How to get the full path for USN journal query?

Question

I am trying to go through the example on MSDN (https://msdn.microsoft.com/en-us/library/windows/desktop/aa365736%28v=vs.85%29.aspx) on how to query USN journal in order to trace file changes on a NTFS drive. The example code works well.

However, in this example code, the USN_RECORD structure only returns me a file reference number and the file name. It does not return me the full path of the file. Does anyone have any idea how to query USN journal to return a full path? Or there is a way to get the full path from file reference number?

Thanks.

Answer 1

The ParentFileReferenceNumber member of the USN_RECORD structure is the reference number for the directory containing the file.

You can use FSCTL_ENUM_USN_DATA to look up a file (or directory!) by reference number. You will need to iterate up the tree to build the complete path. There is some code in this answer which may be helpful as an example.

This code looks up the reference number for the root directory, so you can tell when you're finished:

HANDLE rootdir_handle;
USN_RECORD * rootdir_usn;

printf("Opening root directory.\n");

rootdir_handle = CreateFile(L"\\\\?\\C:\\", GENERIC_READ, 
                            FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_ALWAYS, 
                            FILE_FLAG_BACKUP_SEMANTICS, NULL);

if (rootdir_handle == INVALID_HANDLE_VALUE)
{
    printf("CreateFile: %u\n", GetLastError());
    return 0;
}

if (!DeviceIoControl(rootdir_handle, FSCTL_READ_FILE_USN_DATA, NULL, 0, 
                     buffer, BUFFER_SIZE, &bytecount, NULL))
{
    printf("FSCTL_READ_FILE_USN_DATA: %u\n", GetLastError());
}
else
{
    rootdir_usn = (USN_RECORD *)buffer;
    show_record(rootdir_usn, FALSE);
    rootdir = rootdir_usn->FileReferenceNumber;
}

Answer 2

I have been trying to avoid recursive parent directory search to get full path, as my initial test increased overall time it took to resolve the path.

After spending couple of hours with windbg and a bit of help from OSR Online fourm, I finally got it.

posting the answer to help anyone else who ends up with the same problem.

My current solution is as follows.

The USN_RECORD-> FileReferenceNumber is purely dependent on the version of USN_RECORD, once you extract FILE_ID_DESCRIPTOR from FileReferenceNumber, you can call OpenFileById() and pass the FILE_ID_DESCRIPTOR to get handle for the parent folder.

Then you can call GetFinalPathNameByHandle() to get the ParentDirectory Path.

Below is the code i ended up with for extracting FILE_ID_DESCRIPTOR

If the FileId in USN_RECORD_V2, the FileReferenceNu DWORDLONG.

FILE_ID_DESCRIPTOR getFileIdDescriptor(const DWORDLONG fileId)
{
    FILE_ID_DESCRIPTOR fileDescriptor;
    fileDescriptor.Type = FileIdType;
    fileDescriptor.FileId.QuadPart = fileId;
    fileDescriptor.dwSize = sizeof(fileDescriptor);

    return fileDescriptor;
}

If you endup with UNS_RECORD_V3, the fileId is of type FILE_ID_128, and here is the code to extract the FileId.

FILE_ID_DESCRIPTOR getFileIdDescriptor(const FILE_ID_128& fileId)
{
    FILE_ID_DESCRIPTOR fileDescriptor;
    fileDescriptor.Type = ExtendedFileIdType;
    fileDescriptor.ExtendedFileId = fileId;
    fileDescriptor.dwSize = sizeof(fileDescriptor);
    return fileDescriptor;
}

Once you extract the FileId, here is how you can get the parent path.

TCHAR filePath[MAX_PATH];
HANDLE hh= OpenFileById(volume_, &(getFileIdDescriptor(UsnRecord->FileReferenceNumber)), 0, 0, 0, 0);
GetFinalPathNameByHandle(hh,filePath, MAX_PATH, 0);

you can find the reference implementation @ https://github.com/kirankumarcelestial/NTFSChangeJournalUserMode

However I found that GetFilePathNameByHandle() is actually slow, and this API will eventually call GetFileInformationByHandleEx(), and GetFileInformationByHandleEx() is a single call to KernelMode, and this would be effective way to get get Parent Information.