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Peng Xue1e7e382017-02-24 01:30:16 -08001/*
2 * Copyright (C) 2017 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17/**
18 * @addtogroup Memory
19 * @{
20 */
21
22/**
23 * @file sharedmem.h
Elliott Hughes8a6843d2019-11-12 11:54:46 -080024 * @brief Shared memory buffers that can be shared between processes.
Peng Xue1e7e382017-02-24 01:30:16 -080025 */
26
27#ifndef ANDROID_SHARED_MEMORY_H
28#define ANDROID_SHARED_MEMORY_H
29
30#include <stddef.h>
Ryan Prichard2fb1d472018-07-19 20:32:19 -070031#include <sys/cdefs.h>
Peng Xue1e7e382017-02-24 01:30:16 -080032
33/******************************************************************
34 *
35 * IMPORTANT NOTICE:
36 *
37 * This file is part of Android's set of stable system headers
38 * exposed by the Android NDK (Native Development Kit).
39 *
40 * Third-party source AND binary code relies on the definitions
41 * here to be FROZEN ON ALL UPCOMING PLATFORM RELEASES.
42 *
43 * - DO NOT MODIFY ENUMS (EXCEPT IF YOU ADD NEW 32-BIT VALUES)
44 * - DO NOT MODIFY CONSTANTS OR FUNCTIONAL MACROS
45 * - DO NOT CHANGE THE SIGNATURE OF FUNCTIONS IN ANY WAY
46 * - DO NOT CHANGE THE LAYOUT OR SIZE OF STRUCTURES
47 */
48
Peng Xue1e7e382017-02-24 01:30:16 -080049#ifdef __cplusplus
50extern "C" {
51#endif
52
Ryan Prichard2fb1d472018-07-19 20:32:19 -070053#if __ANDROID_API__ >= 26
54
Peng Xue1e7e382017-02-24 01:30:16 -080055/**
56 * Create a shared memory region.
57 *
58 * Create shared memory region and returns an file descriptor. The resulting file descriptor can be
59 * mmap'ed to process memory space with PROT_READ | PROT_WRITE | PROT_EXEC. Access to shared memory
60 * region can be restricted with {@link ASharedMemory_setProt}.
61 *
62 * Use close() to release the shared memory region.
63 *
Elliott Hughes8a6843d2019-11-12 11:54:46 -080064 * Use {@link android.os.ParcelFileDescriptor} to pass the file descriptor to
65 * another process.
66 *
Elliott Hughes0c757122018-07-31 12:10:19 -070067 * Available since API level 26.
68 *
Peng Xue1e7e382017-02-24 01:30:16 -080069 * \param name an optional name.
70 * \param size size of the shared memory region
Elliott Hughes8a6843d2019-11-12 11:54:46 -080071 * \return file descriptor that denotes the shared memory; -1 and sets errno on failure, or -EINVAL if the error is that size was 0.
Peng Xue1e7e382017-02-24 01:30:16 -080072 */
Elliott Hughes78e548d2018-06-18 12:28:46 -070073int ASharedMemory_create(const char *name, size_t size) __INTRODUCED_IN(26);
Peng Xue1e7e382017-02-24 01:30:16 -080074
75/**
76 * Get the size of the shared memory region.
77 *
Elliott Hughes0c757122018-07-31 12:10:19 -070078 * Available since API level 26.
79 *
Peng Xue1e7e382017-02-24 01:30:16 -080080 * \param fd file descriptor of the shared memory region
81 * \return size in bytes; 0 if fd is not a valid shared memory file descriptor.
82 */
Elliott Hughes78e548d2018-06-18 12:28:46 -070083size_t ASharedMemory_getSize(int fd) __INTRODUCED_IN(26);
Peng Xue1e7e382017-02-24 01:30:16 -080084
85/**
86 * Restrict access of shared memory region.
87 *
88 * This function restricts access of a shared memory region. Access can only be removed. The effect
89 * applies globally to all file descriptors in all processes across the system that refer to this
90 * shared memory region. Existing memory mapped regions are not affected.
91 *
92 * It is a common use case to create a shared memory region, map it read/write locally to intialize
93 * content, and then send the shared memory to another process with read only access. Code example
Quddus Chong51633572017-05-09 10:39:23 -070094 * as below (error handling omited).
Peng Xue1e7e382017-02-24 01:30:16 -080095 *
Peng Xue1e7e382017-02-24 01:30:16 -080096 *
Quddus Chong51633572017-05-09 10:39:23 -070097 * int fd = ASharedMemory_create("memory", 128);
Peng Xue1e7e382017-02-24 01:30:16 -080098 *
Quddus Chong51633572017-05-09 10:39:23 -070099 * // By default it has PROT_READ | PROT_WRITE | PROT_EXEC.
Phong Trane0df58f2018-10-14 09:39:10 +0700100 * size_t memSize = ASharedMemory_getSize(fd);
101 * char *buffer = (char *) mmap(NULL, memSize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
Peng Xue1e7e382017-02-24 01:30:16 -0800102 *
Quddus Chong51633572017-05-09 10:39:23 -0700103 * strcpy(buffer, "This is an example."); // trivially initialize content
Peng Xue1e7e382017-02-24 01:30:16 -0800104 *
Quddus Chong51633572017-05-09 10:39:23 -0700105 * // limit access to read only
106 * ASharedMemory_setProt(fd, PROT_READ);
107 *
108 * // share fd with another process here and the other process can only map with PROT_READ.
Peng Xue1e7e382017-02-24 01:30:16 -0800109 *
Elliott Hughes0c757122018-07-31 12:10:19 -0700110 * Available since API level 26.
111 *
Peng Xue1e7e382017-02-24 01:30:16 -0800112 * \param fd file descriptor of the shared memory region.
113 * \param prot any bitwise-or'ed combination of PROT_READ, PROT_WRITE, PROT_EXEC denoting
114 * updated access. Note access can only be removed, but not added back.
Elliott Hughes8a6843d2019-11-12 11:54:46 -0800115 * \return 0 for success, -1 and sets errno on failure.
Peng Xue1e7e382017-02-24 01:30:16 -0800116 */
Elliott Hughes78e548d2018-06-18 12:28:46 -0700117int ASharedMemory_setProt(int fd, int prot) __INTRODUCED_IN(26);
Peng Xue1e7e382017-02-24 01:30:16 -0800118
Ryan Prichard2fb1d472018-07-19 20:32:19 -0700119#endif // __ANDROID_API__ >= 26
120
Peng Xue1e7e382017-02-24 01:30:16 -0800121#ifdef __cplusplus
122};
123#endif
124
125#endif // ANDROID_SHARED_MEMORY_H
126
127/** @} */