Sync to upstream AOSP

context_node.cpp

@@ -0,0 +1,98 @@
+/*
+ * 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 "system_properties/context_node.h"
+
+#include <limits.h>
+#include <unistd.h>
+
+#include <async_safe/log.h>
+
+#include "system_properties/system_properties.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", 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", filename_, context_);
+  if (len < 0 || len >= PROP_FILENAME_MAX) {
+    return false;
+  }
+
+  return access(filename, R_OK) == 0;
+}
+
+void ContextNode::Unmap() {
+  prop_area::unmap_prop_area(&pa_);
+}

contexts_serialized.cpp

@@ -0,0 +1,172 @@
+/*
+ * Copyright (C) 2017 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 "system_properties/contexts_serialized.h"
+
+#include <fcntl.h>
+#include <limits.h>
+#include <sys/mman.h>
+#include <sys/prctl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#include <new>
+
+#include <async_safe/log.h>
+
+#include "system_properties/system_properties.h"
+
+bool ContextsSerialized::InitializeContextNodes() {
+  auto num_context_nodes = property_info_area_file_->num_contexts();
+  auto context_nodes_mmap_size = sizeof(ContextNode) * num_context_nodes;
+  // We want to avoid malloc in system properties, so we take an anonymous map instead (b/31659220).
+  void* const map_result = mmap(nullptr, context_nodes_mmap_size, PROT_READ | PROT_WRITE,
+                                MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  if (map_result == MAP_FAILED) {
+    return false;
+  }
+
+  prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, map_result, context_nodes_mmap_size,
+        "System property context nodes");
+
+  context_nodes_ = reinterpret_cast<ContextNode*>(map_result);
+  num_context_nodes_ = num_context_nodes;
+  context_nodes_mmap_size_ = context_nodes_mmap_size;
+
+  for (size_t i = 0; i < num_context_nodes; ++i) {
+    new (&context_nodes_[i]) ContextNode(property_info_area_file_->context(i), filename_);
+  }
+
+  return true;
+}
+
+bool ContextsSerialized::MapSerialPropertyArea(bool access_rw, bool* fsetxattr_failed) {
+  char filename[PROP_FILENAME_MAX];
+  int len = async_safe_format_buffer(filename, sizeof(filename), "%s/properties_serial", filename_);
+  if (len < 0 || len >= PROP_FILENAME_MAX) {
+    serial_prop_area_ = nullptr;
+    return false;
+  }
+
+  if (access_rw) {
+    serial_prop_area_ =
+        prop_area::map_prop_area_rw(filename, "u:object_r:properties_serial:s0", fsetxattr_failed);
+  } else {
+    serial_prop_area_ = prop_area::map_prop_area(filename);
+  }
+  return serial_prop_area_;
+}
+
+bool ContextsSerialized::InitializeProperties() {
+  if (!property_info_area_file_.LoadDefaultPath()) {
+    return false;
+  }
+
+  if (!InitializeContextNodes()) {
+    FreeAndUnmap();
+    return false;
+  }
+
+  return true;
+}
+
+bool ContextsSerialized::Initialize(bool writable, const char* filename, bool* fsetxattr_failed) {
+  filename_ = filename;
+  if (!InitializeProperties()) {
+    return false;
+  }
+
+  if (writable) {
+    mkdir(filename_, S_IRWXU | S_IXGRP | S_IXOTH);
+    bool open_failed = false;
+    if (fsetxattr_failed) {
+      *fsetxattr_failed = false;
+    }
+
+    for (size_t i = 0; i < num_context_nodes_; ++i) {
+      if (!context_nodes_[i].Open(true, fsetxattr_failed)) {
+        open_failed = true;
+      }
+    }
+    if (open_failed || !MapSerialPropertyArea(true, fsetxattr_failed)) {
+      FreeAndUnmap();
+      return false;
+    }
+  } else {
+    if (!MapSerialPropertyArea(false, nullptr)) {
+      FreeAndUnmap();
+      return false;
+    }
+  }
+  return true;
+}
+
+prop_area* ContextsSerialized::GetPropAreaForName(const char* name) {
+  uint32_t index;
+  property_info_area_file_->GetPropertyInfoIndexes(name, &index, nullptr);
+  if (index == ~0u || index >= num_context_nodes_) {
+    async_safe_format_log(ANDROID_LOG_ERROR, "libc", "Could not find context for property \"%s\"",
+                          name);
+    return nullptr;
+  }
+  auto* context_node = &context_nodes_[index];
+  if (!context_node->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.
+    context_node->Open(false, nullptr);
+  }
+  return context_node->pa();
+}
+
+void ContextsSerialized::ForEach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) {
+  for (size_t i = 0; i < num_context_nodes_; ++i) {
+    if (context_nodes_[i].CheckAccessAndOpen()) {
+      context_nodes_[i].pa()->foreach (propfn, cookie);
+    }
+  }
+}
+
+void ContextsSerialized::ResetAccess() {
+  for (size_t i = 0; i < num_context_nodes_; ++i) {
+    context_nodes_[i].ResetAccess();
+  }
+}
+
+void ContextsSerialized::FreeAndUnmap() {
+  property_info_area_file_.Reset();
+  if (context_nodes_ != nullptr) {
+    for (size_t i = 0; i < num_context_nodes_; ++i) {
+      context_nodes_[i].Unmap();
+    }
+    munmap(context_nodes_, context_nodes_mmap_size_);
+    context_nodes_ = nullptr;
+  }
+  prop_area::unmap_prop_area(&serial_prop_area_);
+  serial_prop_area_ = nullptr;
+}

contexts_split.cpp

@@ -0,0 +1,361 @@
+/*
+ * 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 "system_properties/contexts_split.h"
+
+#include <ctype.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+
+#include <async_safe/log.h>
+
+#include "system_properties/context_node.h"
+#include "system_properties/system_properties.h"
+
+class ContextListNode : public ContextNode {
+ public:
+  ContextListNode(ContextListNode* next, const char* context, const char* filename)
+      : ContextNode(strdup(context), filename), 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.
+
+// 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;
+}
+
+bool ContextsSplit::MapSerialPropertyArea(bool access_rw, bool* fsetxattr_failed) {
+  char filename[PROP_FILENAME_MAX];
+  int len = async_safe_format_buffer(filename, sizeof(filename), "%s/properties_serial", filename_);
+  if (len < 0 || len >= PROP_FILENAME_MAX) {
+    serial_prop_area_ = nullptr;
+    return false;
+  }
+
+  if (access_rw) {
+    serial_prop_area_ =
+        prop_area::map_prop_area_rw(filename, "u:object_r:properties_serial:s0", fsetxattr_failed);
+  } else {
+    serial_prop_area_ = prop_area::map_prop_area(filename);
+  }
+  return serial_prop_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, filename_);
+      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, since we don't always have all of these partitions.
+    // E.g. In case of recovery, the vendor partition will not have mounted and we
+    // still need the system / platform properties to function.
+    if (access("/vendor/etc/selinux/vendor_property_contexts", R_OK) != -1) {
+      InitializePropertiesFromFile("/vendor/etc/selinux/vendor_property_contexts");
+    }
+  } else {
+    if (!InitializePropertiesFromFile("/plat_property_contexts")) {
+      return false;
+    }
+    if (access("/vendor_property_contexts", R_OK) != -1) {
+      InitializePropertiesFromFile("/vendor_property_contexts");
+    }
+  }
+
+  return true;
+}
+
+bool ContextsSplit::Initialize(bool writable, const char* filename, bool* fsetxattr_failed) {
+  filename_ = filename;
+  if (!InitializeProperties()) {
+    return false;
+  }
+
+  if (writable) {
+    mkdir(filename_, S_IRWXU | S_IXGRP | S_IXOTH);
+    bool open_failed = false;
+    if (fsetxattr_failed) {
+      *fsetxattr_failed = false;
+    }
+
+    ListForEach(contexts_, [&fsetxattr_failed, &open_failed](ContextListNode* l) {
+      if (!l->Open(true, fsetxattr_failed)) {
+        open_failed = true;
+      }
+    });
+    if (open_failed || !MapSerialPropertyArea(true, fsetxattr_failed)) {
+      FreeAndUnmap();
+      return false;
+    }
+  } else {
+    if (!MapSerialPropertyArea(false, nullptr)) {
+      FreeAndUnmap();
+      return false;
+    }
+  }
+  return true;
+}
+
+PrefixNode* ContextsSplit::GetPrefixNodeForName(const char* name) {
+  auto entry = ListFind(prefixes_, [name](PrefixNode* l) {
+    return l->prefix[0] == '*' || !strncmp(l->prefix, name, l->prefix_len);
+  });
+
+  return entry;
+}
+
+prop_area* ContextsSplit::GetPropAreaForName(const char* name) {
+  auto entry = GetPrefixNodeForName(name);
+  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_);
+  prop_area::unmap_prop_area(&serial_prop_area_);
+}

