sysdeps/posix/writev.c

   1 /* Copyright (C) 1991, 1992, 1996 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 not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 #include <stdlib.h>
  20 #include <unistd.h>
  21 #include <string.h>
  22 #include <sys/uio.h>
  23
  24 /* Write data pointed by the buffers described by VECTOR, which
  25    is a vector of COUNT `struct iovec's, to file descriptor FD.
  26    The data is written in the order specified.
  27    Operates just like `write' (see <unistd.h>) except that the data
  28    are taken from VECTOR instead of a contiguous buffer.  */
  29 ssize_t
  30 writev (fd, vector, count)
  31      int fd;
  32      const struct iovec *vector;
  33      int count;
  34 {
  35   char *buffer;
  36   register char *bp;
  37   size_t bytes, to_copy;
  38   int i;
  39
  40   /* Find the total number of bytes to be written.  */
  41   bytes = 0;
  42   for (i = 0; i < count; ++i)
  43     bytes += vector[i].iov_len;
  44
  45   /* Allocate a temporary buffer to hold the data.  */
  46   buffer = (char *) __alloca (bytes);
  47
  48   /* Copy the data into BUFFER.  */
  49   to_copy = bytes;
  50   bp = buffer;
  51   for (i = 0; i < count; ++i)
  52     {
  53 #define min(a, b)       ((a) > (b) ? (b) : (a))
  54       size_t copy = min (vector[i].iov_len, to_copy);
  55
  56       (void) memcpy ((void *) bp, (void *) vector[i].iov_base, copy);
  57
  58       bp += copy;
  59       to_copy -= copy;
  60       if (bytes == 0)
  61         break;
  62     }
  63
  64   return write (fd, buffer, bytes);
  65 }