Provided by: freebsd-manpages_8.2-1_all bug

NAME

     cd ā€” SCSI CD-ROM driver

SYNOPSIS

     device cd
     options "CHANGER_MIN_BUSY_SECONDS=3"
     options "CHANGER_MAX_BUSY_SECONDS=11"

DESCRIPTION

     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 ad(4) and da(4).

     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.

KERNEL CONFIGURATION

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

IOCTLS

     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>.

     DIOCGDINFO

     DIOCSDINFO           (struct disklabel) Read or write the in-core copy of the disklabel for
                          the drive.  The disklabel is initialized with information read from the
                          scsi inquiry commands, and should be the same as the information
                          printed at boot.  This structure is defined in disklabel(5).

     CDIOCCAPABILITY      (struct ioc_capability) Retrieve information from the drive on what
                          features it supports.  The information is returned in the following
                          structure:

                                struct ioc_capability {
                                        u_long  play_function;
                                #define CDDOPLAYTRK     0x00000001
                                        /* Can play tracks/index */
                                #define CDDOPLAYMSF     0x00000002
                                        /* Can play msf to msf */
                                #define CDDOPLAYBLOCKS  0x00000004
                                        /* Can play range of blocks */
                                #define CDDOPAUSE       0x00000100
                                        /* Output can be paused */
                                #define CDDORESUME      0x00000200
                                        /* Output can be resumed */
                                #define CDDORESET       0x00000400
                                        /* Drive can be completely reset */
                                #define CDDOSTART       0x00000800
                                        /* Audio can be started */
                                #define CDDOSTOP        0x00001000
                                        /* Audio can be stopped */
                                #define CDDOPITCH       0x00002000
                                        /* Audio pitch can be changed */

                                        u_long  routing_function;
                                #define CDREADVOLUME    0x00000001
                                        /* Volume settings can be read */
                                #define CDSETVOLUME     0x00000002
                                        /* Volume settings can be set */
                                #define CDSETMONO       0x00000100
                                        /* Output can be set to mono */
                                #define CDSETSTEREO     0x00000200
                                        /* Output can be set to stereo (def) */
                                #define CDSETLEFT       0x00000400
                                        /* Output can be set to left only */
                                #define CDSETRIGHT      0x00000800
                                        /* Output can be set to right only */
                                #define CDSETMUTE       0x00001000
                                        /* Output can be muted */
                                #define CDSETPATCH      0x00008000
                                        /* Direct routing control allowed */

                                        u_long  special_function;
                                #define CDDOEJECT       0x00000001
                                        /* The tray can be opened */
                                #define CDDOCLOSE       0x00000002
                                        /* The tray can be closed */
                                #define CDDOLOCK        0x00000004
                                        /* The tray can be locked */
                                #define CDREADHEADER    0x00000100
                                        /* Can read Table of Contents */
                                #define CDREADENTRIES   0x00000200
                                        /* Can read TOC Entries */
                                #define CDREADSUBQ      0x00000200
                                        /* Can read Subchannel info */
                                #define CDREADRW        0x00000400
                                        /* Can read subcodes R-W */
                                #define CDHASDEBUG      0x00004000
                                        /* The tray has dynamic debugging */
                                };

     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 structure:

                                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 structure:

                                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 */
                                };

     CDIOCGETVOL

     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 channel.

     CDIOCSETMUTE         Mute output without changing the volume settings.

     CDIOCSETLEFT

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

     CDIOCSETDEBUG

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

     CDIOCPAUSE

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

     CDIOCRESET           Reset the drive.

     CDIOCSTART

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

     CDIOCALLOW

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

     CDIOCEJECT           Eject the CD-ROM.

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

     CDIOCPITCH           (struct ioc_pitch) For drives that support it, this command instructs
                          the drive to play the audio at a faster or slower rate than normal.
                          Values of speed between -32767 and -1 result in slower playback; a zero
                          value indicates normal speed; and values from 1 to 32767 give faster
                          playback.  Drives with less than 16 bits of resolution will silently
                          ignore less-significant bits.  The structure is defined thusly:

                                struct  ioc_pitch
                                {
                                        short   speed;
                                };

NOTES

     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.

CHANGER OPERATION

     This driver has built-in support for LUN-based CD changers.  A LUN-based CD changer is a
     drive that can hold two or more CDs, but only has one CD player mechanism.  Each CD in the
     drive shows up as a separate logical unit on the SCSI bus.  The cd driver automatically
     recognizes LUN-based changers, and routes commands for changers through an internal
     scheduler.  The scheduler prevents changer "thrashing", which is caused by sending commands
     to different LUNs in the changer at the same time.

     The scheduler honors minimum and maximum time quanta that the driver will spend on a
     particular LUN.  The minimum time is the guaranteed minimum amount of time that the driver
     will spend on a given LUN, even if there is no outstanding I/O for that LUN.  The maximum
     time is the maximum amount of time the changer will spend on a LUN if there is outstanding
     I/O for another LUN.  If there is no outstanding I/O for another LUN, the driver will allow
     indefinite access to a given LUN.

     The minimum and maximum time quanta are configurable via kernel options and also via sysctl
     and kernel tunable variables.  The kernel options are:

     options "CHANGER_MIN_BUSY_SECONDS=3"
     options "CHANGER_MAX_BUSY_SECONDS=11"

     The sysctl/kernel tunable variables are:

     kern.cam.cd.changer.min_busy_seconds
     kern.cam.cd.changer.max_busy_seconds

     It is suggested that the user try experimenting with the minimum and maximum timeouts via
     the sysctl variables to arrive at the proper values for your changer.  Once you have settled
     on the proper timeouts for your changer, you can then put them in your kernel config file.

     If your system does have a LUN-based changer, you may notice that the probe messages for the
     various LUNs of the changer will continue to appear while the boot process is going on.
     This is normal, and is caused by the changer scheduling code.

SYSCTL VARIABLES

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

     kern.cam.cd.retry_count

         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.

     kern.cam.cd.%d.minimum_cmd_size

         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 ā€œ%dā€ 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.

     kern.cam.cd.changer.min_busy_seconds

     kern.cam.cd.changer.max_busy_seconds

         Tune how long individual LUNs are 'locked' for I/O operations to optimize changer
         operation.  See CHANGER OPERATION section for information on how to use these items.

FILES

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

DIAGNOSTICS

     None.

SEE ALSO

     cam(4), da(4), disklabel(5), disklabel(8), cd(9)

HISTORY

     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.

BUGS

     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.

     There is no mechanism currently to set different minimum and maximum timeouts for different
     CD changers; the timeout values set by the kernel options or the sysctl variables apply to
     all LUN-based CD changers in the system.  It is possible to implement such support, but the
     sysctl implementation at least would be rather inelegant, because of the current inability
     of the sysctl code to handle the addition of nodes after compile time.  Thus, it would take
     one dynamically sized sysctl variable and a userland utility to get/set the timeout values.
     Implementation of separate timeouts for different CD devices in the kernel config file would
     likely require modification of config(8) to support the two timeouts when hardwiring cd
     devices.