include/api/_system_properties.h

@@ -0,0 +1,137 @@
+/*
+ * 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 _INCLUDE_SYS__SYSTEM_PROPERTIES_H
+#define _INCLUDE_SYS__SYSTEM_PROPERTIES_H
+
+#include <sys/cdefs.h>
+#include <stdint.h>
+
+#ifndef _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
+#error you should #include <sys/system_properties.h> instead
+#endif
+
+#include <sys/system_properties.h>
+
+__BEGIN_DECLS
+
+#define PROP_SERVICE_NAME "property_service"
+#define PROP_FILENAME "/dev/__properties__"
+
+#define PROP_MSG_SETPROP 1
+#define PROP_MSG_SETPROP2 0x00020001
+
+#define PROP_SUCCESS 0
+#define PROP_ERROR_READ_CMD 0x0004
+#define PROP_ERROR_READ_DATA 0x0008
+#define PROP_ERROR_READ_ONLY_PROPERTY 0x000B
+#define PROP_ERROR_INVALID_NAME 0x0010
+#define PROP_ERROR_INVALID_VALUE 0x0014
+#define PROP_ERROR_PERMISSION_DENIED 0x0018
+#define PROP_ERROR_INVALID_CMD 0x001B
+#define PROP_ERROR_HANDLE_CONTROL_MESSAGE 0x0020
+#define PROP_ERROR_SET_FAILED 0x0024
+
+/*
+** This was previously for testing, but now that SystemProperties is its own testable class,
+** there is never a reason to call this function and its implementation simply returns -1.
+*/
+int __system_property_set_filename(const char* __filename);
+
+/*
+** Initialize the area to be used to store properties.  Can
+** only be done by a single process that has write access to
+** the property area.
+*/
+int __system_property_area_init(void);
+
+/* Read the global serial number of the system properties
+**
+** Called to predict if a series of cached __system_property_find
+** objects will have seen __system_property_serial values change.
+** But also aids the converse, as changes in the global serial can
+** also be used to predict if a failed __system_property_find
+** could in-turn now find a new object; thus preventing the
+** cycles of effort to poll __system_property_find.
+**
+** Typically called at beginning of a cache cycle to signal if _any_ possible
+** changes have occurred since last. If there is, one may check each individual
+** __system_property_serial to confirm dirty, or __system_property_find
+** to check if the property now exists. If a call to __system_property_add
+** or __system_property_update has completed between two calls to
+** __system_property_area_serial then the second call will return a larger
+** value than the first call. Beware of race conditions as changes to the
+** properties are not atomic, the main value of this call is to determine
+** whether the expensive __system_property_find is worth retrying to see if
+** a property now exists.
+**
+** Returns the serial number on success, -1 on error.
+*/
+uint32_t __system_property_area_serial(void);
+
+/* Add a new system property.  Can only be done by a single
+** process that has write access to the property area, and
+** that process must handle sequencing to ensure the property
+** does not already exist and that only one property is added
+** or updated at a time.
+**
+** Returns 0 on success, -1 if the property area is full.
+*/
+int __system_property_add(const char* __name, unsigned int __name_length, const char* __value, unsigned int __value_length);
+
+/* Update the value of a system property returned by
+** __system_property_find.  Can only be done by a single process
+** that has write access to the property area, and that process
+** must handle sequencing to ensure that only one property is
+** updated at a time.
+**
+** Returns 0 on success, -1 if the parameters are incorrect.
+*/
+int __system_property_update(prop_info* __pi, const char* __value, unsigned int __value_length);
+
+/* Read the serial number of a system property returned by
+** __system_property_find.
+**
+** Returns the serial number on success, -1 on error.
+*/
+uint32_t __system_property_serial(const prop_info* __pi);
+
+/* Initialize the system properties area in read only mode.
+ * Should be done by all processes that need to read system
+ * properties.
+ *
+ * Returns 0 on success, -1 otherwise.
+ */
+int __system_properties_init(void);
+
+/* Deprecated: use __system_property_wait instead. */
+uint32_t __system_property_wait_any(uint32_t __old_serial);
+
+__END_DECLS
+
+#endif

include/api/system_properties.h

@@ -0,0 +1,99 @@
+/*
+ * 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 _INCLUDE_SYS_SYSTEM_PROPERTIES_H
+#define _INCLUDE_SYS_SYSTEM_PROPERTIES_H
+
+#include <sys/cdefs.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+__BEGIN_DECLS
+
+typedef struct prop_info prop_info;
+
+#define PROP_VALUE_MAX  92
+
+/*
+ * Sets system property `name` to `value`, creating the system property if it doesn't already exist.
+ */
+int __system_property_set(const char* __name, const char* __value);
+
+/*
+ * Returns a `prop_info` corresponding system property `name`, or nullptr if it doesn't exist.
+ * Use __system_property_read_callback to query the current value.
+ *
+ * Property lookup is expensive, so it can be useful to cache the result of this function.
+ */
+const prop_info* __system_property_find(const char* __name);
+
+/*
+ * Calls `callback` with a consistent trio of name, value, and serial number for property `pi`.
+ */
+void __system_property_read_callback(const prop_info* __pi,
+    void (*__callback)(void* __cookie, const char* __name, const char* __value, uint32_t __serial),
+    void* __cookie) __INTRODUCED_IN(26);
+
+/*
+ * Passes a `prop_info` for each system property to the provided
+ * callback.  Use __system_property_read_callback() to read the value.
+ *
+ * This method is for inspecting and debugging the property system, and not generally useful.
+ */
+int __system_property_foreach(void (*__callback)(const prop_info* __pi, void* __cookie), void* __cookie)
+  __INTRODUCED_IN(19);
+
+/*
+ * Waits for the specific system property identified by `pi` to be updated
+ * past `old_serial`. Waits no longer than `relative_timeout`, or forever
+ * if `relaive_timeout` is null.
+ *
+ * If `pi` is null, waits for the global serial number instead.
+ *
+ * If you don't know the current serial, use 0.
+ *
+ * Returns true and updates `*new_serial_ptr` on success, or false if the call
+ * timed out.
+ */
+struct timespec;
+bool __system_property_wait(const prop_info* __pi, uint32_t __old_serial, uint32_t* __new_serial_ptr, const struct timespec* __relative_timeout)
+    __INTRODUCED_IN(26);
+
+/* Deprecated. In Android O and above, there's no limit on property name length. */
+#define PROP_NAME_MAX   32
+/* Deprecated. Use __system_property_read_callback instead. */
+int __system_property_read(const prop_info* __pi, char* __name, char* __value);
+/* Deprecated. Use __system_property_read_callback instead. */
+int __system_property_get(const char* __name, char* __value);
+/* Deprecated. Use __system_property_foreach instead. */
+const prop_info* __system_property_find_nth(unsigned __n);
+
+__END_DECLS
+
+#endif

