES_CONTEXT_NODE_H
+#define SYSTEM_PROPERTIES_CONTEXT_NODE_H
+
+#include "private/bionic_lock.h"
+
+#include "prop_area.h"
+
+class ContextNode {
+ public:
+  ContextNode(const char* context) : context_(context), pa_(nullptr), no_access_(false) {
+    lock_.init(false);
+  }
+  ~ContextNode() {
+    Unmap();
+  }
+  bool Open(bool access_rw, bool* fsetxattr_failed);
+  bool CheckAccessAndOpen();
+  void ResetAccess();
+
+  const char* context() const {
+    return context_;
+  }
+  prop_area* pa() {
+    return pa_;
+  }
+
+ private:
+  bool CheckAccess();
+  void Unmap();
+
+  Lock lock_;
+  const char* context_;
+  prop_area* pa_;
+  bool no_access_;
+};
+
+#endif
diff --git a/libc/system_properties/contexts.h b/libc/system_properties/contexts.h
new file mode 100644
index 0000000..9910ed1
--- /dev/null
+++ b/libc/system_properties/contexts.h
@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef SYSTEM_PROPERTIES_CONTEXTS_H
+#define SYSTEM_PROPERTIES_CONTEXTS_H
+
+#include "prop_area.h"
+#include "prop_info.h"
+
+class Contexts {
+ public:
+  virtual ~Contexts() {
+  }
+
+  virtual bool Initialize(bool writable) = 0;
+  virtual prop_area* GetPropAreaForName(const char* name) = 0;
+  virtual void ForEach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) = 0;
+  virtual void ResetAccess() = 0;
+  virtual void FreeAndUnmap() = 0;
+};
+
+#endif
diff --git a/libc/system_properties/contexts_pre_split.h b/libc/system_properties/contexts_pre_split.h
new file mode 100644
index 0000000..7e83a37
--- /dev/null
+++ b/libc/system_properties/contexts_pre_split.h
@@ -0,0 +1,71 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef SYSTEM_PROPERTIES_CONTEXTS_PRE_SPLIT_H
+#define SYSTEM_PROPERTIES_CONTEXTS_PRE_SPLIT_H
+
+#include <sys/mman.h>
+
+#include "contexts.h"
+#include "prop_area.h"
+#include "prop_info.h"
+#include "system_property_globals.h"
+
+class ContextsPreSplit : public Contexts {
+ public:
+  virtual ~ContextsPreSplit() override {
+  }
+
+  // We'll never initialize this legacy option as writable, so don't even check the arg.
+  virtual bool Initialize(bool) override {
+    __system_property_area__ = prop_area::map_prop_area(property_filename);
+    return __system_property_area__ != nullptr;
+  }
+
+  virtual prop_area* GetPropAreaForName(const char*) override {
+    return __system_property_area__;
+  }
+
+  virtual void ForEach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) override {
+    __system_property_area__->foreach (propfn, cookie);
+  }
+
+  // This is a no-op for pre-split properties as there is only one property file and it is
+  // accessible by all domains
+  virtual void ResetAccess() override {
+  }
+
+  virtual void FreeAndUnmap() override {
+    if (__system_property_area__ != nullptr) {
+      munmap(__system_property_area__, pa_size);
+      __system_property_area__ = nullptr;
+    }
+  }
+};
+
+#endif
diff --git a/libc/system_properties/contexts_split.cpp b/libc/system_properties/contexts_split.cpp
new file mode 100644
index 0000000..964a1e4
--- /dev/null
+++ b/libc/system_properties/contexts_split.cpp
@@ -0,0 +1,355 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "contexts_split.h"
+
+#include <ctype.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+
+#include <async_safe/log.h>
+
+#include "context_node.h"
+#include "system_property_globals.h"
+
+class ContextListNode : public ContextNode {
+ public:
+  ContextListNode(ContextListNode* next, const char* context)
+      : ContextNode(strdup(context)), next(next) {
+  }
+
+  ~ContextListNode() {
+    free(const_cast<char*>(context()));
+  }
+
+  ContextListNode* next;
+};
+
+struct PrefixNode {
+  PrefixNode(struct PrefixNode* next, const char* prefix, ContextListNode* context)
+      : prefix(strdup(prefix)), prefix_len(strlen(prefix)), context(context), next(next) {
+  }
+  ~PrefixNode() {
+    free(prefix);
+  }
+  char* prefix;
+  const size_t prefix_len;
+  ContextListNode* context;
+  PrefixNode* next;
+};
+
+template <typename List, typename... Args>
+static inline void ListAdd(List** list, Args... args) {
+  *list = new List(*list, args...);
+}
+
+static void ListAddAfterLen(PrefixNode** list, const char* prefix, ContextListNode* context) {
+  size_t prefix_len = strlen(prefix);
+
+  auto next_list = list;
+
+  while (*next_list) {
+    if ((*next_list)->prefix_len < prefix_len || (*next_list)->prefix[0] == '*') {
+      ListAdd(next_list, prefix, context);
+      return;
+    }
+    next_list = &(*next_list)->next;
+  }
+  ListAdd(next_list, prefix, context);
+}
+
+template <typename List, typename Func>
+static void ListForEach(List* list, Func func) {
+  while (list) {
+    func(list);
+    list = list->next;
+  }
+}
+
+template <typename List, typename Func>
+static List* ListFind(List* list, Func func) {
+  while (list) {
+    if (func(list)) {
+      return list;
+    }
+    list = list->next;
+  }
+  return nullptr;
+}
+
+template <typename List>
+static void ListFree(List** list) {
+  while (*list) {
+    auto old_list = *list;
+    *list = old_list->next;
+    delete old_list;
+  }
+}
+
+// The below two functions are duplicated from label_support.c in libselinux.
+// TODO: Find a location suitable for these functions such that both libc and
+// libselinux can share a common source file.
+
+// The read_spec_entries and read_spec_entry functions may be used to
+// replace sscanf to read entries from spec files. The file and
+// property services now use these.
+
+// Read an entry from a spec file (e.g. file_contexts)
+static inline int read_spec_entry(char** entry, char** ptr, int* len) {
+  *entry = nullptr;
+  char* tmp_buf = nullptr;
+
+  while (isspace(**ptr) && **ptr != '\0') (*ptr)++;
+
+  tmp_buf = *ptr;
+  *len = 0;
+
+  while (!isspace(**ptr) && **ptr != '\0') {
+    (*ptr)++;
+    (*len)++;
+  }
+
+  if (*len) {
+    *entry = strndup(tmp_buf, *len);
+    if (!*entry) return -1;
+  }
+
+  return 0;
+}
+
+// line_buf - Buffer containing the spec entries .
+// num_args - The number of spec parameter entries to process.
+// ...      - A 'char **spec_entry' for each parameter.
+// returns  - The number of items processed.
+//
+// This function calls read_spec_entry() to do the actual string processing.
+static int read_spec_entries(char* line_buf, int num_args, ...) {
+  char **spec_entry, *buf_p;
+  int len, rc, items, entry_len = 0;
+  va_list ap;
+
+  len = strlen(line_buf);
+  if (line_buf[len - 1] == '\n')
+    line_buf[len - 1] = '\0';
+  else
+    // Handle case if line not \n terminated by bumping
+    // the len for the check below (as the line is NUL
+    // terminated by getline(3))
+    len++;
+
+  buf_p = line_buf;
+  while (isspace(*buf_p)) buf_p++;
+
+  // Skip comment lines and empty lines.
