sysdeps/posix/readv.c

   1 /* Copyright (C) 1991, 1992, 1996, 1997, 2002 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, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <stdlib.h>
  20 #include <unistd.h>
  21 #include <string.h>
  22 #include <limits.h>
  23 #include <stdbool.h>
  24 #include <sys/param.h>
  25 #include <sys/uio.h>
  26 #include <errno.h>
  27
  28 /* Read data from file descriptor FD, and put the result in the
  29    buffers described by VECTOR, which is a vector of COUNT `struct iovec's.
  30    The buffers are filled in the order specified.
  31    Operates just like `read' (see <unistd.h>) except that data are
  32    put in VECTOR instead of a contiguous buffer.  */
  33 ssize_t
  34 __libc_readv (int fd, const struct iovec *vector, int count)
  35 {
  36   char *buffer;
  37   char *buffer_start;
  38   size_t bytes;
  39   ssize_t bytes_read;
  40   int i;
  41   bool use_malloc = false;
  42
  43   /* Find the total number of bytes to be read.  */
  44   bytes = 0;
  45   for (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   if (__libc_use_alloca (bytes))
  61     buffer = (char *) __alloca (bytes);
  62   else
  63     {
  64       buffer = (char *) malloc (bytes);
  65       if (buffer == NULL)
  66         /* XXX I don't know whether it is acceptable to try reading
  67            the data in chunks.  Probably not so we just fail here.  */
  68         return -1;
  69
  70       use_malloc = true;
  71     }
  72
  73   /* Read the data.  */
  74   bytes_read = __read (fd, buffer, bytes);
  75   if (bytes_read <= 0)
  76     return -1;
  77
  78   /* Copy the data from BUFFER into the memory specified by VECTOR.  */
  79   bytes = bytes_read;
  80   buffer_start = buffer;
  81   for (i = 0; i < count; ++i)
  82     {
  83       size_t copy = MIN (vector[i].iov_len, bytes);
  84
  85       (void) memcpy ((void *) vector[i].iov_base, (void *) buffer, copy);
  86
  87       buffer += copy;
  88       bytes -= copy;
  89       if (bytes == 0)
  90         break;
  91     }
  92
  93   if (use_malloc)
  94     free (buffer_start);
  95
  96   return bytes_read;
  97 }
  98 #ifndef __libc_readv
  99 strong_alias (__libc_readv, __readv)
 100 weak_alias (__libc_readv, readv)
 101 #endif