cd — CDROM driver
for the CAM SCSI subsystem
The cd device driver provides a read-only
interface for CDROM drives (SCSI type 5) and WORM drives (SCSI type 4) that
support CDROM type commands. Some drives do not behave as the driver
expects. See the QUIRKS section for
information on possible flags.
Each CD-ROM device can have different interpretations of the SCSI
spec. This can lead to drives requiring special handling in the driver. The
following is a list of quirks that the driver recognize.
CD_Q_NO_TOUCH- This flag tells the driver not to probe the drive at attach time to see if
there is a disk in the drive and find out what size it is. This flag is
currently unimplemented in the CAM
cd driver.
CD_Q_BCD_TRACKS- This flag is for broken drives that return the track numbers in packed BCD
instead of straight decimal. If the drive seems to skip tracks (tracks
10-15 are skipped) then you have a drive that is in need of this
flag.
CD_Q_NO_CHANGER- This flag tells the driver that the device in question is not a changer.
This is only necessary for a CDROM device with multiple luns that are not
a part of a changer.
CD_Q_CHANGER- This flag tells the driver that the given device is a multi-lun changer.
In general, the driver will figure this out automatically when it sees a
LUN greater than 0. Setting this flag only has the effect of telling the
driver to run the initial read capacity command for LUN 0 of the changer
through the changer scheduling code.
CD_Q_10_BYTE_ONLY- This flag tells the driver that the given device only accepts 10 byte MODE
SENSE/MODE SELECT commands. In general these types of quirks should not be
added to the cd(4) driver. The reason is that the driver
does several things to attempt to determine whether the drive in question
needs 10 byte commands. First, it issues a CAM Path Inquiry command to
determine whether the protocol that the drive speaks typically only allows
10 byte commands. (ATAPI and USB are two prominent examples of protocols
where you generally only want to send 10 byte commands.) Then, if it gets
an ILLEGAL REQUEST error back from a 6 byte MODE SENSE or MODE SELECT
command, it attempts to send the 10 byte version of the command instead.
The only reason you would need a quirk is if your drive uses a protocol
(e.g., SCSI) that typically does not have a problem with 6 byte
commands.
- /sys/cam/scsi/scsi_cd.c
- is the driver source file.
The cd manual page first appeared in
FreeBSD 2.2.