[This is preliminary documentation and subject to change.]
Each reparse point has an identifier tag so that you can efficiently differentiate between the different types of reparse points, without having to examine the user-defined data in the reparse point. Windows NT has a set of predefined tags and a range of tags reserved for Microsoft. If you use any of the reserved tags when setting a reparse point, the operation will fail. Tags not included in these ranges are not reserved are available for you to use in your application. In a future beta release, it will be possible for you to create a unique tag to identify your reparse points.
When you set a reparse point, you must tag the data to be placed in the reparse point. After the reparse point has been established, a new set operation fails if the tag for the new data does not match the tag for the existing data. If the tags match, the set operation overwrites the existing reparse point.
Reparse tags are stored as a ULONG value. The bits define certain attributes, as shown in the following diagram.
3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+-+-+-+-------------------------+-------------------------------+
|M|L|N| Reserved bits | Tag Value |
+-+-+-+-------------------------+-------------------------------+
The low 16 bits are used to determine the kind of reparse point. The high 16 bits have 13 bits reserved for future use, and three bits that denote specific attributes of the tags and entities represented by the reparse point. The following table describes these bits.
| Bit | Description |
|---|---|
| M | Microsoft bit. If this bit is set, the tag is owned by Microsoft. All other tags must use zero for this bit. |
| L | High-latency bit. If this bit is set, the system is expected to be slow to retrieve the first byte of data. The application should display some indication to the user that the operation is in progress. |
| N | Name surrogate bit. If this bit is set, the file represents another named entity in the system. |