os_config.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1999-2005
 *      Sleepycat Software.  All rights reserved.
 *
 * $Id: os_config.c,v 12.2 2005/06/16 20:23:28 bostic Exp $
 */

#include "db_config.h"

#include "db_int.h"

/*
 * __os_is_winnt --
 *      Return 1 if Windows/NT, otherwise 0.
 *
 * PUBLIC: int __os_is_winnt __P((void));
 */
int
__os_is_winnt()
{
        static int __os_type = -1;

        /*
         * The value of __os_type is computed only once, and cached to
         * avoid the overhead of repeated calls to GetVersion().
         */
        if (__os_type == -1) {
                if ((GetVersion() & 0x80000000) == 0)
                        __os_type = 1;
                else
                        __os_type = 0;
        }
        return (__os_type);
}

/*
 * __os_fs_notzero --
 *      Return 1 if allocated filesystem blocks are not zeroed.
 */
int
__os_fs_notzero()
{
        static int __os_notzero = -1;
        OSVERSIONINFO osvi;

        /*
         * Windows/NT zero-fills pages that were never explicitly written to
         * the file.  Note however that this is *NOT* documented.  In fact, the
         * Win32 documentation makes it clear that there are no guarantees that
         * uninitialized bytes will be zeroed:
         *
         *   If the file is extended, the contents of the file between the old
         *   EOF position and the new position are not defined.
         *
         * Experiments confirm that NT/2K/XP all zero fill for both NTFS and
         * FAT32.  Cygwin also relies on this behavior.  This is the relevant
         * comment from Cygwin:
         *
         *    Oops, this is the bug case - Win95 uses whatever is on the disk
         *    instead of some known (safe) value, so we must seek back and fill
         *    in the gap with zeros. - DJ
         *    Note: this bug doesn't happen on NT4, even though the
         *    documentation for WriteFile() says that it *may* happen on any OS.
         *
         * We're making a bet, here, but we made it a long time ago and haven't
         * yet seen any evidence that it was wrong.
         *
         * Windows 95/98 and On-Time give random garbage, and that breaks
         * Berkeley DB.
         *
         * The value of __os_notzero is computed only once, and cached to
         * avoid the overhead of repeated calls to GetVersion().
         */
        if (__os_notzero == -1) {
                if (__os_is_winnt()) {
                        osvi.dwOSVersionInfoSize = sizeof(OSVERSIONINFO);
                        GetVersionEx(&osvi);
                        if (_tcscmp(osvi.szCSDVersion, _T("RTTarget-32")) == 0)
                                __os_notzero = 1;       /* On-Time */
                        else
                                __os_notzero = 0;       /* Windows/NT */
                } else
                        __os_notzero = 1;               /* Not Windows/NT */
        }
        return (__os_notzero);
}

/*
 * __os_support_db_register --
 *      Return 1 if the system supports DB_REGISTER.
 */
int
__os_support_db_register()
{
        return (__os_is_winnt());
}

/*
 * __os_support_replication --
 *      Return 1 if the system supports replication.
 */
int
__os_support_replication()
{
        return (__os_is_winnt());
}

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