Top Half of LVDD
The top half of the LVDD contains the code that runs in the context of a process address space and can page fault.
It contains the following entry points:
| Item | Description |
|---|---|
| ddopen | Called by the file system when a logical volume is mounted, to open the logical volume specified. |
| ddclose | Called by the file system when a logical volume is unmounted, to close the logical volume specified. |
| ddconfig | Initializes data structures for the LVDD. |
| ddread | Called by the read subroutine to translate character
I/O requests to block I/O requests. This entry point verifies that
the request is on a 512-byte boundary and is a multiple of 512 bytes
in length. Most of the time a request will be sent down as a single request to the LVDD ddstrategy entry point which handles logical block I/O requests. However, the ddread routine might divide very large requests into multiple requests that are passed to the LVDD ddstrategy entry point. If the ext parameter is set (called by the readx subroutine), the ddread entry point passes this parameter to the LVDD ddstrategy routine in the b_options field of the buffer header. |
| ddwrite | Called by the write subroutine to translate character I/O requests to block I/O requests. The LVDD ddwrite routine performs the same processing for a write request as the LVDD ddread routine does for read requests. |
| ddioctl | Supports the following operations:
|