sysdeps/posix/pwritev.c

   1 /* Copyright (C) 2009-2014 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  19 #include <stdlib.h>
  20 #include <unistd.h>
  21 #include <string.h>
  22 #include <limits.h>
  23 #include <stdbool.h>
  24 #include <sys/param.h>
  25 #if __WORDSIZE == 64 && !defined PWRITEV
  26 /* Hide the pwritev64 declaration.  */
  27 # define pwritev64 __redirect_pwritev64
  28 #endif
  29 #include <sys/uio.h>
  30 #include <bits/wordsize.h>
  31
  32 #ifndef PWRITEV
  33 # define PWRITEV pwritev
  34 # define PWRITE __pwrite
  35 # define OFF_T off_t
  36 #endif
  37
  38
  39 static void
  40 ifree (char **ptrp)
  41 {
  42   free (*ptrp);
  43 }
  44
  45
  46 /* Write data pointed by the buffers described by IOVEC, which is a
  47    vector of COUNT 'struct iovec's, to file descriptor FD at the given
  48    position OFFSET without change the file pointer.  The data is
  49    written in the order specified.  Operates just like 'write' (see
  50    <unistd.h>) except that the data are taken from IOVEC instead of a
  51    contiguous buffer.  */
  52 ssize_t
  53 PWRITEV (int fd, const struct iovec *vector, int count, OFF_T offset)
  54 {
  55   /* Find the total number of bytes to be read.  */
  56   size_t bytes = 0;
  57   for (int i = 0; i < count; ++i)
  58     {
  59       /* Check for ssize_t overflow.  */
  60       if (SSIZE_MAX - bytes < vector[i].iov_len)
  61         {
  62           __set_errno (EINVAL);
  63           return -1;
  64         }
  65       bytes += vector[i].iov_len;
  66     }
  67
  68   /* Allocate a temporary buffer to hold the data.  We should normally
  69      use alloca since it's faster and does not require synchronization
  70      with other threads.  But we cannot if the amount of memory
  71      required is too large.  */
  72   char *buffer;
  73   char *malloced_buffer __attribute__ ((__cleanup__ (ifree))) = NULL;
  74   if (__libc_use_alloca (bytes))
  75     buffer = (char *) __alloca (bytes);
  76   else
  77     {
  78       malloced_buffer = buffer = (char *) malloc (bytes);
  79       if (buffer == NULL)
  80         return -1;
  81     }
  82
  83   /* Copy the data from BUFFER into the memory specified by VECTOR.  */
  84   char *ptr = buffer;
  85   for (int i = 0; i < count; ++i)
  86     ptr = __mempcpy ((void *) ptr, (void *) vector[i].iov_base,
  87                      vector[i].iov_len);
  88
  89   /* Write the data.  */
  90   return PWRITE (fd, buffer, bytes, offset);
  91 }
  92 #if __WORDSIZE == 64 && defined pwritev64
  93 # undef pwritev64
  94 strong_alias (pwritev, pwritev64)
  95 #endif