QEMU emulating MS-DOS cannot access CD-ROM

Question

I am using qemu-system-i386 on a Windows 10 PC to emulate an MS-DOS system. I have installed MS-DOS 6.22 successfully from disk images from original Microsoft media.

I am starting QEMU using this command:

c:\program files\qemu\qemu-system-i386.exe -hda msdos.disk -m 64 -L . -soundhw sb16,adlib,pcspk -k en-gb -vga cirrus -nic user,model=pcnet -boot order=d -drive file=.\cdrom.iso,media=cdrom,index=2,if=ide,format=raw

cdrom.iso is an image created by mkisofs (running under WSL) using this command:

mkisofs -pad -b disks/msdos/msd622_b.img -R -J -o cdrom.iso cdrom

This includes an El Torito boot floppy of MS-DOS 6.22. When running QEMU with the above command, it successfully boots from CD-ROM into MS-DOS. XDVD2.SYS detects the CD-ROM correctly, identifying it as a QEMU virtual DVD-ROM. MSCDEX runs correctly and assigns the CD drive a drive letter, as illustrated:

SeaBIOS (version rel-1.12.0-0-ga698c8995f-prebuilt.qemu.org)


iPXE (http://ipxe.org) 00:03.0 C980 PCI2.10 PnP PMM+03F914B0+03EF14B0 C980



Booting from DVD/CD...
Starting MS-DOS...


XDVD2, 1-05-2016.   CD/DVD name is DVDROM.
IDE0 Controller at I-O address C020h, Chip I.D. 80867010h
CD0:  IDE0 Secondary-master, QEMU DVD-ROM, ATA-100.

MODE prepare code page function completed

MODE select code page function completed
MSCDEX Version 2.23
Copyright (C) Microsoft Corp. 1986-1993. All rights reserved.
       Drive D: = Driver DVDROM unit 0
A:\>_

However, whenever I try to access the CD - for example, with dir d:\, I get this error:

CDR101: Not ready reading drive D
Abort, Retry, Fail?

The QEMU virtual CD-ROM and the ISO file are both clearly valid, otherwise QEMU would not have been able to boot the El Torito image. I have repeated the test using an old Windows 95 setup boot disk that uses a different CD driver and it too fails in the same way, so this appears to be something specific about MSCDEX inside QEMU. I have also tried a different ISO image in case there is a problem with my ISO image, with no difference in results.

How can I access the QEMU virtual CD-ROM from MS-DOS?

---

For reference, here are the boot disk's startup files.

CONFIG.SYS

DOS=HIGH,UMB
BUFFERS=11,0
FILES=60
LASTDRIVE=H
FCBS=1,0
STACKS=0,0
DEVICE=A:\DOS\HIMEM.SYS /TESTMEM:OFF
DEVICE=A:\DOS\EMM386.EXE X=B800-C7FF I=B000-B7FF A=64 H=128 D=256 ON
DEVICEHIGH=A:\DOS\SETVER.EXE
COUNTRY=044,,A:\DOS\COUNTRY.SYS
DEVICEHIGH=A:\DOS\DISPLAY.SYS CON=(EGA,,1)
DEVICEHIGH=A:\EXTRAS\XDVD2.SYS /D:DVDROM
SET TEMP=A:\TEMP
SET TMP=A:\TEMP

AUTOEXEC.BAT

@ECHO OFF
A:\DOS\SMARTDRV.EXE /X
PROMPT $p$g
PATH A:\DOS
A:\DOS\MODE.COM CON CODEPAGE PREPARE=((437) A:\DOS\EGA.CPI)
A:\DOS\MODE.COM CON CODEPAGE SELECT=437
LH A:\DOS\KEYB.COM UK,,A:\DOS\KEYBOARD.SYS
LH A:\DOS\DOSKEY.COM /INSERT
LH A:\DOS\MSCDEX.EXE /D:DVDROM /M:20 /E

Answer 1

There's reason to believe that this is a qemu bug (actually a problem caused by the configuration of SeaBIOS in qemu 3.0 and 3.1). If this is the case, the CD driver will work fine in qemu 2.12.1 or older (SeaBIOS will be 1.11.1 or older), or qemu 4.0.0 or newer (SeaBIOS will be 1.12.1 or newer). A qemu displaying a SeaBIOS version of 1.11.2 or 1.12.0 will not work.