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- /*
- * 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;
- }
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