1 /* An interface to read and write that retries after interrupts.
   2 
   3    Copyright (C) 1993, 1994, 1998, 2002, 2003, 2004, 2005, 2006 Free
   4    Software Foundation, Inc.
   5 
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 2, or (at your option)
   9    any later version.
  10 
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15 
  16    You should have received a copy of the GNU General Public License
  17    along with this program; if not, write to the Free Software Foundation,
  18    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  19 
  20 #include <config.h>
  21 
  22 /* Specification.  */
  23 #ifdef SAFE_WRITE
  24 # include "safe-write.h"
  25 #else
  26 # include "safe-read.h"
  27 #endif
  28 
  29 /* Get ssize_t.  */
  30 #include <sys/types.h>
  31 #include <unistd.h>
  32 
  33 #include <errno.h>
  34 
  35 #ifdef EINTR
  36 # define IS_EINTR(x) ((x) == EINTR)
  37 #else
  38 # define IS_EINTR(x) 0
  39 #endif
  40 
  41 #include <limits.h>
  42 
  43 #ifdef SAFE_WRITE
  44 # define safe_rw safe_write
  45 # define rw write
  46 #else
  47 # define safe_rw safe_read
  48 # define rw read
  49 # undef const
  50 # define const /* empty */
  51 #endif
  52 
  53 /* Read(write) up to COUNT bytes at BUF from(to) descriptor FD, retrying if
  54    interrupted.  Return the actual number of bytes read(written), zero for EOF,
  55    or SAFE_READ_ERROR(SAFE_WRITE_ERROR) upon error.  */
  56 size_t
  57 safe_rw (int fd, void const *buf, size_t count)
  58 {
  59   /* Work around a bug in Tru64 5.1.  Attempting to read more than
  60      INT_MAX bytes fails with errno == EINVAL.  See
  61      <http://lists.gnu.org/archive/html/bug-gnu-utils/2002-04/msg00010.html>.
  62      When decreasing COUNT, keep it block-aligned.  */
  63   enum { BUGGY_READ_MAXIMUM = INT_MAX & ~8191 };
  64 
  65   for (;;)
  66     {
  67       ssize_t result = rw (fd, buf, count);
  68 
  69       if (0 <= result)
  70         return result;
  71       else if (IS_EINTR (errno))
  72         continue;
  73       else if (errno == EINVAL && BUGGY_READ_MAXIMUM < count)
  74         count = BUGGY_READ_MAXIMUM;
  75       else
  76         return result;
  77     }
  78 }