/// <summary>
/// Helper method to construct an asyncResult object and use it to
/// call NativeControl(). Called by BeginAsyncControl().
/// </summary>
private static DeviceAsyncResult <T> AsyncControl <T>(
SafeFileHandle device,
int controlCode,
T outBuffer,
AsyncCallback asyncCallback,
object state
)
{
SafePinnedObject outDeviceBuffer = null;
if (outBuffer != null)
{
outDeviceBuffer = new SafePinnedObject(outBuffer);
}
// Create the async result object
DeviceAsyncResult <T> asyncResult = new DeviceAsyncResult <T>(outDeviceBuffer,
asyncCallback,
state
);
unsafe
{
uint bytesReturned = 0;
NativeAsyncControl(device,
controlCode,
outDeviceBuffer,
ref bytesReturned,
asyncResult.GetNativeOverlapped()
);
}
return(asyncResult);
}
/// <summary>
/// Helper method that actually sends the given IOCTL to the driver by
/// calling the native DeviceIOControl() function. Called by AsyncControl().
/// </summary>
private static unsafe void NativeAsyncControl(
SafeFileHandle device,
int controlCode,
SafePinnedObject outBuffer,
ref uint bytesReturned,
NativeOverlapped *nativeOverlapped
)
{
bool succeeded = Kernel32Import.DeviceIoControl(device,
controlCode,
null,
0,
outBuffer,
outBuffer.Size,
ref bytesReturned,
nativeOverlapped
);
// If DeviceIoControl returns TRUE, the operation completed
// synchronously
if (succeeded)
{
throw new InvalidOperationException($"Async call to DeviceIoControl completed synchronously.");
}
// DeviceIoControl is operating asynchronously; test the returned
// error code to see if it is pending or not
Int32 error = Marshal.GetLastWin32Error();
const Int32 cErrorIOPending = 997; // system-defined code for pending I/O
if (error == cErrorIOPending)
{
return;
}
// Throw an exception if DeviceIoControl fails altogether
throw new InvalidOperationException($"Control failed with error {error}");
}
