INT 21h/440Dh invalid minor should report invalid function

[nakatamaho]

Summary

The generic block-device IOCTL's documented invalid-function response appears to be lost for an unsupported minor function.

Minimal reproducer

With a valid local block drive A, call INT 21h with:

• AH=44h, AL=0Dh
• BL=1 (drive A), CH=08h (disk-drive category), CL=FFh (unsupported minor function)
• DS:DX pointing at a valid writable parameter block surrounded by guard bytes

Expected behavior

CF is set and AX reports error 01h (invalid function code), per the MS-DOS Version 4.0 Programmer's Reference, Function 440Dh, "Generic IOCtl (for Devices)".

Observed source behavior

In the tested component revision, Genblkdev routes an unsupported minor function through failure(E_CMD). DosDevIOctl then maps a device request carrying S_ERROR to DE_ACCESS, so this path reports the generic device/access error instead of DE_INVLDFUNC. The current local guest fixture had encoded that implementation result as its expectation; we are correcting the test oracle to the documented ABI.

The relevant branches are in kernel/dsk.c and kernel/ioctl.c at component commit ac16c8a7401526f99787e03babdb2f4223d48fc4. The bounded M15 candidate was derived from this commit; its task-local dsk.c edits do not alter the unsupported-minor or S_ERROR mapping paths.

Reference

• Microsoft, MS-DOS Version 4.0 Programmer's Reference, Function 44h, code 0Dh: https://www.pcjs.org/documents/books/mspl13/msdos/dosref40/
• Source: https://github.com/lpproj/fdkernel/tree/ac16c8a7401526f99787e03babdb2f4223d48fc4

Could you confirm whether this invalid-minor response is intentional compatibility behavior, or should the kernel return the documented invalid-function error?