Magisk/native/jni/external/systemproperties/include/system_properties/prop_area.h

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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 <string.h>
#include <sys/mman.h>
#include "private/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:
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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);
}
const prop_info* find(const char* name);
bool add(const char* name, unsigned int namelen, const char* value, unsigned int valuelen);
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/* resetprop */
bool del(const char *name);
bool foreach (void (*propfn)(const prop_info* pi, void* cookie), void* cookie);
atomic_uint_least32_t* serial() {
return &serial_;
}
uint32_t magic() const {
return magic_;
}
uint32_t version() const {
return version_;
}
private:
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static prop_area* map_fd_rw(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();
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/* resetprop: Traverse through the trie and find the node */
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prop_bt *find_prop_bt(prop_bt *const bt, const char* name, bool alloc_if_needed);
prop_bt* find_prop_bt(prop_bt* const bt, const char* name, uint32_t namelen, bool alloc_if_needed);
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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];
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BIONIC_DISALLOW_COPY_AND_ASSIGN(prop_area);
};