/*
* 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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