include/platform/bionic/macros.h

@@ -0,0 +1,99 @@
+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+#define BIONIC_DISALLOW_COPY_AND_ASSIGN(TypeName) \
+  TypeName(const TypeName&) = delete;             \
+  void operator=(const TypeName&) = delete
+
+#define BIONIC_DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \
+  TypeName() = delete;                                  \
+  BIONIC_DISALLOW_COPY_AND_ASSIGN(TypeName)
+
+#define BIONIC_ROUND_UP_POWER_OF_2(value) \
+  ((sizeof(value) == 8) \
+    ? (1UL << (64 - __builtin_clzl(static_cast<unsigned long>(value)))) \
+    : (1UL << (32 - __builtin_clz(static_cast<unsigned int>(value)))))
+
+static constexpr uintptr_t align_down(uintptr_t p, size_t align) {
+  return p & ~(align - 1);
+}
+
+static constexpr uintptr_t align_up(uintptr_t p, size_t align) {
+  return (p + align - 1) & ~(align - 1);
+}
+
+template <typename T>
+static inline T* align_down(T* p, size_t align) {
+  return reinterpret_cast<T*>(align_down(reinterpret_cast<uintptr_t>(p), align));
+}
+
+template <typename T>
+static inline T* align_up(T* p, size_t align) {
+  return reinterpret_cast<T*>(align_up(reinterpret_cast<uintptr_t>(p), align));
+}
+
+#if defined(__arm__)
+#define BIONIC_STOP_UNWIND asm volatile(".cfi_undefined r14")
+#elif defined(__aarch64__)
+#define BIONIC_STOP_UNWIND asm volatile(".cfi_undefined x30")
+#elif defined(__i386__)
+#define BIONIC_STOP_UNWIND asm volatile(".cfi_undefined \%eip")
+#elif defined(__riscv)
+#define BIONIC_STOP_UNWIND asm volatile(".cfi_undefined ra")
+#elif defined(__x86_64__)
+#define BIONIC_STOP_UNWIND asm volatile(".cfi_undefined \%rip")
+#endif
+
+// The arraysize(arr) macro returns the # of elements in an array arr.
+// The expression is a compile-time constant, and therefore can be
+// used in defining new arrays, for example.  If you use arraysize on
+// a pointer by mistake, you will get a compile-time error.
+//
+// One caveat is that arraysize() doesn't accept any array of an
+// anonymous type or a type defined inside a function.
+//
+// This template function declaration is used in defining arraysize.
+// Note that the function doesn't need an implementation, as we only
+// use its type.
+template <typename T, size_t N>
+char (&ArraySizeHelper(T (&array)[N]))[N];  // NOLINT(readability/casting)
+
+#define arraysize(array) (sizeof(ArraySizeHelper(array)))
+
+// Used to inform clang's -Wimplicit-fallthrough that a fallthrough is intended. There's no way to
+// silence (or enable, apparently) -Wimplicit-fallthrough in C yet.
+#ifdef __cplusplus
+#define __BIONIC_FALLTHROUGH [[clang::fallthrough]]
+#else
+#define __BIONIC_FALLTHROUGH
+#endif
+
+static inline uintptr_t untag_address(uintptr_t p) {
+#if defined(__aarch64__)
+  return p & ((1ULL << 56) - 1);
+#else
+  return p;
+#endif
+}
+
+template <typename T>
+static inline T* untag_address(T* p) {
+  return reinterpret_cast<T*>(untag_address(reinterpret_cast<uintptr_t>(p)));
+}

include/private/ErrnoRestorer.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <errno.h>
+
+#include "platform/bionic/macros.h"
+
+class ErrnoRestorer {
+ public:
+  explicit ErrnoRestorer() : saved_errno_(errno) {
+  }
+
+  ~ErrnoRestorer() {
+    errno = saved_errno_;
+  }
+
+  void override(int new_errno) {
+    saved_errno_ = new_errno;
+  }
+
+ private:
+  int saved_errno_;
+
+  BIONIC_DISALLOW_COPY_AND_ASSIGN(ErrnoRestorer);
+};

include/private/ScopedFd.h

@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2019 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.
+ */
+
+#pragma once
+
+#include <unistd.h>
+
+#include "platform/bionic/macros.h"
+#include "private/ErrnoRestorer.h"
+
+class ScopedFd final {
+ public:
+  explicit ScopedFd(int fd) : fd_(fd) {
+  }
+
+  ScopedFd() : fd_(-1) {
+  }
+
+  ~ScopedFd() {
+    reset(-1);
+  }
+
+  void reset(int fd = -1) {
+    if (fd_ != -1) {
+      ErrnoRestorer e;
+      close(fd_);
+    }
+    fd_ = fd;
+  }
+
+  int get() const {
+    return fd_;
+  }
+
+ private:
+  int fd_;
+
+  BIONIC_DISALLOW_COPY_AND_ASSIGN(ScopedFd);
+};

include/private/bionic_defs.h

@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) 2017 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 __BIONIC_PRIVATE_BIONIC_DEFS_H_
+#define __BIONIC_PRIVATE_BIONIC_DEFS_H_
+
+/*
+ * This label is used to mark libc/libdl symbols that may need to be replaced
+ * by native bridge implementation.
+ */
+#ifdef __ANDROID_NATIVE_BRIDGE__
+#define __BIONIC_WEAK_FOR_NATIVE_BRIDGE __attribute__((__weak__, __noinline__))
+#define __BIONIC_WEAK_VARIABLE_FOR_NATIVE_BRIDGE __attribute__((__weak__))
+#define __BIONIC_WEAK_FOR_NATIVE_BRIDGE_INLINE \
+  __BIONIC_WEAK_FOR_NATIVE_BRIDGE extern "C" __LIBC_HIDDEN__
+#else
+#define __BIONIC_WEAK_FOR_NATIVE_BRIDGE
+#define __BIONIC_WEAK_VARIABLE_FOR_NATIVE_BRIDGE
+#define __BIONIC_WEAK_FOR_NATIVE_BRIDGE_INLINE static inline
+#endif
+
+#endif /* __BIONIC_PRIVATE_BIONIC_DEFS_H_ */

include/private/bionic_futex.h

@@ -0,0 +1,80 @@
+/*
+ * 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 _BIONIC_FUTEX_H
+#define _BIONIC_FUTEX_H
+
+#include <errno.h>
+#include <linux/futex.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <sys/cdefs.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+struct timespec;
+
+static inline __always_inline int __futex(volatile void* ftx, int op, int value,
+                                          const timespec* timeout, int bitset) {
+  // Our generated syscall assembler sets errno, but our callers (pthread functions) don't want to.
+  int saved_errno = errno;
+  int result = syscall(__NR_futex, ftx, op, value, timeout, NULL, bitset);
+  if (__predict_false(result == -1)) {
+    result = -errno;
+    errno = saved_errno;
+  }
+  return result;
+}
+
+static inline int __futex_wake(volatile void* ftx, int count) {
+  return __futex(ftx, FUTEX_WAKE, count, nullptr, 0);
+}
+
+static inline int __futex_wake_ex(volatile void* ftx, bool shared, int count) {
+  return __futex(ftx, shared ? FUTEX_WAKE : FUTEX_WAKE_PRIVATE, count, nullptr, 0);
+}
+
+static inline int __futex_wait(volatile void* ftx, int value, const timespec* timeout) {
+  return __futex(ftx, FUTEX_WAIT, value, timeout, 0);
+}
+
+static inline int __futex_wait_ex(volatile void* ftx, bool shared, int value) {
+  return __futex(ftx, (shared ? FUTEX_WAIT_BITSET : FUTEX_WAIT_BITSET_PRIVATE), value, nullptr,
+                 FUTEX_BITSET_MATCH_ANY);
+}
+
+__LIBC_HIDDEN__ int __futex_wait_ex(volatile void* ftx, bool shared, int value,
+                                    bool use_realtime_clock, const timespec* abs_timeout);
+
+static inline int __futex_pi_unlock(volatile void* ftx, bool shared) {
+  return __futex(ftx, shared ? FUTEX_UNLOCK_PI : FUTEX_UNLOCK_PI_PRIVATE, 0, nullptr, 0);
+}
+
+__LIBC_HIDDEN__ int __futex_pi_lock_ex(volatile void* ftx, bool shared, bool use_realtime_clock,
+                                       const timespec* abs_timeout);
+
+#endif /* _BIONIC_FUTEX_H */

