用于C＃的C库，用于从操作系统队列中删除消息

Question

I have been developing an application in c# and I want to do some validation when a USB mass storage is inserted.

The problem is that during that validation I want to pull off that message of the mass storage from the message queue out.

A guy told me that you cannot do that in C# but only in C using Assembly language.

Can you guys help me find a C library that I can use from C# for pulling the messages from the operating system message queue?

protected override void WndProc(ref Message m)
        {
            switch (m.Msg)
            {

                case Win32.WM_DEVICECHANGE: 


                    //OnDeviceChange(ref m);                

                    break;
            }
            base.WndProc(ref m);

        }

        void OnDeviceChange(ref Message msg)
        {
            int wParam = (int)msg.WParam;

            if (wParam == Win32.DBT_DEVICEARRIVAL)
            {
                label1.Text = "Arrival";
                //MessageBox.Show("" + wParam);
                //msg = Message.Create(new IntPtr(),1,new IntPtr(),new IntPtr());
            }
            else if (wParam == Win32.DBT_DEVICEREMOVECOMPLETE) label1.Text =
             "Remove";
        }

I have done this but it just tells you that what happened.

I want to pull the message off so that the operating system won't know abut the device and then put the message on again if the validation is validated.

Answer 1

Not going to happen, man. By the time you get a Win32 WM_DEVICECHANGE message, the device is already very much loaded. The kernel has become aware of the device, loaded drivers, and in this case as a mass storage device, already created a volume. That's all (mostly) kernel-mode activity. Then Win32 (user-mode) broadcasts this message to all top-level windows. You simply can't do it in any language at the Win32 level, and this WM_DEVICECHANGE mechanism.

To do this, you're going to have to write a device driver. These are written in C, run in kernel-mode, and are much, much trickier to implement than a simple C# app. I recommend you look for some other solution that accomplishes what you are trying to do. Which is... what, by the way?

"else it discards the message so that the operating system won't know about it"

Sorry, but you're completely missing the point. WM_DEVICECHANGE is sent from the OS (namely the Win32 subsystem) to all top-level windows . It is just a notification, there is no control associated with this message. WM_DEVICECHANGE does not help in your goals of preventing access to the device. Like I said, for this you would need a device driver, quite possibly a filesystem filter driver. To that driver you would send an IOCTL (from user-mode) which would allow access to the device.

Answer 2

The OS does not depend on WM_DEVICECHANGE to learn about a device, so blocking the message won't do anything useful.

What you are asking to do is very difficult, because the OS drivers and filesystem have to be loaded in order for you to access the device and perform your validation, but it sounds like you want to prevent any other programs from using it. Even antivirus software implemented in the kernel doesn't prevent a device from appearing before it is scanned.

You could possibly implement a file system filter driver that reports that there are no files on the device, until the scan completes, but this will badly confuse software that sees the device appear, but the files aren't available until later. And C# is not useful for implementing Windows drivers. Not even with a "library of C to be used in C#" (I assume you mean p/invoke). C# code just isn't compatible with the environment inside the kernel.