1 files changed, 42 insertions, 7 deletions

diff --git a/db/os_win32/os_config.c b/db/os_win32/os_config.c
index 87dfe3422..41daebd37 100644
--- a/db/os_win32/os_config.c
+++ b/db/os_win32/os_config.c
@@ -1,16 +1,14 @@
 /*-
  * See the file LICENSE for redistribution information.
  *
- * Copyright (c) 1999-2003
+ * Copyright (c) 1999-2004
  *	Sleepycat Software.  All rights reserved.
+ *
+ * $Id: os_config.c,v 11.18 2004/02/09 20:54:27 mjc Exp $
  */
 
 #include "db_config.h"
 
-#ifndef lint
-static const char revid[] = "$Id: os_config.c,v 11.15 2003/01/08 05:34:00 bostic Exp $";
-#endif /* not lint */
-
 #include "db_int.h"
 
 /*
@@ -44,10 +42,47 @@ __os_is_winnt()
 int
 __os_fs_notzero()
 {
+	static int __os_notzero = -1;
+	OSVERSIONINFO osvi;
+
 	/*
 	 * Windows/NT zero-fills pages that were never explicitly written to
-	 * the file.  Windows 95/98 gives you random garbage, and that breaks
+	 * 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().
 	 */
-	return (__os_is_winnt() ? 0 : 1);
+	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);
 }