+  if (*buf_p == '#' || *buf_p == '\0') return 0;
+
+  // Process the spec file entries
+  va_start(ap, num_args);
+
+  items = 0;
+  while (items < num_args) {
+    spec_entry = va_arg(ap, char**);
+
+    if (len - 1 == buf_p - line_buf) {
+      va_end(ap);
+      return items;
+    }
+
+    rc = read_spec_entry(spec_entry, &buf_p, &entry_len);
+    if (rc < 0) {
+      va_end(ap);
+      return rc;
+    }
+    if (entry_len) items++;
+  }
+  va_end(ap);
+  return items;
+}
+
+static bool MapSystemPropertyArea(bool access_rw, bool* fsetxattr_failed) {
+  char filename[PROP_FILENAME_MAX];
+  int len = async_safe_format_buffer(filename, sizeof(filename), "%s/properties_serial",
+                                     property_filename);
+  if (len < 0 || len > PROP_FILENAME_MAX) {
+    __system_property_area__ = nullptr;
+    return false;
+  }
+
+  if (access_rw) {
+    __system_property_area__ =
+        prop_area::map_prop_area_rw(filename, "u:object_r:properties_serial:s0", fsetxattr_failed);
+  } else {
+    __system_property_area__ = prop_area::map_prop_area(filename);
+  }
+  return __system_property_area__;
+}
+
+bool ContextsSplit::InitializePropertiesFromFile(const char* filename) {
+  FILE* file = fopen(filename, "re");
+  if (!file) {
+    return false;
+  }
+
+  char* buffer = nullptr;
+  size_t line_len;
+  char* prop_prefix = nullptr;
+  char* context = nullptr;
+
+  while (getline(&buffer, &line_len, file) > 0) {
+    int items = read_spec_entries(buffer, 2, &prop_prefix, &context);
+    if (items <= 0) {
+      continue;
+    }
+    if (items == 1) {
+      free(prop_prefix);
+      continue;
+    }
+
+    // init uses ctl.* properties as an IPC mechanism and does not write them
+    // to a property file, therefore we do not need to create property files
+    // to store them.
+    if (!strncmp(prop_prefix, "ctl.", 4)) {
+      free(prop_prefix);
+      free(context);
+      continue;
+    }
+
+    auto old_context = ListFind(
+        contexts_, [context](ContextListNode* l) { return !strcmp(l->context(), context); });
+    if (old_context) {
+      ListAddAfterLen(&prefixes_, prop_prefix, old_context);
+    } else {
+      ListAdd(&contexts_, context);
+      ListAddAfterLen(&prefixes_, prop_prefix, contexts_);
+    }
+    free(prop_prefix);
+    free(context);
+  }
+
+  free(buffer);
+  fclose(file);
+
+  return true;
+}
+
+bool ContextsSplit::InitializeProperties() {
+  // If we do find /property_contexts, then this is being
+  // run as part of the OTA updater on older release that had
+  // /property_contexts - b/34370523
+  if (InitializePropertiesFromFile("/property_contexts")) {
+    return true;
+  }
+
+  // Use property_contexts from /system & /vendor, fall back to those from /
+  if (access("/system/etc/selinux/plat_property_contexts", R_OK) != -1) {
+    if (!InitializePropertiesFromFile("/system/etc/selinux/plat_property_contexts")) {
+      return false;
+    }
+    // Don't check for failure here, so we always have a sane list of properties.
+    // E.g. In case of recovery, the vendor partition will not have mounted and we
+    // still need the system / platform properties to function.
+    InitializePropertiesFromFile("/vendor/etc/selinux/nonplat_property_contexts");
+  } else {
+    if (!InitializePropertiesFromFile("/plat_property_contexts")) {
+      return false;
+    }
+    InitializePropertiesFromFile("/nonplat_property_contexts");
+  }
+
+  return true;
+}
+
+bool ContextsSplit::Initialize(bool writable) {
+  if (!InitializeProperties()) {
+    return false;
+  }
+
+  if (writable) {
+    mkdir(property_filename, S_IRWXU | S_IXGRP | S_IXOTH);
+    bool open_failed = false;
+    bool fsetxattr_failed = false;
+    ListForEach(contexts_, [&fsetxattr_failed, &open_failed](ContextListNode* l) {
+      if (!l->Open(true, &fsetxattr_failed)) {
+        open_failed = true;
+      }
+    });
+    if (open_failed || !MapSystemPropertyArea(true, &fsetxattr_failed)) {
+      FreeAndUnmap();
+      return false;
+    }
+
+    return !fsetxattr_failed;
+  } else {
+    if (!MapSystemPropertyArea(false, nullptr)) {
+      FreeAndUnmap();
+      return false;
+    }
+  }
+  return true;
+}
+
+prop_area* ContextsSplit::GetPropAreaForName(const char* name) {
+  auto entry = ListFind(prefixes_, [name](PrefixNode* l) {
+    return l->prefix[0] == '*' || !strncmp(l->prefix, name, l->prefix_len);
+  });
+  if (!entry) {
+    return nullptr;
+  }
+
+  auto cnode = entry->context;
+  if (!cnode->pa()) {
+    // We explicitly do not check no_access_ in this case because unlike the
+    // case of foreach(), we want to generate an selinux audit for each
+    // non-permitted property access in this function.
+    cnode->Open(false, nullptr);
+  }
+  return cnode->pa();
+}
+
+void ContextsSplit::ForEach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) {
+  ListForEach(contexts_, [propfn, cookie](ContextListNode* l) {
+    if (l->CheckAccessAndOpen()) {
+      l->pa()->foreach (propfn, cookie);
+    }
+  });
+}
+
+void ContextsSplit::ResetAccess() {
+  ListForEach(contexts_, [](ContextListNode* l) { l->ResetAccess(); });
+}
+
+void ContextsSplit::FreeAndUnmap() {
+  ListFree(&prefixes_);
+  ListFree(&contexts_);
+  if (__system_property_area__) {
+    munmap(__system_property_area__, pa_size);
+    __system_property_area__ = nullptr;
+  }
+}
diff --git a/libc/system_properties/contexts_split.h b/libc/system_properties/contexts_split.h
new file mode 100644
index 0000000..fced33c
--- /dev/null
+++ b/libc/system_properties/contexts_split.h
@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef SYSTEM_PROPERTIES_CONTEXTS_SPLIT_H
+#define SYSTEM_PROPERTIES_CONTEXTS_SPLIT_H
+
+#include "contexts.h"
+
+struct PrefixNode;
+class ContextListNode;
+
+class ContextsSplit : public Contexts {
+ public:
+  virtual ~ContextsSplit() override {
+  }
+
+  virtual bool Initialize(bool writable) override;
+  virtual prop_area* GetPropAreaForName(const char* name) override;
+  virtual void ForEach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) override;
+  virtual void ResetAccess() override;
+  virtual void FreeAndUnmap() override;
+
+ private:
+  bool InitializePropertiesFromFile(const char* filename);
+  bool InitializeProperties();
+
+  PrefixNode* prefixes_ = nullptr;
+  ContextListNode* contexts_ = nullptr;
+};
+
+#endif
diff --git a/libc/system_properties/prop_area.cpp b/libc/system_properties/prop_area.cpp
new file mode 100644
index 0000000..f6c7fa1
--- /dev/null
+++ b/libc/system_properties/prop_area.cpp
@@ -0,0 +1,373 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <fcntl.h>
+#include <stdlib.h>
+#include <sys/cdefs.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/xattr.h>
+#include <unistd.h>
+
+#include <new>
+
+#include <async_safe/log.h>
+
+#include "prop_area.h"
+#include "system_property_globals.h"
+
+constexpr size_t PA_SIZE = 128 * 1024;
+constexpr uint32_t PROP_AREA_MAGIC = 0x504f5250;
+constexpr uint32_t PROP_AREA_VERSION = 0xfc6ed0ab;
+
+static size_t pa_data_size;
+
+prop_area* prop_area::map_prop_area_rw(const char* filename, const char* context,
+                                       bool* fsetxattr_failed) {
+  /* dev is a tmpfs that we can use to carve a shared workspace
+   * out of, so let's do that...
