Reading a drive's serial number

[rmgillmore]

When running in a 32-bit console, I am able (in 16-bit assembly language), to read a DOS drive serial number by executing this procedure:

public absoluteDiskRead

diskReadFrame struc
diskRead_OldFrame Dw ?
diskRead_RtnAddr Dd ?
driveNumber Db ?
driveNumberIsByte Db ?
controlPacketPtr Dd ?
statusPtr Dd ?
diskReadFrame ends

absoluteDiskRead proc far
Push Bp
Mov Bp, Sp

; ensure that DOS knows the disk media format by executing
; interrupt 21h, function 47h

Mov Ah, 47h
Mov Dl, [Bp].driveNumber
Inc Dx
Mov Si, sysCallAsmModule_Data
Push Si
Pop Ds
Mov Si, offset diskBuffer
Int 21h

; use interrupt 25h to read the requested sector(s)

Mov Al, [Bp].driveNumber ; the drive number is only a byte, so
Xor Ah, Ah ; ignore the upper byte in the word
Lds Bx, [Bp].controlPacketPtr
Mov Cx, -1
Int 25h ; absolute disk read

Les Bx, [Bp].statusPtr ; prepare for save of error value
Mov Word Ptr Es:[Bx], Ax

Add Sp, 2 ; handle DOS disk read anomaly
Pop Bp
ret
absoluteDiskRead endp

The serial number is located at the 29h offset into the buffer whose address is specified in the control packet.

HOWEVER, when trying the same code in vDOS, I get an error 0103h (259) when attempting to read from sector zero.

What I am trying to capture is reported by the vDos internal DIR command (reported as "Volume Serial Number").

I am not afraid to write ASM, been doing it for almost 40 years now.  But where is the serial number?

[Jos]

vDos doesn't support low level disk access.
The Volume Serial Number reported by DIR is fake. It's based on the also fake drive name, A_DRIVE, B_DRIVE etc.

Jos