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