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 * @brief Shared memory buffers that can be shared between processes. 25 */ 26 27 #ifndef ANDROID_SHARED_MEMORY_H 28 #define ANDROID_SHARED_MEMORY_H 29 30 #include <stddef.h> 31 #include <sys/cdefs.h> 32 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 49 #ifdef __cplusplus 50 extern "C" { 51 #endif 52 53 /** 54 * Create a shared memory region. 55 * 56 * Create a shared memory region and returns a file descriptor. The resulting file descriptor can be 57 * mapped into the process' memory using mmap(2) with `PROT_READ | PROT_WRITE | PROT_EXEC`. 58 * Access to shared memory regions can be restricted with {@link ASharedMemory_setProt}. 59 * 60 * Use close(2) to release the shared memory region. 61 * 62 * Use <a href="/reference/android/os/ParcelFileDescriptor">android.os.ParcelFileDescriptor</a> 63 * to pass the file descriptor to another process. File descriptors may also be sent to other 64 * processes over a Unix domain socket with sendmsg(2) and `SCM_RIGHTS`. See sendmsg(3) and 65 * cmsg(3) man pages for more information. 66 * 67 * If you intend to share this file descriptor with a child process after 68 * calling exec(3), note that you will need to use fcntl(2) with `F_SETFD` 69 * to clear the `FD_CLOEXEC` flag for this to work on all versions of Android. 70 * 71 * Available since API level 26. 72 * 73 * \param name an optional name. 74 * \param size size of the shared memory region 75 * \return file descriptor that denotes the shared memory; 76 * -1 and sets `errno` on failure, or `-EINVAL` if the error is that size was 0. 77 */ 78 int ASharedMemory_create(const char *name, size_t size) __INTRODUCED_IN(26); 79 80 /** 81 * Get the size of the shared memory region. 82 * 83 * Available since API level 26. 84 * 85 * \param fd file descriptor of the shared memory region 86 * \return size in bytes; 0 if `fd` is not a valid shared memory file descriptor. 87 */ 88 size_t ASharedMemory_getSize(int fd) __INTRODUCED_IN(26); 89 90 /** 91 * Restrict access of shared memory region. 92 * 93 * This function restricts access of a shared memory region. Access can only be removed. The effect 94 * applies globally to all file descriptors in all processes across the system that refer to this 95 * shared memory region. Existing memory mapped regions are not affected. 96 * 97 * It is a common use case to create a shared memory region, map it read/write locally to intialize 98 * content, and then send the shared memory to another process with read only access. Code example 99 * as below (error handling omited). 100 * 101 * 102 * int fd = ASharedMemory_create("memory", 128); 103 * 104 * // By default it has PROT_READ | PROT_WRITE | PROT_EXEC. 105 * size_t memSize = ASharedMemory_getSize(fd); 106 * char *buffer = (char *) mmap(NULL, memSize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); 107 * 108 * strcpy(buffer, "This is an example."); // trivially initialize content 109 * 110 * // limit access to read only 111 * ASharedMemory_setProt(fd, PROT_READ); 112 * 113 * // share fd with another process here and the other process can only map with PROT_READ. 114 * 115 * Available since API level 26. 116 * 117 * \param fd file descriptor of the shared memory region. 118 * \param prot any bitwise-or'ed combination of `PROT_READ`, `PROT_WRITE`, `PROT_EXEC` denoting 119 * updated access. Note access can only be removed, but not added back. 120 * \return 0 for success, -1 and sets `errno` on failure. 121 */ 122 int ASharedMemory_setProt(int fd, int prot) __INTRODUCED_IN(26); 123 124 #ifdef __cplusplus 125 }; 126 #endif 127 128 #endif // ANDROID_SHARED_MEMORY_H 129 130 /** @} */ 131