lib/safe-read.c

   1 /* An interface to read and write that retries after interrupts.
   2    Copyright (C) 1993, 1994, 1998, 2002 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 2, or (at your option)
   7    any later version.
   8
   9    This program 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
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, write to the Free Software Foundation,
  16    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  17
  18 #if HAVE_CONFIG_H
  19 # include <config.h>
  20 #endif
  21
  22 /* Get ssize_t.  */
  23 #include <sys/types.h>
  24 #if HAVE_UNISTD_H
  25 # include <unistd.h>
  26 #endif
  27
  28 #include <errno.h>
  29 #ifndef errno
  30 extern int errno;
  31 #endif
  32
  33 #ifdef EINTR
  34 # define IS_EINTR(x) ((x) == EINTR)
  35 #else
  36 # define IS_EINTR(x) 0
  37 #endif
  38
  39 #include <limits.h>
  40
  41 #ifndef CHAR_BIT
  42 # define CHAR_BIT 8
  43 #endif
  44
  45 /* The extra casts work around common compiler bugs.  */
  46 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
  47 /* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
  48    It is necessary at least when t == time_t.  */
  49 #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
  50                               ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
  51 #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
  52
  53 #ifndef INT_MAX
  54 # define INT_MAX TYPE_MAXIMUM (int)
  55 #endif
  56
  57 #ifdef SAFE_WRITE
  58 # include "safe-write.h"
  59 # define safe_rw safe_write
  60 # define rw write
  61 #else
  62 # include "safe-read.h"
  63 # define safe_rw safe_read
  64 # define rw read
  65 # undef const
  66 # define const /* empty */
  67 #endif
  68
  69 /* Read(write) up to COUNT bytes at BUF from(to) descriptor FD, retrying if
  70    interrupted.  Return the actual number of bytes read(written), zero for EOF,
  71    or SAFE_READ_ERROR(SAFE_WRITE_ERROR) upon error.  */
  72 size_t
  73 safe_rw (int fd, void const *buf, size_t count)
  74 {
  75   ssize_t result;
  76
  77   /* POSIX limits COUNT to SSIZE_MAX, but we limit it further, requiring
  78      that COUNT <= INT_MAX, to avoid triggering a bug in Tru64 5.1.
  79      When decreasing COUNT, keep the file pointer block-aligned.
  80      Note that in any case, read(write) may succeed, yet read(write)
  81      fewer than COUNT bytes, so the caller must be prepared to handle
  82      partial results.  */
  83   if (count > INT_MAX)
  84     count = INT_MAX & ~8191;
  85
  86   do
  87     {
  88       result = rw (fd, buf, count);
  89     }
  90   while (result < 0 && IS_EINTR (errno));
  91
  92   return (size_t) result;
  93 }