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The information in this article applies to:
The documentation for DeviceIoControl is incomplete. It should warn you
that unexpected behavior may occur when both the following are true:
- A DeviceIoControl request is followed by another DeviceIoControl request
on the same handle.
- There was no OVERLAPPED structure passed into DeviceIoControl after the
handle to the device or file was opened with FILE_FLAG_OVERLAPPED.
The following is a list of some of the unexpected behavior that may occur:
- Requests complete before expected.
- There's undefined data in the returned buffers.
- Unknown error codes are returned.
- IRPs are held in a driver while the DeviceIoControl call has already
returned.
When a handle is requested to a driver or file with FILE_FLAG_OVERLAPPED
specified, the executive prepares itself for all requests on that handle to
be asynchronous. Usually, when the request is sent down with an OVERLAPPED
structure, an event is placed in that OVERLAPPED structure. This event is
then stored in the FILE_OBJECT in kernel mode to use later to signal the
user-mode application when that IRP has been completed. If an event is not
specified, the value will be 0 in the FILE_OBJECT, when a second request is
sent down before the first request completes (and completes), the IO
manager will not have separate signals for the completion of the requests.
Therefore, the request will appear to be completed, while in reality the
IRP has not been completed by the underlying driver.
Please see the current documentation of GetOverlappedResult for more
information on the behavior of the executive when no OVERLAPPED structure
is specified when the handle to the driver or file was opened with
FILE_FLAG_OVERLAPPED.
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