sysdeps/posix/writev.c

   1 /* Copyright (C) 1991-2013 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 <stdlib.h>
  19 #include <unistd.h>
  20 #include <string.h>
  21 #include <limits.h>
  22 #include <stdbool.h>
  23 #include <sys/param.h>
  24 #include <sys/uio.h>
  25 #include <errno.h>
  26
  27
  28 static void
  29 ifree (char **ptrp)
  30 {
  31   free (*ptrp);
  32 }
  33
  34
  35 /* Write data pointed by the buffers described by VECTOR, which
  36    is a vector of COUNT 'struct iovec's, to file descriptor FD.
  37    The data is written in the order specified.
  38    Operates just like 'write' (see <unistd.h>) except that the data
  39    are taken from VECTOR instead of a contiguous buffer.  */
  40 ssize_t
  41 __libc_writev (int fd, const struct iovec *vector, int count)
  42 {
  43   /* Find the total number of bytes to be written.  */
  44   size_t bytes = 0;
  45   for (int i = 0; i < count; ++i)
  46     {
  47       /* Check for ssize_t overflow.  */
  48       if (SSIZE_MAX - bytes < vector[i].iov_len)
  49         {
  50           __set_errno (EINVAL);
  51           return -1;
  52         }
  53       bytes += vector[i].iov_len;
  54     }
  55
  56   /* Allocate a temporary buffer to hold the data.  We should normally
  57      use alloca since it's faster and does not require synchronization
  58      with other threads.  But we cannot if the amount of memory
  59      required is too large.  */
  60   char *buffer;
  61   char *malloced_buffer __attribute__ ((__cleanup__ (ifree))) = NULL;
  62   if (__libc_use_alloca (bytes))
  63     buffer = (char *) __alloca (bytes);
  64   else
  65     {
  66       malloced_buffer = buffer = (char *) malloc (bytes);
  67       if (buffer == NULL)
  68         /* XXX I don't know whether it is acceptable to try writing
  69            the data in chunks.  Probably not so we just fail here.  */
  70         return -1;
  71     }
  72
  73   /* Copy the data into BUFFER.  */
  74   size_t to_copy = bytes;
  75   char *bp = buffer;
  76   for (int i = 0; i < count; ++i)
  77     {
  78       size_t copy = MIN (vector[i].iov_len, to_copy);
  79
  80       bp = __mempcpy ((void *) bp, (void *) vector[i].iov_base, copy);
  81
  82       to_copy -= copy;
  83       if (to_copy == 0)
  84         break;
  85     }
  86
  87   ssize_t bytes_written = __write (fd, buffer, bytes);
  88
  89   return bytes_written;
  90 }
  91 #ifndef __libc_writev
  92 strong_alias (__libc_writev, __writev)
  93 weak_alias (__libc_writev, writev)
  94 #endif