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     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.

                      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.


     cd(4), scsi(4)


     The cd manual page first appeared in FreeBSD 2.2.


     This manual page was written by John-Mark Gurney <>.  It was updated for CAM
     and FreeBSD 3.0 by Kenneth Merry <>.