User-mode application for USB flash disk

Post subject: User-mode application for USB flash disk    

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I had completed the firmware of the flash disk and now I want develop a user-mode application to write some special command to the USB device to do some certain work.
I use SetupDiGetClassDevs(..) function with GUID=a5dcbf10-6530-11d2-901f-00c04fb951ed(Interface class for USB devices) and check the PID and VID to indicate the device.
The problem is that I can CreateFile successfully and WriteFile or ReadFile failed. I had comfirmed the pipe and they have no wrong.
Why I can't read/write data from/to the USB flash disk via my application?

(Somewhere, I had read an article and it said that the mass storge device has already opened by windows and other read/write access will be denied. But I notice that I can use CreateFile(..) function to open it and it returns TRUE, but I also notice that I change the PIPE in the device path name to "PIPE09", the CreateFile function still return TRUE.why?)

I only want to make an application to access my USB flash disk device and do something I want to do, how should I do?
That is to say, how to develop a flash disk tool?
(My develop environment is VC + DDK.)

http://www.driverdevelop.com/forum/html_84397.html?1104824119