1/*
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
24 */
25
26#ifndef ANDROID_SHARED_MEMORY_H
27#define ANDROID_SHARED_MEMORY_H
28
29#include <stddef.h>
30
31/******************************************************************
32 *
33 * IMPORTANT NOTICE:
34 *
35 *   This file is part of Android's set of stable system headers
36 *   exposed by the Android NDK (Native Development Kit).
37 *
38 *   Third-party source AND binary code relies on the definitions
39 *   here to be FROZEN ON ALL UPCOMING PLATFORM RELEASES.
40 *
41 *   - DO NOT MODIFY ENUMS (EXCEPT IF YOU ADD NEW 32-BIT VALUES)
42 *   - DO NOT MODIFY CONSTANTS OR FUNCTIONAL MACROS
43 *   - DO NOT CHANGE THE SIGNATURE OF FUNCTIONS IN ANY WAY
44 *   - DO NOT CHANGE THE LAYOUT OR SIZE OF STRUCTURES
45 */
46
47/**
48 * Structures and functions for a shared memory buffer that can be shared across process.
49 */
50
51#ifdef __cplusplus
52extern "C" {
53#endif
54
55#if __ANDROID_API__ >= __ANDROID_API_O__
56
57/**
58 * Create a shared memory region.
59 *
60 * Create shared memory region and returns an file descriptor.  The resulting file descriptor can be
61 * mmap'ed to process memory space with PROT_READ | PROT_WRITE | PROT_EXEC. Access to shared memory
62 * region can be restricted with {@link ASharedMemory_setProt}.
63 *
64 * Use close() to release the shared memory region.
65 *
66 * \param name an optional name.
67 * \param size size of the shared memory region
68 * \return file descriptor that denotes the shared memory; error code on failure.
69 */
70int ASharedMemory_create(const char *name, size_t size);
71
72/**
73 * Get the size of the shared memory region.
74 *
75 * \param fd file descriptor of the shared memory region
76 * \return size in bytes; 0 if fd is not a valid shared memory file descriptor.
77 */
78size_t ASharedMemory_getSize(int fd);
79
80/**
81 * Restrict access of shared memory region.
82 *
83 * This function restricts access of a shared memory region. Access can only be removed. The effect
84 * applies globally to all file descriptors in all processes across the system that refer to this
85 * shared memory region. Existing memory mapped regions are not affected.
86 *
87 * It is a common use case to create a shared memory region, map it read/write locally to intialize
88 * content, and then send the shared memory to another process with read only access. Code example
89 * as below (error handling omited).
90 *
91 *
92 *     int fd = ASharedMemory_create("memory", 128);
93 *
94 *     // By default it has PROT_READ | PROT_WRITE | PROT_EXEC.
95 *     char *buffer = (char *) mmap(NULL, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
96 *
97 *     strcpy(buffer, "This is an example."); // trivially initialize content
98 *
99 *     // limit access to read only
100 *     ASharedMemory_setProt(fd, PROT_READ);
101 *
102 *     // share fd with another process here and the other process can only map with PROT_READ.
103 *
104 * \param fd   file descriptor of the shared memory region.
105 * \param prot any bitwise-or'ed combination of PROT_READ, PROT_WRITE, PROT_EXEC denoting
106 *             updated access. Note access can only be removed, but not added back.
107 * \return 0 for success, error code on failure.
108 */
109int ASharedMemory_setProt(int fd, int prot);
110
111#endif
112
113#ifdef __cplusplus
114};
115#endif
116
117#endif // ANDROID_SHARED_MEMORY_H
118
119/** @} */
120