include/private/bionic_lock.h

@@ -0,0 +1,99 @@
+/*
+ * Copyright (C) 2015 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.
+ */
+
+#pragma once
+
+#include <stdatomic.h>
+#include "private/bionic_futex.h"
+#include "platform/bionic/macros.h"
+
+// Lock is used in places like pthread_rwlock_t, which can be initialized without calling
+// an initialization function. So make sure Lock can be initialized by setting its memory to 0.
+class Lock {
+ private:
+  enum LockState {
+    Unlocked = 0,
+    LockedWithoutWaiter,
+    LockedWithWaiter,
+  };
+  _Atomic(LockState) state;
+  bool process_shared;
+
+ public:
+  void init(bool process_shared) {
+    atomic_init(&state, Unlocked);
+    this->process_shared = process_shared;
+  }
+
+  bool trylock() {
+    LockState old_state = Unlocked;
+    return __predict_true(atomic_compare_exchange_strong_explicit(&state, &old_state,
+                        LockedWithoutWaiter, memory_order_acquire, memory_order_relaxed));
+  }
+
+  void lock() {
+    LockState old_state = Unlocked;
+    if (__predict_true(atomic_compare_exchange_strong_explicit(&state, &old_state,
+                         LockedWithoutWaiter, memory_order_acquire, memory_order_relaxed))) {
+      return;
+    }
+    while (atomic_exchange_explicit(&state, LockedWithWaiter, memory_order_acquire) != Unlocked) {
+      // TODO: As the critical section is brief, it is a better choice to spin a few times befor sleeping.
+      __futex_wait_ex(&state, process_shared, LockedWithWaiter);
+    }
+    return;
+  }
+
+  void unlock() {
+    bool shared = process_shared; /* cache to local variable */
+    if (atomic_exchange_explicit(&state, Unlocked, memory_order_release) == LockedWithWaiter) {
+      // The Lock object may have been deallocated between the atomic exchange and the futex wake
+      // call, so avoid accessing any fields of Lock here. In that case, the wake call may target
+      // unmapped memory or trigger a spurious futex wakeup. The same situation happens with
+      // pthread mutexes. References:
+      //  - https://lkml.org/lkml/2014/11/27/472
+      //  - http://austingroupbugs.net/view.php?id=811#c2267
+      __futex_wake_ex(&state, shared, 1);
+    }
+  }
+};
+
+class LockGuard {
+ public:
+  explicit LockGuard(Lock& lock) : lock_(lock) {
+    lock_.lock();
+  }
+  ~LockGuard() {
+    lock_.unlock();
+  }
+
+  BIONIC_DISALLOW_COPY_AND_ASSIGN(LockGuard);
+
+ private:
+  Lock& lock_;
+};

include/property_info_parser/property_info_parser.h

@@ -0,0 +1,224 @@
+//
+// Copyright (C) 2017 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#ifndef PROPERTY_INFO_PARSER_H
+#define PROPERTY_INFO_PARSER_H
+
+#include <stdint.h>
+#include <stdlib.h>
+
+namespace android {
+namespace properties {
+
+// The below structs intentionally do not end with char name[0] or other tricks to allocate
+// with a dynamic size, such that they can be added onto in the future without breaking
+// backwards compatibility.
+struct PropertyEntry {
+  uint32_t name_offset;
+  uint32_t namelen;
+
+  // This is the context match for this node_; ~0u if it doesn't correspond to any.
+  uint32_t context_index;
+  // This is the type for this node_; ~0u if it doesn't correspond to any.
+  uint32_t type_index;
+};
+
+struct TrieNodeInternal {
+  // This points to a property entry struct, which includes the name for this node
+  uint32_t property_entry;
+
+  // Children are a sorted list of child nodes_; binary search them.
+  uint32_t num_child_nodes;
+  uint32_t child_nodes;
+
+  // Prefixes are terminating prefix matches at this node, sorted longest to smallest
+  // Take the first match sequentially found with StartsWith().
+  uint32_t num_prefixes;
+  uint32_t prefix_entries;
+
+  // Exact matches are a sorted list of exact matches at this node_; binary search them.
+  uint32_t num_exact_matches;
+  uint32_t exact_match_entries;
+};
+
+struct PropertyInfoAreaHeader {
+  // The current version of this data as created by property service.
+  uint32_t current_version;
+  // The lowest version of libc that can properly parse this data.
+  uint32_t minimum_supported_version;
+  uint32_t size;
+  uint32_t contexts_offset;
+  uint32_t types_offset;
+  uint32_t root_offset;
+};
+
+class SerializedData {
+ public:
+  uint32_t size() const {
+    return reinterpret_cast<const PropertyInfoAreaHeader*>(data_base_)->size;
+  }
+
+  const char* c_string(uint32_t offset) const {
+    if (offset != 0 && offset > size()) return nullptr;
+    return static_cast<const char*>(data_base_ + offset);
+  }
+
+  const uint32_t* uint32_array(uint32_t offset) const {
+    if (offset != 0 && offset > size()) return nullptr;
+    return reinterpret_cast<const uint32_t*>(data_base_ + offset);
+  }
+
+  uint32_t uint32(uint32_t offset) const {
+    if (offset != 0 && offset > size()) return ~0u;
+    return *reinterpret_cast<const uint32_t*>(data_base_ + offset);
+  }
+
+  const char* data_base() const { return data_base_; }
+
+ private:
+  const char data_base_[0];
+};
+
+class TrieNode {
+ public:
+  TrieNode() : serialized_data_(nullptr), trie_node_base_(nullptr) {}
+  TrieNode(const SerializedData* data_base, const TrieNodeInternal* trie_node_base)
+      : serialized_data_(data_base), trie_node_base_(trie_node_base) {}
+
+  const char* name() const {
+    return serialized_data_->c_string(node_property_entry()->name_offset);
+  }
+
+  uint32_t context_index() const { return node_property_entry()->context_index; }
+  uint32_t type_index() const { return node_property_entry()->type_index; }
+
+  uint32_t num_child_nodes() const { return trie_node_base_->num_child_nodes; }
+  TrieNode child_node(int n) const {
+    uint32_t child_node_offset = serialized_data_->uint32_array(trie_node_base_->child_nodes)[n];
+    const TrieNodeInternal* trie_node_base =
+        reinterpret_cast<const TrieNodeInternal*>(serialized_data_->data_base() + child_node_offset);
+    return TrieNode(serialized_data_, trie_node_base);
+  }
+
+  bool FindChildForString(const char* input, uint32_t namelen, TrieNode* child) const;
+
+  uint32_t num_prefixes() const { return trie_node_base_->num_prefixes; }
+  const PropertyEntry* prefix(int n) const {
+    uint32_t prefix_entry_offset =
+        serialized_data_->uint32_array(trie_node_base_->prefix_entries)[n];
+    return reinterpret_cast<const PropertyEntry*>(serialized_data_->data_base() +
+                                                  prefix_entry_offset);
+  }
+
+  uint32_t num_exact_matches() const { return trie_node_base_->num_exact_matches; }
+  const PropertyEntry* exact_match(int n) const {
+    uint32_t exact_match_entry_offset =
+        serialized_data_->uint32_array(trie_node_base_->exact_match_entries)[n];
+    return reinterpret_cast<const PropertyEntry*>(serialized_data_->data_base() +
+                                                  exact_match_entry_offset);
+  }
+
+ private:
+  const PropertyEntry* node_property_entry() const {
+    return reinterpret_cast<const PropertyEntry*>(serialized_data_->data_base() +
+                                                  trie_node_base_->property_entry);
+  }
+
+  const SerializedData* serialized_data_;
+  const TrieNodeInternal* trie_node_base_;
+};
+
+class PropertyInfoArea : private SerializedData {
+ public:
+  void GetPropertyInfoIndexes(const char* name, uint32_t* context_index, uint32_t* type_index) const;
+  void GetPropertyInfo(const char* property, const char** context, const char** type) const;
+
+  int FindContextIndex(const char* context) const;
+  int FindTypeIndex(const char* type) const;
+
+  const char* context(uint32_t index) const {
+    uint32_t context_array_size_offset = contexts_offset();
+    const uint32_t* context_array = uint32_array(context_array_size_offset + sizeof(uint32_t));
+    return data_base() + context_array[index];
+  }
+
+  const char* type(uint32_t index) const {
+    uint32_t type_array_size_offset = types_offset();
+    const uint32_t* type_array = uint32_array(type_array_size_offset + sizeof(uint32_t));
+    return data_base() + type_array[index];
+  }
+
+  uint32_t current_version() const { return header()->current_version; }
+  uint32_t minimum_supported_version() const { return header()->minimum_supported_version; }
+
+  uint32_t size() const { return SerializedData::size(); }
+
+  uint32_t num_contexts() const { return uint32_array(contexts_offset())[0]; }
+  uint32_t num_types() const { return uint32_array(types_offset())[0]; }
+
+  TrieNode root_node() const { return trie(header()->root_offset); }
+
+ private:
+  void CheckPrefixMatch(const char* remaining_name, const TrieNode& trie_node,
+                        uint32_t* context_index, uint32_t* type_index) const;
+
+  const PropertyInfoAreaHeader* header() const {
+    return reinterpret_cast<const PropertyInfoAreaHeader*>(data_base());
+  }
+  uint32_t contexts_offset() const { return header()->contexts_offset; }
+  uint32_t contexts_array_offset() const { return contexts_offset() + sizeof(uint32_t); }
+  uint32_t types_offset() const { return header()->types_offset; }
+  uint32_t types_array_offset() const { return types_offset() + sizeof(uint32_t); }
+
+  TrieNode trie(uint32_t offset) const {
+    if (offset != 0 && offset > size()) return TrieNode();
+    const TrieNodeInternal* trie_node_base =
+        reinterpret_cast<const TrieNodeInternal*>(data_base() + offset);
+    return TrieNode(this, trie_node_base);
+  }
+};
+
+// This is essentially a smart pointer for read only mmap region for property contexts.
+class PropertyInfoAreaFile {
+ public:
+  PropertyInfoAreaFile() : mmap_base_(nullptr), mmap_size_(0) {}
+  ~PropertyInfoAreaFile() { Reset(); }
+
+  PropertyInfoAreaFile(const PropertyInfoAreaFile&) = delete;
+  void operator=(const PropertyInfoAreaFile&) = delete;
+  PropertyInfoAreaFile(PropertyInfoAreaFile&&) = default;
+  PropertyInfoAreaFile& operator=(PropertyInfoAreaFile&&) = default;
+
+  bool LoadDefaultPath();
+  bool LoadPath(const char* filename);
+
+  const PropertyInfoArea* operator->() const {
+    return reinterpret_cast<const PropertyInfoArea*>(mmap_base_);
+  }
+
+  explicit operator bool() const { return mmap_base_ != nullptr; }
+
+  void Reset();
+
+ private:
+  void* mmap_base_;
+  size_t mmap_size_;
+};
+
+}  // namespace properties
+}  // namespace android
+
+#endif