+   */
+  const int fd = open(filename, O_RDWR | O_CREAT | O_NOFOLLOW | O_CLOEXEC | O_EXCL, 0444);
+
+  if (fd < 0) {
+    if (errno == EACCES) {
+      /* for consistency with the case where the process has already
+       * mapped the page in and segfaults when trying to write to it
+       */
+      abort();
+    }
+    return nullptr;
+  }
+
+  if (context) {
+    if (fsetxattr(fd, XATTR_NAME_SELINUX, context, strlen(context) + 1, 0) != 0) {
+      async_safe_format_log(ANDROID_LOG_ERROR, "libc",
+                            "fsetxattr failed to set context (%s) for \"%s\"", context, filename);
+      /*
+       * fsetxattr() will fail during system properties tests due to selinux policy.
+       * We do not want to create a custom policy for the tester, so we will continue in
+       * this function but set a flag that an error has occurred.
+       * Init, which is the only daemon that should ever call this function will abort
+       * when this error occurs.
+       * Otherwise, the tester will ignore it and continue, albeit without any selinux
+       * property separation.
+       */
+      if (fsetxattr_failed) {
+        *fsetxattr_failed = true;
+      }
+    }
+  }
+
+  if (ftruncate(fd, PA_SIZE) < 0) {
+    close(fd);
+    return nullptr;
+  }
+
+  pa_size = PA_SIZE;
+  pa_data_size = pa_size - sizeof(prop_area);
+
+  void* const memory_area = mmap(nullptr, pa_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+  if (memory_area == MAP_FAILED) {
+    close(fd);
+    return nullptr;
+  }
+
+  prop_area* pa = new (memory_area) prop_area(PROP_AREA_MAGIC, PROP_AREA_VERSION);
+
+  close(fd);
+  return pa;
+}
+
+prop_area* prop_area::map_fd_ro(const int fd) {
+  struct stat fd_stat;
+  if (fstat(fd, &fd_stat) < 0) {
+    return nullptr;
+  }
+
+  if ((fd_stat.st_uid != 0) || (fd_stat.st_gid != 0) ||
+      ((fd_stat.st_mode & (S_IWGRP | S_IWOTH)) != 0) ||
+      (fd_stat.st_size < static_cast<off_t>(sizeof(prop_area)))) {
+    return nullptr;
+  }
+
+  pa_size = fd_stat.st_size;
+  pa_data_size = pa_size - sizeof(prop_area);
+
+  void* const map_result = mmap(nullptr, pa_size, PROT_READ, MAP_SHARED, fd, 0);
+  if (map_result == MAP_FAILED) {
+    return nullptr;
+  }
+
+  prop_area* pa = reinterpret_cast<prop_area*>(map_result);
+  if ((pa->magic() != PROP_AREA_MAGIC) || (pa->version() != PROP_AREA_VERSION)) {
+    munmap(pa, pa_size);
+    return nullptr;
+  }
+
+  return pa;
+}
+
+prop_area* prop_area::map_prop_area(const char* filename) {
+  int fd = open(filename, O_CLOEXEC | O_NOFOLLOW | O_RDONLY);
+  if (fd == -1) return nullptr;
+
+  prop_area* map_result = map_fd_ro(fd);
+  close(fd);
+
+  return map_result;
+}
+
+void* prop_area::allocate_obj(const size_t size, uint_least32_t* const off) {
+  const size_t aligned = __BIONIC_ALIGN(size, sizeof(uint_least32_t));
+  if (bytes_used_ + aligned > pa_data_size) {
+    return nullptr;
+  }
+
+  *off = bytes_used_;
+  bytes_used_ += aligned;
+  return data_ + *off;
+}
+
+prop_bt* prop_area::new_prop_bt(const char* name, uint32_t namelen, uint_least32_t* const off) {
+  uint_least32_t new_offset;
+  void* const p = allocate_obj(sizeof(prop_bt) + namelen + 1, &new_offset);
+  if (p != nullptr) {
+    prop_bt* bt = new (p) prop_bt(name, namelen);
+    *off = new_offset;
+    return bt;
+  }
+
+  return nullptr;
+}
+
+prop_info* prop_area::new_prop_info(const char* name, uint32_t namelen, const char* value,
+                                    uint32_t valuelen, uint_least32_t* const off) {
+  uint_least32_t new_offset;
+  void* const p = allocate_obj(sizeof(prop_info) + namelen + 1, &new_offset);
+  if (p == nullptr) return nullptr;
+
+  prop_info* info;
+  if (valuelen >= PROP_VALUE_MAX) {
+    uint32_t long_value_offset = 0;
+    char* long_location = reinterpret_cast<char*>(allocate_obj(valuelen + 1, &long_value_offset));
+    if (!long_location) return nullptr;
+
+    memcpy(long_location, value, valuelen);
+    long_location[valuelen] = '\0';
+
+    // Both new_offset and long_value_offset are offsets based off of data_, however prop_info
+    // does not know what data_ is, so we change this offset to be an offset from the prop_info
+    // pointer that contains it.
