I applied the patch you requested.  I suspect this has fixed the lower
level problem with this particular CD-ROM.  But I'm unable to load a
CD-R I used to get my system to the state it now is 8-)  Here is a
script of what I did and got (the CD-R was cut on a 1.3.3/i386 box):
(I'm now able to probe for a label and eject the CD at least)

    Script started on Fri Feb 12 18:52:23 1999

    pc164sx# disklabel cd0

    # /dev/rcd0c:
    type: ATAPI
    disk: \277\002\000
    label: fictitious
    flags: removable
    bytes/sector: 2048
    sectors/track: 100
    tracks/cylinder: 1
    sectors/cylinder: 100
    cylinders: 4001
    total sectors: 400000
    rpm: 300
    interleave: 1
    trackskew: 0
    cylinderskew: 0
    headswitch: 0       # milliseconds
    track-to-track seek: 0  # milliseconds
    drivedata: 0 

    3 partitions:
    #        size   offset     fstype   [fsize bsize   cpg]
      a:  1600000        0    ISO9660                     # (Cyl.    0 - 15999)
      c:  1600000        0    ISO9660                     # (Cyl.    0 - 15999)
    disklabel: boot block size 0
    disklabel: super block size 0
    disklabel: partition a: partition extends past end of unit
    disklabel: partition c: partition extends past end of unit

    pc164sx# mount_cd9660 -e -o rdonly /dev/cd0c /mnt
    mount_cd9660: : Invalid argument

    pc164sx# mount_cd9660 /dev/cd0a /mnt
    mount_cd9660: : Invalid argument

    pc164sx# eject cd0

    pc164sx# exit

    Script done on Fri Feb 12 18:53:20 1999

> From bouyer@antioche.lip6.fr Thu Feb 11 08:13:54 1999
> 
> I added the code to issue REQUEST SENSE commands at 1998/11/17. So maybe your
> precedent shapshots didn't use REQUEST SENSE.
> It's know that some ATAPI drives don't handle REQUEST SENSE properly, there's
> a quirk flag for that. But they usually reject the command, or fail to issue
> an interrupt. In your case it seems the command completed, but the data
> returned are all 0xff (sense error code mask = 0x7f, err code valid = 0x80,
> 16777215 = 0xffffff). That's why I posted a mail to -i386 asking if
> someone has such a drive working with current.
> 
> However, the appended patch should allow you to use your drive. Can you
> confirm it works ?
> 
> --
> Manuel Bouyer, LIP6, Universite Paris VI.           Manuel.Bouyer@lip6.fr
> --
> 
> Index: atapiconf.c
> ===================================================================
> RCS file: /cvsroot/src/sys/dev/scsipi/atapiconf.c,v
> retrieving revision 1.23
> diff -u -r1.23 atapiconf.c
> --- atapiconf.c   1999/01/26 10:00:08 1.23
> +++ atapiconf.c   1999/02/11 13:13:29
> @@ -85,6 +85,8 @@
>   {{T_CDROM, T_REMOV,
>    "GCD-R580B", "", "1.00"},      ADEV_LITTLETOC},
>   {{T_CDROM, T_REMOV,
> +  "GCD-R580B", "", "1.03"},      ADEV_NOSENSE},
> + {{T_CDROM, T_REMOV,
>    "MATSHITA CR-574", "", "1.02"},    ADEV_NOCAPACITY},
>   {{T_CDROM, T_REMOV,
>    "MATSHITA CR-574", "", "1.06"},    ADEV_NOCAPACITY},