include/system_properties/context_node.h

@@ -0,0 +1,67 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include "private/bionic_lock.h"
+
+#include "prop_area.h"
+
+class ContextNode {
+ public:
+  ContextNode(const char* context, const char* filename)
+      : context_(context), pa_(nullptr), no_access_(false), filename_(filename) {
+    lock_.init(false);
+  }
+  ~ContextNode() {
+    Unmap();
+  }
+
+  BIONIC_DISALLOW_COPY_AND_ASSIGN(ContextNode);
+
+  bool Open(bool access_rw, bool* fsetxattr_failed);
+  bool CheckAccessAndOpen();
+  void ResetAccess();
+  void Unmap();
+
+  const char* context() const {
+    return context_;
+  }
+  prop_area* pa() {
+    return pa_;
+  }
+
+ private:
+  bool CheckAccess();
+
+  Lock lock_;
+  const char* context_;
+  prop_area* pa_;
+  bool no_access_;
+  const char* filename_;
+};

include/system_properties/contexts.h

@@ -0,0 +1,45 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include "prop_area.h"
+#include "prop_info.h"
+
+class Contexts {
+ public:
+  virtual ~Contexts() {
+  }
+
+  virtual bool Initialize(bool writable, const char* filename, bool* fsetxattr_failed) = 0;
+  virtual prop_area* GetPropAreaForName(const char* name) = 0;
+  virtual prop_area* GetSerialPropArea() = 0;
+  virtual void ForEach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) = 0;
+  virtual void ResetAccess() = 0;
+  virtual void FreeAndUnmap() = 0;
+};

include/system_properties/contexts_pre_split.h

@@ -0,0 +1,69 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include "contexts.h"
+#include "prop_area.h"
+#include "prop_info.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, const char* filename, bool*) override {
+    pre_split_prop_area_ = prop_area::map_prop_area(filename);
+    return pre_split_prop_area_ != nullptr;
+  }
+
+  virtual prop_area* GetPropAreaForName(const char*) override {
+    return pre_split_prop_area_;
+  }
+
+  virtual prop_area* GetSerialPropArea() override {
+    return pre_split_prop_area_;
+  }
+
+  virtual void ForEach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) override {
+    pre_split_prop_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 {
+    prop_area::unmap_prop_area(&pre_split_prop_area_);
+  }
+
+ private:
+  prop_area* pre_split_prop_area_ = nullptr;
+};

include/system_properties/contexts_serialized.h

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2017 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.
+ */
+
+#pragma once
+
+#include <property_info_parser/property_info_parser.h>
+
+#include "context_node.h"
+#include "contexts.h"
+
+class ContextsSerialized : public Contexts {
+ public:
+  virtual ~ContextsSerialized() override {
+  }
+
+  virtual bool Initialize(bool writable, const char* filename, bool* fsetxattr_failed) override;
+  virtual prop_area* GetPropAreaForName(const char* name) override;
+  virtual prop_area* GetSerialPropArea() override {
+    return serial_prop_area_;
+  }
+  virtual void ForEach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) override;
+  virtual void ResetAccess() override;
+  virtual void FreeAndUnmap() override;
+
+ private:
+  bool InitializeContextNodes();
+  bool InitializeProperties();
+  bool MapSerialPropertyArea(bool access_rw, bool* fsetxattr_failed);
+
+  const char* filename_;
+  android::properties::PropertyInfoAreaFile property_info_area_file_;
+  ContextNode* context_nodes_ = nullptr;
+  size_t num_context_nodes_ = 0;
+  size_t context_nodes_mmap_size_ = 0;
+  prop_area* serial_prop_area_ = nullptr;
+};

include/system_properties/contexts_split.h

@@ -0,0 +1,61 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include "contexts.h"
+
+struct PrefixNode;
+class ContextListNode;
+
+class ContextsSplit : public Contexts {
+ public:
+  virtual ~ContextsSplit() override {
+  }
+
+  virtual bool Initialize(bool writable, const char* filename, bool* fsetxattr_failed) override;
+  virtual prop_area* GetPropAreaForName(const char* name) override;
+  virtual prop_area* GetSerialPropArea() override {
+    return serial_prop_area_;
+  }
+  virtual void ForEach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) override;
+  virtual void ResetAccess() override;
+  virtual void FreeAndUnmap() override;
+
+  PrefixNode* GetPrefixNodeForName(const char* name);
+
+ protected:
+  bool MapSerialPropertyArea(bool access_rw, bool* fsetxattr_failed);
+  bool InitializePropertiesFromFile(const char* filename);
+  bool InitializeProperties();
+
+  PrefixNode* prefixes_ = nullptr;
+  ContextListNode* contexts_ = nullptr;
+  prop_area* serial_prop_area_ = nullptr;
+  const char* filename_ = nullptr;
+};

include/system_properties/prop_area.h

@@ -0,0 +1,179 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include <stdatomic.h>
+#include <stdint.h>
+#include <string.h>
+#include <sys/mman.h>
+
+#include "platform/bionic/macros.h"
+
+#include "prop_info.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:
+  BIONIC_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);
+  static void unmap_prop_area(prop_area** pa) {
+    if (*pa) {
+      munmap(*pa, pa_size_);
+      *pa = nullptr;
+    }
+  }
+
+  prop_area(const uint32_t magic, const uint32_t version) : magic_(magic), version_(version) {
+    atomic_init(&serial_, 0u);
+    memset(reserved_, 0, sizeof(reserved_));
+    // Allocate enough space for the root node.
+    bytes_used_ = sizeof(prop_bt);
+    // To make property reads wait-free, we reserve a
+    // PROP_VALUE_MAX-sized block of memory, the "dirty backup area",
+    // just after the root node. When we're about to modify a
+    // property, we copy the old value into the dirty backup area and
+    // copy the new value into the prop_info structure. Before
+    // starting the latter copy, we mark the property's serial as
+    // being dirty. If a reader comes along while we're doing the
+    // property update and sees a dirty serial, the reader copies from
+    // the dirty backup area instead of the property value
+    // proper. After the copy, the reader checks whether the property
+    // serial is the same: if it is, the dirty backup area hasn't been
+    // reused for something else and we can complete the
+    // read immediately.
+    bytes_used_ +=  __BIONIC_ALIGN(PROP_VALUE_MAX, sizeof(uint_least32_t));
+  }
+
+  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_;
+  }
+  char* dirty_backup_area() {
+    return data_ + sizeof (prop_bt);
+  }
+
+ 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);
+
+  // The original design doesn't include pa_size or pa_data_size in the prop_area struct itself.
+  // Since we'll need to be backwards compatible with that design, we don't gain much by adding it
+  // now, especially since we don't have any plans to make different property areas different sizes,
+  // and thus we share these two variables among all instances.
+  static size_t pa_size_;
+  static size_t pa_data_size_;
+
+  uint32_t bytes_used_;
+  atomic_uint_least32_t serial_;
+  uint32_t magic_;
+  uint32_t version_;
+  uint32_t reserved_[28];
+  char data_[0];
+
+  BIONIC_DISALLOW_COPY_AND_ASSIGN(prop_area);
+};

