| /* |
| * 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. |
| static constexpr 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. |
| static constexpr 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"); |