ashmem-dev.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 devices, which have our
 * ashmem-enabled kernel. See ashmem-sim.c for the "fake" tmp-based version,
 * used by the simulator.
 */
#define LOG_TAG "ashmem"

#include <errno.h>
#include <fcntl.h>
#include <pthread.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include <linux/ashmem.h>

#include <cutils/ashmem.h>
#include <log/log.h>

#define ASHMEM_DEVICE "/dev/ashmem"

/* ashmem identity */
static dev_t __ashmem_rdev;
/*
 * If we trigger a signal handler in the middle of locked activity and the
 * signal handler calls ashmem, we could get into a deadlock state.
 */
static pthread_mutex_t __ashmem_lock = PTHREAD_MUTEX_INITIALIZER;

/* logistics of getting file descriptor for ashmem */
static int __ashmem_open_locked()
{
    int ret;
    struct stat st;

    int fd = TEMP_FAILURE_RETRY(open(ASHMEM_DEVICE, O_RDWR));
    if (fd < 0) {
        return fd;
    }

    ret = TEMP_FAILURE_RETRY(fstat(fd, &st));
    if (ret < 0) {
        int save_errno = errno;
        close(fd);
        errno = save_errno;
        return ret;
    }
    if (!S_ISCHR(st.st_mode) || !st.st_rdev) {
        close(fd);
        errno = ENOTTY;
        return -1;
    }