Bug 29495

There are conditions for which FreeBSD crashes on invoking the command

	mount -t cd9660 /dev/acd0c /cdrom

This is what may happen:

	There appear error messages such as 

	acd0: READ_TOC - ILLEGAL REQUEST asc=24 ascq=00 error=00

	fatal trap 12

	page fault while in kernel mode

	... reboot ...

	and the FreeBSD system indeed crashes and reboots.

CONDITIONS

On my system (see above) the crash __consistently__ happens when the
mounted CD disk previously was burnt __without fixation__,  e.g., with
the command

	burncd -f /dev/acd0c data image.iso

where image.iso is an image file created with mkisofs. I have tested 
this several times with a CDRW disk.

The same type of crash occurred when I had put in a CDRW disk
that previously had been burnt __under Win98__ as an __audio__ disk. I have
previously reported on this problem, thinking that it was the disk
carrying an __audio__ record that caused the problem; but this does no
longer seem to be the whole truth (Mounting an intact commercial audio
disk does not seem to cause a system crash.) So the "audio case" of crash
is not consistently reproducible, as opposed to the "non-fixation case"
mentioned above.

Another case of cd-mounting system crash with restricted reproducibility
occurred when a CDRW disk previously merely had been blanked, using burncd.
This seems to happen only occasionally, depending on conditions
unkown to me.

RELATED OBSERVATIONS

1. Concerning 'burncd':

I have repeatedly tested burncd on my system by both
blanking, and writing data (iso 9660) on, a CDRW disk. This
essentially works, i.e., at the end the disk is in the desired state.
However, at the end of the burning process there consistently appears the
somewhat alarming message

	acd0: READ_TOC - ILLEGAL REQUEST asc=24 ascq=00 error=00

This message appears - with some delay - several times, and burncd does
not properly return to the command line prompt; a CR from the 
keyboard is required to get burncd returning to the shell command line.

2. Behavior under Win98 and Linux:

Can also boot Win98 and Linux 2.2.13 on the same hardware. No problems
with attempts to read/mount the non-fixated cdrom (i.e., no crash or
hanging). So a hardware problem appears unlikely.

How-To-Repeat: 
1. Write an iso9660 file system on a CDRW disk __without fixating__, e.g.,
		burncd -f /dev/acd0c data image.iso
   (omitting 'fixate' at the end).

2. Mount that disk, i.e.,
		mount -t cd9660 /dev/acd0c /cdrom
   !!! be prepared that the system may crash !!!