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/* An interface to read that retries after interrupts.
Copyright (C) 1993, 1994, 1998, 2002 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software Foundation,
Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
#if HAVE_CONFIG_H
# include <config.h>
#endif
/* Specification. */
#include "safe-read.h"
/* Get ssize_t. */
#include <sys/types.h>
#if HAVE_UNISTD_H
# include <unistd.h>
#endif
#include <errno.h>
#ifndef errno
extern int errno;
#endif
#include <limits.h>
#ifndef CHAR_BIT
# define CHAR_BIT 8
#endif
/* The extra casts work around common compiler bugs. */
#define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
/* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
It is necessary at least when t == time_t. */
#define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
#define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
#ifndef INT_MAX
# define INT_MAX TYPE_MAXIMUM (int)
#endif
/* We don't pass an nbytes count > SSIZE_MAX to read() - POSIX says the
effect would be implementation-defined. Also we don't pass an nbytes
count > INT_MAX but <= SSIZE_MAX to read() - this triggers a bug in
Tru64 5.1. */
#define MAX_BYTES_TO_READ INT_MAX
#ifndef EINTR
/* If a system doesn't have support for EINTR, define it
to be a value to which errno will never be set. */
# define EINTR (INT_MAX - 10)
#endif
/* Read up to COUNT bytes at BUF from descriptor FD, retrying if interrupted.
Return the actual number of bytes read, zero for EOF, or SAFE_READ_ERROR
upon error. */
size_t
safe_read (int fd, void *buf, size_t count)
{
size_t nbytes_to_read = count;
ssize_t result;
/* Limit the number of bytes to read, to avoid running
into unspecified behaviour. But keep the file pointer block
aligned when doing so. */
if (nbytes_to_read > MAX_BYTES_TO_READ)
nbytes_to_read = MAX_BYTES_TO_READ & ~8191;
do
{
result = read (fd, buf, nbytes_to_read);
}
while (result < 0 && errno == EINTR);
return (size_t) result;
}
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