int KernelStub_Open() {
    char *localCopy[MaxFileNameSize + 1];

// Check that the stack pointer is valid and that the arguments are stored at
// valid addresses.

    if (!validUserAddressRange(userStackPointer, userStackPointer + size of arguments))
        return error_code;

// Fetch pointer to file name from user stack and convert it to a kernel pointer.

    filename = VirtualToKernel(userStackPointer);	
	
// Make a local copy of the filename.  This prevents the application 
// from changing the name surreptitiously.

// The string copy needs to check each address in the string before use to make sure 
// it is valid.

// The string copy terminates after it copies MaxFileNameSize to ensure we 
// do not overwrite our internal buffer.

    if (!VirtualToKernelStringCopy(filename, localCopy, MaxFileNameSize))
        return error_code;  

// Make sure the local copy of the file name is null terminated.

    localCopy[MaxFileNameSize] = 0;

// Check if the user is permitted to access this file.

    if (!UserFileAccessPermitted(localCopy, current_process) 
        return error_code;

// Finally, call the actual routine to open the file.  This returns a file 
// handle on success, or an error code on failure.

    return Kernel_Open(localCopy);
}