Command Section
CD(4)                  FreeBSD Kernel Interfaces Manual                  CD(4)

     cd - SCSI CD-ROM driver

     device cd

     The cd driver provides support for a SCSI CD-ROM (Compact Disc-Read Only
     Memory) drive.  In an attempt to look like a regular disk, the cd driver
     synthesizes a partition table, with one partition covering the entire
     CD-ROM.  It is possible to modify this partition table using
     disklabel(8), but it will only last until the CD-ROM is unmounted.  In
     general the interfaces are similar to those described by ada(4) and

     As the SCSI adapter is probed during boot, the SCSI bus is scanned for
     devices.  Any devices found which answer as CDROM (type 5) or WORM (type
     4) type devices will be `attached' to the cd driver.  Prior to
     FreeBSD 2.1, the first device found will be attached as cd0 the next,
     cd1, etc.  Beginning in FreeBSD 2.1 it is possible to specify what cd
     unit a device should come on line as; refer to scsi(4) for details on
     kernel configuration.

     The system utility disklabel(8) may be used to read the synthesized disk
     label structure, which will contain correct figures for the size of the
     CD-ROM should that information be required.

     Any number of CD-ROM devices may be attached to the system regardless of
     system configuration as all resources are dynamically allocated.

     The following ioctl(2) calls which apply to SCSI CD-ROM drives are
     defined in the header files <sys/cdio.h> and <sys/disklabel.h>.

     CDIOCPLAYTRACKS      (struct ioc_play_track) Start audio playback given a
                          track address and length.  The structure is defined
                          as follows:

                                struct ioc_play_track
                                        u_char  start_track;
                                        u_char  start_index;
                                        u_char  end_track;
                                        u_char  end_index;

     CDIOCPLAYBLOCKS      (struct ioc_play_blocks) Start audio playback given
                          a block address and length.  The structure is
                          defined as follows:

                                struct ioc_play_blocks
                                        int     blk;
                                        int     len;

     CDIOCPLAYMSF         (struct ioc_play_msf) Start audio playback given a
                          `minutes-seconds-frames' address and length.  The
                          structure is defined as follows:

                                struct ioc_play_msf
                                        u_char  start_m;
                                        u_char  start_s;
                                        u_char  start_f;
                                        u_char  end_m;
                                        u_char  end_s;
                                        u_char  end_f;

     CDIOCREADSUBCHANNEL  (struct ioc_read_subchannel) Read information from
                          the subchannel at the location specified by this

                                struct ioc_read_subchannel {
                                        u_char address_format;
                                #define CD_LBA_FORMAT   1
                                #define CD_MSF_FORMAT   2
                                        u_char data_format;
                                #define CD_SUBQ_DATA            0
                                #define CD_CURRENT_POSITION     1
                                #define CD_MEDIA_CATALOG        2
                                #define CD_TRACK_INFO           3
                                        u_char track;
                                        int     data_len;
                                        struct  cd_sub_channel_info *data;

     CDIOREADTOCHEADER    (struct ioc_toc_header) Return summary information
                          about the table of contents for the mounted CD-ROM.
                          The information is returned into the following

                                struct ioc_toc_header {
                                        u_short len;
                                        u_char  starting_track;
                                        u_char  ending_track;

     CDIOREADTOCENTRYS    (struct ioc_read_toc_entry) Return information from
                          the table of contents entries mentioned.  (Yes, this
                          command name is misspelled.) The argument structure
                          is defined as follows:

                                struct ioc_read_toc_entry {
                                        u_char  address_format;
                                        u_char  starting_track;
                                        u_short data_len;
                                        struct  cd_toc_entry *data;
                          The requested data is written into an area of size
                          data_len and pointed to by data.

     CDIOCSETPATCH        (struct ioc_patch) Attach various audio channels to
                          various output channels.  The argument structure is
                          defined thusly:

                                struct ioc_patch {
                                        u_char  patch[4];
                                        /* one for each channel */


     CDIOCSETVOL          (struct ioc_vol) Get (set) information about the
                          volume settings of the output channels.  The
                          argument structure is as follows:

                                struct  ioc_vol
                                        u_char  vol[4];
                                        /* one for each channel */

     CDIOCSETMONO         Patch all output channels to all source channels.

     CDIOCSETSTEREO       Patch left source channel to the left output channel
                          and the right source channel to the right output

     CDIOCSETMUTE         Mute output without changing the volume settings.


     CDIOCSETRIGHT        Attach both output channels to the left (right)
                          source channel.


     CDIOCCLRDEBUG        Turn on (off) debugging for the appropriate device.


     CDIOCRESUME          Pause (resume) audio play, without resetting the
                          location of the read-head.

     CDIOCRESET           Reset the drive.


     CDIOCSTOP            Tell the drive to spin-up (-down) the CD-ROM.


     CDIOCPREVENT         Tell the drive to allow (prevent) manual ejection of
                          the CD-ROM disc.  Not all drives support this

     CDIOCEJECT           Eject the CD-ROM.

     CDIOCCLOSE           Tell the drive to close its door and load the media.
                          Not all drives support this feature.

     When a CD-ROM is changed in a drive controlled by the cd driver, then the
     act of changing the media will invalidate the disklabel and information
     held within the kernel.  To stop corruption, all accesses to the device
     will be discarded until there are no more open file descriptors
     referencing the device.  During this period, all new open attempts will
     be rejected.  When no more open file descriptors reference the device,
     the first next open will load a new set of parameters (including
     disklabel) for the drive.

     The audio code in the cd driver only support SCSI-2 standard audio
     commands.  As many CD-ROM manufacturers have not followed the standard,
     there are many CD-ROM drives for which audio will not work.  Some work is
     planned to support some of the more common `broken' CD-ROM drives;
     however, this is not yet under way.

     The following variables are available as both sysctl(8) variables and
     loader(8) tunables:

         This variable determines how many times the cd driver will retry a
         READ or WRITE command.  This does not affect the number of retries
         used during probe time or for the cd driver dump routine.  This value
         currently defaults to 4.

         The cd driver attempts to automatically determine whether the drive
         it is talking to supports 6 byte or 10 byte MODE SENSE/MODE SELECT
         operations.  Many SCSI drives only support 6 byte commands, and ATAPI
         drives only support 10 byte commands.  The cd driver first attempts
         to determine whether the protocol in use typically supports 6 byte
         commands by issuing a CAM Path Inquiry CCB.  It will then default to
         6 byte or 10 byte commands as appropriate.  After that, the cd driver
         defaults to using 6 byte commands (assuming the protocol the drive
         speaks claims to support 6 byte commands), until one fails with a
         SCSI ILLEGAL REQUEST error.  Then it tries the 10 byte version of the
         command to see if that works instead.  Users can change the default
         via per-drive sysctl variables and loader tunables.  Where ``%d'' is
         the unit number of the drive in question.  Valid minimum command
         sizes are 6 and 10.  Any value above 6 will be rounded to 10, and any
         value below 6 will be rounded to 6.

     /dev/cd[0-9][a-h]  raw mode CD-ROM devices


     cam(4), da(4), disklabel(8), cd(9)

     This cd driver is based upon the cd driver written by Julian Elischer,
     which appeared in 386BSD-0.1.  The CAM version of the cd driver was
     written by Kenneth Merry and first appeared in FreeBSD 3.0.

     The names of the structures used for the third argument to ioctl() were
     poorly chosen, and a number of spelling errors have survived in the names
     of the ioctl() commands.

FreeBSD 11.1-RELEASE-p4          April 9, 2014         FreeBSD 11.1-RELEASE-p4
Command Section