How to read info from a file in filter driver?

I just want to read some config infomation from my config file.
I put the code into driverentry and some place else,but the return value from
ZwReadFile is always not success, what shoud I do?

Are there any easy way to get info from file in filter driver?  
//

RtlInitUnicodeString(&filename,L\"\\\\DosDevices\\\\C:\\\\config.dat\");
    InitializeObjectAttributes( &attributes,&filename,
        OBJ_CASE_INSENSITIVE,NULL,NULL);
    status = ZwOpenFile(&hFile,FILE_READ_DATA,&attributes,&sb,FILE_SHARE_READ,FILE_NON_DIRECTORY_FILE);
    if (!NT_SUCCESS(status)) {
         ret = 0;
         goto OUTWAY;
    }
    
    buffer = ExAllocatePoolWithTag( NonPagedPool, buflen, FILESPY_POOL_TAG );
    if (NULL == buffer){
         ret = 0;
         goto OUTWAY;
    }
    
    status = ZwReadFile(hFile,NULL,NULL,NULL,&sb,buffer,buflen,NULL,NULL);
    if (!NT_SUCCESS(status)) {
        ret = 0;                 //always go here, why? how can I correct it?
        goto OUTWAY;
    }