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          break;
  34
  35       total += ret;
  36    } while (total != len);
  37
  38    return total ? total : err;
  39 }
  40
  41 char *
  42 os_read_file(const char *filename)
  43 {
  44    /* Note that this also serves as a slight margin to avoid a 2x grow when
  45     * the file is just a few bytes larger when we read it than when we
  46     * fstat'ed it.
  47     * The string's NULL terminator is also included in here.
  48     */
  49    size_t len = 64;
  50
  51    int fd = open(filename, O_RDONLY);
  52    if (fd == -1) {
  53       /* errno set by open() */
  54       return NULL;
  55    }
  56
  57    /* Pre-allocate a buffer at least the size of the file if we can read
  58     * that information.
  59     */
  60    struct stat stat;
  61    if (fstat(fd, &stat) == 0)
  62       len += stat.st_size;
  63
  64    char *buf = malloc(len);
  65    if (!buf) {
  66       close(fd);
  67       errno = -ENOMEM;
  68       return NULL;
  69    }
  70
  71    ssize_t read;
  72    size_t offset = 0, remaining = len - 1;
  73    while ((read = readN(fd, buf + offset, remaining)) == remaining) {
  74       char *newbuf = realloc(buf, 2 * len);
  75       if (!newbuf) {
  76          free(buf);
  77          close(fd);
  78          errno = -ENOMEM;
  79          return NULL;
  80       }
  81
  82       buf = newbuf;
  83       len *= 2;
  84       offset += read;
  85       remaining = len - offset - 1;
  86    }
  87
  88    close(fd);
  89
  90    if (read > 0)
  91       offset += read;
  92
  93    buf[offset] = '\0';
  94
  95    return buf;
  96 }
  97
  98 #else
  99
 100 char *
 101 os_read_file(const char *filename)
 102 {
 103    errno = -ENOSYS;
 104    return NULL;
 105 }
 106
 107 #endif