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CD(4)			 BSD Kernel Interfaces Manual			 CD(4)

     cd	-- SCSI	CD-ROM driver

     device cd
     options "CHANGER_MAX_BUSY_SECONDS=11"

     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.

     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>.


     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

     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	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.

     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

				struct	ioc_pitch
					short	speed;

     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 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:

     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.

     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

     options "CHANGER_MAX_BUSY_SECONDS=11"

     The sysctl/kernel tunable variables are:

     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 ap-
     pear while	the boot process is going on.  This is normal, and is caused
     by	the changer scheduling code.

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


     da(4), scsi(4), disklabel(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.

     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 in-
     ability 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	sepa-
     rate 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.

BSD			       September 2, 2003			   BSD


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