+    long_value_offset -= new_offset;
+
+    info = new (p) prop_info(name, namelen, long_value_offset);
+  } else {
+    info = new (p) prop_info(name, namelen, value, valuelen);
+  }
+  *off = new_offset;
+  return info;
+}
+
+void* prop_area::to_prop_obj(uint_least32_t off) {
+  if (off > pa_data_size) return nullptr;
+
+  return (data_ + off);
+}
+
+inline prop_bt* prop_area::to_prop_bt(atomic_uint_least32_t* off_p) {
+  uint_least32_t off = atomic_load_explicit(off_p, memory_order_consume);
+  return reinterpret_cast<prop_bt*>(to_prop_obj(off));
+}
+
+inline prop_info* prop_area::to_prop_info(atomic_uint_least32_t* off_p) {
+  uint_least32_t off = atomic_load_explicit(off_p, memory_order_consume);
+  return reinterpret_cast<prop_info*>(to_prop_obj(off));
+}
+
+inline prop_bt* prop_area::root_node() {
+  return reinterpret_cast<prop_bt*>(to_prop_obj(0));
+}
+
+static int cmp_prop_name(const char* one, uint32_t one_len, const char* two, uint32_t two_len) {
+  if (one_len < two_len)
+    return -1;
+  else if (one_len > two_len)
+    return 1;
+  else
+    return strncmp(one, two, one_len);
+}
+
+prop_bt* prop_area::find_prop_bt(prop_bt* const bt, const char* name, uint32_t namelen,
+                                 bool alloc_if_needed) {
+  prop_bt* current = bt;
+  while (true) {
+    if (!current) {
+      return nullptr;
+    }
+
+    const int ret = cmp_prop_name(name, namelen, current->name, current->namelen);
+    if (ret == 0) {
+      return current;
+    }
+
+    if (ret < 0) {
+      uint_least32_t left_offset = atomic_load_explicit(&current->left, memory_order_relaxed);
+      if (left_offset != 0) {
+        current = to_prop_bt(&current->left);
+      } else {
+        if (!alloc_if_needed) {
+          return nullptr;
+        }
+
+        uint_least32_t new_offset;
+        prop_bt* new_bt = new_prop_bt(name, namelen, &new_offset);
+        if (new_bt) {
+          atomic_store_explicit(&current->left, new_offset, memory_order_release);
+        }
+        return new_bt;
+      }
+    } else {
+      uint_least32_t right_offset = atomic_load_explicit(&current->right, memory_order_relaxed);
+      if (right_offset != 0) {
+        current = to_prop_bt(&current->right);
+      } else {
+        if (!alloc_if_needed) {
+          return nullptr;
+        }
+
+        uint_least32_t new_offset;
+        prop_bt* new_bt = new_prop_bt(name, namelen, &new_offset);
+        if (new_bt) {
+          atomic_store_explicit(&current->right, new_offset, memory_order_release);
+        }
+        return new_bt;
+      }
+    }
+  }
+}
+
+const prop_info* prop_area::find_property(prop_bt* const trie, const char* name, uint32_t namelen,
+                                          const char* value, uint32_t valuelen,
+                                          bool alloc_if_needed) {
+  if (!trie) return nullptr;
+
+  const char* remaining_name = name;
+  prop_bt* current = trie;
+  while (true) {
+    const char* sep = strchr(remaining_name, '.');
+    const bool want_subtree = (sep != nullptr);
+    const uint32_t substr_size = (want_subtree) ? sep - remaining_name : strlen(remaining_name);
+
+    if (!substr_size) {
+      return nullptr;
+    }
+
+    prop_bt* root = nullptr;
+    uint_least32_t children_offset = atomic_load_explicit(&current->children, memory_order_relaxed);
+    if (children_offset != 0) {
+      root = to_prop_bt(&current->children);
+    } else if (alloc_if_needed) {
+      uint_least32_t new_offset;
+      root = new_prop_bt(remaining_name, substr_size, &new_offset);
+      if (root) {
+        atomic_store_explicit(&current->children, new_offset, memory_order_release);
+      }
+    }
+
+    if (!root) {
+      return nullptr;
+    }
+
+    current = find_prop_bt(root, remaining_name, substr_size, alloc_if_needed);
+    if (!current) {
+      return nullptr;
+    }
+
+    if (!want_subtree) break;
+
+    remaining_name = sep + 1;
+  }
+
+  uint_least32_t prop_offset = atomic_load_explicit(&current->prop, memory_order_relaxed);
+  if (prop_offset != 0) {
+    return to_prop_info(&current->prop);
+  } else if (alloc_if_needed) {
+    uint_least32_t new_offset;
+    prop_info* new_info = new_prop_info(name, namelen, value, valuelen, &new_offset);
+    if (new_info) {
+      atomic_store_explicit(&current->prop, new_offset, memory_order_release);
+    }
+
+    return new_info;
+  } else {
+    return nullptr;
+  }
+}
+
+bool prop_area::foreach_property(prop_bt* const trie,
+                                 void (*propfn)(const prop_info* pi, void* cookie), void* cookie) {
+  if (!trie) return false;
+
+  uint_least32_t left_offset = atomic_load_explicit(&trie->left, memory_order_relaxed);
+  if (left_offset != 0) {
+    const int err = foreach_property(to_prop_bt(&trie->left), propfn, cookie);
+    if (err < 0) return false;
+  }
+  uint_least32_t prop_offset = atomic_load_explicit(&trie->prop, memory_order_relaxed);
+  if (prop_offset != 0) {
+    prop_info* info = to_prop_info(&trie->prop);
+    if (!info) return false;
+    propfn(info, cookie);
+  }
+  uint_least32_t children_offset = atomic_load_explicit(&trie->children, memory_order_relaxed);
+  if (children_offset != 0) {
+    const int err = foreach_property(to_prop_bt(&trie->children), propfn, cookie);
+    if (err < 0) return false;
+  }
+  uint_least32_t right_offset = atomic_load_explicit(&trie->right, memory_order_relaxed);
+  if (right_offset != 0) {
+    const int err = foreach_property(to_prop_bt(&trie->right), propfn, cookie);
+    if (err < 0) return false;
+  }
+
+  return true;
+}
+
+const prop_info* prop_area::find(const char* name) {
+  return find_property(root_node(), name, strlen(name), nullptr, 0, false);
+}
+
+bool prop_area::add(const char* name, unsigned int namelen, const char* value,
+                    unsigned int valuelen) {
+  return find_property(root_node(), name, namelen, value, valuelen, true);
+}
+
+bool prop_area::foreach (void (*propfn)(const prop_info* pi, void* cookie), void* cookie) {
+  return foreach_property(root_node(), propfn, cookie);
+}
diff --git a/libc/system_properties/prop_area.h b/libc/system_properties/prop_area.h
new file mode 100644
index 0000000..6b74e10
--- /dev/null
+++ b/libc/system_properties/prop_area.h
@@ -0,0 +1,151 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdatomic.h>
+#include <stdint.h>
+#include <string.h>
+
+#include "private/bionic_macros.h"
+
+#include "prop_info.h"
+
+#ifndef SYSTEM_PROPERTIES_PROP_AREA_H
+#define SYSTEM_PROPERTIES_PROP_AREA_H
+
+// Properties are stored in a hybrid trie/binary tree structure.
+// Each property's name is delimited at '.' characters, and the tokens are put
+// into a trie structure.  Siblings at each level of the trie are stored in a
+// binary tree.  For instance, "ro.secure"="1" could be stored as follows:
+//
+// +-----+   children    +----+   children    +--------+
+// |     |-------------->| ro |-------------->| secure |
+// +-----+               +----+               +--------+
+//                       /    \                /   |
+//                 left /      \ right   left /    |  prop   +===========+
+//                     v        v            v     +-------->| ro.secure |
+//                  +-----+   +-----+     +-----+            +-----------+
+//                  | net |   | sys |     | com |            |     1     |
+//                  +-----+   +-----+     +-----+            +===========+
+
+// Represents a node in the trie.
+struct prop_bt {
+  uint32_t namelen;
+
+  // The property trie is updated only by the init process (single threaded) which provides
+  // property service. And it can be read by multiple threads at the same time.
+  // As the property trie is not protected by locks, we use atomic_uint_least32_t types for the
+  // left, right, children "pointers" in the trie node. To make sure readers who see the
+  // change of "pointers" can also notice the change of prop_bt structure contents pointed by
+  // the "pointers", we always use release-consume ordering pair when accessing these "pointers".
+
+  // prop "points" to prop_info structure if there is a propery associated with the trie node.
