Bottom Half of the LVDD

The bottom half of the device driver supports the ddstrategy entry point. This entry point processes all logical block requests and performs the following functions:

• Validates I/O requests.
• Checks requests for conflicts (such as overlapping block ranges) with requests currently in progress.
• Translates logical addresses to physical addresses.
• Handles mirroring and bad-block relocation.

The bottom half of the LVDD runs on interrupt levels and, as a result, is not permitted to page fault.

Each logical I/O request passes down through the bottom three layers before reaching the physical disk device driver. Once the I/O is complete, the request returns back up through the layers to handle the I/O completion processing at each layer. Finally, control returns to the original requestor.

The bottom half of the LVDD is divided into the following three layers: