MOUNTMGR_TARGET_NAME - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTIOAPI_H

// Input structure for IOCTL_MOUNTMGR_KEEP_LINKS_WHEN_OFFLINE,
// IOCTL_MOUNTMGR_VOLUME_ARRIVAL_NOTIFICATION,
// IOCTL_MOUNTMGR_QUERY_DOS_VOLUME_PATH, and
// IOCTL_MOUNTMGR_QUERY_DOS_VOLUME_PATHS.
// IOCTL_MOUNTMGR_PREPARE_VOLUME_DELETE
// IOCTL_MOUNTMGR_CANCEL_VOLUME_DELETE
typedef struct _MOUNTMGR_TARGET_NAME
{
    USHORT DeviceNameLength;
    _Field_size_bytes_(DeviceNameLength) WCHAR DeviceName[1];
} MOUNTMGR_TARGET_NAME, *PMOUNTMGR_TARGET_NAME;

#endif

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This structure is documented in Windows Driver Kit.