Access denied when using long filenames


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Article ID: Q400002

The information in this article applies to:

  • Direct I/O, version 4.0, 4.1


If the program trying to open a handle to a Direct I/O device has a long filename the access to Direct I/O is denied. This article tries to give the background info and possible actions to be taken.


Direct I/O introduces a security concept where only selected applications are allowed to use the resources provided by the driver. Therefore the driver needs to check whether a process is allowed or not by examining the processes name.
Unfortunately these process names are limited by the Windows NT kernel to 15 characters including the dot. If your program has a longer filename the match will always fail and an Access Denied error will be returned.


Use MS-DOS compatible 8.3 filenames i.e. 8 characters file base name and 3 characters file extension.


This limitation has been removed in Direct I/O version 4.2.

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Last modified: 2018-04-24.
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