include/system_properties/prop_info.h

@@ -0,0 +1,89 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include <stdatomic.h>
+#include <stdint.h>
+#include <sys/system_properties.h>
+
+#include "platform/bionic/macros.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:
+  BIONIC_DISALLOW_IMPLICIT_CONSTRUCTORS(prop_info);
+};
+
+static_assert(sizeof(prop_info) == 96, "sizeof struct prop_info must be 96 bytes");

include/system_properties/system_properties.h

@@ -0,0 +1,90 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include <sys/param.h>
+#include <sys/system_properties.h>
+
+#include "contexts.h"
+#include "contexts_pre_split.h"
+#include "contexts_serialized.h"
+#include "contexts_split.h"
+
+constexpr int PROP_FILENAME_MAX = 1024;
+
+class SystemProperties {
+ public:
+  friend struct LocalPropertyTestState;
+  friend class SystemPropertiesTest;
+  // Note that system properties are initialized before libc calls static initializers, so
+  // doing any initialization in this constructor is an error.  Even a Constructor that zero
+  // initializes this class will clobber the previous property initialization.
+  // We rely on the static SystemProperties in libc to be placed in .bss and zero initialized.
+  SystemProperties() = default;
+  // Special constructor for testing that also zero initializes the important members.
+  explicit SystemProperties(bool initialized) : initialized_(initialized) {
+  }
+
+  BIONIC_DISALLOW_COPY_AND_ASSIGN(SystemProperties);
+
+  bool Init(const char* filename);
+  bool AreaInit(const char* filename, bool* fsetxattr_failed);
+  uint32_t AreaSerial();
+  const prop_info* Find(const char* name);
+  int Read(const prop_info* pi, char* name, char* value);
+  void ReadCallback(const prop_info* pi,
+                    void (*callback)(void* cookie, const char* name, const char* value,
+                                     uint32_t serial),
+                    void* cookie);
+  int Get(const char* name, char* value);
+  int Update(prop_info* pi, const char* value, unsigned int len);
+  int Add(const char* name, unsigned int namelen, const char* value, unsigned int valuelen);
+  uint32_t WaitAny(uint32_t old_serial);
+  bool Wait(const prop_info* pi, uint32_t old_serial, uint32_t* new_serial_ptr,
+            const timespec* relative_timeout);
+  const prop_info* FindNth(unsigned n);
+  int Foreach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie);
+
+ private:
+  uint32_t ReadMutablePropertyValue(const prop_info* pi, char* value);
+
+  // We don't want to use new or malloc in properties (b/31659220), and we don't want to waste a
+  // full page by using mmap(), so we set aside enough space to create any context of the three
+  // contexts.
+  static constexpr size_t kMaxContextsAlign =
+      MAX(alignof(ContextsSerialized), MAX(alignof(ContextsSplit), alignof(ContextsPreSplit)));
+  static constexpr size_t kMaxContextsSize =
+      MAX(sizeof(ContextsSerialized), MAX(sizeof(ContextsSplit), sizeof(ContextsPreSplit)));
+  alignas(kMaxContextsAlign) char contexts_data_[kMaxContextsSize];
+  Contexts* contexts_;
+
+  bool initialized_;
+  char property_filename_[PROP_FILENAME_MAX];
+};

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 "system_properties/prop_area.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <sys/cdefs.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/xattr.h>
+#include <unistd.h>
+
+#include <new>
+
+#include <async_safe/log.h>
+
+constexpr size_t PA_SIZE = 128 * 1024;
+constexpr uint32_t PROP_AREA_MAGIC = 0x504f5250;
+constexpr uint32_t PROP_AREA_VERSION = 0xfc6ed0ab;
+
+size_t prop_area::pa_size_ = 0;
+size_t prop_area::pa_data_size_ = 0;
+
+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);
+}

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 "system_properties/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;
+}

property_info_parser.cpp

@@ -0,0 +1,246 @@
+//
+// Copyright (C) 2017 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#include "property_info_parser/property_info_parser.h"
+
+#include <fcntl.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+namespace android {
+namespace properties {
+
+namespace {
+
+// Binary search to find index of element in an array compared via f(search).
+template <typename F>
+int Find(uint32_t array_length, F&& f) {
+  int bottom = 0;
+  int top = array_length - 1;
+  while (top >= bottom) {
+    int search = (top + bottom) / 2;
+
+    auto cmp = f(search);
+
+    if (cmp == 0) return search;
+    if (cmp < 0) bottom = search + 1;
+    if (cmp > 0) top = search - 1;
+  }
+  return -1;
+}
+
+}  // namespace
+
+// Binary search the list of contexts to find the index of a given context string.
+// Only should be used for TrieSerializer to construct the Trie.
+int PropertyInfoArea::FindContextIndex(const char* context) const {
+  return Find(num_contexts(), [this, context](auto array_offset) {
+    auto string_offset = uint32_array(contexts_array_offset())[array_offset];
+    return strcmp(c_string(string_offset), context);
+  });
+}
+
+// Binary search the list of types to find the index of a given type string.
+// Only should be used for TrieSerializer to construct the Trie.
+int PropertyInfoArea::FindTypeIndex(const char* type) const {
+  return Find(num_types(), [this, type](auto array_offset) {
+    auto string_offset = uint32_array(types_array_offset())[array_offset];
+    return strcmp(c_string(string_offset), type);
+  });
+}
+
+// Binary search the list of children nodes to find a TrieNode for a given property piece.
+// Used to traverse the Trie in GetPropertyInfoIndexes().
+bool TrieNode::FindChildForString(const char* name, uint32_t namelen, TrieNode* child) const {
+  auto node_index = Find(trie_node_base_->num_child_nodes, [this, name, namelen](auto array_offset) {
+    const char* child_name = child_node(array_offset).name();
+    int cmp = strncmp(child_name, name, namelen);
+    if (cmp == 0 && child_name[namelen] != '\0') {
+      // We use strncmp() since name isn't null terminated, but we don't want to match only a
+      // prefix of a child node's name, so we check here if we did only match a prefix and
+      // return 1, to indicate to the binary search to search earlier in the array for the real
+      // match.
+      return 1;
+    }
+    return cmp;
+  });
+
+  if (node_index == -1) {
+    return false;
+  }
+  *child = child_node(node_index);
+  return true;
+}
+
+void PropertyInfoArea::CheckPrefixMatch(const char* remaining_name, const TrieNode& trie_node,
+                                        uint32_t* context_index, uint32_t* type_index) const {
+  const uint32_t remaining_name_size = strlen(remaining_name);
+  for (uint32_t i = 0; i < trie_node.num_prefixes(); ++i) {
+    auto prefix_len = trie_node.prefix(i)->namelen;
+    if (prefix_len > remaining_name_size) continue;
+
+    if (!strncmp(c_string(trie_node.prefix(i)->name_offset), remaining_name, prefix_len)) {
+      if (trie_node.prefix(i)->context_index != ~0u) {
+        *context_index = trie_node.prefix(i)->context_index;
+      }
+      if (trie_node.prefix(i)->type_index != ~0u) {
+        *type_index = trie_node.prefix(i)->type_index;
+      }
+      return;
+    }
+  }
+}
+
+void PropertyInfoArea::GetPropertyInfoIndexes(const char* name, uint32_t* context_index,
+                                              uint32_t* type_index) const {
+  uint32_t return_context_index = ~0u;
+  uint32_t return_type_index = ~0u;
+  const char* remaining_name = name;
+  auto trie_node = root_node();
+  while (true) {
+    const char* sep = strchr(remaining_name, '.');
+
+    // Apply prefix match for prefix deliminated with '.'
+    if (trie_node.context_index() != ~0u) {
+      return_context_index = trie_node.context_index();
+    }
+    if (trie_node.type_index() != ~0u) {
+      return_type_index = trie_node.type_index();
+    }
+
+    // Check prefixes at this node.  This comes after the node check since these prefixes are by
+    // definition longer than the node itself.
+    CheckPrefixMatch(remaining_name, trie_node, &return_context_index, &return_type_index);
+
+    if (sep == nullptr) {
+      break;
+    }
+
+    const uint32_t substr_size = sep - remaining_name;
+    TrieNode child_node;
+    if (!trie_node.FindChildForString(remaining_name, substr_size, &child_node)) {
+      break;
+    }
+
+    trie_node = child_node;
+    remaining_name = sep + 1;
+  }
+
+  // We've made it to a leaf node, so check contents and return appropriately.
+  // Check exact matches
+  for (uint32_t i = 0; i < trie_node.num_exact_matches(); ++i) {
+    if (!strcmp(c_string(trie_node.exact_match(i)->name_offset), remaining_name)) {
+      if (context_index != nullptr) {
+        if (trie_node.exact_match(i)->context_index != ~0u) {
+          *context_index = trie_node.exact_match(i)->context_index;
+        } else {
+          *context_index = return_context_index;
+        }
+      }
+      if (type_index != nullptr) {
+        if (trie_node.exact_match(i)->type_index != ~0u) {
+          *type_index = trie_node.exact_match(i)->type_index;
+        } else {
+          *type_index = return_type_index;
+        }
+      }
+      return;
+    }
+  }
+  // Check prefix matches for prefixes not deliminated with '.'
+  CheckPrefixMatch(remaining_name, trie_node, &return_context_index, &return_type_index);
+  // Return previously found prefix match.
+  if (context_index != nullptr) *context_index = return_context_index;
+  if (type_index != nullptr) *type_index = return_type_index;
+  return;
+}
+
+void PropertyInfoArea::GetPropertyInfo(const char* property, const char** context,
+                                       const char** type) const {
+  uint32_t context_index;
+  uint32_t type_index;
+  GetPropertyInfoIndexes(property, &context_index, &type_index);
+  if (context != nullptr) {
+    if (context_index == ~0u) {
+      *context = nullptr;
+    } else {
+      *context = this->context(context_index);
+    }
+  }
+  if (type != nullptr) {
+    if (type_index == ~0u) {
+      *type = nullptr;
+    } else {
+      *type = this->type(type_index);
+    }
+  }
+}
+
+bool PropertyInfoAreaFile::LoadDefaultPath() {
+  return LoadPath("/dev/__properties__/property_info");
+}
+
+bool PropertyInfoAreaFile::LoadPath(const char* filename) {
+  int fd = open(filename, O_CLOEXEC | O_NOFOLLOW | O_RDONLY);
+
+  struct stat fd_stat;
+  if (fstat(fd, &fd_stat) < 0) {
+    close(fd);
+    return false;
+  }
+
+  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(PropertyInfoArea)))) {
+    close(fd);
+    return false;
+  }
+
+  auto mmap_size = fd_stat.st_size;
+
+  void* map_result = mmap(nullptr, mmap_size, PROT_READ, MAP_SHARED, fd, 0);
+  if (map_result == MAP_FAILED) {
+    close(fd);
+    return false;
+  }
+
+  auto property_info_area = reinterpret_cast<PropertyInfoArea*>(map_result);
+  if (property_info_area->minimum_supported_version() > 1 ||
+      property_info_area->size() != mmap_size) {
+    munmap(map_result, mmap_size);
+    close(fd);
+    return false;
+  }
+
+  close(fd);
+  mmap_base_ = map_result;
+  mmap_size_ = mmap_size;
+  return true;
+}
+
+void PropertyInfoAreaFile::Reset() {
+  if (mmap_size_ > 0) {
+    munmap(mmap_base_, mmap_size_);
+  }
+  mmap_base_ = nullptr;
+  mmap_size_ = 0;
+}
+
+}  // namespace properties
+}  // namespace android

