This entry point allows the FSD to inform the physical disk device driver of its FSD_EndOfInt and FSD_AccValidate entry points. The physical disk device driver allows DD_SetFSDInfo to be called exactly once, and ignores subsequent calls.

──────────────────────────────────────────────────────────────────────────

ENTRY
    ES:BX   16:16 pointer to the FSDInfo structure.
EXIT
    CF      Set, if call was ignored.

──────────────────────────────────────────────────────────────────────────

The format of the FSDInfo structure is:

┌──────────────────────────────┬──────────────────────────────┐
│Field                         │Length                        │
├──────────────────────────────┼──────────────────────────────┤
│Reserved.  Must be 0.         │DWORD                         │
├──────────────────────────────┼──────────────────────────────┤
│FSD_EndOfInt                  │DWORD                         │
├──────────────────────────────┼──────────────────────────────┤
│Reserved.  Must be 0.         │DWORD                         │
├──────────────────────────────┼──────────────────────────────┤
│FSD_AccValidate               │DWORD                         │
└──────────────────────────────┴──────────────────────────────┘

FSD_EndOfInt

The 16:16 entry point of the FSD's FSD_EndOfInt routine. This field is set to 0 if the FSD does not provide an FSD_EndofInt routine. The entry point is called by the physical device driver when it has completed interrupt processing and after it has called DevHlp_EOI. FSD_EndOfInt takes no parameters and leaves all registers intact.
FSD_AccValidate
The 16:16 entry point of the FSD's FSD_AccValidate routine. This field is set to 0 if the FSD does not provide an FSD_AccValidate routine. The entry point is called whenever direct I/O is done through a Category 08h or 09h IOCtl to an HPFS volume or whenever direct I/O is done to the Master Startup (Boot) record through a Category 09h IOCtl.

For Category 09h IOCtls, the physical device driver must use the Head, Cylinder, and Sector values passed in the IOCtl. These values are used to determine whether the I/O request falls within an HPFS volume, because the unit number in the IOCtl represents the entire physical disk and not the logical volume.

The physical device driver should call FSD_AccValidate with:

──────────────────────────────────────────────────────────────────────────

AL  Operation Code
    00  Non-destructive (READ, VERIFY)
    01  Destructive (WRITE, FORMAT TRACK, and so forth)

──────────────────────────────────────────────────────────────────────────

On return from the FSD:

──────────────────────────────────────────────────────────────────────────

NC  I/O access is allowed.
CF  If set, access is denied. The physical device driver should
    return error code 00h (Write-protection violation) to the caller.

──────────────────────────────────────────────────────────────────────────

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