Wow64DisableWow64FsRedirection function (wow64apiset.h)

Article
04/21/2022

Disables file system redirection for the calling thread. File system redirection is enabled by default.

Syntax

BOOL Wow64DisableWow64FsRedirection(
  [out] PVOID *OldValue
);

Parameters

[out] OldValue

The WOW64 file system redirection value. The system uses this parameter to store information necessary to revert (re-enable) file system redirection.

Note This value is for system use only. To avoid unpredictable behavior, do not modify this value in any way.

Return value

If the function succeeds, the return value is a nonzero value.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

This function is useful for 32-bit applications that want to gain access to the native system32 directory. By default, WOW64 file system redirection is enabled.

The Wow64DisableWow64FsRedirection/Wow64RevertWow64FsRedirection function pairing is a replacement for the functionality of the Wow64EnableWow64FsRedirection function.

To restore file system redirection, call the Wow64RevertWow64FsRedirection function. Every successful call to the Wow64DisableWow64FsRedirection function must have a matching call to the Wow64RevertWow64FsRedirection function. This will ensure redirection is re-enabled and frees associated system resources.

Note The Wow64DisableWow64FsRedirection function affects all file operations performed by the current thread, which can have unintended consequences if file system redirection is disabled for any length of time. For example, DLL loading depends on file system redirection, so disabling file system redirection will cause DLL loading to fail. Also, many feature implementations use delayed loading and will fail while redirection is disabled. The failure state of the initial delay-load operation is persisted, so any subsequent use of the delay-load function will fail even after file system redirection is re-enabled. To avoid these problems, disable file system redirection immediately before calls to specific file I/O functions (such as CreateFile) that must not be redirected, and re-enable file system redirection immediately afterward using Wow64RevertWow64FsRedirection.

Disabling file system redirection affects only operations made by the current thread. Some functions, such as CreateProcessAsUser, do their work on another thread, which is not affected by the state of file system redirection in the calling thread.

In Windows 8 and Windows Server 2012, this function is supported by the following technologies.

Technology	Supported
Server Message Block (SMB) 3.0 protocol	No
SMB 3.0 Transparent Failover (TFO)	No
SMB 3.0 with Scale-out File Shares (SO)	No
Cluster Shared Volume File System (CsvFS)	Yes
Resilient File System (ReFS)	No

Examples

The following example uses Wow64DisableWow64FsRedirection to disable file system redirection so that a 32-bit application that is running under WOW64 can open the 64-bit version of Notepad.exe in %SystemRoot%\System32 instead of being redirected to the 32-bit version in %SystemRoot%\SysWOW64.

#ifdef _WIN32_WINNT
#undef _WIN32_WINNT
#endif
#define _WIN32_WINNT 0x0501

#ifdef NTDDI_VERSION
#undef NTDDI_VERSION
#endif
#define NTDDI_VERSION 0x05010000

#include <Windows.h>

void main()
{
    HANDLE hFile = INVALID_HANDLE_VALUE;
    PVOID OldValue = NULL;

    //  Disable redirection immediately prior to the native API
    //  function call.
    if( Wow64DisableWow64FsRedirection(&OldValue) ) 
    {
        //  Any function calls in this block of code should be as concise
        //  and as simple as possible to avoid unintended results.
        hFile = CreateFile(TEXT("C:\\Windows\\System32\\Notepad.exe"),
            GENERIC_READ,
            FILE_SHARE_READ,
            NULL,
            OPEN_EXISTING,
            FILE_ATTRIBUTE_NORMAL,
            NULL);

        //  Immediately re-enable redirection. Note that any resources
        //  associated with OldValue are cleaned up by this call.
        if ( FALSE == Wow64RevertWow64FsRedirection(OldValue) )
        {
            //  Failure to re-enable redirection should be considered
            //  a critical failure and execution aborted.
            return;
        }
    }
    
    //  The handle, if valid, now can be used as usual, and without
    //  leaving redirection disabled. 
    if( INVALID_HANDLE_VALUE != hFile )  
    {
        // Use the file handle
    }
}

Requirements

Requirement	Value
Minimum supported client	Windows Vista, Windows XP Professional x64 Edition [desktop apps only]
Minimum supported server	Windows Server 2008, Windows Server 2003 with SP1 [desktop apps only]
Target Platform	Windows
Header	wow64apiset.h (include Windows.h)
Library	Kernel32.lib
DLL	Kernel32.dll

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