MirBSD manpage: cd(4)

CD(4)                      BSD Programmer's Manual                       CD(4)


     cd - ATAPI and SCSI CD-ROM driver


     cd* at scsibus? target ? lun ?
     #cd0 at scsibus0 target 6 lun 0 (fixed-configuration example)


     The cd driver provides support for ATAPI and SCSI CD-ROM (Compact Disc
     Read-Only Memory) drives, via scsibus(4). In an attempt to look like a
     regular disk, the cd driver synthesizes a partition table, with one par-
     tition covering the entire CD-ROM. It is possible to modify this parti-
     tion 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
     wd(4) and sd(4).

     As the SCSI adapter is probed during boot, the SCSI bus is scanned for
     devices. Any devices found which answer as "Read-only" and "removable"
     CD-ROM or WORM devices will be "attached" to the cd driver.

     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 CD-ROM drives are defined in
     the header files <sys/cdio.h> and <sys/disklabel.h>.

             (struct disklabel) Read or write the in-core copy of the diskla-
             bel 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

             (struct ioc_play_track) Start audio playback given a track ad-
             dress 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;

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

                   struct ioc_play_blocks {
                           int     blk;
                           int     len;

             (struct ioc_play_msf) Start audio playback given a "minutes-
             seconds-frames" address and length. The structure is defined as

                   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;

             (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;

             (struct ioc_toc_header) Return summary information about the
             table of contents for the mounted CD-ROM. The information is re-
             turned into the following structure:

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

             (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.

             (struct ioc_patch) Attach various audio channels to various out-
             put channels. The argument structure is defined thusly:

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

             (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 */

             Patch all output channels to all source channels.

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

             Mute output without changing the volume settings.

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

             Turn on (off) debugging for the appropriate device.

             Pause (resume) audio play, without resetting the location of the

             Reset the drive.

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

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

             Eject the CD-ROM.

     FIBMAP  Return the physical block number (in 512-byte sectors) given the
             logical block number. The argument is a pointer to an integer. On
             invocation, it should contain the logical block. On return, it
             contains the physical block number.

     In addition the general scsi(4) ioctls may be used with the cd driver, if
     used against the `whole disk' partition (i.e., /dev/rcd0c).


     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 reject-
     ed. When no more open file descriptors reference the device, the first
     next open will load a new set of parameters (including disklabel) for the

     The audio code in the cd driver only supports 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; howev-
     er, this is not yet under way.


     /dev/cd[0-9][a-p]   block mode CD-ROM devices
     /dev/rcd[0-9][a-p]  raw mode CD-ROM devices




     intro(4), scsi(4), sd(4), disklabel(5), disklabel(8)


     The cd driver appeared in 386BSD 0.1.


     Reads from the raw mode devices must be aligned to and multiples of the
     hardware sector size, i.e. 2048 octets. disklabel(8) and fdisk(8) take
     care of this, but dd(1) needs a bs=2048 argument.


     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.

MirBSD #10-current             August 14, 2010                               3

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