safe-read.c revision 9663:ace9a2ac3683 
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.  */
56size_t
57safe_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}
79