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
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 defined 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:
CDIOCPLAYBLOCKS- (
struct ioc_play_blocks) Start
audio playback given a block address and length. The structure is defined
as follows:
CDIOCPLAYMSF- (
struct ioc_play_msf) Start audio
playback given a `minutes-seconds-frames' address and length. The
structure is defined as follows:
CDIOCREADSUBCHANNEL- (
struct ioc_read_subchannel) Read
information from the subchannel at the location specified by this
structure:
- (
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:
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:
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:
CDIOCGETVOL-
CDIOCSETVOL- (
struct ioc_vol) Get (set)
information about the volume settings of the output channels. The argument
structure is as follows:
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.
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.
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.
- /dev/cd[0-9][a-h]
- raw mode CD-ROM devices
None.
cam(4),
da(4),
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 written 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.