Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
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	de-
     fined 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	de-
			  fined	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_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 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

     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 lo-
			  cation 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	fea-

     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 referenc-
     ing the device.  During this period, all new open attempts	will be	re-
     jected.  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.  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;	how-
     ever, 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), cd9660(5), 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 writ-
     ten 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	13.0			 April 8, 2022			  FreeBSD 13.0


Want to link to this manual page? Use this URL:

home | help