+  // Its situation is similar to the left, right, children "pointers". So we use
+  // atomic_uint_least32_t and release-consume ordering to protect it as well.
+
+  // We should also avoid rereading these fields redundantly, since not
+  // all processor implementations ensure that multiple loads from the
+  // same field are carried out in the right order.
+  atomic_uint_least32_t prop;
+
+  atomic_uint_least32_t left;
+  atomic_uint_least32_t right;
+
+  atomic_uint_least32_t children;
+
+  char name[0];
+
+  prop_bt(const char* name, const uint32_t name_length) {
+    this->namelen = name_length;
+    memcpy(this->name, name, name_length);
+    this->name[name_length] = '\0';
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(prop_bt);
+};
+
+class prop_area {
+ public:
+  static prop_area* map_prop_area_rw(const char* filename, const char* context,
+                                     bool* fsetxattr_failed);
+  static prop_area* map_prop_area(const char* filename);
+
+  prop_area(const uint32_t magic, const uint32_t version) : magic_(magic), version_(version) {
+    atomic_init(&serial_, 0);
+    memset(reserved_, 0, sizeof(reserved_));
+    // Allocate enough space for the root node.
+    bytes_used_ = sizeof(prop_bt);
+  }
+
+  const prop_info* find(const char* name);
+  bool add(const char* name, unsigned int namelen, const char* value, unsigned int valuelen);
+
+  bool foreach (void (*propfn)(const prop_info* pi, void* cookie), void* cookie);
+
+  atomic_uint_least32_t* serial() {
+    return &serial_;
+  }
+  uint32_t magic() const {
+    return magic_;
+  }
+  uint32_t version() const {
+    return version_;
+  }
+
+ private:
+  static prop_area* map_fd_ro(const int fd);
+
+  void* allocate_obj(const size_t size, uint_least32_t* const off);
+  prop_bt* new_prop_bt(const char* name, uint32_t namelen, uint_least32_t* const off);
+  prop_info* new_prop_info(const char* name, uint32_t namelen, const char* value, uint32_t valuelen,
+                           uint_least32_t* const off);
+  void* to_prop_obj(uint_least32_t off);
+  prop_bt* to_prop_bt(atomic_uint_least32_t* off_p);
+  prop_info* to_prop_info(atomic_uint_least32_t* off_p);
+
+  prop_bt* root_node();
+
+  prop_bt* find_prop_bt(prop_bt* const bt, const char* name, uint32_t namelen, bool alloc_if_needed);
+
+  const prop_info* find_property(prop_bt* const trie, const char* name, uint32_t namelen,
+                                 const char* value, uint32_t valuelen, bool alloc_if_needed);
+
+  bool foreach_property(prop_bt* const trie, void (*propfn)(const prop_info* pi, void* cookie),
+                        void* cookie);
+
+  uint32_t bytes_used_;
+  atomic_uint_least32_t serial_;
+  uint32_t magic_;
+  uint32_t version_;
+  uint32_t reserved_[28];
+  char data_[0];
+
+  DISALLOW_COPY_AND_ASSIGN(prop_area);
+};
+
+#endif
diff --git a/libc/system_properties/prop_info.cpp b/libc/system_properties/prop_info.cpp
new file mode 100644
index 0000000..5123f92
--- /dev/null
+++ b/libc/system_properties/prop_info.cpp
@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "prop_info.h"
+
+#include <string.h>
+
+constexpr static const char kLongLegacyError[] =
+    "Must use __system_property_read_callback() to read";
+static_assert(sizeof(kLongLegacyError) < prop_info::kLongLegacyErrorBufferSize,
+              "Error message for long properties read by legacy libc must fit within 56 chars");
+
+prop_info::prop_info(const char* name, uint32_t namelen, const char* value, uint32_t valuelen) {
+  memcpy(this->name, name, namelen);
+  this->name[namelen] = '\0';
+  atomic_init(&this->serial, valuelen << 24);
+  memcpy(this->value, value, valuelen);
+  this->value[valuelen] = '\0';
+}
+
+prop_info::prop_info(const char* name, uint32_t namelen, uint32_t long_offset) {
+  memcpy(this->name, name, namelen);
+  this->name[namelen] = '\0';
+
+  auto error_value_len = sizeof(kLongLegacyError) - 1;
+  atomic_init(&this->serial, error_value_len << 24 | kLongFlag);
+  memcpy(this->long_property.error_message, kLongLegacyError, sizeof(kLongLegacyError));
+
+  this->long_property.offset = long_offset;
+}
diff --git a/libc/system_properties/prop_info.h b/libc/system_properties/prop_info.h
new file mode 100644
index 0000000..99bcaaf
--- /dev/null
+++ b/libc/system_properties/prop_info.h
@@ -0,0 +1,92 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdatomic.h>
+#include <stdint.h>
+#include <sys/system_properties.h>
+
+#include "private/bionic_macros.h"
+
+#ifndef SYSTEM_PROPERTIES_PROP_INFO_H
+#define SYSTEM_PROPERTIES_PROP_INFO_H
+
+// The C11 standard doesn't allow atomic loads from const fields,
+// though C++11 does.  Fudge it until standards get straightened out.
+static inline uint_least32_t load_const_atomic(const atomic_uint_least32_t* s, memory_order mo) {
+  atomic_uint_least32_t* non_const_s = const_cast<atomic_uint_least32_t*>(s);
+  return atomic_load_explicit(non_const_s, mo);
+}
+
+struct prop_info {
+  // Read only properties will not set anything but the bottom most bit of serial and the top byte.
+  // We borrow the 2nd from the top byte for extra flags, and use the bottom most bit of that for
+  // our first user, kLongFlag.
+  constexpr static uint32_t kLongFlag = 1 << 16;
+
+  // The error message fits in part of a union with the previous 92 char property value so there
+  // must be room left over after the error message for the offset to the new longer property value
+  // and future expansion fields if needed. Note that this value cannot ever increase.  The offset
+  // to the new longer property value appears immediately after it, so an increase of this size will
+  // break compatibility.
+  constexpr static size_t kLongLegacyErrorBufferSize = 56;
+
+ public:
+  atomic_uint_least32_t serial;
+  // we need to keep this buffer around because the property
+  // value can be modified whereas name is constant.
+  union {
+    char value[PROP_VALUE_MAX];
+    struct {
+      char error_message[kLongLegacyErrorBufferSize];
+      uint32_t offset;
+    } long_property;
+  };
+  char name[0];
+
+  bool is_long() const {
+    return (load_const_atomic(&serial, memory_order_relaxed) & kLongFlag) != 0;
+  }
+
+  const char* long_value() const {
+    // We can't store pointers here since this is shared memory that will have different absolute
+    // pointers in different processes.  We don't have data_ from prop_area, but since we know
+    // `this` is data_ + some offset and long_value is data_ + some other offset, we calculate the
+    // offset from `this` to long_value and store it as long_property.offset.
