libcutils/ashmem-host.c

/*
 * 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.
 */

/*
 * Implementation of the user-space ashmem API for the simulator, which lacks
 * an ashmem-enabled kernel. See ashmem-dev.c for the real ashmem-based version.
 */

#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <pthread.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>

#include <cutils/ashmem.h>

#ifndef __unused
#define __unused __attribute__((__unused__))
#endif

static pthread_once_t seed_initialized = PTHREAD_ONCE_INIT;
static void initialize_random() {
    srand(time(NULL) + getpid());
}

int ashmem_create_region(const char *ignored __unused, size_t size)
{
    static const char txt[] = "abcdefghijklmnopqrstuvwxyz"
            "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    char name[64];
    unsigned int retries = 0;
    pid_t pid = getpid();
    int fd;
    if (pthread_once(&seed_initialized, &initialize_random) != 0) {
        return -1;
    }
    do {
        /* not beautiful, its just wolf-like loop unrolling */
        snprintf(name, sizeof(name), "/tmp/android-ashmem-%d-%c%c%c%c%c%c%c%c",
        pid,
        txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))],
        txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))],
        txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))],
        txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))],
        txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))],
        txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))],
        txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))],
        txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))]);

        /* open O_EXCL & O_CREAT: we are either the sole owner or we fail */
        fd = open(name, O_RDWR | O_CREAT | O_EXCL, 0600);
        if (fd == -1) {
            /* unlikely, but if we failed because `name' exists, retry */
            if (errno != EEXIST || ++retries >= 6) {
                return -1;
            }
        }
    } while (fd == -1);
    /* truncate the file to `len' bytes */
    if (ftruncate(fd, size) != -1 && unlink(name) != -1) {
        return fd;
    }
    close(fd);
    return -1;
}

int ashmem_set_prot_region(int fd __unused, int prot __unused)
{
    return 0;
}

int ashmem_pin_region(int fd __unused, size_t offset __unused, size_t len __unused)
{
    return ASHMEM_NOT_PURGED;
}

int ashmem_unpin_region(int fd __unused, size_t offset __unused, size_t len __unused)
{
    return ASHMEM_IS_UNPINNED;
}

int ashmem_get_size_region(int fd)
{
    struct stat buf;
    int result;

    result = fstat(fd, &buf);
    if (result == -1) {
        return -1;
    }

    // Check if this is an "ashmem" region.
    // TODO: This is very hacky, and can easily break. We need some reliable indicator.
    if (!(buf.st_nlink == 0 && S_ISREG(buf.st_mode))) {
        errno = ENOTTY;
        return -1;
    }

    return (int)buf.st_size;    // TODO: care about overflow (> 2GB file)?
}