common/utils/full-rw.c

   1 /* nbdkit
   2  * Copyright (C) 2021 Red Hat Inc.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions are
   6  * met:
   7  *
   8  * * Redistributions of source code must retain the above copyright
   9  * notice, this list of conditions and the following disclaimer.
  10  *
  11  * * Redistributions in binary form must reproduce the above copyright
  12  * notice, this list of conditions and the following disclaimer in the
  13  * documentation and/or other materials provided with the distribution.
  14  *
  15  * * Neither the name of Red Hat nor the names of its contributors may be
  16  * used to endorse or promote products derived from this software without
  17  * specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  21  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  22  * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
  23  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  24  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  25  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
  26  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  27  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  28  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  29  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  */
  32
  33 /* These functions are like pread(2)/pwrite(2) but they always read or
  34  * write the full amount, or fail.
  35  */
  36
  37 #include <config.h>
  38
  39 #include <stdio.h>
  40 #include <stdlib.h>
  41 #include <unistd.h>
  42 #include <errno.h>
  43
  44 #include "pread.h"
  45 #include "pwrite.h"
  46
  47 ssize_t
  48 full_pread (int fd, void *buf, size_t count, off_t offset)
  49 {
  50   ssize_t ret = 0, r;
  51
  52   while (count > 0) {
  53     r = pread (fd, buf, count, offset);
  54     if (r == -1) return -1;
  55     if (r == 0) {
  56       /* Presumably the caller wasn't expecting end-of-file here, so
  57        * return an error.
  58        */
  59       errno = EIO;
  60       return -1;
  61     }
  62     ret += r;
  63     offset += r;
  64     count -= r;
  65   }
  66
  67   return ret;
  68 }
  69
  70 ssize_t
  71 full_pwrite (int fd, const void *buf, size_t count, off_t offset)
  72 {
  73   ssize_t ret = 0, r;
  74
  75   while (count > 0) {
  76     r = pwrite (fd, buf, count, offset);
  77     if (r == -1) return -1;
  78     ret += r;
  79     offset += r;
  80     count -= r;
  81   }
  82
  83   return ret;
  84 }