+    return reinterpret_cast<const char*>(this) + long_property.offset;
+  }
+
+  prop_info(const char* name, uint32_t namelen, const char* value, uint32_t valuelen);
+  prop_info(const char* name, uint32_t namelen, uint32_t long_offset);
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(prop_info);
+};
+
+static_assert(sizeof(prop_info) == 96, "sizeof struct prop_info must be 96 bytes");
+
+#endif
diff --git a/libc/system_properties/system_properties.cpp b/libc/system_properties/system_properties.cpp
new file mode 100644
index 0000000..5d13404
--- /dev/null
+++ b/libc/system_properties/system_properties.cpp
@@ -0,0 +1,656 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <netinet/in.h>
+#include <poll.h>
+#include <stdatomic.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/select.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/uio.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
+#include <sys/_system_properties.h>
+#include <sys/system_properties.h>
+
+#include <async_safe/log.h>
+
+#include "private/ErrnoRestorer.h"
+#include "private/bionic_defs.h"
+#include "private/bionic_futex.h"
+#include "private/bionic_macros.h"
+#include "private/bionic_sdk_version.h"
+
+#include "context_node.h"
+#include "contexts.h"
+#include "contexts_pre_split.h"
+#include "contexts_split.h"
+#include "prop_area.h"
+#include "prop_info.h"
+#include "system_property_globals.h"
+
+// We don't want to use new or malloc in properties (b/31659220), and since these classes are
+// small enough and don't have non-trivial constructors, it's easier to just statically declare
+// them than anything else.
+static ContextsSplit contexts_split;
+static ContextsPreSplit contexts_pre_split;
+static Contexts* contexts = nullptr;
+
+#define SERIAL_DIRTY(serial) ((serial)&1)
+#define SERIAL_VALUE_LEN(serial) ((serial) >> 24)
+
+static const char property_service_socket[] = "/dev/socket/" PROP_SERVICE_NAME;
+static const char* kServiceVersionPropertyName = "ro.property_service.version";
+
+// This is public because it was exposed in the NDK. As of 2017-01, ~60 apps reference this symbol.
+__BIONIC_WEAK_VARIABLE_FOR_NATIVE_BRIDGE
+prop_area* __system_property_area__ = nullptr;
+
+char property_filename[PROP_FILENAME_MAX] = PROP_FILENAME;
+size_t pa_size;
+
+class PropertyServiceConnection {
+ public:
+  PropertyServiceConnection() : last_error_(0) {
+    socket_ = ::socket(AF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0);
+    if (socket_ == -1) {
+      last_error_ = errno;
+      return;
+    }
+
+    const size_t namelen = strlen(property_service_socket);
+    sockaddr_un addr;
+    memset(&addr, 0, sizeof(addr));
+    strlcpy(addr.sun_path, property_service_socket, sizeof(addr.sun_path));
+    addr.sun_family = AF_LOCAL;
+    socklen_t alen = namelen + offsetof(sockaddr_un, sun_path) + 1;
+
+    if (TEMP_FAILURE_RETRY(connect(socket_, reinterpret_cast<sockaddr*>(&addr), alen)) == -1) {
+      last_error_ = errno;
+      close(socket_);
+      socket_ = -1;
+    }
+  }
+
+  bool IsValid() {
+    return socket_ != -1;
+  }
+
+  int GetLastError() {
+    return last_error_;
+  }
+
+  bool RecvInt32(int32_t* value) {
+    int result = TEMP_FAILURE_RETRY(recv(socket_, value, sizeof(*value), MSG_WAITALL));
+    return CheckSendRecvResult(result, sizeof(*value));
+  }
+
+  int socket() {
+    return socket_;
+  }
+
+  ~PropertyServiceConnection() {
+    if (socket_ != -1) {
+      close(socket_);
+    }
+  }
+
+ private:
+  bool CheckSendRecvResult(int result, int expected_len) {
+    if (result == -1) {
+      last_error_ = errno;
+    } else if (result != expected_len) {
+      last_error_ = -1;
+    } else {
+      last_error_ = 0;
+    }
+
+    return last_error_ == 0;
+  }
+
+  int socket_;
+  int last_error_;
+
+  friend class SocketWriter;
+};
+
+class SocketWriter {
+ public:
+  explicit SocketWriter(PropertyServiceConnection* connection)
+      : connection_(connection), iov_index_(0), uint_buf_index_(0) {
+  }
+
+  SocketWriter& WriteUint32(uint32_t value) {
+    CHECK(uint_buf_index_ < kUintBufSize);
+    CHECK(iov_index_ < kIovSize);
+    uint32_t* ptr = uint_buf_ + uint_buf_index_;
+    uint_buf_[uint_buf_index_++] = value;
+    iov_[iov_index_].iov_base = ptr;
+    iov_[iov_index_].iov_len = sizeof(*ptr);
+    ++iov_index_;
+    return *this;
+  }
+
+  SocketWriter& WriteString(const char* value) {
+    uint32_t valuelen = strlen(value);
+    WriteUint32(valuelen);
+    if (valuelen == 0) {
+      return *this;
+    }
+
+    CHECK(iov_index_ < kIovSize);
+    iov_[iov_index_].iov_base = const_cast<char*>(value);
+    iov_[iov_index_].iov_len = valuelen;
+    ++iov_index_;
+
+    return *this;
+  }
+
+  bool Send() {
+    if (!connection_->IsValid()) {
+      return false;
+    }
+
+    if (writev(connection_->socket(), iov_, iov_index_) == -1) {
+      connection_->last_error_ = errno;
+      return false;
+    }
+
+    iov_index_ = uint_buf_index_ = 0;
+    return true;
+  }
+
+ private:
+  static constexpr size_t kUintBufSize = 8;
+  static constexpr size_t kIovSize = 8;
+
+  PropertyServiceConnection* connection_;
+  iovec iov_[kIovSize];
+  size_t iov_index_;
+  uint32_t uint_buf_[kUintBufSize];
+  size_t uint_buf_index_;
+
+  DISALLOW_IMPLICIT_CONSTRUCTORS(SocketWriter);
+};
+
+struct prop_msg {
+  unsigned cmd;
+  char name[PROP_NAME_MAX];
+  char value[PROP_VALUE_MAX];
+};
+
+static int send_prop_msg(const prop_msg* msg) {
+  PropertyServiceConnection connection;
+  if (!connection.IsValid()) {
+    return connection.GetLastError();
+  }
+
+  int result = -1;
+  int s = connection.socket();
+
+  const int num_bytes = TEMP_FAILURE_RETRY(send(s, msg, sizeof(prop_msg), 0));
+  if (num_bytes == sizeof(prop_msg)) {
+    // We successfully wrote to the property server but now we
+    // wait for the property server to finish its work.  It
+    // acknowledges its completion by closing the socket so we
+    // poll here (on nothing), waiting for the socket to close.
+    // If you 'adb shell setprop foo bar' you'll see the POLLHUP
+    // once the socket closes.  Out of paranoia we cap our poll
+    // at 250 ms.
+    pollfd pollfds[1];
+    pollfds[0].fd = s;
+    pollfds[0].events = 0;
+    const int poll_result = TEMP_FAILURE_RETRY(poll(pollfds, 1, 250 /* ms */));
+    if (poll_result == 1 && (pollfds[0].revents & POLLHUP) != 0) {
+      result = 0;
+    } else {
+      // Ignore the timeout and treat it like a success anyway.
+      // The init process is single-threaded and its property
+      // service is sometimes slow to respond (perhaps it's off
+      // starting a child process or something) and thus this
+      // times out and the caller thinks it failed, even though
+      // it's still getting around to it.  So we fake it here,
+      // mostly for ctl.* properties, but we do try and wait 250
+      // ms so callers who do read-after-write can reliably see
+      // what they've written.  Most of the time.
