FSCTL_DISMOUNT_VOLUME
The FSCTL_DISMOUNT_VOLUME
DeviceIoControl
operation dismounts a volume.
dwIoControlCode = FSCTL_DISMOUNT_VOLUME; // operation code
lpInBuffer = NULL; // pointer to input buffer; not
used; must be NULL
nInBufferSize = 0; // size of input buffer; not
used; must be zero
lpOutBuffer ;
// pointer to output buffer; not used; must be NULL
nOutBufferSize ;
// size of output buffer; not used; must be zero
lpBytesReturned ;
// pointer to DWORD used by DeviceIoControl function
Parameters
lpInBuffer
Points to an
input buffer. Not used with this operation. Set to NULL.
nInBufferSize
Specifies the
size, in bytes, of the buffer pointed to by lpInBuffer. Not used with
this operation. Set to zero.
lpOutBuffer
Points to an
output buffer. Not used with this operation. Set to NULL.
nOutBufferSize
Specifies the
size, in bytes, of the buffer pointed to by lpOutBuffer. Not used with
this operation. Set to zero.
lpBytesReturned
Pointer to a DWORD.
This value cannot be NULL. Although the FSCTL_DISMOUNT_VOLUME operation
produces no output data and lpOutBuffer should be NULL, the DeviceIoControl function uses the variable
pointed to by lpBytesReturned. After the operation, the value of this
variable is without meaning.
Return Values
If the
operation succeeds, DeviceIoControl returns TRUE.
If the
operation fails, DeviceIoControl returns FALSE. To get extended error
information, call GetLastError.
Remarks
The hDevice
handle passed to DeviceIoControl must be a handle to a volume,
opened for direct access. An application can obtain such a handle by calling CreateFile with lpFileName set
to a string that looks like this:
\\.\X:
where X is a
hard-drive partition letter, floppy disk drive, or CD-ROM drive. The
application must also specify the FILE_SHARE_READ and FILE_SHARE_WRITE flags in
the dwShareMode parameter of CreateFile.
If the
specified volume is locked, the operation fails.
A dismounted
volume has the following properties:
There are no open files.
The operating system does not know about the
volume.
The operating
system tries to mount an unmounted volume as soon as any attempt is made to
access it. For example, a call to GetLogicalDrives triggers the operating
system to mount any unmounted volumes.
Dismounting a
volume is useful whenever a volume needs to disappear for a while. For example,
an application that changes a volume s
file system from FAT to NTFS might follow these steps:
1. Open the volume
2. Lock the volume
3. Format the volume
4. Unlock the volume
5. Dismount the volume
6. Close the volume handle
A dismounting
operation removes the volume from the FAT file system s awareness. When the operating system mounts the volume, it
appears as an NTFS volume.
See Also