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 <fcntl.h>
  10 #include <stdlib.h>
  11 #include <sys/stat.h>
  12
  13
  14 #if defined(WIN32)
  15 #include <io.h>
  16 #define open _open
  17 #define fdopen _fdopen
  18 #define O_CREAT _O_CREAT
  19 #define O_EXCL _O_EXCL
  20 #define O_WRONLY _O_WRONLY
  21 #endif
  22
  23
  24 FILE *
  25 os_file_create_unique(const char *filename, int filemode)
  26 {
  27    int fd = open(filename, O_CREAT | O_EXCL | O_WRONLY, filemode);
  28    if (fd == -1)
  29       return NULL;
  30    return fdopen(fd, "w");
  31 }
  32
  33
  34 #if defined(__linux__)
  35
  36 #include <fcntl.h>
  37 #include <sys/stat.h>
  38 #include <sys/syscall.h>
  39 #include <unistd.h>
  40
  41 /* copied from <linux/kcmp.h> */
  42 #define KCMP_FILE 0
  43
  44 static ssize_t
  45 readN(int fd, char *buf, size_t len)
  46 {
  47    int err = -ENODATA;
  48    size_t total = 0;
  49    do {
  50       ssize_t ret = read(fd, buf + total, len - total);
  51
  52       if (ret < 0)
  53          ret = -errno;
  54
  55       if (ret == -EINTR || ret == -EAGAIN)
  56          continue;
  57
  58       if (ret <= 0) {
  59          err = ret;
  60          break;
  61       }
  62
  63       total += ret;
  64    } while (total != len);
  65
  66    return total ? (ssize_t)total : err;
  67 }
  68
  69 char *
  70 os_read_file(const char *filename)
  71 {
  72    /* Note that this also serves as a slight margin to avoid a 2x grow when
  73     * the file is just a few bytes larger when we read it than when we
  74     * fstat'ed it.
  75     * The string's NULL terminator is also included in here.
  76     */
  77    size_t len = 64;
  78
  79    int fd = open(filename, O_RDONLY);
  80    if (fd == -1) {
  81       /* errno set by open() */
  82       return NULL;
  83    }
  84
  85    /* Pre-allocate a buffer at least the size of the file if we can read
  86     * that information.
  87     */
  88    struct stat stat;
  89    if (fstat(fd, &stat) == 0)
  90       len += stat.st_size;
  91
  92    char *buf = malloc(len);
  93    if (!buf) {
  94       close(fd);
  95       errno = -ENOMEM;
  96       return NULL;
  97    }
  98
  99    ssize_t actually_read;
 100    size_t offset = 0, remaining = len - 1;
 101    while ((actually_read = readN(fd, buf + offset, remaining)) == (ssize_t)remaining) {
 102       char *newbuf = realloc(buf, 2 * len);
 103       if (!newbuf) {
 104          free(buf);
 105          close(fd);
 106          errno = -ENOMEM;
 107          return NULL;
 108       }
 109
 110       buf = newbuf;
 111       len *= 2;
 112       offset += actually_read;
 113       remaining = len - offset - 1;
 114    }
 115
 116    close(fd);
 117
 118    if (actually_read > 0)
 119       offset += actually_read;
 120
 121    /* Final resize to actual size */
 122    len = offset + 1;
 123    char *newbuf = realloc(buf, len);
 124    if (!newbuf) {
 125       free(buf);
 126       errno = -ENOMEM;
 127       return NULL;
 128    }
 129    buf = newbuf;
 130
 131    buf[offset] = '\0';
 132
 133    return buf;
 134 }
 135
 136 bool
 137 os_same_file_description(int fd1, int fd2)
 138 {
 139    pid_t pid = getpid();
 140
 141    return syscall(SYS_kcmp, pid, pid, KCMP_FILE, fd1, fd2) == 0;
 142 }
 143
 144 #else
 145
 146 #include "u_debug.h"
 147
 148 char *
 149 os_read_file(const char *filename)
 150 {
 151    errno = -ENOSYS;
 152    return NULL;
 153 }
 154
 155 bool
 156 os_same_file_description(int fd1, int fd2)
 157 {
 158    if (fd1 == fd2)
 159       return true;
 160
 161    debug_warn_once("Can't tell if different file descriptors reference the same"
 162                    " file description, false negatives might cause trouble!\n");
 163    return false;
 164 }
 165
 166 #endif