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/*
* 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");
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