src/util/os_file.c

   1 /*
   2  * Copyright 2019 Intel Corporation
   3  * SPDX-License-Identifier: MIT
   4  */
   5
   6 #include "os_file.h"
   7
   8 #include <errno.h>
   9 #include <stdlib.h>
  10
  11 #if defined(__linux__)
  12
  13 #include <fcntl.h>
  14 #include <sys/stat.h>
  15 #include <unistd.h>
  16
  17
  18 static ssize_t
  19 readN(int fd, char *buf, size_t len)
  20 {
  21    int err = -ENODATA;
  22    size_t total = 0;
  23    do {
  24       ssize_t ret = read(fd, buf + total, len - total);
  25
  26       if (ret < 0)
  27          ret = -errno;
  28
  29       if (ret == -EINTR || ret == -EAGAIN)
  30          continue;
  31
  32       if (ret <= 0) {
  33          err = ret;
  34          break;
  35       }
  36
  37       total += ret;
  38    } while (total != len);
  39
  40    return total ? total : err;
  41 }
  42
  43 char *
  44 os_read_file(const char *filename)
  45 {
  46    /* Note that this also serves as a slight margin to avoid a 2x grow when
  47     * the file is just a few bytes larger when we read it than when we
  48     * fstat'ed it.
  49     * The string's NULL terminator is also included in here.
  50     */
  51    size_t len = 64;
  52
  53    int fd = open(filename, O_RDONLY);
  54    if (fd == -1) {
  55       /* errno set by open() */
  56       return NULL;
  57    }
  58
  59    /* Pre-allocate a buffer at least the size of the file if we can read
  60     * that information.
  61     */
  62    struct stat stat;
  63    if (fstat(fd, &stat) == 0)
  64       len += stat.st_size;
  65
  66    char *buf = malloc(len);
  67    if (!buf) {
  68       close(fd);
  69       errno = -ENOMEM;
  70       return NULL;
  71    }
  72
  73    ssize_t read;
  74    size_t offset = 0, remaining = len - 1;
  75    while ((read = readN(fd, buf + offset, remaining)) == remaining) {
  76       char *newbuf = realloc(buf, 2 * len);
  77       if (!newbuf) {
  78          free(buf);
  79          close(fd);
  80          errno = -ENOMEM;
  81          return NULL;
  82       }
  83
  84       buf = newbuf;
  85       len *= 2;
  86       offset += read;
  87       remaining = len - offset - 1;
  88    }
  89
  90    close(fd);
  91
  92    if (read > 0)
  93       offset += read;
  94
  95    buf[offset] = '\0';
  96
  97    return buf;
  98 }
  99
 100 #else
 101
 102 char *
 103 os_read_file(const char *filename)
 104 {
 105    errno = -ENOSYS;
 106    return NULL;
 107 }
 108
 109 #endif