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91 lines
3.8 KiB
C++
91 lines
3.8 KiB
C++
/*
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* Copyright (C) 2008 The Android Open Source Project
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#pragma once
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#include <stdatomic.h>
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#include <stdint.h>
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#include <sys/system_properties.h>
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#include "private/bionic_macros.h"
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#include "hacks.h"
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// The C11 standard doesn't allow atomic loads from const fields,
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// though C++11 does. Fudge it until standards get straightened out.
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static inline uint_least32_t load_const_atomic(const atomic_uint_least32_t* s, memory_order mo) {
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atomic_uint_least32_t* non_const_s = const_cast<atomic_uint_least32_t*>(s);
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return atomic_load_explicit(non_const_s, mo);
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}
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struct prop_info {
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// Read only properties will not set anything but the bottom most bit of serial and the top byte.
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// We borrow the 2nd from the top byte for extra flags, and use the bottom most bit of that for
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// our first user, kLongFlag.
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constexpr static uint32_t kLongFlag = 1 << 16;
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// The error message fits in part of a union with the previous 92 char property value so there
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// must be room left over after the error message for the offset to the new longer property value
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// and future expansion fields if needed. Note that this value cannot ever increase. The offset
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// to the new longer property value appears immediately after it, so an increase of this size will
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// break compatibility.
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constexpr static size_t kLongLegacyErrorBufferSize = 56;
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public:
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atomic_uint_least32_t serial;
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// we need to keep this buffer around because the property
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// value can be modified whereas name is constant.
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union {
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char value[PROP_VALUE_MAX];
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struct {
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char error_message[kLongLegacyErrorBufferSize];
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uint32_t offset;
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} long_property;
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};
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char name[0];
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bool is_long() const {
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return (load_const_atomic(&serial, memory_order_relaxed) & kLongFlag) != 0;
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}
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const char* long_value() const {
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// We can't store pointers here since this is shared memory that will have different absolute
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// pointers in different processes. We don't have data_ from prop_area, but since we know
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// `this` is data_ + some offset and long_value is data_ + some other offset, we calculate the
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// offset from `this` to long_value and store it as long_property.offset.
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return reinterpret_cast<const char*>(this) + long_property.offset;
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}
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prop_info(const char* name, uint32_t namelen, const char* value, uint32_t valuelen);
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prop_info(const char* name, uint32_t namelen, uint32_t long_offset);
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private:
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BIONIC_DISALLOW_IMPLICIT_CONSTRUCTORS(prop_info);
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};
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static_assert(sizeof(prop_info) == 96, "sizeof struct prop_info must be 96 bytes");
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