system_properties.cpp

@@ -0,0 +1,375 @@
+/*
+ * 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 "system_properties/system_properties.h"
+
+#include <errno.h>
+#include <stdatomic.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <new>
+
+#include <async_safe/log.h>
+
+#include "private/ErrnoRestorer.h"
+#include "private/bionic_futex.h"
+
+#include "system_properties/context_node.h"
+#include "system_properties/prop_area.h"
+#include "system_properties/prop_info.h"
+
+#define SERIAL_DIRTY(serial) ((serial)&1)
+#define SERIAL_VALUE_LEN(serial) ((serial) >> 24)
+
+static bool is_dir(const char* pathname) {
+  struct stat info;
+  if (stat(pathname, &info) == -1) {
+    return false;
+  }
+  return S_ISDIR(info.st_mode);
+}
+
+bool SystemProperties::Init(const char* filename) {
+  // This is called from __libc_init_common, and should leave errno at 0 (http://b/37248982).
+  ErrnoRestorer errno_restorer;
+
+  if (initialized_) {
+    contexts_->ResetAccess();
+    return true;
+  }
+
+  if (strlen(filename) >= PROP_FILENAME_MAX) {
+    return false;
+  }
+  strcpy(property_filename_, filename);
+
+  if (is_dir(property_filename_)) {
+    if (access("/dev/__properties__/property_info", R_OK) == 0) {
+      contexts_ = new (contexts_data_) ContextsSerialized();
+      if (!contexts_->Initialize(false, property_filename_, nullptr)) {
+        return false;
+      }
+    } else {
+      contexts_ = new (contexts_data_) ContextsSplit();
+      if (!contexts_->Initialize(false, property_filename_, nullptr)) {
+        return false;
+      }
+    }
+  } else {
+    contexts_ = new (contexts_data_) ContextsPreSplit();
+    if (!contexts_->Initialize(false, property_filename_, nullptr)) {
+      return false;
+    }
+  }
+  initialized_ = true;
+  return true;
+}
+
+bool SystemProperties::AreaInit(const char* filename, bool* fsetxattr_failed) {
+  if (strlen(filename) >= PROP_FILENAME_MAX) {
+    return false;
+  }
+  strcpy(property_filename_, filename);
+
+  contexts_ = new (contexts_data_) ContextsSerialized();
+  if (!contexts_->Initialize(true, property_filename_, fsetxattr_failed)) {
+    return false;
+  }
+  initialized_ = true;
+  return true;
+}
+
+uint32_t SystemProperties::AreaSerial() {
+  if (!initialized_) {
+    return -1;
+  }
+
+  prop_area* pa = contexts_->GetSerialPropArea();
+  if (!pa) {
+    return -1;
+  }
+
+  // Make sure this read fulfilled before __system_property_serial
+  return atomic_load_explicit(pa->serial(), memory_order_acquire);
+}
+
+const prop_info* SystemProperties::Find(const char* name) {
+  if (!initialized_) {
+    return nullptr;
+  }
+
+  prop_area* pa = contexts_->GetPropAreaForName(name);
+  if (!pa) {
+    async_safe_format_log(ANDROID_LOG_WARN, "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;
+}
+
+uint32_t SystemProperties::ReadMutablePropertyValue(const prop_info* pi, char* value) {
+  // We assume the memcpy below gets serialized by the acquire fence.
+  uint32_t new_serial = load_const_atomic(&pi->serial, memory_order_acquire);
+  uint32_t serial;
+  unsigned int len;
+  for (;;) {
+    serial = new_serial;
+    len = SERIAL_VALUE_LEN(serial);
+    if (__predict_false(SERIAL_DIRTY(serial))) {
+      // See the comment in the prop_area constructor.
+      prop_area* pa = contexts_->GetPropAreaForName(pi->name);
+      memcpy(value, pa->dirty_backup_area(), len + 1);
+    } else {
+      memcpy(value, pi->value, len + 1);
+    }
+    atomic_thread_fence(memory_order_acquire);
+    new_serial = load_const_atomic(&pi->serial, memory_order_relaxed);
+    if (__predict_true(serial == new_serial)) {
+      break;
+    }
+    // We need another fence here because we want to ensure that the memcpy in the
+    // next iteration of the loop occurs after the load of new_serial above. We could
+    // get this guarantee by making the load_const_atomic of new_serial
+    // memory_order_acquire instead of memory_order_relaxed, but then we'd pay the
+    // penalty of the memory_order_acquire even in the overwhelmingly common case
+    // that the serial number didn't change.
+    atomic_thread_fence(memory_order_acquire);
+  }
+  return serial;
+}
+
+int SystemProperties::Read(const prop_info* pi, char* name, char* value) {
+  uint32_t serial = ReadMutablePropertyValue(pi, value);
+  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 SERIAL_VALUE_LEN(serial);
+}
+
+void SystemProperties::ReadCallback(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.  We use relaxed memory order on the serial load for the same reason.
+  if (is_read_only(pi->name)) {
+    uint32_t serial = load_const_atomic(&pi->serial, memory_order_relaxed);
+    if (pi->is_long()) {
+      callback(cookie, pi->name, pi->long_value(), serial);
+    } else {
+      callback(cookie, pi->name, pi->value, serial);
+    }
+    return;
+  }
+
+  char value_buf[PROP_VALUE_MAX];
+  uint32_t serial = ReadMutablePropertyValue(pi, value_buf);
+  callback(cookie, pi->name, value_buf, serial);
+}
+
+int SystemProperties::Get(const char* name, char* value) {
+  const prop_info* pi = Find(name);
+
+  if (pi != nullptr) {
+    return Read(pi, nullptr, value);
+  } else {
+    value[0] = 0;
+    return 0;
+  }
+}
+
+int SystemProperties::Update(prop_info* pi, const char* value, unsigned int len) {
+  if (len >= PROP_VALUE_MAX) {
+    return -1;
+  }
+
+  if (!initialized_) {
+    return -1;
+  }
+
+  prop_area* serial_pa = contexts_->GetSerialPropArea();
+  if (!serial_pa) {
+    return -1;
+  }
+  prop_area* pa = contexts_->GetPropAreaForName(pi->name);
+  if (__predict_false(!pa)) {
+    async_safe_format_log(ANDROID_LOG_ERROR, "libc", "Could not find area for \"%s\"", pi->name);
+    return -1;
+  }
+
+  uint32_t serial = atomic_load_explicit(&pi->serial, memory_order_relaxed);
+  unsigned int old_len = SERIAL_VALUE_LEN(serial);
+
+  // The contract with readers is that whenever the dirty bit is set, an undamaged copy
+  // of the pre-dirty value is available in the dirty backup area. The fence ensures
+  // that we publish our dirty area update before allowing readers to see a
+  // dirty serial.
+  memcpy(pa->dirty_backup_area(), pi->value, old_len + 1);
+  atomic_thread_fence(memory_order_release);
+  serial |= 1;
+  atomic_store_explicit(&pi->serial, serial, memory_order_relaxed);
+  strlcpy(pi->value, value, len + 1);
+  // Now the primary value property area is up-to-date. Let readers know that they should
+  // look at the property value instead of the backup area.
+  atomic_thread_fence(memory_order_release);
+  atomic_store_explicit(&pi->serial, (len << 24) | ((serial + 1) & 0xffffff), memory_order_relaxed);
+  __futex_wake(&pi->serial, INT32_MAX);  // Fence by side effect
+  atomic_store_explicit(serial_pa->serial(),
+                        atomic_load_explicit(serial_pa->serial(), memory_order_relaxed) + 1,
+                        memory_order_release);
+  __futex_wake(serial_pa->serial(), INT32_MAX);
+
+  return 0;
+}
+
+int SystemProperties::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 (!initialized_) {
+    return -1;
+  }
+
+  prop_area* serial_pa = contexts_->GetSerialPropArea();
+  if (serial_pa == 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(serial_pa->serial(),
+                        atomic_load_explicit(serial_pa->serial(), memory_order_relaxed) + 1,
+                        memory_order_release);
+  __futex_wake(serial_pa->serial(), INT32_MAX);
+  return 0;
+}
+
+uint32_t SystemProperties::WaitAny(uint32_t old_serial) {
+  uint32_t new_serial;
+  Wait(nullptr, old_serial, &new_serial, nullptr);
+  return new_serial;
+}
+
+bool SystemProperties::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 (!initialized_) {
+      return -1;
+    }
+
+    prop_area* serial_pa = contexts_->GetSerialPropArea();
+    if (serial_pa == nullptr) {
+      return -1;
+    }
+
+    serial_ptr = serial_pa->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;
+}
+
+const prop_info* SystemProperties::FindNth(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);
+  Foreach(find_nth::fn, &state);
+  return state.result;
+}
+
+int SystemProperties::Foreach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) {
+  if (!initialized_) {
+    return -1;
+  }
+
+  contexts_->ForEach(propfn, cookie);
+
+  return 0;
+}