+      // TODO: fix the system properties design.
+      async_safe_format_log(ANDROID_LOG_WARN, "libc",
+                            "Property service has timed out while trying to set \"%s\" to \"%s\"",
+                            msg->name, msg->value);
+      result = 0;
+    }
+  }
+
+  return result;
+}
+
+static bool is_dir(const char* pathname) {
+  struct stat info;
+  if (stat(pathname, &info) == -1) {
+    return false;
+  }
+  return S_ISDIR(info.st_mode);
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_properties_init() {
+  // This is called from __libc_init_common, and should leave errno at 0 (http://b/37248982).
+  ErrnoRestorer errno_restorer;
+
+  if (contexts != nullptr) {
+    contexts->ResetAccess();
+    return 0;
+  }
+  contexts = nullptr;
+  if (is_dir(property_filename)) {
+    if (!contexts_split.Initialize(false)) {
+      return -1;
+    }
+    contexts = &contexts_split;
+  } else {
+    if (!contexts_pre_split.Initialize(false)) {
+      return -1;
+    }
+    contexts = &contexts_pre_split;
+  }
+  return 0;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_set_filename(const char* filename) {
+  size_t len = strlen(filename);
+  if (len >= sizeof(property_filename)) return -1;
+
+  strcpy(property_filename, filename);
+  return 0;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_area_init() {
+  if (contexts != nullptr) {
+    contexts->FreeAndUnmap();
+  }
+  // We set this unconditionally as we want tests to continue on regardless of if this failed
+  // and property_service will abort on an error condition, so no harm done.
+  contexts = &contexts_split;
+  if (!contexts_split.Initialize(true)) {
+    return -1;
+  }
+  return 0;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+uint32_t __system_property_area_serial() {
+  prop_area* pa = __system_property_area__;
+  if (!pa) {
+    return -1;
+  }
+  // Make sure this read fulfilled before __system_property_serial
+  return atomic_load_explicit(pa->serial(), memory_order_acquire);
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+const prop_info* __system_property_find(const char* name) {
+  if (contexts == nullptr) {
+    return nullptr;
+  }
+
+  prop_area* pa = contexts->GetPropAreaForName(name);
+  if (!pa) {
+    async_safe_format_log(ANDROID_LOG_ERROR, "libc", "Access denied finding property \"%s\"", name);
+    return nullptr;
+  }
+
+  return pa->find(name);
+}
+
+static bool is_read_only(const char* name) {
+  return strncmp(name, "ro.", 3) == 0;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_read(const prop_info* pi, char* name, char* value) {
+  while (true) {
+    uint32_t serial = __system_property_serial(pi);  // acquire semantics
+    size_t len = SERIAL_VALUE_LEN(serial);
+    memcpy(value, pi->value, len + 1);
+    // TODO: Fix the synchronization scheme here.
+    // There is no fully supported way to implement this kind
+    // of synchronization in C++11, since the memcpy races with
+    // updates to pi, and the data being accessed is not atomic.
+    // The following fence is unintuitive, but would be the
+    // correct one if memcpy used memory_order_relaxed atomic accesses.
+    // In practice it seems unlikely that the generated code would
+    // would be any different, so this should be OK.
+    atomic_thread_fence(memory_order_acquire);
+    if (serial == load_const_atomic(&(pi->serial), memory_order_relaxed)) {
+      if (name != nullptr) {
+        size_t namelen = strlcpy(name, pi->name, PROP_NAME_MAX);
+        if (namelen >= PROP_NAME_MAX) {
+          async_safe_format_log(ANDROID_LOG_ERROR, "libc",
+                                "The property name length for \"%s\" is >= %d;"
+                                " please use __system_property_read_callback"
+                                " to read this property. (the name is truncated to \"%s\")",
+                                pi->name, PROP_NAME_MAX - 1, name);
+        }
+      }
+      if (is_read_only(pi->name) && pi->is_long()) {
+        async_safe_format_log(
+            ANDROID_LOG_ERROR, "libc",
+            "The property \"%s\" has a value with length %zu that is too large for"
+            " __system_property_get()/__system_property_read(); use"
+            " __system_property_read_callback() instead.",
+            pi->name, strlen(pi->long_value()));
+      }
+      return len;
+    }
+  }
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+void __system_property_read_callback(const prop_info* pi,
+                                     void (*callback)(void* cookie, const char* name,
+                                                      const char* value, uint32_t serial),
+                                     void* cookie) {
+  // Read only properties don't need to copy the value to a temporary buffer, since it can never
+  // change.
+  if (is_read_only(pi->name)) {
+    uint32_t serial = __system_property_serial(pi);
+    if (pi->is_long()) {
+      callback(cookie, pi->name, pi->long_value(), serial);
+    } else {
+      callback(cookie, pi->name, pi->value, serial);
+    }
+    return;
+  }
+
+  while (true) {
+    uint32_t serial = __system_property_serial(pi);  // acquire semantics
+    size_t len = SERIAL_VALUE_LEN(serial);
+    char value_buf[len + 1];
+
+    memcpy(value_buf, pi->value, len);
+    value_buf[len] = '\0';
+
+    // TODO: see todo in __system_property_read function
+    atomic_thread_fence(memory_order_acquire);
+    if (serial == load_const_atomic(&(pi->serial), memory_order_relaxed)) {
+      callback(cookie, pi->name, value_buf, serial);
+      return;
+    }
+  }
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_get(const char* name, char* value) {
+  const prop_info* pi = __system_property_find(name);
+
+  if (pi != 0) {
+    return __system_property_read(pi, nullptr, value);
+  } else {
+    value[0] = 0;
+    return 0;
+  }
+}
+
+static constexpr uint32_t kProtocolVersion1 = 1;
+static constexpr uint32_t kProtocolVersion2 = 2;  // current
+
+static atomic_uint_least32_t g_propservice_protocol_version = 0;
+
+static void detect_protocol_version() {
+  char value[PROP_VALUE_MAX];
+  if (__system_property_get(kServiceVersionPropertyName, value) == 0) {
+    g_propservice_protocol_version = kProtocolVersion1;
+    async_safe_format_log(ANDROID_LOG_WARN, "libc",
+                          "Using old property service protocol (\"%s\" is not set)",
+                          kServiceVersionPropertyName);
+  } else {
+    uint32_t version = static_cast<uint32_t>(atoll(value));
+    if (version >= kProtocolVersion2) {
+      g_propservice_protocol_version = kProtocolVersion2;
+    } else {
+      async_safe_format_log(ANDROID_LOG_WARN, "libc",
+                            "Using old property service protocol (\"%s\"=\"%s\")",
+                            kServiceVersionPropertyName, value);
+      g_propservice_protocol_version = kProtocolVersion1;
+    }
+  }
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_set(const char* key, const char* value) {
+  if (key == nullptr) return -1;
+  if (value == nullptr) value = "";
+
+  if (g_propservice_protocol_version == 0) {
+    detect_protocol_version();
+  }
+
+  if (g_propservice_protocol_version == kProtocolVersion1) {
+    // Old protocol does not support long names or values
+    if (strlen(key) >= PROP_NAME_MAX) return -1;
+    if (strlen(value) >= PROP_VALUE_MAX) return -1;
+
+    prop_msg msg;
+    memset(&msg, 0, sizeof msg);
+    msg.cmd = PROP_MSG_SETPROP;
+    strlcpy(msg.name, key, sizeof msg.name);
+    strlcpy(msg.value, value, sizeof msg.value);
+
+    return send_prop_msg(&msg);
+  } else {
+    // New protocol only allows long values for ro. properties only.
