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

NAME
     cd -- SCSI CD-ROM driver

SYNOPSIS
     device cd
     device cd1 at scbus0 target 4 unit 0
     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 target string is followed by the device's standard SCSI device ID
     number.  The unit string is followed by the Logical Unit Number (LUN) of
     the SCSI device's sub-device, if any, or zero.

     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 ini-
                          tialized 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 infor-
                          mation 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 argu-
                          ment 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 fea-
                          ture.

     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 referenc-
     ing 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 com-
     mands.  Because 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; how-
     ever, this is not yet under way.

     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 sup-
     port 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 com-
     mands), 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 tun-
     ables.  The variable names are the same in both instances:

     kern.cam.cd.%d.minimum_cmd_size

     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.

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 max-
     imum 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.

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

DIAGNOSTICS
     None.

SEE ALSO
     da(4), scsi(4), disklabel(5), disklabel(8), cd(9)

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 imple-
     mentation at least would be rather inelegant, because of the current
     inability of the sysctl code to handle the addition of nodes after com-
     pile time.  Thus, it would take one dynamically sized sysctl variable and
     a userland utility to get/set the timeout values.  Implementation of sep-
     arate 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.

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 writ-
     ten by Kenneth Merry and first appeared in FreeBSD 3.0.

FreeBSD 4.10                   September 2, 2003                  FreeBSD 4.10

NAME | SYNOPSIS | DESCRIPTION | KERNEL CONFIGURATION | IOCTLS | NOTES | CHANGER OPERATION | FILES | DIAGNOSTICS | SEE ALSO | BUGS | HISTORY

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