Int 21h Function 440Dh Minor Code 6Bh (FAT32)

Unlocks the physical volume or decrements the lock level.

mov ax, 440Dh      ; generic IOCTL
mov bl, DriveNum   ; see below
mov ch, DeviceCat  ; see below
mov cl, 6Bh        ; Unlock Physical Volume
int 21h
 
jc error_handler

Parameters

DriveNum

Drive to unlock. This parameter must be one of these values (same device unit numbers as for Interrupt 13h):

Value	Description
00 - 7Fh	Floppy disk drive (00 for the first floppy drive, 01 for the second, and so on).
80 - FFh	Hard disk drive (80 for the first hard disk drive, 81 for the second, and so on).

DeviceCat

Specifies a FAT16, FAT12 or FAT32 drive.

Value	Description
08h	FAT32, FAT16, or FAT12 drive.
48h	FAT32, FAT16, or FAT12 drive. This value is supported on Windows 95 OEM Service Release 2 and later.

Note: Because this call may be implemented in the device driver, the 48h form of this call may fail on FAT16 or FAT12 media. Therefore, applications making the 48h form of this call must fall back on the 08h form if the 48h call fails.

Return Values

Clears the carry flag if successful. Otherwise, the function sets the carry flag and sets the AX register to an error value.

Remarks

This function is used to release the lock obtained by using Lock Physical Volume (Interrupt 21h Function 440Dh Minor Code 4Bh). Only the lock owner can release the lock on a volume.

To release the lock on the volume, an application must call Unlock Physical Volume the same number of times that Lock Physical Volume was called.