+    if (strlen(value) >= PROP_VALUE_MAX && !is_read_only(key)) return -1;
+    // Use proper protocol
+    PropertyServiceConnection connection;
+    if (!connection.IsValid()) {
+      errno = connection.GetLastError();
+      async_safe_format_log(
+          ANDROID_LOG_WARN, "libc",
+          "Unable to set property \"%s\" to \"%s\": connection failed; errno=%d (%s)", key, value,
+          errno, strerror(errno));
+      return -1;
+    }
+
+    SocketWriter writer(&connection);
+    if (!writer.WriteUint32(PROP_MSG_SETPROP2).WriteString(key).WriteString(value).Send()) {
+      errno = connection.GetLastError();
+      async_safe_format_log(ANDROID_LOG_WARN, "libc",
+                            "Unable to set property \"%s\" to \"%s\": write failed; errno=%d (%s)",
+                            key, value, errno, strerror(errno));
+      return -1;
+    }
+
+    int result = -1;
+    if (!connection.RecvInt32(&result)) {
+      errno = connection.GetLastError();
+      async_safe_format_log(ANDROID_LOG_WARN, "libc",
+                            "Unable to set property \"%s\" to \"%s\": recv failed; errno=%d (%s)",
+                            key, value, errno, strerror(errno));
+      return -1;
+    }
+
+    if (result != PROP_SUCCESS) {
+      async_safe_format_log(ANDROID_LOG_WARN, "libc",
+                            "Unable to set property \"%s\" to \"%s\": error code: 0x%x", key, value,
+                            result);
+      return -1;
+    }
+
+    return 0;
+  }
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_update(prop_info* pi, const char* value, unsigned int len) {
+  if (len >= PROP_VALUE_MAX) {
+    return -1;
+  }
+
+  prop_area* pa = __system_property_area__;
+
+  if (!pa) {
+    return -1;
+  }
+
+  uint32_t serial = atomic_load_explicit(&pi->serial, memory_order_relaxed);
+  serial |= 1;
+  atomic_store_explicit(&pi->serial, serial, memory_order_relaxed);
+  // The memcpy call here also races.  Again pretend it
+  // used memory_order_relaxed atomics, and use the analogous
+  // counterintuitive fence.
+  atomic_thread_fence(memory_order_release);
+  strlcpy(pi->value, value, len + 1);
+
+  atomic_store_explicit(&pi->serial, (len << 24) | ((serial + 1) & 0xffffff), memory_order_release);
+  __futex_wake(&pi->serial, INT32_MAX);
+
+  atomic_store_explicit(pa->serial(), atomic_load_explicit(pa->serial(), memory_order_relaxed) + 1,
+                        memory_order_release);
+  __futex_wake(pa->serial(), INT32_MAX);
+
+  return 0;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_add(const char* name, unsigned int namelen, const char* value,
+                          unsigned int valuelen) {
+  if (valuelen >= PROP_VALUE_MAX && !is_read_only(name)) {
+    return -1;
+  }
+
+  if (namelen < 1) {
+    return -1;
+  }
+
+  if (__system_property_area__ == nullptr || contexts == nullptr) {
+    return -1;
+  }
+
+  prop_area* pa = contexts->GetPropAreaForName(name);
+
+  if (!pa) {
+    async_safe_format_log(ANDROID_LOG_ERROR, "libc", "Access denied adding property \"%s\"", name);
+    return -1;
+  }
+
+  bool ret = pa->add(name, namelen, value, valuelen);
+  if (!ret) {
+    return -1;
+  }
+
+  // There is only a single mutator, but we want to make sure that
+  // updates are visible to a reader waiting for the update.
+  atomic_store_explicit(
+      __system_property_area__->serial(),
+      atomic_load_explicit(__system_property_area__->serial(), memory_order_relaxed) + 1,
+      memory_order_release);
+  __futex_wake(__system_property_area__->serial(), INT32_MAX);
+  return 0;
+}
+
+// Wait for non-locked serial, and retrieve it with acquire semantics.
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+uint32_t __system_property_serial(const prop_info* pi) {
+  uint32_t serial = load_const_atomic(&pi->serial, memory_order_acquire);
+  while (SERIAL_DIRTY(serial)) {
+    __futex_wait(const_cast<_Atomic(uint_least32_t)*>(&pi->serial), serial, nullptr);
+    serial = load_const_atomic(&pi->serial, memory_order_acquire);
+  }
+  return serial;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+uint32_t __system_property_wait_any(uint32_t old_serial) {
+  uint32_t new_serial;
+  __system_property_wait(nullptr, old_serial, &new_serial, nullptr);
+  return new_serial;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+bool __system_property_wait(const prop_info* pi, uint32_t old_serial, uint32_t* new_serial_ptr,
+                            const timespec* relative_timeout) {
+  // Are we waiting on the global serial or a specific serial?
+  atomic_uint_least32_t* serial_ptr;
+  if (pi == nullptr) {
+    if (__system_property_area__ == nullptr) return -1;
+    serial_ptr = __system_property_area__->serial();
+  } else {
+    serial_ptr = const_cast<atomic_uint_least32_t*>(&pi->serial);
+  }
+
+  uint32_t new_serial;
+  do {
+    int rc;
+    if ((rc = __futex_wait(serial_ptr, old_serial, relative_timeout)) != 0 && rc == -ETIMEDOUT) {
+      return false;
+    }
+    new_serial = load_const_atomic(serial_ptr, memory_order_acquire);
+  } while (new_serial == old_serial);
+
+  *new_serial_ptr = new_serial;
+  return true;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+const prop_info* __system_property_find_nth(unsigned n) {
+  struct find_nth {
+    const uint32_t sought;
+    uint32_t current;
+    const prop_info* result;
+
+    explicit find_nth(uint32_t n) : sought(n), current(0), result(nullptr) {
+    }
+    static void fn(const prop_info* pi, void* ptr) {
+      find_nth* self = reinterpret_cast<find_nth*>(ptr);
+      if (self->current++ == self->sought) self->result = pi;
+    }
+  } state(n);
+  __system_property_foreach(find_nth::fn, &state);
+  return state.result;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_foreach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) {
+  if (contexts == nullptr) {
+    return -1;
+  }
+
+  contexts->ForEach(propfn, cookie);
+
+  return 0;
+}
diff --git a/libc/system_properties/system_property_globals.h b/libc/system_properties/system_property_globals.h
new file mode 100644
index 0000000..e37a4ac
--- /dev/null
+++ b/libc/system_properties/system_property_globals.h
@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef SYSTEM_PROPERTIES_SYSTEM_PROPERTY_GLOBALS_H
+#define SYSTEM_PROPERTIES_SYSTEM_PROPERTY_GLOBALS_H
+
+#include "prop_area.h"
+
+// These were essentially globals before the refactoring.
+
+constexpr int PROP_FILENAME_MAX = 1024;
+
+extern char property_filename[PROP_FILENAME_MAX];
+extern size_t pa_size;
+
+extern prop_area* __system_property_area__;
+
+#endif