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      1 /*
      2  * Copyright (C) 2008 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 /*
     18  * Implementation of the user-space ashmem API for the simulator, which lacks
     19  * an ashmem-enabled kernel. See ashmem-dev.c for the real ashmem-based version.
     20  */
     21 
     22 #include <errno.h>
     23 #include <fcntl.h>
     24 #include <limits.h>
     25 #include <pthread.h>
     26 #include <stdbool.h>
     27 #include <stdio.h>
     28 #include <stdlib.h>
     29 #include <string.h>
     30 #include <sys/stat.h>
     31 #include <sys/types.h>
     32 #include <time.h>
     33 #include <unistd.h>
     34 
     35 #include <cutils/ashmem.h>
     36 
     37 #ifndef __unused
     38 #define __unused __attribute__((__unused__))
     39 #endif
     40 
     41 static pthread_once_t seed_initialized = PTHREAD_ONCE_INIT;
     42 static void initialize_random() {
     43     srand(time(NULL) + getpid());
     44 }
     45 
     46 int ashmem_create_region(const char *ignored __unused, size_t size)
     47 {
     48     static const char txt[] = "abcdefghijklmnopqrstuvwxyz"
     49             "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
     50     char name[64];
     51     unsigned int retries = 0;
     52     pid_t pid = getpid();
     53     int fd;
     54     if (pthread_once(&seed_initialized, &initialize_random) != 0) {
     55         return -1;
     56     }
     57     do {
     58         /* not beautiful, its just wolf-like loop unrolling */
     59         snprintf(name, sizeof(name), "/tmp/android-ashmem-%d-%c%c%c%c%c%c%c%c",
     60         pid,
     61         txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))],
     62         txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))],
     63         txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))],
     64         txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))],
     65         txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))],
     66         txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))],
     67         txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))],
     68         txt[(int) ((sizeof(txt) - 1) * (rand() / (RAND_MAX + 1.0)))]);
     69 
     70         /* open O_EXCL & O_CREAT: we are either the sole owner or we fail */
     71         fd = open(name, O_RDWR | O_CREAT | O_EXCL, 0600);
     72         if (fd == -1) {
     73             /* unlikely, but if we failed because `name' exists, retry */
     74             if (errno != EEXIST || ++retries >= 6) {
     75                 return -1;
     76             }
     77         }
     78     } while (fd == -1);
     79     /* truncate the file to `len' bytes */
     80     if (ftruncate(fd, size) != -1 && unlink(name) != -1) {
     81         return fd;
     82     }
     83     close(fd);
     84     return -1;
     85 }
     86 
     87 int ashmem_set_prot_region(int fd __unused, int prot __unused)
     88 {
     89     return 0;
     90 }
     91 
     92 int ashmem_pin_region(int fd __unused, size_t offset __unused, size_t len __unused)
     93 {
     94     return ASHMEM_NOT_PURGED;
     95 }
     96 
     97 int ashmem_unpin_region(int fd __unused, size_t offset __unused, size_t len __unused)
     98 {
     99     return ASHMEM_IS_UNPINNED;
    100 }
    101 
    102 int ashmem_get_size_region(int fd)
    103 {
    104     struct stat buf;
    105     int result;
    106 
    107     result = fstat(fd, &buf);
    108     if (result == -1) {
    109         return -1;
    110     }
    111 
    112     // Check if this is an "ashmem" region.
    113     // TODO: This is very hacky, and can easily break. We need some reliable indicator.
    114     if (!(buf.st_nlink == 0 && S_ISREG(buf.st_mode))) {
    115         errno = ENOTTY;
    116         return -1;
    117     }
    118 
    119     return (int)buf.st_size;    // TODO: care about overflow (> 2GB file)?
    120 }
    121