system_property_api.cpp

@@ -0,0 +1,131 @@
+/*
+ * Copyright (C) 2017 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.
+ */
+
+#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
+#include <sys/_system_properties.h>
+
+#include <system_properties/prop_area.h>
+#include <system_properties/system_properties.h>
+
+#include "private/bionic_defs.h"
+
+static SystemProperties system_properties;
+static_assert(__is_trivially_constructible(SystemProperties),
+              "System Properties must be trivially constructable");
+
+// This is public because it was exposed in the NDK. As of 2017-01, ~60 apps reference this symbol.
+// It is set to nullptr and never modified.
+__BIONIC_WEAK_VARIABLE_FOR_NATIVE_BRIDGE
+prop_area* __system_property_area__ = nullptr;
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_properties_init() {
+  return system_properties.Init(PROP_FILENAME) ? 0 : -1;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_set_filename(const char*) {
+  return -1;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_area_init() {
+  bool fsetxattr_failed = false;
+  return system_properties.AreaInit(PROP_FILENAME, &fsetxattr_failed) && !fsetxattr_failed ? 0 : -1;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+uint32_t __system_property_area_serial() {
+  return system_properties.AreaSerial();
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+const prop_info* __system_property_find(const char* name) {
+  return system_properties.Find(name);
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_read(const prop_info* pi, char* name, char* value) {
+  return system_properties.Read(pi, name, value);
+}
+
+__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) {
+  return system_properties.ReadCallback(pi, callback, cookie);
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_get(const char* name, char* value) {
+  return system_properties.Get(name, value);
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_update(prop_info* pi, const char* value, unsigned int len) {
+  return system_properties.Update(pi, value, len);
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_add(const char* name, unsigned int namelen, const char* value,
+                          unsigned int valuelen) {
+  return system_properties.Add(name, namelen, value, valuelen);
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+uint32_t __system_property_serial(const prop_info* pi) {
+  // N.B. a previous version of this function was much heavier-weight
+  // and enforced acquire semantics, so give our load here acquire
+  // semantics just in case somebody depends on
+  // __system_property_serial enforcing memory order, e.g., in case
+  // someone spins on the result of this function changing before
+  // loading some value.
+  return atomic_load_explicit(&pi->serial, memory_order_acquire);
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+uint32_t __system_property_wait_any(uint32_t old_serial) {
+  return system_properties.WaitAny(old_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) {
+  return system_properties.Wait(pi, old_serial, new_serial_ptr, relative_timeout);
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+const prop_info* __system_property_find_nth(unsigned n) {
+  return system_properties.FindNth(n);
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_foreach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) {
+  return system_properties.Foreach(propfn, cookie);
+}

system_property_set.cpp

@@ -0,0 +1,309 @@
+/*
+ * Copyright (C) 2017 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 <poll.h>
+#include <stdatomic.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <sys/uio.h>
+#include <sys/un.h>
+#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
+#include <sys/_system_properties.h>
+#include <unistd.h>
+
+#include <async_safe/log.h>
+#include <async_safe/CHECK.h>
+
+#include "private/bionic_defs.h"
+#include "platform/bionic/macros.h"
+#include "private/ScopedFd.h"
+
+static const char property_service_socket[] = "/dev/socket/" PROP_SERVICE_NAME;
+static const char* kServiceVersionPropertyName = "ro.property_service.version";
+
+class PropertyServiceConnection {
+ public:
+  PropertyServiceConnection() : last_error_(0) {
+    socket_.reset(::socket(AF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0));
+    if (socket_.get() == -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_.get(),
+                                   reinterpret_cast<sockaddr*>(&addr), alen)) == -1) {
+      last_error_ = errno;
+      socket_.reset();
+    }
+  }
+
+  bool IsValid() {
+    return socket_.get() != -1;
+  }
+
+  int GetLastError() {
+    return last_error_;
+  }
+
+  bool RecvInt32(int32_t* value) {
+    int result = TEMP_FAILURE_RETRY(recv(socket_.get(), value, sizeof(*value), MSG_WAITALL));
+    return CheckSendRecvResult(result, sizeof(*value));
+  }
+
+  int socket() {
+    return socket_.get();
+  }
+
+ 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;
+  }
+
+  ScopedFd 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_;
+
+  BIONIC_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.
+      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 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 && strncmp(key, "ro.", 3) != 0) 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;
+  }
+}