sysdeps/posix/writev.c

   1 /* Copyright (C) 1991, 1992 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 Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 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 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <ansidecl.h>
  20 #include <stdlib.h>
  21 #include <unistd.h>
  22 #include <string.h>
  23 #include <sys/uio.h>
  24
  25 /* Write data pointed by the buffers described by VECTOR, which
  26    is a vector of COUNT `struct iovec's, to file descriptor FD.
  27    The data is written in the order specified.
  28    Operates just like `write' (see <unistd.h>) except that the data
  29    are taken from VECTOR instead of a contiguous buffer.  */
  30 int
  31 DEFUN(writev, (fd, vector, count),
  32       int fd AND CONST struct iovec *vector AND size_t count)
  33 {
  34   char *buffer;
  35   register char *bp;
  36   size_t bytes, to_copy;
  37   register size_t i;
  38
  39   /* Find the total number of bytes to be written.  */
  40   bytes = 0;
  41   for (i = 0; i < count; ++i)
  42     bytes += vector[i].iov_len;
  43
  44   /* Allocate a temporary buffer to hold the data.  */
  45   buffer = (char *) __alloca(bytes);
  46
  47   /* Copy the data into BUFFER.  */
  48   to_copy = bytes;
  49   bp = buffer;
  50   for (i = 0; i < count; ++i)
  51     {
  52 #define min(a, b)       ((a) > (b) ? (b) : (a))
  53       size_t copy = min(vector[i].iov_len, to_copy);
  54
  55       (void) memcpy((PTR) bp, (PTR) vector[i].iov_base, copy);
  56
  57       bp += copy;
  58       to_copy -= copy;
  59       if (bytes == 0)
  60         break;
  61     }
  62
  63   return write(fd, buffer, bytes);
  64 }