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NAME
cd — 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 ada(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 the header file <sys/disklabel.h>.
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 “%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.
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(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.
Debian February 8, 2012 CD(4)