glibc/sysdeps/posix/readv.c

/* Copyright (C) 1991, 1992, 1996, 1997 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/uio.h>

/* Read data from file descriptor FD, and put the result in the
   buffers described by VECTOR, which is a vector of COUNT `struct iovec's.
   The buffers are filled in the order specified.
   Operates just like `read' (see <unistd.h>) except that data are
   put in VECTOR instead of a contiguous buffer.  */
ssize_t
__readv (fd, vector, count)
     int fd;
     const struct iovec *vector;
     int count;
{
  char *buffer;
  size_t bytes;
  int bytes_read;
  int i;

  /* Find the total number of bytes to be read.  */
  bytes = 0;
  for (i = 0; i < count; ++i)
    bytes += vector[i].iov_len;

  /* Allocate a temporary buffer to hold the data.  */
  buffer = (char *) __alloca (bytes);

  /* Read the data.  */
  bytes_read = __read (fd, buffer, bytes);
  if (bytes_read <= 0)
    return -1;

  /* Copy the data from BUFFER into the memory specified by VECTOR.  */
  bytes = bytes_read;
  for (i = 0; i < count; ++i)
    {
#define	min(a, b)	((a) > (b) ? (b) : (a))
      size_t copy = min (vector[i].iov_len, bytes);

      (void) memcpy ((void *) vector[i].iov_base, (void *) buffer, copy);

      buffer += copy;
      bytes -= copy;
      if (bytes == 0)
	break;
    }

  return bytes_read;
}
#ifndef __readv
weak_alias (__readv, readv)
#endif