| /* |
| * Copyright (C) 2008 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| #include "ashmem.h" |
| |
| #include <dlfcn.h> |
| #include <errno.h> |
| #include <pthread.h> |
| #include <unistd.h> |
| #include <stdlib.h> |
| #include <string.h> |
| #include <sys/mman.h> |
| #include <sys/types.h> |
| #include <sys/stat.h> |
| #include <sys/ioctl.h> |
| #include <sys/stat.h> /* for fdstat() */ |
| #include <fcntl.h> |
| |
| #include <linux/ashmem.h> |
| #include <sys/system_properties.h> |
| |
| #define ASHMEM_DEVICE "/dev/ashmem" |
| |
| /* Technical note regarding reading system properties. |
| * |
| * Try to use the new __system_property_read_callback API that appeared in |
| * Android O / API level 26 when available. Otherwise use the deprecated |
| * __system_property_get function. |
| * |
| * For more technical details from an NDK maintainer, see: |
| * https://bugs.chromium.org/p/chromium/issues/detail?id=392191#c17 |
| */ |
| |
| /* Weak symbol import */ |
| void __system_property_read_callback( |
| const prop_info* info, |
| void (*callback)( |
| void* cookie, const char* name, const char* value, uint32_t serial), |
| void* cookie) __attribute__((weak)); |
| |
| /* Callback used with __system_property_read_callback. */ |
| static void prop_read_int(void* cookie, |
| const char* name, |
| const char* value, |
| uint32_t serial) { |
| *(int *)cookie = atoi(value); |
| (void)name; |
| (void)serial; |
| } |
| |
| static int system_property_get_int(const char* name) { |
| int result = 0; |
| if (__system_property_read_callback) { |
| const prop_info* info = __system_property_find(name); |
| if (info) |
| __system_property_read_callback(info, &prop_read_int, &result); |
| } else { |
| char value[PROP_VALUE_MAX] = {}; |
| if (__system_property_get(name, value) >= 1) |
| result = atoi(value); |
| } |
| return result; |
| } |
| |
| static int device_api_level() { |
| static int s_api_level = -1; |
| if (s_api_level < 0) |
| s_api_level = system_property_get_int("ro.build.version.sdk"); |
| return s_api_level; |
| } |
| |
| typedef enum { |
| ASHMEM_STATUS_INIT, |
| ASHMEM_STATUS_NOT_SUPPORTED, |
| ASHMEM_STATUS_SUPPORTED, |
| } AshmemStatus; |
| |
| static AshmemStatus s_ashmem_status = ASHMEM_STATUS_INIT; |
| static dev_t s_ashmem_dev; |
| |
| /* Return the dev_t of a given file path, or 0 if not available, */ |
| static dev_t ashmem_find_dev(const char* path) { |
| struct stat st; |
| dev_t result = 0; |
| if (stat(path, &st) == 0 && S_ISCHR(st.st_mode)) |
| result = st.st_dev; |
| return result; |
| } |
| |
| static AshmemStatus ashmem_get_status(void) { |
| /* NOTE: No need to make this thread-safe, assuming that |
| * all threads will find the same value. */ |
| if (s_ashmem_status != ASHMEM_STATUS_INIT) |
| return s_ashmem_status; |
| |
| s_ashmem_dev = ashmem_find_dev(ASHMEM_DEVICE); |
| s_ashmem_status = (s_ashmem_dev == 0) ? ASHMEM_STATUS_NOT_SUPPORTED |
| : ASHMEM_STATUS_SUPPORTED; |
| return s_ashmem_status; |
| } |
| |
| /* Returns true iff the ashmem device ioctl should be used for a given fd. |
| * NOTE: Try not to use fstat() when possible to avoid performance issues. */ |
| static int ashmem_dev_fd_check(int fd) { |
| if (device_api_level() <= __ANDROID_API_O_MR1__) |
| return 1; |
| if (ashmem_get_status() == ASHMEM_STATUS_SUPPORTED) { |
| struct stat st; |
| return (fstat(fd, &st) == 0 && S_ISCHR(st.st_mode) && |
| st.st_dev != 0 && st.st_dev == s_ashmem_dev); |
| } |
| return 0; |
| } |
| |
| /* |
| * ashmem_create_region - creates a new ashmem region and returns the file |
| * descriptor, or <0 on error |
| * |
| * `name' is an optional label to give the region (visible in /proc/pid/maps) |
| * `size' is the size of the region, in page-aligned bytes |
| */ |
| static int ashmem_dev_create_region(const char *name, size_t size) { |
| int fd = open(ASHMEM_DEVICE, O_RDWR); |
| if (fd < 0) |
| return fd; |
| |
| int ret; |
| if (name) { |
| char buf[ASHMEM_NAME_LEN]; |
| strlcpy(buf, name, sizeof(buf)); |
| ret = ioctl(fd, ASHMEM_SET_NAME, buf); |
