sysdeps/posix/readv.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 /* Read data from file descriptor FD, and put the result in the
  26    buffers described by VECTOR, which is a vector of COUNT `struct iovec's.
  27    The buffers are filled in the order specified.
  28    Operates just like `read' (see <unistd.h>) except that data are
  29    put in VECTOR instead of a contiguous buffer.  */
  30 int
  31 DEFUN(readv, (fd, vector, count),
  32       int fd AND CONST struct iovec *vector AND size_t count)
  33 {
  34   char *buffer;
  35   size_t bytes;
  36   int bytes_read;
  37   register size_t i;
  38
  39   /* Find the total number of bytes to be read.  */
  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   /* Read the data.  */
  48   bytes_read = read(fd, buffer, bytes);
  49   if (bytes_read <= 0)
  50     return -1;
  51
  52   /* Copy the data from BUFFER into the memory specified by VECTOR.  */
  53   bytes = bytes_read;
  54   for (i = 0; i < count; ++i)
  55     {
  56 #define min(a, b)       ((a) > (b) ? (b) : (a))
  57       size_t copy = min(vector[i].iov_len, bytes);
  58
  59       (void) memcpy((PTR) vector[i].iov_base, (PTR) buffer, copy);
  60
  61       buffer += copy;
  62       bytes -= copy;
  63       if (bytes == 0)
  64         break;
  65     }
  66
  67   return bytes_read;
  68 }