Storage IOCTLs reserved for "dependent disk support"

NTDEV
1

My disk driver recieves IOCTLs device=2d (FILE_DEVICE_MASS_STORAGE) with function 0x464. The comment in ntddstor.h says, “IOCTLs 0x0463 to 0x0468 reserved for dependent disk support.” Can anyone shed any light on what this IOCTL might be? The input buffer is 8 bytes 01 00 00 00 00 00 00 00 and the output buffer length is 20 bytes.

I’ve been having troubles with drive letter assignment oddities, and I notice a volume guid in the MountedDevices registry key with data of “01 00 00 …”. I’m suspecting that this ioctl and the mounted devices entry are connected… Any info is appreciated.

2

I can give you API suggestions:
GetStorageDependencyInformation(GET_STORAGE_DEPENDENCY_FLAG_HOST_VOLUMES | GET_STORAGE_DEPENDENCY_FLAG_DISK_HANDLE)

And a scenario suggestion:
diskpart> select vdisk file=“c:\VHD\MyDisk.vhd”
diskpart> attach vdisk
diskpart> assign letter=V