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 52 extern "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 */ 70 int 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 */ 78 size_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 */ 109 int 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