#ifndef _NTIOAPI_H
// Input structure for IOCTL_MOUNTMGR_NEXT_DRIVE_LETTER.
typedef struct _MOUNTMGR_DRIVE_LETTER_TARGET
{
USHORT DeviceNameLength;
_Field_size_bytes_(DeviceNameLength) WCHAR DeviceName[1];
} MOUNTMGR_DRIVE_LETTER_TARGET, *PMOUNTMGR_DRIVE_LETTER_TARGET;
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This structure is documented in Windows Driver Kit.