| if (ret < 0) |
| goto error; |
| } |
| ret = ioctl(fd, ASHMEM_SET_SIZE, size); |
| if (ret < 0) |
| goto error; |
| |
| return fd; |
| |
| error: |
| close(fd); |
| return ret; |
| } |
| |
| static int ashmem_dev_set_prot_region(int fd, int prot) { |
| return ioctl(fd, ASHMEM_SET_PROT_MASK, prot); |
| } |
| |
| static int ashmem_dev_get_prot_region(int fd) { |
| return ioctl(fd, ASHMEM_GET_PROT_MASK); |
| } |
| |
| static int ashmem_dev_pin_region(int fd, size_t offset, size_t len) { |
| struct ashmem_pin pin = { offset, len }; |
| return ioctl(fd, ASHMEM_PIN, &pin); |
| } |
| |
| static int ashmem_dev_unpin_region(int fd, size_t offset, size_t len) { |
| struct ashmem_pin pin = { offset, len }; |
| return ioctl(fd, ASHMEM_UNPIN, &pin); |
| } |
| |
| static size_t ashmem_dev_get_size_region(int fd) { |
| return ioctl(fd, ASHMEM_GET_SIZE, NULL); |
| } |
| |
| // Starting with API level 26, the following functions from |
| // libandroid.so should be used to create shared memory regions. |
| typedef int(*ASharedMemory_createFunc)(const char*, size_t); |
| typedef size_t(*ASharedMemory_getSizeFunc)(int fd); |
| typedef int(*ASharedMemory_setProtFunc)(int fd, int prot); |
| |
| // Function pointers to shared memory functions. |
| typedef struct { |
| ASharedMemory_createFunc create; |
| ASharedMemory_getSizeFunc getSize; |
| ASharedMemory_setProtFunc setProt; |
| } ASharedMemoryFuncs; |
| |
| static ASharedMemoryFuncs s_ashmem_funcs = {}; |
| static pthread_once_t s_ashmem_funcs_once = PTHREAD_ONCE_INIT; |
| |
| static void ashmem_init_funcs() { |
| ASharedMemoryFuncs* funcs = &s_ashmem_funcs; |
| if (device_api_level() >= __ANDROID_API_O__) { |
| /* Leaked intentionally! */ |
| void* lib = dlopen("libandroid.so", RTLD_NOW); |
| funcs->create = |
| (ASharedMemory_createFunc)dlsym(lib, "ASharedMemory_create"); |
| funcs->getSize = |
| (ASharedMemory_getSizeFunc)dlsym(lib, "ASharedMemory_getSize"); |
| funcs->setProt = |
| (ASharedMemory_setProtFunc)dlsym(lib, "ASharedMemory_setProt"); |
| } else { |
| funcs->create = &ashmem_dev_create_region; |
| funcs->getSize = &ashmem_dev_get_size_region; |
| funcs->setProt = &ashmem_dev_set_prot_region; |
| } |
| } |
| |
| static const ASharedMemoryFuncs* ashmem_get_funcs() { |
| pthread_once(&s_ashmem_funcs_once, ashmem_init_funcs); |
| return &s_ashmem_funcs; |
| } |
| |
| int ashmem_create_region(const char* name, size_t size) { |
| return ashmem_get_funcs()->create(name, size); |
| } |
| |
| int ashmem_set_prot_region(int fd, int prot) { |
| return ashmem_get_funcs()->setProt(fd, prot); |
| } |
| |
| int ashmem_get_prot_region(int fd) { |
| if (ashmem_dev_fd_check(fd)) |
| return ashmem_dev_get_prot_region(fd); |
| /* There are only two practical values to return here: either |
| * PROT_READ|PROT_WRITE or just PROT_READ, so try to determine |
| * the flags by trying to mmap() the region read-write first. |
| */ |
| int result = PROT_READ; |
| const size_t page_size = (size_t)sysconf(_SC_PAGESIZE); |
| void* m = mmap(NULL, page_size, PROT_READ|PROT_WRITE, |
| MAP_SHARED, fd, 0); |
| if (m != MAP_FAILED) { |
| munmap(m, page_size); |
| result = PROT_READ|PROT_WRITE; |
| } |
| return result; |
| } |
| |
| int ashmem_pin_region(int fd, size_t offset, size_t len) { |
| if (ashmem_dev_fd_check(fd)) |
| return ashmem_dev_pin_region(fd, offset, len); |
| return ASHMEM_NOT_PURGED; |
| } |
| |
| int ashmem_unpin_region(int fd, size_t offset, size_t len) { |
| if (ashmem_dev_fd_check(fd)) |
| return ashmem_dev_unpin_region(fd, offset, len); |
| /* NOTE: It is not possible to use madvise() here because it requires a |
| * memory address. This could be done in the caller though, instead of |
| * this function. */ |
| return 0; |
| } |
| |
| int ashmem_get_size_region(int fd) { |
| /* NOTE: Original API returns an int. Avoid breaking it. */ |
| return (int)ashmem_get_funcs()->getSize(fd); |
| } |
| |
| int ashmem_device_is_supported(void) { |
| return ashmem_get_status() == ASHMEM_STATUS_SUPPORTED; |
| } |